AVL用户手册

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 < pb/2V < 0.10

-0.03 < qc/2V < 0.03

-0.25 < rb/2V < 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 1/B = 1/sqrt(1 - M^2),

where

which shows the expected range of validity.

M 1/B

--- -----

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 image/anti-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 defin ed

（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 = i

ncidence 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 keyword

s, 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 x/c range

]

1.0 0.0 | x/c(1) y/c(1)

0.98 0.002 | x/c(2) y/c(2)

. . | . .

. . | . .

. . | . .

1.0 -0.01 | x/c(N) y/c(N)

The AIRFOIL keyword declares that the airfoil definition is input

as a set of x/c, y/c pairs.

x/c,y/c = airfoil coordinates

The x/c, y/c 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 y/c 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

x/c 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 x/c range ]

filename | filename string

The AFILE keyword is essentially the same as AIRFOIL, except that the x/c,y/c

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 x/c 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

（< /p>

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

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 sections.

This 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

x/c=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 | dCL/da scaling factor

This scales the effective dcl/da of the section airfoil as follows:

dcl/da = 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 dcl/da values

than thin airfoils. A good estimate for CLaf from 2D potential

flow theory is

CLaf = 1 + 0.77 t/c

where t/c is the airfoil's thickness/chord 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 dcl/da = 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

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

rag ged

（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

m

the

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

Constan ts

(

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