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Foundation ::
Thermal Tools ::
DFFSM
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DFFSM
Dynamic Fluid Flow Simulation Models
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Moderators:
Adopt This Application!
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SOURCE CODE AVAILABLE
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DFFSM (Dynamic Fluid Flow Simulation Models) is a set of executables
that have been developed to model pressure-fed cryogenic rocket propellant
run systems, pressurized gas systems, and coolant water feed systems.
These systems are integral parts of rocket engine and aerospace component
ground test facilities currently or soon to be in operation at NASA Stennis
Space Center.
These simulation models use standard algorithms for computing fluid
flows and pressure drops. They also utilize fluid property curve-fit subroutines
in which fluid properties of viscosity, density (or supercompressibility
factor for gases), enthalpy, speed of sound, ratio of specific
heats (for compressible gases), and thermal conductivity are polynomial
equation curve-fits along isobars or isotherms. The respective subroutines
then interpolate (using either linear interpolation or Lagrangian
three point quadratic interpolation) between isobars or isotherms to obtain
the calculated property as a function of pressure and temperature.
DFFSM also uses polynomial curve-fit equations to compute isentropic temperature
changes as a function of pressure for liquids.
In cases where the programs need to compute an unknown temperature
from a known pressure and another known property, a numerical finite difference
Newton-Rhaphson Iteration technique is used. For example, as the
program marches upstream or downstream along a pipe or tube, it continuously
recalculates a new fluid temperature from a new pressure and a known
enthalpy (which is constant in cases where the assumption of isenthalpic
fluid flow is used in the program or which would change in relation to the
pipe/tube wall heat transfer rate and fluid mass flow for programs coupling
heat transfer and pressure drop effects).
On the systems level scale, the program reads in the user inputs for
system configuration, liquid and gas vessel initial conditions, fluid flow
rate, pressure requirements, and temperature requirements. The simulation
model then computes the fluid conditions in the lines, components, and
vessels by marching in user-selected length increments upstream or downstream
through various series of singular or parallel lines and components.
For each line section and at each user input time step, the respective simulation
model also calculates the effects of elevation change and momentum
change in addition to frictional pressure drops, for all fluid (liquid and
gas) flows.
A number of the simulation models incorporate an iterative process to
match specific stagnation pressure and enthalpy of fluid at vessel-to-line
interfaces with computed vessel fluid pressure and temperature based on
isentropic pressurization or depressurization of fluid in the vessel. Many
of the simulation models also calculate the liquid volume changes in liquid
water and cryogen run tanks, as well as the resulting liquid level changes
and tank pressurant gas mass flow and pressure requirements. These volume
change calculations are based on the run tank discharge pressures, liquid
level head pressure, and ullage volume rates of change in the run tank.
DFFSM carries the NASA case number SSC-00036. It was originally released as part of the NASA COSMIC collection.
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More software from National Technology Transfer Center
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