Use of VLLOFT and VLCOMP to Obtain Loads

The Fortran programs VLLOFT and VLCOMP can be used to obtain aerodynamic load information as well as aerodynamic coefficients. Aerodynamic loads can be obtained from the output file called VLPLT.DAT. Instructions on using VLLOFT and/or VLCOMP can be obtained from Dr. L. A. Carlson in 750 H.R. Bright. These programs are vortex lattice codes and suitable for subsonic (not transonic) speeds. They do not include any viscous effects.

The VLPLT.DAT file contains a lot of information.

First Line : A Value for JPLT. This should be 1.

Next Four Lines: The coordinates of the corner points of the wing, starting at the apex and going counterclockwise around the wing.

Sixth Line: The number of Chordwise Panels (NC) and the number of Spanwise Panels (NS). These values are typically 10 and 32 or 20 and 32.

Seventh Line and following:

For each panel the following information is printed out starting with the left wing-tip leading edge, moving aft, and then moving in-board:

X1, X2, Y, , and local panel chord (not local chord,

Note that.)

Next NS Lines: Numbers related to the local spanwise circulation, i.e. lift coefficient values.

Last Line: , A Ridiculous CD value for 1 Radian plus Alpha (don’t worry about), and sweep in radians of outboard leading edge.

Obviously the primary part you are concerned with is the seventh line and following. This information has the following meaning.

Location of Pressure Force is at X = (X1 + X2)/2 and Y = Y

The pressure at that point can be obtained from the definition of . I.E.

value.

Panel width = Absolute Value (X2 – X1)

Panel Length =

So you should be able to take the output file and convert into your finite element input file by appropriate deleting and massaging of data. This action could be accomplished by using Excel (one possibility) or reading the file into a Fortran program you write. Then use the Fortran program to "convert” the data into the form and format you need at the locations you need the data. I suggest linear interpolation.

Note this approach only gives vertical forces. It does not give axial forces.

I have put the VLLOFT and VLCOMP codes into aeroserver/classnotes/carlson/aero405.

Lee Carlson, March 19, 2002

Aero405 Loads.doc 11/16/18 5:19PM