Engineering topics

Praharaj, Sarat C.

Publications and source records attributed to Praharaj, Sarat C..

11 records

NASA NTRS1991

External tank aerothermal design criteria verification

If a Space Shuttle Main Engine (SSME) fails during the initial 160 seconds of the Shuttle flight, a return-to-launch-site maneuver will be implemented. The period of concern for this task is the pitch-around maneuver when the vehicle is flying backward. The intent of this report is to identify and define the flowfield at the most critical locations from an environment perspective. The solution procedure used to predict the plume heating rates involves both computational analysis and engineering modeling.

Praharaj, Sarat C.↗

NASA NTRS1991

Two-species variable gamma formulation for a forward-firing rocket nozzle

The object of the paper is to develop an algorithm for an axisymmetric case to study the effects of variable gamma on the flowfield of a two-species mixture. This algorithm forms the basis for extension to three-dimensional SSME application where the Shuttle executes a return-to-launch-site maneuver. The PARC2DR code was used as the foundation for the Navier-Stokes solver, and the species continuity equation for the exhaust species was coupled in an explicit fashion to the Navier-Stokes equation via the variable gamma. The species continuity equation could not be solved with explicit boundary conditions; instead, implicit boundary conditions were implemented.

Saladino, Anthony J.↗

NASA NTRS1991

PARCEQ2D heat transfer grid sensitivity analysis

The material presented in this paper is an extension of two-dimensional Aeroassist Flight Experiment (AFE) results shown previously. This study has focused on the heating rate calculations to the AFE obtained from an equilibrium real gas code, with attention placed on the sensitivity of grid dependence and wall temperature. Heat transfer results calculated by the PARCEQ2D code compare well with those computed by other researchers. Temperature convergence in the case of kinetic transport has been accomplished by increasing the wall temperature gradually from 300 K to the wall temperature of 1700 K.

Saladino, Anthony J.↗

NASA NTRS1990

PARC Navier-Stokes code upgrade and validation for high speed aeroheating predictions

Applications of the PARC full Navier-Stokes code for hypersonic flowfield and aeroheating predictions around blunt bodies such as the Aeroassist Flight Experiment (AFE) and Aeroassisted Orbital Transfer Vehicle (AOTV) are evaluated. Two-dimensional/axisymmetric and three-dimensional perfect gas versions of the code were upgraded and tested against benchmark wind tunnel cases of hemisphere-cylinder, three-dimensional AFE forebody, and axisymmetric AFE and AOTV aerobrake/wake flowfields. PARC calculations are in good agreement with experimental data and results of similar computer codes. Difficulties encountered in flowfield and heat transfer predictions due to effects of grid density, boundary conditions such as singular stagnation line axis and artificial dissipation terms are presented together with subsequent improvements made to the code. The experience gained with the perfect gas code is being currently utilized in applications of an equilibrium air real gas PARC version developed at REMTECH.

Liver, Peter A.↗

NASA NTRS1990

Upgrade of PARC2D to include real gas effects

This paper presents a description of the changes and additions to the perfect gas PARC2D code to include chemical equilibrium effects, resulting in a code called PARCEQ2D. The work developed out of a need to have the capability of more accurately representing the flowfield surrounding the aeroassist flight experiment (AFE) vehicle. Use is made of the partition function of statistical mechanics in the evaluation of the thermochemical properties. This approach will allow the PARC code to be extended to thermal nonequilibrium when this task is undertaken in the future. The transport properties follow from formulae from the kinetic theory of gases. Results are presented for a two-dimensional AFE that compare perfect gas and real gas solutions at flight conditions, showing vast differences between the two cases.

Saladino, Anthony↗

NASA NTRS1989

Boundary layer simulator improvement

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Praharaj, Sarat C.↗

NASA NTRS1987

Boundary layer simulation improvement

The current Boundary Layer Integral Matrix Procedure - Version J (BLIMPJ) is advanced with regard to the previously modeled calculation methods accounting for surface roughness, relaminarization, condensed phase, and thick boundary layer effects. Current analytical limitations will be relaxed to permit more realistic wall and flow conditions and to use appropriate turbulence models with specific emphasis for the projected Orbit Transfer Vehicle (OTV) engine application. The updates will be incorporated into the BLIMPJ computer program, and the modified program will be made operational on the MSFC CRAY computer system. Experimental feasibility studies were conducted to find out how to obtain quality test data with advanced instrumentation for concept verification purposes.

