AVL用户手册
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AVL 3.14 User Primer
last update 28 Aug 2004
Mark Drela, MIT
Aero & Astro
Harold Youngren, Aerocraft, Inc.
History
AVL (Athena Vortex Lattice) 1.0
was originally written by Harold Youngren circa
1988 for the MIT Athena TODOR aero software
collection. A number of
modifications have
since been added by Mark Drela and Harold
Youngren,to the
point where only a trace of
the original code remains.
General Description
AVL now has a large number of features
intended for rapid aircraft
configuration
analysis. The major features are as follows:
Aerodynamic components
Lifting surfaces
Slender bodies
Configuration
description
Keyword-driven geometry input
file
Defined sections with linear
interpolation
Section properties
camberline is NACA xxxx, or from airfoil file
control deflections
parabolic profile
drag polar, Re-scaling
Scaling,
translation, rotation of entire surface or body
Duplication of entire surface or body
Singularities
Horseshoe vortices
(surfaces)
Source+doublet lines (bodies)
Finite-core option
Discretization
Uniform
Sine
Cosine
Blend
Control deflections
Via normal-vector
tilting
Leading edge flaps
Trailing
edge flaps
Hinge lines independent of
discretization
General freestream description
alpha,beta flow angles
1
p,q,r aircraft rotation components
Subsonic Prandtl-Glauert compressibility
treatment
Aerodynamic outputs
Direct
forces and moments
Trefftz-plane
Derivatives of forces and moments, w.r.t
freestream, rotation, controls
In body or
stability axes
Trim calculation
Operating variables
alpha,beta
p,q,r
control deflections
Constraints
direct constraints on
variables
indirect constraints via
specified CL, moments
Multiple trim run
cases can be defined
Saving of trim run
case setups for later recall
Optional mass
definition file (only for trim setup, eigenmode
analysis)
User-chosen units
Itemized
component location, mass, inertias
Trim setup
of constraints
level or banked horizontal
flight
steady pitch rate (looping) flight
Eigenmode analysis
Rigid-body analysis
with quasi-steady aero model
Display of
eigenvalue root progression with a parameter
Display of eigenmode motion in real time
Output of dynamic system matrices
Vortex-
Lattice Modeling Principles
Like any
computational method, AVL has limitations on what
it can must
be kept in mind in any given
application.
Configurations
A vortex-
lattice model like AVL is best suited for
aerodynamic
configurationswhich consist mainly
of thin lifting surfaces at small angles of
attack and sideslip. These surfaces and their
trailing wakes are represented
as single-layer
vortex sheets, discretized into horseshoe vortex
filaments,
whose trailing legs are assumed to
be parallel to the x-axis. AVL provides the
capability to also model slender bodies such
as fuselages and nacelles via
source+doublet
filaments. The resulting force and moment
predictions are
consistent with slender-body
theory, but the experience with this model is
relatively limited, and hence modeling of
bodies should be done with caution.
If a
fuselage is expected to have little influence on
the aerodynamic loads,
2
it's
simplest to just leave it out of the AVL model.
Unsteady flow
AVL assumes quasi-steady
flow, meaning that unsteady vorticity shedding
is neglected. More precisely, it assumes the
limit of small reduced frequency,
which means
that any oscillatory motion (e.g. in pitch) must
be slow enough
so that the period of
oscillation is much longer than the time it takes
the flow to traverse an airfoil chord. This
is true for virtually any
expected flight
maneuver. Also, the roll, pitch, and yaw rates
used
in the computations must be slow enough
so that the resulting relative
flow angles
are small. This can be judged by the
dimensionless
rotation rate parameters, which
should fall within the following
practical
limits.
-0.10 < pb2V < 0.10
-0.03 <
qc2V < 0.03
-0.25 < rb2V < 0.25
These
represent extremely violent aircraft motion, and
are unlikely
to exceeded in any typical flight
situation, except possibly during
low-airspeed
aerobatic maneuvers. In any case, if any of these
parameters falls outside of these limits, the
results should be
interpreted with caution.
Compressibility
---------------
Compressibility is treated using the Prandtl-
Glauert (PG) transformation.
Its relative
importance can be judged by the PG factor 1B =
1sqrt(1 - M^2),
where
which shows the
expected range of validity.
M 1B
--- -----
0.0 1.000 |
0.1 1.005 |
0.2 1.021 |
0.3 1.048 |- PG expected
valid
0.4 1.091 |
0.5 1.155 |
0.6
1.250 |
0.7 1.400 PG suspect
(transonic flow likely)
0.8 1.667 PG
unreliable (transonic flow certain)
0.9 2.294
PG hopeless
3
For swept-
wing configurations, the validity of the PG model
is best judged using the wing-perpendicular
Mach number
Mperp = M cos(sweep)
Since Mperp < M, swept-wing cases can be
modeled up to higher
M values than unswept
cases. For example, a 45 degree swept wing
operating at freestream M = 0.8 has
Mperp = 0.8 * cos(45) = 0.566
which
is still within the expected range of PG validity
in the above table. So reasonable results can
be expected
from AVL for this case.
When doing velocity parameter sweeps at the
lowest Mach numbers,
say below M = 0.2, it is
best to simply hold M = 0. This will
greatly
speed up the calculations, since changing the Mach
number
requires recomputation and re-
factorization of the VL influence matrix,
which consumes most of the computational
effort. If the Mach number
is held fixed,
this computation needs to be done only once.
Input Files
===========
AVL works
with three input files, all in plain text format.
Ideally
these all have a common arbitrary
prefix
required main input file
defining the configuration geometry
optional file giving masses and inertias, and
dimensional units
optional file defining
the parameter for some number of run cases
The user provides files and , which are
typically created
using any text editor.
Sample files are provided for use as templates.
The file is written by AVL itself with a user
command.
It can be manually edited, although
this is not really necessary
since it is more
convenient to edit the contents in AVL and then
write out the file again.
Geometry Input File --
4
==============================
This file describes the vortex lattice
geometry and aerodynamic
section properties.
Sample input files are in the runs subdirectory.
Coordinate system
-----------------
The geometry is
described in the following Cartesian system:
注意坐标系和机体坐标系相同
X downstream
Y
out the right wing
Z up
The free
stream must be at a reasonably small angle to the
X axis
(alpha and beta must be small), since
the trailing vorticity
is oriented parallel
to the X axis. The length unit used in
this
file is referred to as
but must be the same
throughout this file.
File format
-----------
Header data
- - - - -
-
The input file begins with the following
information in the first 5 non-blank,
non-
comment lines:
Abc... | case
title
# | comment line
begins with
0.0 | Mach
1 0 0.0 | iYsym iZsym Zsym
4.0 0.4 0.1 | Sref Cref Bref
0.1 0.0 0.0 | Xref Yref Zref
0.020 | CDp (optional)
Mach = default freestream Mach
number for Prandtl-Glauert correction
5
iYsym = 1 case is symmetric
about Y=0 , (X-Z plane is a solid wall)
= -1 case is antisymmetric about Y=0, (X-Z plane
is at const. Cp)
= 0 no Y-symmetry
is assumed
是否存在纵向对称
iZsym = 1
case is symmetric about Z=Zsym , (X-Y plane is
a solid wall)
= -1 case is
antisymmetric about Z=Zsym, (X-Y plane is at
const. Cp)
= 0 no Z-symmetry is
assumed (Zsym ignored)
好像可以考虑地效
Sref = reference area used to define all
coefficients (CL, CD, Cm, etc)
Cref =
reference chord used to define pitching moment
(Cm)
Bref = reference span used to define
roll,yaw moments (Cl,Cn)
X,Y,Zref =
default location about which moments and rotation
rates are defined
(if doing
trim平衡calculations, XYZref must be the CG
location,
which can be imposed
with the MSET command described later)
CDp = default profile drag coefficient added to
geometry, applied at XYZref
(assumed
zero if this line is absent, for previous-version
compatibility)
The default
Mach, XYZref, and CDp values are superseded取代by
the values
in the .run file (described
later), if it is present. They can also
be
changed at runtime.
