Computer program, AREAX, calculates properties of compressible fluid flow with friction and area change. Program carries out quasi-one-dimensional flow analysis which is valid for laminar and turbulent flows under both subsonic and choked flow conditions. Program was written to be applied to gas film seals

Smith, P. J.

Zuk, J.

English

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Aril 1975	 B75-10020 
•	 NASA TECH BRIEF 
Lewis Research Center 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Compressible Flow Computer Program 
for Gas Film Seals 
A computer program, AREAX, has been developed 
which calculates the properties of compressible fluid flow 
with friction and area change. The program carries out a 
quasi-one-dimensional flow analysis which is valid for 
laminar and turbulent flows under both subsonic and 
choked flow conditions. The program was written to be 
applied to gas film seals. 
Some shaft seals in advanced rotating machinery, such 
as in advanced aircraft turbine engines, may operate at 
higher speeds, temperatures, and pressures than the 
contacting shaft seals in current use. Because of these 
severe operating conditions, a positive face separation (no 
rubbing contact) is required for long life and reliability. 
However, seal-face deformation is very likely to occur. 
These deformations may be caused by various distor-
tions (thermal, centrifugal, pressure, etc.). Seal-face distor-
tions become more pronounced under severe operating 
conditions and are usually detrimental to seal, perform-
ance. Hence, prediction of these face deformation effects 
on gas-film-seal performance is of paramount importance. 
This computer program enables the prediction of gas-
film-face-seal performance when face deformations and/or 
radial area change is significant. The analysis is especially 
useful for choked flow conditions. 
Computer programs have proven useful in seal design 
where much of the physical information of interest is 
difficult to determine experimentally. AREAX should be 
used when the effects of seal-face distortions are desired 
and when the radial area change is significant. 
The program must be supplied with the geometry of 
the seal, the gas properties, the sealed gas reservoir 
conditions, the constants for determining the variation of 
mean friction factor with Reynolds number, and certain 
logical variables which control output. Input and output 
can be in either the International System (SI) or the U.S. 
customary system of units.
In analyzing the flow across the seal, AREAX first 
reads the input data. It then analyzes the flow for each 
combination of film thickness and deformation angle. The 
program first solves the Mach number equation and 
determines the Mach number distribution across the seal 
face. AREAX then determines the distributions across the 
seal face of pressure, temperature, density, velocity, mean 
friction factor, Reynolds number, mass and volume flow 
rates, Knudsen number, seal opening force, center of 
pressure, and, where appropriate, rotational Reynolds 
number, variables associated with power dissipation, and 
axial film stiffness. When all the data for all the film 
thicknesses have been calculated, AREAX writes the 
output data with appropriate labels and headings. 
Results obtained using AREAX showed excellent 
agreement with analytical solutions for pure radial viscous 
flow and for viscous flow with a small tilt of the sealing 
surfaces. Also, AREAX agreed with computer programs 
that analyze only parallel sealing surfaces.. 
Notes: 
1. The program is written in FORTRAN IV for use on an 
IBM 7094 11/7044 direct couple computer. 
2. Inquiries concerning this program should be directed 
to:
COSMIC 
Information Services 
112 Barrow Hall 
University of Georgia 
Athens, Georgia 30602 
Reference: LEW- 12286 
Source: J. Zuk and P.J. Smith

Lewis Research Center 
(LEW-1 2286) 
Category 09 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this.document, or warrants that such use 
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Compressible flow computer program for gas film seals

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