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This computer program can be used to predict the gas dynamic and
chemical properties of underexpanded rocket plumes from sea level to
the altitude above which the viscous continuum flow assumption, with
distinct shocks, is no longer valid. The program computes the plume
shock structure while simultaneously accounting for turbulent mixing,
nonequilibrium chemistry, and gas/particle nonequilibrium effects.
The program also has the ability to calculate plume properties in the
subsonic region downstream from the Mach disc, downstream of the shock
reflected from the triple point, and in the far field. The program
can readily be used to determine plume optical and electrical
properties, which are necessary data for calculating the infrared
radiation pattern and radar cross section. This program was used to
calculate deposition rate of various nitrogen oxides into the
stratosphere caused by the Space Shuttle exhaust plumes.*

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The AIPP code is based on the Multitube code developed by Boyton (which
incorporates the finite difference streamtube calculation technique) and
has been expanded to treat particle/gas nonequilibrium, chemical kinetic,
and turbulent mixing effects within exhaust plumes. For the gas flow
upstream of the Mach disc, the governing elliptic Navier-Stokes equations
are reduced to a hyperbolic system (including lateral pressure gradients)
by neglecting diffusion of mass, momentum, and energy along streamlines as
compared with that across streamlines. The conservation equations are then
written in a streamline oriented coordinated system. Shocks are treated as
thin bounding surfaces of the flow across which the Rankine-Hugoniot
relations are applicable. In the subsonic region behind the Mach disc the
inviscid flow governing equations are taken to be elliptic. The equations
of flow must be solved within the supersonic and subsonic regions, while
simultaneously maintaining the equality of pressure and flow direction
along the dividing streamline. In meeting these boundary conditions several
approximations are employed to reduce the amount of computer time and storage
required. For the condensed phases present within the flow a continuum
particle cloud assumption is made and field conservation equations for
continuity, momentum, and energy can be written for the particles.*

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A finite difference formulation of the gas phase and particle cloud
governing equations is utilized on a grid which lies along and
perpendicular to the streamlines. The gas flow equations are solved via
an explicit finite difference marching technique. The chemical production
terms utilize an implicit finite difference formulation because an explicit
formulation leads to an impractically small integration step for
near-equilibrium chemistry. The particle equations have no wave or
diffusive nature and are solved explicitly via a finite difference
formulation.
Initially, all flow properties, streamline positions, and angles must be
known along an orthogonal surface. The streamlines are extended an
incremental distance forming a streamtube. The properties at the upstream
surface are used, along with the governing equations, to determine all
the necessary properties at the downstream surface. Below the Mach disc
a similar procedure using assumed streamlines is performed.*

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The computer program is written so that only minimal judgment by the
user is required to operate it. The input data required are nozzle exit
conditions along a surface orthogonal to the exit streamlines, uniform
supersonic external flow conditions, and a suitable reaction mechanism and
rate coefficients. The output contains the results of all calculations in
a highly readable format. Care must be taken that the program is not used to
predict plume characteristics at altitudes above which the assumption of
continuum flow ahead of the Mach disc starts to break down.
( Aerochem Research Labs., Inc. for NASA Langley)
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This program was released through COSMIC as program LAR-12203. The italicized text above is from the official COSMIC release.

- Go to the page of references for the AIPP program.
- Download aipp.zip, containing the original source code and the source code converted to modern Fortran.