Only the half (non-
image) geometry must be input if symmetry is
specified.
Ground effect is simulated with
iZsym = 1, and Zsym = location of ground.
（该程序可以计算地效）
Forces are not calculated on
the imageanti-image映像surfaces.
Sref and Bref
are assumed to correspond to the total geometry.
In practice there is little reason to run
Y-symmetric image cases,
unless one is
desperate不顾一切的for CPU savings.
Surface and Body data
- - - - - - - - - -
-
The remainder of the file consists of a set
of keywords and associated data.
Each keyword
expects a certain number of lines of data to
immediately follow
6
it, the
exceptions being inline-coordinate keyword AIRFOIL
which is followed
by an arbitrary number of
coordinate data lines. The keywords must also be
nested嵌套的properly in the hierarchy层次shown
below. Only the first four
characters of each
keyword are actually significant, the rest are
just a mnemonic
帮助记忆的.
SURFACE
INDEX
YDUPLICATE
SCALE
TRANSLATE
ANGLE
SECTION
SECTION
NACA
SECTION
AIRFOIL
CLAF
CDCL
SECTION
AFILE
CONTROL
CONTROL
BODY
YDUPLICATE
SCALE
TRANSLATE
BFILE
SURFACE
YDUPLICATE
SECTION
SECTION
SURFACE
.
7
.
etc.
The INDEX, YDUPLICATE, SCALE,
TRANSLATE, and ANGLE keywords
can all be used
together. If more than one of these appears for
a surface, the last one will be used and the
previous ones ignored.
At least two
SECTION keywords must be used for each surface.
The NACA, AIRFOIL, AFILE, keywords are
alternatives.
If more than one of these
appears after a SECTION keyword,
the last one
will be used and the previous ones ignored. i.e.
SECTION
NACA
AFILE
is equivalent to
SECTION
AFILE
Multiple CONTROL keywords can
appear after a SECTION keyword and data
Surface-definition keywords and data formats
- - - - - - - - - - - - - - - - - - - - - - -
*****
SURFACE |
(keyword)
Main Wing | surface name
string
12 1.0 20 -1.5 | Nchord Cspace
[ Nspan Sspace ]
The SURFACE keyword
declares that a surface is being defined until
the next SURFACE or BODY keyword, or the end
of file is reached.
A surface does not
really have any significance to the underlying
AVL vortex lattice solver, which only
recognizes the overall
collection of all the
individual horseshoe vortices. SURFACE
is
provided only as a configuration-defining device,
and also
as a means of defining individual
surface forces. This is
necessary for
structural load calculations, for example.
8
Nchord = number of chord
wise horseshoe vortices placed on the surface
Cspace = chordwise vortex spacing parameter
(described later)
Nspan = number of
spanwise horseshoe vortices placed on the surface
[optional]
Sspace = spanwise vortex
spacing parameter (described later)
[optional]
If Nspan and Sspace are
omitted (i.e. only Nchord and Cspace are present
on line),
then the Nspan and Sspace parameters
will be expected for each section interval,
as
described later.
*****
INDEX | (keyword)
3
| Lsurf
This optional keyword allows
declaring that multiple input SURFACEs
actually constitute one physical surface, by
giving them all the
same Lsurf value. This
declaration is necessary for AVL to properly
perform calculations using finite core radii
for the horseshoe vortices
(the default case).
A finite core radius is normally used for each
horseshoe vortex, except when computing the
influence of that vortex
on a control point
lying on the same physical surface. Using a
finite core radius within the same surface
would seriously corrupt
the calculation.
If each physical surface is specified via only
a single SURFACE block,
then the INDEX
declaration is unnecessary.
*****
YDUPLICATE | (keyword)
0.0
| Ydupl
The YDUPLICATE keyword is a
convenient shorthand device for creating 。another
surface which is a geometric mirror image of
the one being defined（创建一个
和正在定义的面几何对称的另外一个面）.
The duplicated surface is _not_ assumed
to be
（注意：气动上是不对称的）an aerodynamic image or anti-image,
but is truly
independent.
A typical
application would be for cases, which have,
geometric
symmetry, but not aerodynamic
symmetry, such as a wing in yaw.
9
Defining the right wing together with
YDUPLICATE will conveniently
create the
entire wing（这样创建了右机翼就创建了整个机翼）
典型的例子是存在侧滑的机翼，它的几何是对称的，但是气动是不对称的.
The
YDUPLICATE keyword can _only_ be used if iYsym = 0
is specified.
（只有在设置了气动不对称的情况下才能使用）
Otherwise, the duplicated real surface will be
identical to the
Implied（暗指） aerodynamic image
surface, and velocities will be computed
directly on the line-vortex segments of the
images. This will
almost certainly produce
an arithmetic fault.(算法错误)
The duplicated
surface gets the same Lsurf value as the parent
surface,
so they are considered to be the same
physical surface. There is
no significant
effect on the results if they are in reality
two physical surfaces.
Ydupl =
Y position of X-Z plane about which the current
surface is
reflected to make the
duplicate geometric-image surface.
*****
SCALE | (keyword)
1.0 1.0 0.8 | Xscale Yscale Zscale
The SCALE allows convenient rescaling for the
entire surface.
The scaling is applied before
the TRANSLATE operation described below.
Xscale,Yscale,Zscale = scaling factors
applied to all x,y,z coordinates
(chords are also scaled by Xscale)
*****
TRANSLATE | (keyword)
10.0 0.0 0.5 | dX dY dZ
The
TRANSLATE keyword allows convenient relocation of
the entire
surface without the need to change
the Xle,Yle,Zle locations
for all the
defining sections. A body can be translated
without
the need to modify the body shape
coordinates.
dX,dY,dZ = offset added
on to all X,Y,Z values in this surface.
10
*****
ANGLE
| (keyword)
2.0 | dAinc
The
ANGLE keyword allows convenient changing of the
incidence angle
of the entire surface without
the need to change the Ainc values
for all
the defining sections. The rotation is performed
about
the spanwise axis projected onto the y-z
plane.
dAinc = offset added on to the
Ainc values for all the defining sections
in this surface
*****
SECTION
| (keyword)
0.0 5.0 0.2 0.50 1.50 5 -2.0
| Xle Yle Zle Chord Ainc [ Nspan
Sspace ]
The SECTION keyword defines an airfoil-
section camber line at some
spanwise location
on the surface.
Xle,Yle,Zle =
airfoil's leading edge location
Chord
= the airfoil's chord (trailing edge is at
Xle+Chord,Yle,Zle)
Ainc = incidence
angle, taken as a rotation (+ by RH rule) about
the surface's spanwise axis
projected onto the Y-Z plane.
Nspan
= number of spanwise vortices until the next
section [ optional ]
Sspace = controls
the spanwise spacing of the vortices
[
optional ]
Nspan and Sspace are used
here only if the overall Nspan and Sspace
for
the whole surface is not specified after the
SURFACE keyword.
The Nspan and Sspace for the
last section in the surface are always ignored.
Note that Ainc is used only to modify the
flow tangency boundary
condition on the
airfoil camber line, and does not rotate the
geometry
of the airfoil section itself. This
approximation is consistent with
linearized
airfoil theory.
注意：section的作用只是修改中面的切向流条件，并不对几何面进行旋转
The local chord and incidence angle are
linearly interpolated between
defining
sections. Obviously, at least two sections (root
and tip)
11
must be specified
for each surface.
