The Generalized Fluid System Simulation Program (GFSSP) version 2.01 is a general-purpose computer program for analyzing steady-state and time-dependent flowrates, pressures, temperatures, and concentrations in a complex flow network. The program is capable of modeling phase changes, compressibility, mixture thermodynamics, and external body forces, such as gravity and centrifugal.

The program contains subroutines for computing "real fluid" thermodynamic and thermophysical properties for 12 fluids. The fluids are helium, methane, neon, nitrogen, carbon monoxide, oxygen, argon, carbon dioxide, fluorine, hydrogen, water, and kerosene (rocket propellant 1). The program also provides the options of using any incompressible fluid with constant density and viscosity.

Seventeen different resistance/source options are provided for modeling momentum sources or sinks in the branches. These options include: pipe flow, flow through a restriction, noncircular duct, pipe flow with entrance and/or exit losses, thin sharp orifice, thick orifice, square edge reduction, square edge expansion, rotating annular duct, rotating radial duct, labyrinth seal, parallel plates, common fittings and valves, pump characteristics, pump power, valve with a given loss coefficient, and a Joule-Thompson device.

GFSSP employs a finite volume formation of mass, momentum, and energy conservation equations in conjunction with the thermodynamic equations of state for real fluids. Mass, energy, and specie conservation equations are solved at the nodes; the momentum conservation equations are solved in the branches. The system of equations describing the fluid network is solved by a hybrid numerical method that is a combination of the Newton-Raphson and successive substitution methods.

The computer program has three major parts. The first part consists of the subroutines for the preprocessor. The preprocessor allows the user to interactively create the flow network model consisting of nodes and branches. All of the input specifications, including the boundary conditions are specified through the preprocessor. The second major part of the program consists of the subroutines that provide the initial conditions and then develop and solve all of the conservation equations in the flow network. The third part of the program consists of the thermodynamic-property programs that provide the necessary thermodynamic- and thermophysical-property data required to solve the resulting system of equations.

GFSSP has been developed, tested, and documented by Sverdrup Technology for Marshall Space Flight Center (MSFC). GFSSP is currently being used at MSFC, and its predictions showed good agreement when compared with test data. GFSSP runs on an IBM-PC compatible computer under Windows 95 and Windows NT and under UNIX operating systems.

This program was written by Alok Kumar Majumdar, John W. Bailey, Paul Alen Schallhorn, and Todd E. Steadman of Sverdrup Technology for Marshall Space Flight Center. NASA seeks companies interested in licensing this technology to make it available as a commercial product or for their own use. Licensing inquires should be directed to Larry Gagliano, MSFC Software Release Authority at (256) 544-7175 or This email address is being protected from spambots. You need JavaScript enabled to view it..

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

the Patent Counsel
Marshall Space Flight Center; (256) 544-0021.

Refer to MFS-31303.


NASA Tech Briefs Magazine

This article first appeared in the January, 2000 issue of NASA Tech Briefs Magazine.

Read more articles from the archives here.