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Sinha, N.

Publications and source records attributed to Sinha, N..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Computational Analysis of Water Film Thickness During Rain Events for Assessing Hydroplaning Risk, Part 1: Nearly Smooth Road Surfaces

In the research work reported here, both two- and three-dimensional computational fluid dynamics (CFD) analysis was used to investigate modern road geometries that were not frequently encountered in the latter half of the 20th century but are much more common today. The relation of newer road geometries to the water film thickness that develops on travel lanes was a major focus of this work.

42 ENGINEERING↗
NASA NTRS1992

Exhaust plumes and their interaction with missile airframes - A new viewpoint

The present, novel treatment of missile airframe-exhaust plume interactions emphasizes their simulation via a formal solution of the Reynolds-averaged Navier-Stokes (RNS) equation and is accordingly able to address the simulation requirements of novel missiles with nonconventional/integrated propulsion systems. The method is made possible by implicit RNS codes with improved artificial dissipation models, generalized geometric capabilities, and improved two-equation turbulence models, as well as by such codes' recent incorporation of plume thermochemistry and multiphase flow effects.

Dash, S. M.↗
NASA NTRS1991

Prediction of jet mean flow structure in support of HSCT noise suppression concepts

The paper describes the application of techniques based on computational fluid dynamics to the simulation of jet flowfields. A solution code for the Reynolds-averaged Navier-Stokes equations is supplemented by conventional two-equation turbulence models based on the Boussinesq approximation. The axisymmetric SCIPVIS code is enhanced with the PARCH and CRAFT codes to examine plug-jet flowfields and imperfectly expanded axisymmetric free round jets. The sensitivity of shock/boundary layer interactions is observed in simulations of the plug case, and the adaptive gridding in the disk region and turbulence levels generated at the triple point are identified as areas in the Mach case that require improvement. Jet-wave structure in the region beyond the first several shock cells can be predicted, and turbulence modeling can be undertaken with respect to improving compressibility, length scale, vorticity, and energy budget. The mean flow structure of imperfectly expanded jets can be studied to develop related noise suppression concepts for the High-Speed Civilian Transport (HSCT).

Sinha, N.↗
NASA NTRS1990

Progress in the development of advanced computational models for the analysis of generalized supersonic jet flowfields

This paper describes two three-dimensional computational codes (PARCH and CRAFT) for computing a generalized supersonic jet flowfields with subsonic external streams, which solve the Reynolds-averaged Navier-Stokes equations in a time asymptotic manner. The application of these codes to an imperfectly expanded jet flowfield is demonstrated. Special attention is given to numerical issues and to turbulence modeling. The application of the PARCH and CRAFT codes to other related flowfield problems, such as gas turbine and nozzle flows, and to generalized missile-plume flowfields is discussed.

Dash, S. M.↗
NASA NTRS1988

Fully-coupled analysis of jet mixing problems. Three-dimensional PNS model, SCIP3D

Numerical procedures formulated for the analysis of 3D jet mixing problems, as incorporated in the computer model, SCIP3D, are described. The overall methodology closely parallels that developed in the earlier 2D axisymmetric jet mixing model, SCIPVIS. SCIP3D integrates the 3D parabolized Navier-Stokes (PNS) jet mixing equations, cast in mapped cartesian or cylindrical coordinates, employing the explicit MacCormack Algorithm. A pressure split variant of this algorithm is employed in subsonic regions with a sublayer approximation utilized for treating the streamwise pressure component. SCIP3D contains both the ks and kW turbulence models, and employs a two component mixture approach to treat jet exhausts of arbitrary composition. Specialized grid procedures are used to adjust the grid growth in accordance with the growth of the jet, including a hybrid cartesian/cylindrical grid procedure for rectangular jets which moves the hybrid coordinate origin towards the flow origin as the jet transitions from a rectangular to circular shape. Numerous calculations are presented for rectangular mixing problems, as well as for a variety of basic unit problems exhibiting overall capabilities of SCIP3D.