The default airfoil
camber line shape is a flat plate. The NACA,
AIRFOIL,
and AFIL keywords, described below,
are available to define non-flat
camber lines.
If one of these is used, it must immediately
follow
the data line of the SECTION keyword.
All the sections in the surface must be
defined in order across the span.
*****
NACA | (keyword)
4300 | section NACA
camberline
The NACA keyword sets the
camber line to the NACA 4-digit shape specified
*****
AIRFOIL X1 X2
|(keyword) [ optional xc range ]
1.0 0.0
| xc(1) yc(1)
0.98 0.002 |
xc(2) yc(2)
. . | .
.
. . | . .
. . | . .
1.0
-0.01 | xc(N) yc(N)
The AIRFOIL keyword declares that the airfoil
definition is input
as a set of xc, yc pairs.
xc,yc = airfoil coordinates
The xc, yc coordinates run from TE, to LE,
back to the TE again
in either direction.
These corrdinates are splined, and the slope
of the camber y(x) function is obtained from
the middle yc values
between top and bottom.
The number of points N is determined
when a
line without two readable numbers is encountered.
If present, the optional X1 X2 parameters
indicate that only the
xc range X1..X2 from
the coordinates is to be assigned to the surface.
If the surface is an 20%-chord flap, for
example, then X1 X2
would be 0.80 1.00. This
allows the camber shape to be easily
assigned
to any number of surfaces in piecewise manner.
12
*****
AFILE X1 X2 | (keyword) [
optional xc range ]
filename
| filename string
The AFILE keyword is
essentially the same as AIRFOIL, except that the
xc,yc
pairs are generated from a standard
(XFOIL-type) set of airfoil coordinates
contained in the file The first line of this
file is assumed to
contain a string with the
name of the airfoil (as written out with XFOIL's
SAVE
command).
The optional X1 X2
parameters are used as in AIRFOIL.
*****
DESIGN |
(keyword)
DName Wdes | design
parameter name, local weight
This
declares that the section angle Ainc is to be
virtually
perturbed by a design parameter,
with name DName and local
Wdes. For example,
the declarations
DESIGN
twist -0.5
DESIGN
bias 1.0
at a
section specifies that the total virtual angle of
the section is
Ainc_total = Ainc -
0.5*twist + 1.0*bias
where twist_value
and bias_value are design parameters specified at
runtime.
The sensitivities of the flow
solution to design variable changes can be
displayed at any time during program
execution. Hence, design variables can
be
used to quickly investigate the effects of twist
changes on lift, moments,
induced drag, etc.
Declaring the same design parameter with
varying weights for multiple
sections in a
surface allows the design parameter to represent a
convenient
13
*****
CONTROL |
(keyword)
elevator 1.0 0.6 0. 1. 0. 1.0
| name, gain, Xhinge, XYZhvec, SgnDup
The CONTROL keyword declares that a hinge
deflection at this section
is to be governed
by one or more control variables. An arbitrary
number of control variables can be used,
limited only by the array
limit NDMAX.
The data line quantities are...
name
name of control variable
gain control
deflection gain, units: degrees deflection
control
variable
Xhinge xc location of
hinge. (舵面铰链位置)
If positive,
control surface extent is Xhinge..1 (TE surface)
If negative, control surface extent
is 0..-Xhinge (LE surface)
XYZhvec vector
giving hinge axis about which surface rotates
+ deflection is + rotation about
hinge by righthand rule
Specifying
XYZhvec = 0. 0. 0. puts the hinge vector along the
hinge
SgnDup sign of deflection for
duplicated surface
An elevator
would have SgnDup = +1
An aileron
would have SgnDup = -1
（对称控制面的偏转，1同向，-1反向）
Control derivatives（导数）will be
generated for all control variables
（所有定义的操纵舵面的操纵倒数都将计算）
which are declared.
More than one variable can
contribute to the motion at a section.
For
example, for the successive declarations
CONTROL
aileron
1.0 0.7 0. 1. 0. -1.0
CONTROL
flap 0.3 0.7 0. 1. 0. 1.0
14
the overall deflection will be
control_surface_deflection = 1.0 *
aileron + 0.3 * flap
The same
control variable can be used on more than one
surface.
For example the wing sections might
have
CONTROL
flap 0.3 0.7 0. 1. 0. 1.0
and the horizontal tail sections might have
CONTROL
flap
0.03 0.5 0. 1. 0. 1.0
with the latter
simulating 10:1 flap -> elevator mixing.
（这样就创建了襟翼和升降舵的混控，即襟翼偏转10度，则升降舵增加1度偏转）
A partial-span （部分翼展）control surface is
specified by declaring CONTROL
data only at
the sections where the control surface exists,
including the two
end sections. For example,
the following wing defined with three sections
(i.e.
two panels) has a flap over the inner
panel, and an aileron over the outer panel.
SECTION
0.0 0.0 0.0 2.0 0.0 | Xle
Yle Zle Chord Ainc
CONTROL
flap 1.0 0.80 0. 0. 0. 1 | name,
gain, Xhinge, XYZhvec, SgnDup
SECTION
0.0 8.0 0.0 2.0 0.0 | Xle Yle Zle
Chord Ainc
CONTROL
flap 1.0 0.80 0. 0. 0. 1 | name,
gain, Xhinge, XYZhvec, SgnDup
CONTROL
aileron 1.0 0.85 0. 0. 0. -1 | name,
gain, Xhinge, XYZhvec, SgnDup
SECTION
0.2 12.0 0.0 1.5 0.0 | Xle Yle Zle
Chord Ainc
CONTROL
aileron 1.0 0.85 0. 0. 0. -1 | name,
gain, Xhinge, XYZhvec, SgnDup
The
control gain for a control surface does not need
to be equal at each section.
15
Spanwise stations between sections
receive a gain which is linearly interpolated
from the two bounding allows specification of
flexible-surface
control example, the
following surface definition models wing
warping which is linear from root to tip.
Note that the is at xc=0.0,
so that the entire
chord rotates in response to the aileron
deflection.
SECTION
0.0 0.0 0.0
2.0 0.0 | Xle Yle Zle Chord Ainc
CONTROL
aileron 0.0 0. 0. 0. 0. -1 | name,
gain, Xhinge, XYZhvec, SgnDup
SECTION
0.2 12.0 0.0 1.5 0.0 | Xle Yle Zle
Chord Ainc
CONTROL
aileron 1.0 0. 0. 0. 0. -1 | name,
gain, Xhinge, XYZhvec, SgnDup
*****
CLAF | (keyword)
CLaf | dCLda scaling factor
This scales the effective dclda of the section
airfoil as follows:
dclda = 2 pi CLaf
The implementation is simply a chordwise shift
of the control point
relative to the bound
vortex on each vortex element.
The intent
is to better represent the lift characteristics
of thick airfoils, which typically have
greater dclda values
than thin airfoils. A
good estimate for CLaf from 2D potential
flow
theory is
CLaf = 1 + 0.77 tc
where tc is the airfoil's thicknesschord
ratio. In practice,
viscous effects will
reduce the 0.77 factor to something less.
Wind
tunnel airfoil data or viscous airfoil
calculations should
be consulted before
choosing a suitable CLaf value.
If the
CLAF keyword is absent for a section, CLaf
defaults to 1.0,
giving the usual thin-
airfoil lift slope dclda = 2 pi.
16
*****
CDCL
| (keyword)
CL1 CD1 CL2 CD2 CL3 CD3 |
CD(CL) function parameters
The CDCL
keyword specifies a simple profile-drag CD(CL)
function
for this section. The function is
parabolic between CL1..CL2 and
CL2..CL3, with
rapid increases in CD below CL1 and above CL3.
See the SUBROUTINE CDCL header (in cdcl.f) for
more details.
