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1993-07-28
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Lamar University Compressible Flow Calculator
FILE and HARDWARE DETAILS
The compressible flow calculator supplied has three files; COMPFLOW.EXE,
SCRNCLRS.DAT, and COMPFLOW.DOC which is this file. COMPFLOW.EXE is the
executable code for the compressible flow calculator and it should be in the
default directory with SCRNCLRS.DAT. The latter file, as the name implies,
is a self explanatory data file which controls the screen colors (added at
the suggestion of Dr. John Adams). The program should run on any DOS 3.x or
later PC with an EGA monitor and card. The program can be executed from
floppy but it may take several minutes to load. The program is distributed
in executable form as freeware provided it is not altered or files added or
deleted. This program may be distributed unaltered by CD-ROM vendors.
GENERAL PROGRAM DESCRIPTION
The program is written for students taking their first course in
compressible flow. It includes 1-dimensional isentropic, normal shock,
Fanno, Rayleigh, isothermal, and general combined change functions and
inverses. The program contains an approximate, numerically integrated,
combined change flow distribution calculator (called a flow simulator). The
program also contains 2-dimensional functions for Prandtl-Meyer flow and
wedge generated oblique shocks. A numerically integrated conical shock
property calculator is also included.
The default gas is air, however, the program has provision for changing to
any one of a number of gases or calculating properties for a mixture of
gases. A crude numerical calculator and a set of 8 memories are included so
that students can obtain flow functions, store them in memory, process them
numerically, store the processed result/s and then use the processed result
as an entry to obtain other flow functions. This is typical of the
sequence of operations a student must perform in working compressible
flow problems. Therefore, this program is designed so that the operations
can all be done without writing down and re-entering intermediate results.
The program is menu driven and should largely be self-explanatory. For
each of the types of flow, a separate list of the nomenclature is given. In
addition, a list of technical references is available from the main menu. A
special feature is included that allows students to calculate a range of
functions or flow distribution and store the results in a comma separated
ASCII file. This allows students to plot results with a standard graphing
program like QUATROPRO.
SIMPLE EXAMPLE
Suppose air flows isentropically from section 1 where the Mach number is 2
to section 2. Suppose further that the area ratio, A2/A1, is 0.9 and the
Mach number at section 2 is desired.
Step 1 - Start the program by typing - "COMPFLOW"
Step 2 - Press the space bar to acknowledge the opening screen
Step 3 - Select "1" for isentropic flow
Step 4 - Select "1" for Mach number, M given
Input the value of Mach number in response to the prompt - "2"
You should see a results screen that displays the isentropic functions for
a Mach number of 2.
Step 5 - Select "m" for memories while looking at this screen
You will be prompted for the memory number, input "1"
You will be asked for the data number, input "2"
You should see A/A* = 1.6875 stored in memory location 1 at the bottom
left of your screen.
Step 6 - Hit the space bar to return to the isentropic menu then select
"C" for the arithemetic calculator
You should see the arithmetic calculator appear.
Step 7 - Input "m1" to bring memory 1 to the calculator display, the
cursor will move down to the operator box when you press enter.
Press "*" for multiply
Press ".9 enter" for the area ratio
The display should read 1.51875 which you should store in memory
2 by pressing "s2".
Exit the arithmetic calculator by pressing "e enter"
Step 8 - Input "2" to select A/A* given
When prompted for the value of A/A*, input "m2" for memory 2
You should see a results screen which includes both a subsonic and a
supersonic solution. If the area monotonically decreases to section 2, then
the solution you want is the supersonic one for this case. In general, you
must know about the physical circumstances to be able to chose which of the
multiple solutions calculated is appropriate for your problem (and in fact,
this is part of learning compressible flow).
COMMENTS, QUESTIONS or CORRECTIONS
Comments, questions or corrections may be sent by letter to the address on
the opening screen of the program or via E-Mail over Internet to
fred@LUB001.LAMAR.EDU.