Continuum breakdown in compressible mixing layers (original) (raw)

Model-free simulations for compressible mixing layer

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2012

Confined supersonic mixing layer is explored through model-free simulations. Both two- and three-dimensional spatio-temporal simulations were carried out employing higher order finite difference scheme as well as finite volume scheme based on open source software (OpenFOAM) to understand the effect of three-dimensionality on the development of mixing layer. It is observed that although the instantaneous structures exhibit three-dimensional features, the average pressure and velocities are predominantly two-dimensional. The computed wall pressures match well with experimental results fairly well, although three-dimensional simulation underpredicts the wall pressure in the downstream direction. The self-similarity of the velocity profiles is obtained within the duct length for all the simulations. Although the mixing layer thicknesses differ among different simulations, their growth rate is nearly the same. Significant differences are observed for species and temperature distribution ...

Turbulence in Compressible Mixing Layers

Journal of Fluids Engineering, 1998

The direct numerical simulation (DNS) of two-dimensional compressible turbulent mixing layers is reported in this paper for convective Mach numbers Mc = 0.5, 0.8 and 1.0. All scales of flow are resolved with a 2562 grid, although results are also obtained for 642, 962 and 1282 grids for the purpose of determining the effective accuracy and grid-independence of our calculations. The effect of Mach number is also reported for all the Reynolds stress tensor components and for the “shear” components of the anisotropy tensor, the dissipation tensor, pressure-strain, and the triple correlation tensor. The short-time behaviors of some of these quantities are similar to those reported by Sarkar (1995) for homogeneous shear flow, in spite of the differences in the problem type and initial and boundary conditions. The relative magnitudes and signs of the unclosed terms in the Reynolds stress equations provide information on those that have to be retained for turbulence modeling as well as the...

Effects of Reacting Flow on Continuum Breakdown in Hypersonic Aerothermodynamics

This study investigates the effects of continuum breakdown on the surface aerothermodynamic properties (pressure, stress, heat transfer rate) of a sphere in Mach 25 flows in regimes varying from continuum to a rarefied gas. Results are generated using both continuum (CFD) and particle (DSMC) approaches. The DSMC method utilizes a chemistry model that calculates the backwards rates from an equilibrium constant. Tests of this model are run to confirm its validity and to compare it to the CFD chemistry model. The inclusion of reacting nitrogen flow did not significantly change the amount of continuum breakdown in the flow. Hence, there is little change in the maximum heat flux or the integrated drag on the surface of the sphere. The second part of this study examines the effect of reacting air flow on continuum breakdown and the surface properties of the sphere. As the global Knudsen number increases, the amount of continuum breakdown in the flow and on the surface increases. This incr...