Wolf, D. E.↗
NASA NTRS1987

Wall jet analysis for circulation control aerodynamics. Part 1: Fundamental CFD and turbulence modeling concepts

An overview of parabolic and PNS (Parabolized Navier-Stokes) methodology developed to treat highly curved sub and supersonic wall jets is presented. The fundamental data base to which these models were applied is discussed in detail. The analysis of strong curvature effects was found to require a semi-elliptic extension of the parabolic modeling to account for turbulent contributions to the normal pressure variations, as well as an extension to the turbulence models utilized, to account for the highly enhanced mixing rates observed in situations with large convex curvature. A noniterative, pressure split procedure is shown to extend parabolic models to account for such normal pressure variations in an efficient manner, requiring minimal additional run time over a standard parabolic approach. A new PNS methodology is presented to solve this problem which extends parabolic methodology via the addition of a characteristic base wave solver. Applications of this approach to analyze the interaction of wave and turbulence processes in wall jets is presented.

Dash, S. M.↗
NASA NTRS1986

Computational models for the analysis/design of hypersonic scramjet components. I - Combustor and nozzle models

An overview of computational models developed for the complete, design-oriented analysis of a scramjet propulsion system is provided. The modular approach taken involves the use of different PNS models to analyze the individual propulsion system components. The external compression and internal inlet flowfields are analyzed by the SCRAMP and SCRINT components discussed in Part II of this paper. The combustor is analyzed by the SCORCH code which is based upon SPLITP PNS pressure-split methodology formulated by Dash and Sinha. The nozzle is analyzed by the SCHNOZ code which is based upon SCIPVIS PNS shock-capturing methodology formulated by Dash and Wolf. The current status of these models, previous developments leading to this status, and, progress towards future hybrid and 3D versions are discussed in this paper.

Dash, S. M.↗
NASA NTRS1986

Progress in the development of parabolized Navier-Stokes (PNS) methodology for analyzing propulsive jet mixing problems

A brief review of 2D PNS methodology is first presented which describes the specialized features of supersonic shock-capturing and subsonic pressure-split models required for the analysis of aircraft, rocket and scramjet jet mixing problems. These features include techniques for dealing with various types of embedded and interfacing subsonic regions, the inclusion of finite-rate chemistry and the direct-coupling with potential flow solutions. Preliminary 3D extensions of this PNS methodology geared to supersonic and subsonic rectangular free jet mixing problems are also reviewed. New 3D PNS work will be described which includes the development of a hybrid supersonic/subsonic free jet mixing model, and, a supersonic model geared to the analysis of turbulent mixing and combustion processes occurring in scramjet combustor/nozzle flowfields.

Dash, S. M.↗
NASA NTRS1986

Parabolized Navier-Stokes analysis of ducted turbulent mixing problems with finite-rate chemistry

A hybrid implicit/explicit approach for analyzing 2D ducted turbulent mixing problems with finite-rate chemistry is presented. The approach combines a fully-implicit parabolic mixing algorithm, an explicit viscous-characteristic based shock-capturing algorithm, and linearized implicit chemical kinetic algorithm. The resultant model provides spatial marching solutions of the parabolized Navier-Stokes (PNS) equations for supersonic combustion and viscous nozzle flowfields. Specialized procedures are incorporated to deal with the near wall sublayer and with small central pockets of subsonic flow. A parabolic option is available which can be utilized in the direct or inverse mode for design applications. The ability of the model to treat shock waves and wave/mixing layer interactions is assessed via comparisons of predictions with those of well established explicit shock-capturing Euler (SCIPPY) and PNS (SCIPVIS) models. Applications to a variety of supersonic combustion flowfield problems involving tangential or moderately inclined fuel injection, and, to a viscous nozzle flow problem, are presented. This paper serves to exhibit overall capabilities of the model developed and no comparisons with supersonic combustion data are presented. Such comparisons serve mainly to validate the modeling of the turbulence and turbulence/chemical interactions and will be the subject of a future paper.

Sinha, N.↗
NASA NTRS1985

Implicit/explicit analysis of interactive phenomena in: supersonic, chemically-reacting, mixing and boundary layer problems

An efficient implicit/explicit procedure for solving the parabolized Navier-Stokes (PNS) equations to analyze supersonic, viscous, chemically-reacting flows is presented. The approach combines a fully-implicit algorithm for solving the parabolic mixing/boundary layer equations with an explicit algorithm for determining the hyperbolic pressure field. The unified model, SPLITP, contains provisions for treating bounding/embedded subsonic regions using a pressure-splitting procedure which suppresses elliptic (upstream influence) effects without recourse to sublayer approximations. Several two-equation turbulence models with compressibility and curvature-correction terms are incorporated into SPLITP. Applications to a variety of flow problems are presented which include: ducted supersonic mixing and combustion flowfields, free jets and plumes, and, curved boundary layers and wall jets.