The CD(CL) function is
interpolated for stations in between
defining
sections. Hence, the CDCL declaration on any
surface
must be used either for all sections
or for none.
Body-definition
keywords and data formats
- - - - - - - - - -
- - - - - - - - - - -
*****
BODY
| (keyword)
Fuselage | body name
string
15 1.0 | Nbody Bspace
The BODY keyword decalres that a body is
being defined until
the next SURFACE or BODY
keyword, or the end of file is reached.
A
body is modeled with a source+doublet line along
its axis,
in accordance with slender-body
theory.
Nbody = number of source-line
nodes
Bspace = lengthwise node spacing
parameter (described later)
*****
YDUPLICATE | (keyword)
0.0
| Ydupl
Same function as for a surface,
described earlier.
*****
SCALE
| (keyword)
17
1.0 1.0 0.8
| Xscale Yscale Zscale
Same function as
for a surface, described earlier.
*****
TRANSLATE | (keyword)
10.0
0.0 0.5 | dX dY dZ
Same function as
for a surface, described earlier.
*****
BFILE | (keyword)
filename | filename string
This specifies the shape of the body as an
or side view of the body, which is assumed to
have a round cross-section. Hence,
the
diameter of the body is the difference between the
top and bottom Y values.
Bodies which are not
round must be approximated with an equivalent
round body
which has roughly the same cross-
sectional areas.
Vortex Lattice Spacing
Distributions
Discretization of the geometry
into vortex lattice panels is controlled by the
spacing parameters described earlier: Sspace,
Cspace, Bspace. These must fall
in the range
-3.0 ... +3.0 , and they determine the spanwise
and lengthwise
horseshoe vortex or body line
node distributions as follows:
parameter
spacing
---------
-------
3.0 equal |
| | | | | | | |
2.0
sine || | | | | | | |
1.0 cosine || | |
| | | ||
0.0 equal
| | | | | | | | |
-1.0
cosine || | | | | | ||
-2.0 -sine | |
| | | | | ||
-3.0
equal | | | | | | | | |
18
Sspace (spanwise) :
first section ==> last section
Cspace (chordwise) : leading edge ==>
trailing edge
Bspace (lengthwise):
frontmost point ==> rearmost point
An intermediate parameter
value(任意典型数值之间的值，如2.3、0.5等) will result
in a
blended distribution. The most efficient
distribution (best accuracy for
a given number
of vortices) is usually the cosine (1.0) chordwise
and spanwise.
If the wing does not have a
significant chord slope discontinuity at the
centerline, such as a straight, elliptical, or
slightly tapered wing, then the
-sine (-2.0)
distribution from root to tip will be more
efficient. This is
equivalent to a cosine
distribution across the whole span. The basic
rule is
that a tight chordwise distribution is
needed at the leading and trailing edges,
and
a tight spanwise distribution is needed wherever
the circulation is changing
rapidly, such as
taper breaks, and especially at flap breaks and
wingtips.
A number of vortex-spacing
rules must be followed to get good results from
AVL,
or any other vortex-lattice method:
1) In a standard VL method, a trailing vortex
leg must not pass close to a
downstream
control point, else the solution will be
garbage（垃圾, 废物）. In
practice, this means that
surfaces which are lined up along the x direction
(i.e.
have the same or nearly the same y,z
coordinates), MUST have the same spanwise
vortex spacing. AVL relaxes this requirement
by employing a finite core size
for each
vortex on a surface which is influencing a control
point in another
aurface (unless the two
surfaces share the same INDEX declaration). This
feature can be disabled by setting the core
size to zero in the OPER sub-menu,
Option sub-
sub-menu, command C. This reverts AVL to the
standard AVL method.
2) Spanwise vortex
spacings should be
spanwise strip width.
Adjust Nspan and Sspace parameters to get a smooth
distribution. Spacing should be bunched at
dihedral（形成上反角的机翼的） and
chord breaks, control
surface ends, and especially at wing tips. If a
single
spanwise spacing distribution is
specified for a surface with multiple sections,
the spanwise distribution will be
fudged（夸大超出某事正常的界限）as needed to
ensure that a
point falls exactly on the section location.
Increase the number
of spanwise points if the
spanwise spacing looks ragged（粗糙的）because of this
fudging.
3) If a surface has a
control surface on it, an adequate number of
chordwise
vortices Nchord should be used to
resolve the discontinuity in the camberline
angle at the hingeline. It is possible to
define the control surface as a
separate
SURFACE entity. Cosine chordwise spacings then
produce bunched points
exactly at the hinge
line, giving the best accuracy. The two surfaces
must be
given the same INDEX and the same
spanwise point spacing for this to work properly.
19
Such extreme measures are
rarely necessary in practice, however. Using a
single
surface with extra chordwise spacing is
usually sufficient.
Mass Input File --
This optional file describes the mass and
inertia properties of the configuration.
It
also defines units to be used for run case setup.
These units may want to
be different than
those used to define the geometry. Sample input
files
are in the runs subdirectory.
Coordinate system
The geometry axes used
in the file are exactly the same as those used
in the file.
File format
A sample
file for an RC glider is shown below. Comment
lines begin with a
and including a is ignored.
Blank lines are ignored.
# SuperGee
#
# Dimensional unit and parameter data.
#
Mass & Inertia breakdown（分类, 分成细目）.
#
Names and scalings for units to be used for trim
and eigenmode calculations.
# The Lunit and
Munit values scale the mass, xyz, and inertia
table data below.
# Lunit value will also
scale all lengths and areas in the AVL input file.
Lunit = 0.0254 m
Munit = 0.001 kg
Tunit = 1.0 s
#-------------------------
# Gravity and
density to be used as default values in trim setup
(saves runtime
typing).
# Must be in the
unit names given above (i.e. m,kg,s).
g =
9.81
rho = 1.225
#-------------------------
# Mass &
Inertia breakdown.
# x y z is location of
item's own CG.
# Ixx... are item's inertias
about item's own CG.
#
# x,y,z system
here must be exactly the same one used in the .avl
input file
# (same orientation, same
origin location, same length units)
#
#
mass x y z Ixx Iyy Izz [
Ixy Ixz Iyz ]
* 1. 1. 1. 1.
1. 1. 1. 1. 1. 1.
20
+ 0. 0. 0. 0. 0. 0.
0. 0. 0. 0.
58.0 3.34 12.0
1.05 4400 180 4580 ! right wing
58.0 3.34 -12.0 1.05 4400 180
4580 ! left wing
16.0 -5.2
0.0 0.0 0 80 80 ! fuselage
pod
18.0 13.25 0.0 0.0 0 700
700 ! boom+rods
22.0 -7.4 0.0
0.0 0 0 0 ! battery
2.0 -2.5 0.0 0.0 0 0 0
! jack
9.0 -3.8 0.0 0.0 0 0
0 ! RX
9.0 -5.1 0.0 0.0
0 0 0 ! rud servo
6.0
-5.9 0.0 0.0 0 0 0 !
ele servo
9.0 2.6 1.0 0.0 0
0 0 ! R wing servo
9.0 2.6
-1.0 0.0 0 0 0 ! L wing
servo
2.0 1.0 0.0 0.5 0 0
0 ! wing connector
1.0 3.0 0.0
0.0 0 0 0 ! wing pins
6.0 29.0 0.0 1.0 70 2 72
! stab
6.0 33.0 0.0 2.0 35 39
4 ! rudder
0.0 -8.3 0.0 0.0
0 0 0 ! nose wt.
