Venkata S. Krishnamurty

Study of compressibility modifications to the k- ε turbulence model

In modeling the effect of compressibility on the turbulence structure, additional physical mechanisms arise in production and dissipation of turbulent kinetic energy. Several proposed treatments dealing with the dilatation dissipation and the pressure dilatation correlation are discussed in the context of the k−e two-equation model. Modifications accounting for the turbulent mass flux, enthalpic production, and baroclinic torque are also assessed along with the nonequilibrium treatment. These compressibility models are evaluated with the aid of experimental data for supersonic flow over an axisymmetric afterbody. With the free-stream Mach number of 2.46, the compressibility and nonequilibrium modifications give marginally better results for the turbulence structure and offer added insight into the mean and fluctuating flow fields.

Compressibility effects in modeling complex turbulent flows

Abstract The effect of compressibility on the structure of turbulence is an important, but difficult, topic in turbulence modeling. Modeling issues in production, dissipation and transport of turbulent kinetic energy need to be addressed to account for Mach number effects. In the present review, the compressibility effect is investigated in the context of engineering models needed for complex flow computations, particularly the k−e model. Issues such as the dissipative nature of compressibility, the complexities arising due to the non-divergent nature of the velocity field, added time-scale effect due to a non-equilibrium between the rates of production and dissipation of turbulent kinetic energy, the enthalpic production term and the term representing the baroclinic effect, have been discussed to facilitate the inclusion of these terms in the solution of compressible turbulent flow fields. Flows characterized by strong streamline curvature and inhomogeneities arising due to strong shocks and rapid expansions, in the form of supersonic flow past an axi-symmetric afterbody and hypersonic flow past a projectile, have been adopted to facilitate computational assessment of these aspects.

Computational Analysis of Hypersonic Turbulent Flows over a Projectile with Aerospike

The effects of compressibility and nonequilibrium in hypersonic turbulent flows are analyzed in the κ-e-based modeling framework with emphasis on the influence of factors such as streamline curvature and shock discontinuities. The flow past a projectile, with and without a drag reduction spike, is investigated to assess the various modeling issues and to shed light on the merit of this interesting aerodynamic concept. The importance of an account for the compressibility and nonequilibrium effects is demonstrated. Regarding the merit of the spike/aerodisk assembly, it is observed that although the addition of the spike reduces the pressure at the nose of the projectile by a factor of 10 it only results in a marginal reduction in the temperature

Treatment of inviscid fluxes in compressible turbulent flow computations

The present study presents a comparative investigation between two methodologies for treating inviscid fluxes, namely, an artificial dissipation-based finite-volume scheme and a second-order upwind difference scheme. Computations made of the turbulent, supersonic flow past an axisymmetric afterbody have revealed certain disadvantages in using the artificial dissipation-based approach to the discretization of inviscid fluxes. Noticeably, the artificial dissipation-based approach does not maintain the integrity of the flow physics and reveals upstream influences of the rapid expansion at the base corner. Accuracy of the results obtained of flow fields with complex features, such as a streamline curvature or strong shocks, depends significantly on the treatment of the inviscid fluxes, and from the comparison presented here, the flux-vector splitting scheme offers better results for the supersonic flow problem involving sharp comers.

Study of two-equation based modelling for compressible, turbulent flows

Effects of compressibility and chemical reaction on the turbulence structure are two important but difficult issues in turbulence modelling. Several proposed treatments dealing with the dilatation dissipation and the pressure dilatation correlation are discussed in the context of the two-equation model. Also, two new modifications are proposed to account for extra terms that appearfor compressible flows. An attempt is made to validate and calibrate these modifications against experimental data for supersonic flow over an axi-symmetric afterbody. These compressibility modifications are also tested for certain simple reacting flows in order to estimate their predictive capabilities. Additionally, proposed modifications to account for the imbalance between the production of turbulent kinetic energy and its rate of dissipation are contrasted against the standard modelling procedure.