Praharaj, Sarat C.↗

NASA NTRS1986

Measurements for liquid rocket engine performance code verification

The goal of the rocket engine performance code verification tests is to obtain the I sub sp with an accuracy of 0.25% or less. This needs to be done during the sequence of four related tests (two reactive and two hot gas simulation) to best utilize the loss separation technique recommended in this study. In addition to I sub sp, the measurements of the input and output parameters for the codes are needed. This study has shown two things in regard to obtaining the I sub sp uncertainty within the 0.25% target. First, this target is generally not being realized at the present time, and second, the instrumentation and testing technology does exist to obtain this 0.25% uncertainty goal. However, to achieve this goal will require carefully planned, designed, and conducted testing. In addition, the test-stand (or system) dynamics must be evaluated in the pre-test and post-test phases of the design of the experiment and data analysis, respectively always keeping in mind that a .25% overall uncertainty in I sub sp is targeted. A table gives the maximum allowable uncertainty required for obtaining I sub sp with 0.25% uncertainty, the currently-quoted instrument specification, and present test uncertainty for the parameters. In general, it appears that measurement of the mass flow parameter within the required uncertainty may be the most difficult.

Praharaj, Sarat C.↗

NASA NTRS1986

Orbital flight test shuttle external tank aerothermal flight evaluation, volume 1

This 3-volume report discusses the evaluation of aerothermal flight measurements made on the orbital flight test Space Shuttle External Tanks (ETs). Six ETs were instrumented to measure various quantities during flight; including heat transfer, pressure, and structural temperature. The flight data was reduced and analyzed against math models established from an extensive wind tunnel data base and empirical heat-transfer relationships. This analysis has supported the validity of the current aeroheating methodology and existing data base; and, has also identified some problem areas which require methodology modifications. This is Volume 1, an Executive Summary. Volume 2 contains Appendices A (Aerothermal Comparisons) and B (Flight Derived h sub 1/h sub u vs. M sub inf. Plots), and Volume 3 contains Appendix C (Comparison of Interference Factors among OFT Flight, Prediction and 1H-97A Data), Appendix D (Freestream Stanton Number and Reynolds Number Correlation for Flight and Tunnel Data), and Appendix E (Flight-Derived h sub i/h sub u Tables).

Praharaj, Sarat C.↗

NASA NTRS1986

Orbital flight test shuttle external tank aerothermal flight evaluation, volume 3

This 3-volume report discusses the evaluation of aerothermal flight measurements made on the orbital flight test Space Shuttle External Tanks (ETs). Six ETs were instrumented to measure various quantities during flight; including heat transfer, pressure, and structural temperature. The flight data was reduced and analyzed against math models established from an extensive wind tunnel data base and empirical heat-transfer relationships. This analysis has supported the validity of the current aeroheating methodology and existing data base; and, has also identified some problem areas which require methodology modifications. Volume 1 is the Executive Summary. Volume 2 contains Appendix A (Aerothermal Comparisons), and Appendix B (Flight-Derived h sub 1/h sub u vs. M sub inf. Plots). This is Volume 3, containing Appendix C (Comparison of Interference Factors between OFT Flight, Prediction and 1H-97A Data), Appendix D (Freestream Stanton Number and Reynolds Number Correlation for Flight and Tunnel Data), and Appendix E (Flight-Derived h sub i/h sub u Tables).

Praharaj, Sarat C.↗

NASA NTRS1986

Orbital flight test shuttle external tank aerothermal flight evaluation, volume 2

This 3-volume report discusses the evaluation of aerothermal flight measurements made on the orbital flight test Space Shuttle External Tanks (ETs). Six ETs were instrumented to measure various quantities during flight; including heat transfer, pressure, and structural temperature. The flight data was reduced and analyzed against math models established from an extensive wind tunnel data base and empirical heat-transfer relationships. This analysis has supported the validity of the current aeroheating methodology and existing data base; and, has also identified some problem areas which require methodology modifications. Volume 1 is the Executive Summary. This is volume 2, containing Appendix A (Aerothermal Comparisons), and Appendix B (Flight-Derived h sub i/h sub u vs. M sub inf. Plots). Volume 3 contains Appendix C (Comparison of Interference Factors between OFT Flight, Prediction and 1H-97A Data), Appendix D (Freestream Stanton Number and Reynolds Number Correlation for Flight and Tunnel Data), and Appendix E (Flight-Derived h sub i/h sub u Tables).

Praharaj, Sarat C.↗