Units
The first three lines
Lunit = 0.0254 m
Munit = 0.001 kg
Tunit = 1.0 s
give the magnitudes and names of the units to
be used for run case setup and
possibly for
eigenmode calculations. In this example, standard
SI units(m,kg,s)
are chosen. But the data in
and is given in units of Lunit
= 1 inch,
which is therefore declared here to be equal to
mthe data
was given in centimeters, the
statement would read
Lunit = 0.01 m
and
if it was given directly in meters, it would read
Lunit = 1.0 m
Similarly, Munit（质量单位）
used here in this file is the gram, but since the
kilogram (kg) is to be used for run case
calculations, the Munit declaration
is
Munit = 0.001 kg
If the masses here were given
in ounces, the declaration would be
Munit =
0.02835 kg
The third line gives the time unit
name and magnitude.
If any of the three unit
lines is absent, that unit's magnitude will be set
to
1.0, and the unit name will simply remain
as
Constants(常数)
The 4th and 5th lines
give the default gravitational acceleration andair
density,
in the units given above. If these
statements are absent, these constants
default
to 1.0, and will need to be changed manually at
runtime.
21
Mass, Position,
and Inertia Data
A line which begins with a
to all subsequent data. If such a line is
absent, these default to 1.
A line which
begins with a
to all subsequent data. If such
a line is absent, these default to 0.
Lines whith only numbers are interpreted as
mass, position, and inertia data.
Each such
line contains values for
mass x
y z Ixx Iyy Izz Ixz
as described in the file comments above. Note
that the inertias are
taken about that item's
own mass centroid given by x,y,z. The finer
the mass breakdown, the less important these
self-inertias become.
Additional
multiplier or adder lines can be put anywhere in
the data lines,
and these then re-define these
mulipliers and adders for all subsequent lines.
For example:
# mass x y z
Ixx Iyy Izz Ixz
* 1.2 1.
1. 1. 1. 1. 1. 1.
+ 0.
0.2 0. 0. 0. 0. 0. 0.
58.0 3.34 12.0 1.05 4400 180
4580 0. ! right wing
58.0
3.34 -12.0 1.05 4400 180 4580 0. !
left wing
* 1. 1. 1.
1. 1. 1. 1. 1.
+ 0. 0.
0. 0. 0. 0. 0. 0.
16.0 -5.2 0.0 0.0 0 80 80
0. ! fuselage pod
18.0 13.25 0.0 0.0
0 700 700 0. ! boom+rods
22.0
-7.4 0.0 0.0 0 0 0 0.
! battery
Data lines 1-2 have all
their masses scaled up by 1.2, and their locations
shifted by delta(x) = 0.2. Data lines 3-5
revert back to the defaults.
Run-Case Save File --
=============================
This
file is generated by AVL itself. It can be edited
with a text editor,
although this is not
really necessary. The parameter values in the
file
can be changed using AVL's menus, and the
file can then be written again.
22
Manipulating and using the contents of
the run file will be described later.
Program Execution
=================
AVL is executed with the
% avl
xxx
If the three filenames do not obey
the recommended
syntax, the full filenames
can be given explicitly:
% avl avl_file
run_file mass_file
As the data files
are read and processed, a considerable
data
dump is displayed. If any file has a bad format,
the offending data line is displayed, and AVL
will stop
if the error is fatal.
After the files are processed, the user is put
into
the main AVL menu:
======
==================================================
==
Quit Exit program
.OPER
Compute operating-point run cases
.MODE
Eigenvalue analysis of run cases
LOAD
f Read configuration input file
MASS f
Read mass distribution file
CASE f Read
run case file
MSET i Apply mass file data
to stored run case(s)
.PLOP Plotting
options
NAME s Specify new configuration
name
AVL c>
The uppercase
words in the menu are commands. They will
also be shown in uppercase in the examples
below, but
23
they are not
case sensitive when typed.
OPER
Routine -- Flow Analysis
=============================
The
OPER command will then bring up the main operating
menu:
Operation of run case 17: 0
deg. bank
======
==================================================
==
variable constraint
------------ ------------------------
A lpha -> CL = 0.7000
B eta -> Cl roll mom = 0.000
R oll rate -> pb2V = 0.000
P itch rate -> qc2V = 0.000
Y aw rate -> rb2V = 0.000
D1 elevator -> Cm pitchmom = 0.000
D2 rudder -> Cn yaw mom = 0.000
------------ ------------------------
C1 set level or banked horizontal
flight constraints
C2 set steady pitch rate
(looping) flight constraints
M odify
parameters
+ add new run case S ave
run cases to file
- delete run case
F etch run cases from file
N ame current run
case W rite forces to file
eX
ecute run case I nitialize variables
G eometry plot T refftz
Plane plot
ST stability
derivatives SB body-axes derivatives
FT total forces FN surface forces
FS strip forces FE element
forces
RE reference
quantities VM strip shear,moment
DE design mods O ptions
24
.OPER (case 17) c>
Geometry Plotting
- - - - - - -
- -
Before a first flow solution is attempted,
the geometry
should be examined in the
geometry plot sub-menu, entered
with the G
command:
G
=========================================
K
eystroke mode V iewpoint
A
nnotate plot O ptions
H
ardcopy plot S elect surfaces
Z oom
U nzoom
CH ordline T
CA amber F
CN tlpoint F TR
ailing legs F
BO ound leg T NO rmal
vector F
LO ading F AX es, xyz
ref. T
Geometry plot command:
The eight bottom commands followed by T or F
are toggles,
which enabledisable plotting of
various stuff of interest.
The loading vector
plotting controlled by the LO toggle
requires
that a converged flow solution is available.
The K command enters a sub-sub menu which
allows interactive rotation
of the aircraft
to a suitable viewing angle, zooming, distortion
for
perspective, etc.
------------------------------------------------
Type keys in graphics window...
L eft R ight (Azimuth )
U p D own (Elevation)
C lear
Z oom on curs. N ormal size
I ngress O utgress
H
ardcopy A nnotate plot
25
...
------------------------------------------------
These commands must be typed with the
cursor in the graphics window,
and their
action is performed immediately. All other menus
work in
the usual text window.
Calculation Setup
- - - - - - - - -
A
flow calculation involves a number of _operating
variables_ which
are additional unknowns
determined as part of the calculation.
The
left column in the top block of the OPER menu
lists the available
operating variables
(alpha, beta, ... rudder):
=============
=============================================
variable constraint
------------ ------------------------
A lpha -> alpha = 3.000
B eta -> beta = 0.000
R oll rate -> pb2V = 0.000
P itch rate -> qc2V = 0.000
Y aw rate -> rb2V = 0.000
D1 elevator -> elevator = 0.000
D2 rudder -> rudder = 0.000
------------ ------------------------
and the right column gives the constraint
for each variable.
The default constraints
are simple direct constraints as shown above.
Variables can also be constrained indirectly.
For example,
typing the alpha command
constraints for selection:
Select
command c> a
constraint
value
- - - - - - - - - - - - - - -
- -
-> A alpha = 3.000
B beta = 0.000
R
pb2V = 0.000
26
P qc2V = 0.000
Y rb2V
= 0.000
C CL =
0.000
RM Cl roll mom = 0.000
PM Cm pitchmom = 0.000
YM Cn yaw mom = 0.000
D1
elevator = 0.000
D2 rudder
= 0.000
Select new
constraint,value for alpha c>
The arrow indicates the current constraint. A
new constraint
and value can be specified.
Typing
C 0.7
at the above
prompt will make alpha be implicitly constrained
by the condition CL = 0.7, as now indicated by
the new main menu:
=========================================
variable constraint
------------- ----------------------
A
lpha -> CL = 0.7000
B eta -> beta = 0.000
R oll rate -> pb2V = 0.000
P itch rate -> qc2V = 0.000
Y aw rate -> rb2V = 0.000
D1 elevator -> elevator = 0.000
D2 rudder -> rudder = 0.000
------------- ----------------------
.
.
A constraint can be used no
more than once.