Dash, S. M.↗
NASA NTRS1985

Noniterative cross-flow integration for the pressure-split analysis of subsonic mixing-layer problems

In utilizing pressure-split methodology for the two-dimensional analysis of curved wall jets and the subsonic regions of underexpanded free jets, Dash et al (1984) employed the cross flow procedure of Bradshaw et al (1979, 1984). In assessing this procedure, it was noted that the iterative steps required between the continuity and cross flow momentum equation solutions could be eliminated by combining these equations into a unified equation for the cross flow velocity, yielding a significant reduction in computer time and eliminating possible convergence problems which occur in iterative approaches. Attention is presently given to the application of this noniterative procedure to a two-dimensional curved wall jet problem.

Dash, S. M.↗
NASA NTRS1985

Two dimensional, transient catalytic combustion of CO-air on platinum

The light off transient of catalytic combustion of lean CO-air mixtures in a platinum coated channel of a honeycomb monolith is studied with a model that resolves transient radial and axial gradients in both the gas and the solid. For the conditions studied it is concluded that: the initial heat release occurs near the entrance at the gas-solid interface and is controlled by heterogeneous reactions; large spatial and temporal temperature gradients occur in the solid near the entrance controlled mostly by the availability of fuel; the temperature of the solid near the entrance achieves almost its steady state value before significant heating of the back; heterogeneous reactions and the gas heated up front and flowing downstream heat the back of the solid; the overall transient time is controlled by the thermal inertia of the solid and by forced convection; radiation significantly influences both transient and steady state particularly near the entrance; the oxidation of CO occurs mostly on the catalyst and becomes diffusion controlled soon into the transient.

Sinha, N.↗
NASA NTRS1984

Parabolized Navier-Stokes analysis of three-dimensional supersonic and subsonic jet mixing problems

Three-dimensional jet mixing problems are addressed by means of two parabolized Navier-Stokes models. The first of these analyzes supersonic, overexpanded or underexpanded nonaxisymmetric jets, and yields results that exhibit complex, three-dimensional interactions. The second model uses the same numerical framework as the first, and analyzes rectangular jets by means of a pressure-split formulation. Square and rectangular mixing jet problems that highlight this model's capabilities and exhibit the distortion of the nearfield jet contours associated with the streamwise vortices generated by two corner regions are presented.

Dash, S. M.↗
NASA NTRS1983

Coupling of Transport and Chemical Processes in Catalytic Combustion

Catalytic combustors have demonstrated the ability to operate efficiently over a much wider range of fuel air ratios than are imposed by the flammability limits of conventional combustors. Extensive commercial use however needs the following: (1) the design of a catalyst with low ignition temperature and high temperature stability, (2) reducing fatigue due to thermal stresses during transient operation, and (3) the development of mathematical models that can be used as design optimization tools to isolate promising operating ranges for the numerous operating parameters. The current program of research involves the development of a two dimensional transient catalytic combustion model and the development of a new catalyst with low temperature light-off and high temperature stablity characteristics.

Bracco, F. V.↗
NASA NTRS1983

Catalytic Combustion of Propane/Air Mixtures on Platinum

A honeycomb catalyst of platinum (4.2 kg/cu m loading) over cordierite, with gamma-alumina washcoat, a cross section of 2.4 x 2.4 sq cm, a length of 7.6 cm, and a characteristic channel diameter of 1.4 mm is used as a steady flow reactor. Measurements are made with C3H8/air mixtures at 650 to 800 K inlet temperatures, 110 KPa pressure, 10 to 40 m/s inlet velocity, 0.19 to 0.32 equivalence ratios, and approximately 1.5 mole percent water content. The measured quantities are the substrate tempeature at ten axial locations, the exhaust gas temperature, the exhaust concentrations of CO, CO2, O2, and total hydrocarbons, and the pressure drop across the monolith. The measured quantities are compared with those computed with a two-dimensional steady-state model for axial and radial convection and diffusion of mass, momentum, energy and homogeneous (three overall reactions) and heterogeneous (infinitely fast) reactions. It is found that, under the tested conditions, most of the fuel is converted to CO2 and H2O at the surface. Gas-phase reactions tend rapidly to become more important as the temperature and equivalence ratio are increased and the flow velocity is decreased. Surface fuel conversion is much more rapid than fuel diffusion, resulting in diffusion-controlled oxidation.

Bruno, C.↗