Engineering topics

Nagaraj, N.

Publications and source records attributed to Nagaraj, N..

10 records

NASA NTRS1989

Computational design aspects of a NASP nozzle/afterbody experiment

This paper highlights the influence of computational methods on design of a wind tunnel experiment which generically models the nozzle/afterbody flow field of the proposed National Aerospace Plane. The rectangular slot nozzle plume flow field is computed using a three-dimensional, upwind, implicit Navier-Stokes solver. Freestream Mach numbers of 5.3, 7.3, and 10 are investigated. Two-dimensional parametric studies of various Mach numbers, pressure ratios, and ramp angles are used to help determine model loads and afterbody ramp angle and length. It was found that the center of pressure on the ramp occurs at nearly the same location for all ramp angles and test conditions computed. Also, to prevent air liquefaction, it is suggested that a helium-air mixture be used as the jet gas for the highest Mach number test case.

Ruffin, Stephen M.↗

NASA NTRS1989

Real gas flow computations using algebraic reduction

It is shown that algebraic reduction can be extensively used in the computation of source terms for chemical species in chemically reacting flow fields. Cases of computation from chemical equilibrium and frozen chemistry are considered. For the case of chemical equilibrium the implementation of algebraic reduction method is shown to produce satisfactory results with computational efficiency better than comparable methods. For the case of finite rate chemistry, algebraic reduction of the source term expression for the species is used to obtain a directly integrable expression.

Nagaraj, N.↗

NASA NTRS1988

Navier-Stokes simulation of 3-D hypersonic equilibrium air flow

A computationally efficient three-dimensional conservative supracharacteristic Navier-Stokes method has been extended to simulate complex external chemically reacting flows of hypersonic reentry vehicles at angle-of-attack. Numerical simulation results of the flow around a sphere-cone-cone-flare reentry vehicle at 10 deg angle-of-attack are presented, in addition to the results of a well-validated two-dimensional code with which the 0-deg axisymmetric flow has been computed. A method for obtaining compositions of species in equilibrium ionized air is proposed.

Nagaraj, N.↗

NASA NTRS1988

Extensions of the CSCM methodology for nonequilibrium reacting gas flows

The paper describes the extension of the CSCM flux difference splitting to produce conservative unconditionally stable implicit upwind methods for the extended equation set. The CSCM-S single data level relaxation algorithm is argued to be particularly advantageous for efficiently solving the set of equations. Attention is given to issues of alternative state variable representations and to complementary thermodynamic relations that parameterize and need to be effectively coupled with the solution procedure for the partial differential equations. Within the framework of iteration, consideration is given to more efficient approximate solution procedures than the full block coupled LU decomposition. Results of early numerical experiments are given to illustrate the developments.

Lombard, C. K.↗

NASA NTRS1987

Navier-Stokes simulation of real gas flows in nozzles

Air flow in a hypersonic nozzle causes real gas effects due to reaction among the species constituting air. Such reactions may be in chemical equilibrium or in chemical nonequilibrium. Here using the CSCM upwind scheme for the compressible Navier-Stokes equations, the real gas flowfield in an arcjet nozzle is computed for both the equilibrium case and the nonequilibrium case. A hypersonic nozzle flow arising from a pebble bed heated plenum is also computed for the equilibrium situation. Between the equilibrium cases, the chemistry is treated by two different schemes and comments are made as to computational complexity. For the nonequilibrium case, a full set of seventeen reactions and full implicit coupling of five species with gasdynamics is employed to compute the flowfield. For all cases considered here the gas is assumed to be a calorically imperfect mixture of ideal gases in thermal equilibrium.

Nagaraj, N.↗

NASA NTRS1987

Aerodynamic design modification of a hypersonic wind tunnel nozzle by CSCM with high order accuracy

An improved version of the CSCM implicit Navier-Stokes solver with a flexible data structure has been applied, in conjunction with a sophisticated patched grid system, to the aerodynamic analysis of hypersonic axisymmetric contoured nozzles of the NASA-Ames 3.5-foot hypersonic wind tunnel. The results obtained are found to be in good agreement with experiment. Based on the analysis, a newly designed throat contour for the Mach 14 nozzle has been recommended.

Yang, J. Y.↗

NASA NTRS1987

Numerical simulation of compressible flow around complex two-dimensional cavities

Compressible viscous flow around two-dimensional cavities, that model the midplane flow in and around an airborne telescope cavity, are obtained through numerical simulation. Numerical solutions using the patched grid CSCM scheme for compressible, unsteady flow are presented for the cavities, with and without blowing. The time evolving solutions show interesting flow features. Relevant results for a limited number of problems presented here show the unsteady nature of the flow and its dependence on various parameters such as Reynolds number, the wall conditions, etc. The voluminous data of time evolving flow field solutions are analyzed through movies of the velocity vectors, and contours of other flow variables.

Venkatapathy, Ethiraj↗

NASA NTRS1987

Simplified algebraic grid generation in patched mesh systems

Some computational tools and techniques are described that are integrated into a simplified algebraic grid generation procedure. Major steps of such a procedure are also outlined. Grids generated via this approach for several complex geometries are shown to demonstrate the potential for wide application.

Luh, Raymond Ching-Chung↗

NASA NTRS1986

Numerical simulation of backward step and jet exhaust flows

Preparatory to a continuing study of efficient, high resolution flow structure capture on patched mesh systems, turbulent flowfield solutions for a tactical missile base flow problem are computed on two first level composite grids of differing topologies. One mesh is of the wraparound character and the other is a step mesh on the Cartesian topology. A simplified Baldwin-Lomax algebraic eddy viscosity model is applied in the wake region. Results for the two meshes are compared with each other and with other computations reported in the literature. The totality of results suggest both mesh topology and resolution are important factors in the accuracy of predictive results as well as turbulence modeling. Related to interests in high altitude laminar flows bluff bodies such as the AOTV, the paper also presents results from a solution from laminar flow over a backward facing step and makes comparison with the available classical experiment of Chapman, et al.

Lombard, C. K.↗

NASA NTRS1985

Numerical simulation of transient inviscid gas flows in a shock tube

Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate 1-D and 2-D transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock-wave diffraction phenomena. Shock-wave and objects interactions with shock Mach-number Ms ranging from 2 to 20 were considered. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, slip surfaces, and vortex are also given.

Yang, J. Y.↗