For convenience, a
variable, its constraint, and the constraint value
can all be specified on one line at the OPER
prompt. For example...
D1 PM 0
D2 YM 0
sets the constraint on d1
(elevator) to be zero pitching moment,
and the
constraint on d2 (rudder) to be zero yawing
moment.
Normally, aileron is constrained by a
zero rolling moment.
27
For a
rudderelevator aircraft, as implied by the above
menu
without aileron, a nonzero sideslip is
determined by the
zero rolling moment
constraint:
B RM 0
This will
be well-posed only if the aircraft's roll moment
is sufficiently dependent on the sideslip
angle (i.e. if it has
sufficient dihedral
effect).
Flow Solution
- - - -
- - -
Once all the appropriate constraints are
set up, the solution
is executed with the X
command. If the variableconstraint
system is
ill-posed, the solution will probably not
converge.
Output(输出输出简介)
- - - -
Everytime a calculation is executed, the
integrated forces are displayed
for the
entire configuration. Forces for the individual
surfaces,
strips, or vortex elements can be
dsplayed with the FN, FS, FE commands.
The
element force printout is rather voluminous and
often not very
informative.
The
force and moment directions are in stability axes
x,y,z, which
are tilted up by the angle alpha
from the body axes X,Y,Z:
| x | |
cos(a) sin(a)| | X |
| y | = | 1
| | Y |
| z | |-sin(a) cos(a)| | Z |
The following standard
normalizations are used, with Q = 0.5 rho V^2
...
CD = F_x (Q Sref) drag
CY = F_y (Q Sref) side force
CL = F_z (Q Sref) lift
Cl =
M_x (Q Sref Bref) roll moment
Cm =
M_y (Q Sref Cref) pitch moment
Cn =
M_z (Q Sref Bref) yaw moment
28
The CD,CY,CL forces are positive
in the direction of the x,y,z axes,
respectively. The moments can be defined in
four possible ways:
Body
axes Stability axes
--------------- --------------
Geometric| X
Y Z x y z
|
Standard
| -X Y -Z -x y -z
Rates
| p q r p' q' r'
Moments |
Cl Cm Cn Cl' Cm' Cn'
with
the rates and moments positive by righthand rule
about
the indicated axes.
The roll,
pitch, and yaw rates (p,q,r) input from the
operating
menu are defined in either the body
axes or the stability axes,
depending on which
is chosen in the Options sub-menu.
It
must be pointed out that if sideslip (beta) is
nonzero, then
CD and CY are not the true
the relative wind direction. Likewise for
moments Cl and Cm.
The wind-axes directions
are given by
| x | | cos(b)
sin(b) | | x |
| y | = |-sin(b)
cos(b) | | y |
| z |_wind |
1 | | z |
| cos(b)cos(a)
sin(b) cos(b)sin(a)| | X |
=
|-sin(b)cos(a) cos(b) -sin(b)sin(a)| | Y |
| -sin(a) 0 cos(a)| | Z |
hence
CD_wind = CD cos(b) + CY
sin(b)
CY_wind = CY cos(b) - CD sin(b)
CL_wind = CL
Cl_wind = Cl cos(b) + Cm
sin(b)
Cm_wind = Cm cos(b) - Cl sin(b)
Cn_wind = Cn
29
AVL
does not display these wind-axes forces since they
are not
relevant to stability and control
calculations, and differ from the
stability-
axes forces only if a steady-state sideslip is
present,
such as perhaps in a steady turn.
The primary quantity of interest
here is the
overall LD = CL_windCD_wind = CLCD_wind, and
CD_wind
is more accurately obtained from the
Trefftz-Plane anyway.
The alternative
Trefftz-Plane drag coefficient CDi is calculated
from the wake trace in the Y-Z plane far
downstream. This is
generally more reliable
than the CD obtained from surface force
integration, and is the appropriate wind-axes
induced drag for
performance prediction.
The span efficiency is defined as
2 2 2
e =
(CL + CY ) (pi A CDi) A = Bref Sref
with Sref being replaced by 2 Sref for
Y-image cases (iYsym = 1).
Stability
derivatives
---------------------
Command ST generates the stability derivative
matrix for the
current conditions.
Derivatives with respect to control
variables
and design parameters are also displayed if
they are available.
Command SB
generates the stability derivative matrix
in
the body axes (AVL's X,Y,Z coordinates).
Flow Results Plotting
---------------------
The T command
starts up the Trefftz Plane plot menu:
=
==================================================
===
Y plot data vs Y
Z plot data vs
Z
D ownwash angle plot toggle (currently
T)
L imits for plot
30
R eset plot limits
N
umber surfaces toggle (currently F)
C olor
hardcopy toggle (currently F)
A nnotate
plot
H ardcopy current plot
ZM
zoom
U nzoom
S ize change
Trefftz plot command:
These plot
options are self-explanatory.
Trimmed Flight Condition Setup
------------------------------
The C1
command in the OPER menu enters the setup routine
for level or banked
trimmed horizontal
flight. This simply provides a convenient way to
set up
the required constraints for OPER
without laborious manual calculations.
An
aircraft mass and air properties are required.
These can be provided by
a mass file which is
read in during program startup, or from the main
AVL menu.
If a mass file was not read in,
the necessary information can be input manually
here in the C1 sub-menu.
The C1
routine works with the following variables and
trim equations:
phi (arbitrary bank
angle, positive to right)
CL (arbitrary
CL, whatever is being specified)
m
(mass)
g (gravity acceleration)
rho
(air density)
S (reference area, given
in input file as SREF)
V = sqrt(2 m g
rho S CL cos(phi)) (airspeed)
R = V^2 g
tan(phi) (turn radius, positive for right
turn)
W = V R (turn rate,
positive for right turn)
p = 0
(roll rate, zero for steady turn)
31
q = W sin(phi) (pitch
rate, positive nose upward)
r = W cos(phi)
(yaw rate, positive for right turn)
These equations are evaluated if possible (if
the parameters are available),
and the
following displaymodification menu is then
entered:
Setup of trimmed run case
17: 0 deg. bank
(level or banked horizontal flight)
=================================================
B bank angle = 0.000 deg
C CL = 0.7000
V
velocity = 5.648 ms
M mass
= 0.9195 kg
D air dens. = 1.225
kgm^3
G . = 9.810 ms^2
turn rad. = 0.000 m
load fac.
= 1.000
X X_cg = 3.400
Lunit
Y Y_cg = 0.000 Lunit
Z Z_cg = 0.5000 Lunit
Enter parameter, value (or # - + N )
c>
A parameter can be changed by
giving its command and value. For example, typing
B 20
changes the bank angle to
20 degrees. The equations are then immediately
re-evaluated with this new parameter, and the
menu is displayed again with
the new resulting
flight variables:
Setup of trimmed
run case 17: 0 deg. bank
(level or banked horizontal flight)
=================================================
B bank angle = 20.00 deg
C CL = 0.7000
V
velocity = 5.891 ms
M mass
= 0.9195 kg
D air dens. = 1.225
kgm^3
G . = 9.810 ms^2
turn rad. = 9.719 m
load fac.
= 1.064
32
X
X_cg = 3.400 Lunit
Y Y_cg
= 0.000 Lunit
Z Z_cg =
0.5000 Lunit
Enter parameter,
value (or # - + N ) c>
Note
that the velocity, turn radius, and load factor
have all been recomputed
to match the new
specified bank angle and the current CL. In
general, any
parameter with a command key in
the menu can be changed, and the others
will
be recomputed to match.
The X_cg, Y_cg,
Z_cg parameters do not enter directly into the
trim calculations
here,
but they are used
to set Xref, Yref, Zref when the VL calculation is
finally
executed.
Hence they will affect
the control deflections needed to enforce trim.
