Engineering topics

Ramamurti, R.

Publications and source records attributed to Ramamurti, R..

6 records

NASA NTRS1991

A semi-elliptic analysis for 2-D viscous flows through cascade configurations

A semielliptic formulation, termed the interacting parabolized Navier-Stokes (IPNS) formulation, is developed for the analysis of a class of subsonic viscous flows for which streamwise diffusion is negligible but which are significantly influenced by upstream interactions. A two-step alternating-direction-explicit numerical scheme is developed to solve the resulting governing equations efficiently. The quasi-linearization and discretization of the equations are carefully examined so that no artificial viscosity is added externally to the scheme. Various simple channel and cascade flow configurations are examined for several values of Re, thickness ratio and Mach number, in order to establish the applicability of the IPNS model for these flows. With this model, solutions to compressible as well as nearly incompressible flows are obtained without any modification either in the analysis or in the solution procedure.

Ramamurti, R.↗

NASA NTRS1988

Simulation of 2-dimensional viscous flow through cascades using a semi-elliptic analysis and hybrid C-H grids

A semi-elliptic formulation, termed the interacting parabolized Navier-Stokes (IPNS) formulation, is developed for the analysis of a class of subsonic viscous flows for which streamwise diffusion is neglible but which are significantly influenced by upstream interactions. The IPNS equations are obtained from the Navier-Stokes equations by dropping the streamwise viscous-diffusion terms but retaining upstream influence via the streamwise pressure-gradient. A two-step alternating-direction-explicit numerical scheme is developed to solve these equations. The quasi-linearization and discretization of the equations are carefully examined so that no artificial viscosity is added externally to the scheme. Also, solutions to compressible as well as nearly compressible flows are obtained without any modification either in the analysis or in the solution process. The procedure is applied to constricted channels and cascade passages formed by airfoils of various shapes. These geometries are represented using numerically generated curilinear boundary-oriented coordinates forming an H-grid. A hybrid C-H grid, more appropriate for cascade of airfoils with rounded leading edges, was also developed. Satisfactory results are obtained for flows through cascades of Joukowski airfoils.

Ramamurti, R.↗

NASA NTRS1988

Solution of the Neumann pressure problem in general orthogonal coordinates using the multigrid technique

The multigrid (MG) technique has been advanced for use with Neumann boundary-value problems in clustered curvilinear orthogonal coordinates. This comprises an important step in the analysis of incompressible flow using the velocity-pressure formulation of the Navier-Stokes equations. The finite-difference representation of the problem and the formulation of the restriction and coarse-grid correction operators are examined in detail. Maintaining consistency between these and the integral constraint associated with the Neumann problem is found to be critical for the success of the MG technique. The influence of the smoothing operator is examined by employing Gauss-Seidel, alternating-direction implicit, and strongly implicit techniques. The MG procedure enhances the efficiency of fine-grid solutions of the Neumann problem by a factor of 3 to 14, depending on the type of smoothing operator employed and the values of the problem parameters.

Ghia, U.↗

NASA NTRS1983

Multi-grid solution of Neumann pressure problem for viscous flows using primitive variables

The multi-grid (MG) technique has been advanced for use with the Neumann boundary-value problem in clustered curvilinear orthogonal coordinates. This comprises an important step in the analysis of viscous flows using the velocity-pressure formulation of the Navier-Stokes equations. With successive over-relaxation (SOR) as the smoothing operator and with suitably formulated restriction and coarse-grid-correction operators, a 4-grid procedure enhances the efficiency of fine-grid solutions of the Neumann problem by a factor of 3 to 5, depending on the problem parameters. Thy influence of the smoothing operator is also examined by employing the alternating-direction implicit and the strongly implicit techniques instead of SOR.

Ghia, U.↗

NASA NTRS1983

Hybrid C-H grids for turbomachinery cascades

The three basic types of grids available for two-dimensional cascade configurations are examined with respect to their relative advantages and disadvantages. Subsequently, a hybrid coordinate system is proposed such that it combines the major advantages of the C-type and the H-type meshes. The development of the hybrid grid system employs the patching of appropriate regions of these two basic mesh systems such that the transformed domain has a multi-block structure. Viewing the transformed domain as a three-dimensional surface enables the coordinates to be continuous across the boundaries of the patches in a natural manner.

Ghia, U.↗

NASA NTRS1983

Two-dimensional internal compressible viscous flows using semi-elliptic analysis

Subsonic viscous flows through planar cascades are examined by means of a semielliptic form of the Navier-Stokes equations, which is obtained by neglecting the streamwise diffusion of momentum and energy in their respective equations and providing upstream interaction through the pressure field. The influence of downstream conditions is propagated upstream in the subsonic flow, via a streamwise implicit determination of the pressure field, in order to permit departure-free solutions for the overall flow problem. The continuity equation is thereby satisfied directly. Governing equations are written in strong conservation law form, in terms of general, nonorthogonal transformed coordinates and Cartesian velocity components.

Ghia, K. N.↗