VIPER (Viscous Interaction Performance Evaluation Routine) was originally developed to help assess boundary layer interactions for high area ratio nozzles. Since the release of Version 1, there have been many improvements and corrections made to the original version.

VIPER Version 2 was developed for the Phillips Laboratory and capabilities added to the original code include the treatment of two-phase flows and implementation of the slip wall boundary condition.  The following is a brief summary of upgrades and enhancements contained in Version 2:

• Two-Phase flow terms have been added to the PNS governing equation.
• The two-phase transonic module TRAN2P, taken from the TDKP code, was incorporated into the VIPER code.
• A slip wall boundary condition was implemented so that an inviscid solution for nozzle flow performance can be predicted.
• Boundary conditions at the centerline and wall were reformulated so that a normal profile at the boundary was not assumed.
• Additional damping control at the symmetry centerline was added, thus allowing a wider range of problems to be solved.
• Corrections to the centerline metrics.
• Corrections and improvements to the chamber, transonic, and boundary layer modules (ODE, ODK, TRAN, and MABL) were made.
• An improved procedure for blending the boundary layer and inviscid solutions at the PNS startline were implemented.
• Additional second order viscous terms which were previously assumed small and neglected were added to the governing equations.
• A source flow option is now available.
• Standard LINPAC matrix routines were incorporated into the basic matrix solvers so that users can take advantage of machine optimized versions of these routines.
• Dimensions of the code were increased to provide higher resolution for the boundary layer region, so that improved predictions can be obtained for cold wall flow problems.

Pump fed engines with either dump cooling, or tangential slot injection of gas generator exhaust into the primary nozzle flow are also treated. The gas generator exhaust product composition can be completely different than that found in the primary core flow. The VIPER Parabolized Navier-Stokes (PNS) computer code is used to compute the entire super sonic flow field, including effects of the finite rate reaction zone produced by mixing of the injectant and core gases.

Other enhancements that are contained in Version 3.5 are listed below.

• In order to view the results of the calculations effectively, a Graphic User Interface (GUI) has been written. The GUI is written for the UNIX operating system using XWINDOWS and the MOTIF protocol.
• An interface has been written that transfers nozzle exit plane flow properties from VIPER to SPF-3, the Standard Plume Flowfield computer program.
• The subsonic/transonic analysis has been upgraded significantly, especially the kinetic boundary layer module, MABL-K.
• The PNS wall boundary conditions have been modified so that a steady state temperature can be calculated for a radiation cooled nozzle.
• Auxiliary calculations and output have been added so that total flow properties for a Pitot tube probe are available. The method assumes frozen flow through a normal shock, followed by stagnation.
• Near plume flowfield option has been added to allow the computation to proceed past the nozzle exitplane for one or two nozzle exit radii.

• IBM RS 6000 (AIX 3.2)
• Silicon Graphics (IRIX 6.5)
• SUN SPARC (SunOS 5.7)