Special commands
- - - - -
- - - -
The special commands (# - + N) have
exactly the same action as in the OPER menu.
The
N 20 deg. bank
A
different case can be brought up just by typing
its index. For example,
5
shows the parameters for case 5:
Setup of trimmed run case 57: 40 deg. bank
(level or banked horizontal flight)
=================================================
B bank angle = 40.00 deg
C CL = 0.7000
V
velocity = 6.453 ms
M mass
= 0.9195 kg
D air dens. = 1.225
kgm^3
G . = 9.810 ms^2
turn rad. = 5.059 m
33
load fac. = 1.305
X X_cg
= 3.400 Lunit
Y Y_cg =
0.000 Lunit
Z Z_cg = 0.5000
Lunit
Enter parameter, value (or #
- + N ) c>
The current case can be
deleted with the
A new case can be created
with the
Multiple-case commands
- - - - - - - - - - - -
Frequently, it is
desirable to set a parameter to one value for all
run cases,
such as the air density, for
example. Rather than repetitively switching
to each run case and setting its density, e.g.
1
D 0.8
2
D 0.8
3
D 0.8
.
.
one can set the
value for ALL the run cases by typing the
parameter command twice:
DD 0.8
This works for all parameters in the menu, and
can save considerable typing.
Moment
trim setup（力矩配平设置）
- - - - - - - - -
Once
the C1 trim menu is exited by just typing
still be necessary to set up zero-moment
constraints for the
various control
deflections. The C1 menu cannot do this for the
user,
since it has no way of knowing what each
control variable does.
Execution（计算）
- - - - -
Execution after the C1 trim
setup is performed with the X command as usual.
34
It is easy to compute each
run case that is set up simply by typing its
integer index, followed by X. For example,
1
X
2
X
.
.
Any one computed run case can of course
be examined via the listings or plotting.
An alternative to converging each run case
separately, one can
issue the XX command,
which will converge ALL the run cases.
It is
a good idea to converge all the cases before
saving the
run case file with the S command,
so that all the parameters
in the file have
their converged values.
Looping-Flight Condition Setup
------------------------------
The C2
command in the OPER menu allows a convenient way
to set up constraints required to achieve a
specified
looping flight. The necessary AVL
parameters are computed
using the following
variables and equations:
CL
(arbitrary CL, whatever is being specified)
m
(mass)
g (gravity acceleration)
rho
(air density)
R (turn radius)
N
(load factor)
S (reference area, given
in input file as SREF)
R = 2 m ( rho S
CL )
N = 0.5 rho V^2 S CL (m g)
p = 0
(roll rate)
q = VR
(pitch rate)
r = 0
(yaw rate)
35
These
equations are evaluated if possible (if the
parameters are available),
and the following
displaymodification menu is then entered:
Setup of trimmed run case 17: looping
flight
(steady pitch rate - looping
flight)
=================================================
C CL = 0.7000
V
velocity = 5.648 ms
M mass
= 0.9195 kg
D air dens. = 1.225
kgm^3
G . = 9.810 ms^2
R turn rad. = 3.324 m
L load
fac. = 1.000
X X_cg =
3.400 Lunit
Y Y_cg = 0.000
Lunit
Z Z_cg = 0.5000 Lunit
Enter parameter, value (or # - + N
) c>
The procedure here is the
same as with the C1 menu. Any parameter
can
be specified, and the remaining ones are computed
to match.
The case is then executed in the
OPER menu with the X command.
Parameter Modification Menu
---------------------------
The M command
enters the general parameter modification sub-
menu:
Parameters of run case
17: 0 deg. bank
B bank = 0.000 deg
E
elevation = 0.000 deg
MA Mach no.
= 0.000
V velocity = 5.648
ms
D air dens. = 1.225 kgm^3
G . = 9.810 ms^2
M mass =
0.9195 kg
IX Ixx = 0.2052
kg-m^2
IY Iyy = 0.7758E-01 kg-m^2
IZ Izz = 0.2790 kg-m^2
X X_cg = 3.400 Lunit
Y Y_cg
= 0.000 Lunit
Z Z_cg =
0.5000 Lunit
36
CD
CDo = 0.1700E-01
LA dCL_a =
0.000
LU dCL_u = 0.000
MA dCM_a = 0.000
MU dCM_u = 0.000
Enter
parameter, value (or # - + N ) c>
This is in effect a
It simply accepts new
parameter values without trying to apply
any
trim equations. Only a few of these parameters,
such as
Mach and XYZ_cg will affect OPER's
solution calculation.
The remaining
parameters are used for eigenmode calculations
described next.
Run Case File
Contents（计算状态文件内容）
----------------------
A run case file can be listed to show its
contents.
One case block in the file is
shown below:
---------------------------------------------
Run case 1: VIAS=220 mph
alpha -> alpha = 4.00000
beta -> beta = 0.00000
pb2V -> pb2V = 0.00000
qc2V -> qc2V = 0.00000
rb2V -> rb2V = 0.00000
flap -> flap = 0.00000
aileron -> Cl roll mom = 0.00000
elevator -> Cm pitchmom = 0.00000
rudder -> Cn yaw mom = 0.00000
alpha = 2.31230 deg
beta = 0.00000 deg
pb2V = 0.00000
qc2V = -0.361446E-15
rb2V = 0.00000
CL = 0.312309
CDo = 0.420000E-01
bank = 0.00000 deg
37
elevation = 0.00000
deg
heading =
0.00000 deg
Mach = 0.00000
velocity = 312.000 fts
density = 0.176000E-02 slugft^3
. = 32.0000 fts^2
turn_rad. = 0.00000 ft
load_fac. = 1.00000
X_cg = 2.42374
Y_cg = 0.00000
Z_cg = -0.103875
mass = 800.000 slug
Ixx = 121787. slug-ft^2
Iyy = 59146.4 slug-ft^2
Izz = 173515. slug-ft^2
Ixy = -0.113010E-03 slug-ft^2
Iyz = 0.00000 slug-ft^2
Izx = 1621.01 slug-ft^2
visc CL_a = 0.00000
visc CL_u = 0.00000
visc CM_a = 0.00000
visc CM_u = 0.00000
The upper sub-block specifies the
constraint associated with each
operating
parameter, and is exactly what appears at the top
of the
OPER menu.
The lower sub-
block simply lists all the current parameter
values.
If this run case was not converged
before the run case file was written,
the
operating parameter values may not correspond to
the specified
constraints. For example, the
top constraint
alpha -> alpha
= 4.00000
indicates that alpha is
to be driven to 4.0 degrees, so the alpha value
line
alpha = 2.31230 deg
is not
CL = 0.312309
is therefore probably not up to date
either. Such
38
values may or
may not be of consequence. A stale alpha or CL
value
doesn't matter, since the run case will
always be converged before
it is used for
plotting, listing output, or eigenmode analysis.
In any case, issuing the XX command in OPER
before saving the
run case file will ensure
that alpha and CL are up to date.
The dimensional parameter values related to
the aircraft mass, e.g.
density =
1.22500 kgm^3
.
= 9.81000 ms^2
X_cg =
2.95775
Y_cg = 0.00000
Z_cg
= 0.609524
mass = 0.231000 kg
Ixx = 0.165803E-01 kg-m^2
Iyy = 0.113692E-01 kg-m^2
Izz = 0.278108E-01 kg-m^2
Ixy = 0.304560E-10 kg-m^2
Iyz = -0.135360E-10 kg-m^2
Izx = -0.362168E-03 kg-m^2
may also be
has since been modified.
The stale data can be changed to reflect the
new mass file using the MSET command at top
level.
Finally, the velocity, turn
radius, and load factor data,
velocity
= 5.42671 ms
turn_rad. = 0.00000 m
load_fac. = 1.00000
which depends on the mass file as well as
the CL, will probably
need to be updated is
the mass file is changed. This can be
done
manually, or by using the C1 or C2 trim menus of
OPER.
MODE Routine -- Eigenmode
Analysis
==================================
AVL has the capability to perform
eigenmode analysis and display
the results in
a number of ways. Meaningful use of this facility
requires that a realistic configuration is
defined, along with
39
realistic mass, inertia, and CG data.
The mass, inertia, and CG
data can be input
directly (in OPER's C1,C2, or M submenus),
or
obtained from a file.
One or more
trimmed run cases must also be first set up and
checked
for correctness in the OPER menu.
These cases can be saved to the
file from
OPER, which is then read in later during AVL
startup.
Any other run case file can be read
in later using the CASE command
from the main
menu.
Typing MODE from the main AVL
menu brings up the MODE menu,
preceded by the
currently-defined run cases, if any.
Run-case parameters for eigenmode analyses
...
run alpha beta CL
CDo bank velocity density X_cg
mass
deg deg
deg ms kgm^3
kg
1 2.69 0.00 0.700 0.170E-01 0.00 5.65
1.23 3.40
0.920
2 2.69
0.00 0.700 0.170E-01 10.0 5.69 1.23
3.40
0.920
> 3 2.69 0.00
0.700 0.170E-01 20.0 5.83 1.23 3.40
0.920
4 2.69 0.00 0.700
0.170E-01 30.0 6.07 1.23 3.40
0.920
5 2.69 0.00 0.700
0.170E-01 40.0 6.45 1.23 3.40
0.920
6 2.69 0.00 0.700
0.170E-01 50.0 7.04 1.23 3.40
0.920
7 2.69 0.00 0.700
0.170E-01 60.0 7.99 1.23 3.40
0.920
================================
==========================
M
odify parameters
N ew eigenmode
calculation
P lot root locus
40
B lowup window
R eset to
normal size
eX amine selected eigenmode
A nnotate current plot
H ardcopy
current plot
S ystem matrix output
W rite eigenvalues to file
D ata file
overlay toggle
Z oom
U nzoom
.MODE c>
The run cases
serve as the baseline states about which the
eigenmodes are defined.
The indicator in the
menu above shows that run case 3 is currently the
chosen
baseline state. This is changed just
by typing the new run case index.
Typing
of
all their roots will then
create root locii. This is useful for
investigating
the effect of an operating
parameter (e.g. V, CL, X_cg, bank, etc.) on the
roots.
Parameter editing
- - - -
- - - - -
If the run case parameters are not
correct, they can be changed with the M command.
For example:
M
Parameters of run case 17: 0 deg. bank
B bank = 0.000 deg
E elevation = 0.000 deg
V
velocity = 5.648 ms
D air dens.
= 1.225 kgm^3
G . = 9.810
ms^2
M mass = 0.9195 kg
IX Ixx = 0.2052 kg-m^2
IY Iyy
= 0.7758E-01 kg-m^2
IZ Izz =
0.2790 kg-m^2
41
X
X_cg = 3.400 Lunit
Y Y_cg
= 0.000 Lunit
Z Z_cg =
0.5000 Lunit
CD CDo =
0.1700E-01
LA dCL_a = 0.000
LU dCL_u = 0.000
MA dCM_a = 0.000
MU dCM_u
= 0.000
Enter parameter,
value (or # - + N ) c>
This
menu is the same as in OPER. Note that changing a
parameter may not
then represent a trimmed
flight condition. If the baseline state is to be
trimmed, as is done with traditional eigenmode
analyses, the parameter changes
are probably
best performed in the C1 or C2 menu in OPER.
CL,CM derivative modifiers
- - - - -
- - - - - - - - -
The LA,LU,MA,MU commands in
the M menu allow specifying explicit
added
changes to the CL and CM derivatives with respect
to alpha
and speed. The alpha derivative
modifications dCL_a, dCM_a might
represent
stall, or perhaps effects of separation bubble
movement.
The speed derivative modifications
dCL_u, dCM_u might represent
Mach or Reynolds
number effects on the wing or tail airfoils.
These derivative modifiers are used only for
the eigenmode calculations
in the MODE menu.
They do not in any way affect the analysis
calculations
in OPER.
Mode
calculation
- - - - - - - - -
The
eigenmodes for one or all run cases are computed
with the N command.
The eigenvalues and
eigenvectors are listed, and the eigenvalues are
also
plotted on a root map. This can be re-
plotted at anytime with the P command,
or
examined more closely with Z or B.
Mode Examination
- - - - - - - - -
The
motion of any mode can be viewed in real time by
issuing the X command,
and then clicking on
the root symbol. This brings up the mode-view
menu:
42
------------------------------
L eft
R ight
U p D own
C lear
Z
oom N ormal size
I ngress
O utgress
H ardcopy A nnotate
P anning camera toggle: T
<
> 0 mode play -- real time
- + 1 mode
scale
S mode sign change
Type in plot window: Command, or
All commands must be
typed with the cursor in the graphics window.
The viewpoint can be set with the L,R,U,D,C
keys, like in the
geometry viewer in OPER.
The mode motion is rewound or advanced in
time with the < and > keys
(shift key is not
necessary). Holding down these keys will play the
mode forward or backward in real time. Typing
0 will jump back to
the starting time.
The mode scale will decay or grow in time
depending on the real part
of the eigenvalue.
But this can be arbitrarily scaled up or down
with the - and + keys. The 1 key sets the
scale factor to a nominal
The P
command controls the camera-panning toggle. If
panning is on,
the camera follows the aircraft
at the baseline motion, so that the
baseline
state appears stationary. If panning is off, the
baseline
state moves, with the eigenmode
motion superimposed on top of it.
Viewing
either with or without panning may be best,
depending
on the mode.
System
matrix output
- - - - - - - - - - -
Eigenmode analysis begins by considering that
the unsteady flight variables
43
U(t) consist of the steady baseline
state Uo plus an unsteady perturbation u(t).
The control variables D are considered the
same way.
U(t) = Uo + u(t)
D(t) =
Do + d(t)
The perturbations are governed
by the following linear system:
.
u = A
u + B d
The A and B system matrices
depend on Uo and Do. They can be listed
with
the S command from the MODE menu. The 12
components of the u(t)
vector are ordered as
follows:
u x velocity (+
forward)
w z velocity (+ down)
q
pitch rate (+ nose up)
theta pitch angle (+
nose up)
v y velocity (+ to right)
p roll rate (+ to right)
r yaw
rate (+ to right)
phi roll angle (+ to
right)
x x displacement (+ forward)
y y displacement (+ to right)
z
z displacement (+ down)
psi heading angle
(+ to right)
The d(t) control vector
components are whatever controls were declared
in the file, in the order that they appeared.
Plotting Options
================
The top-level PLOP
command produces the plot option menu,
shown
below with the default values. Most of these
parameters
must be changed before the first
plot is made, otherwise they
may not have the
intended effect.
44
...............................................
G raphics-enable flag T
C
olor PostScript output? F
I ndividual PS
file output? F
A spect ratio of plot
object 0.0000
S ize of plot object
9.00
P age dimensions 11.00 x
8.50
M argins from page edges 0.00
F ont size (relative) 0.0170
W
indowscreen size fraction 0.7000
O
rientation of plot: Landscape
B
lowup input method: Keyboard
Option, Value (or
Toggling the Graphics-enable flag to F is
recommended if
AVL is being executed in batch
mode using a command file.
Normally, all
hardcopy goes to the single multi-page file.
Toggling the Individual PS file flag to T will
place successive
hardcopy pages in an
individual files, named
etc.
These may then be used to create mode
animation, etc.
The other parameters and
options are mostly self-explanatory.
45