The compressible turbulent shear layer: an experimental study

Abstract

The growth rate and turbulent structure of the compressible, plane shear layer are investigated experimentally in a novel facility. I n this facility, it is possible to flow similar or dissimilar gases of different densities and to select different Mach numbers for each stream. Ten combinations of gases and Mach numbers are studied in which the free-stream Mach numbers range from 0.2 to 4. Schlieren photography of 20-ns exposure time reveals very low spreading rates and large-scale structures. The growth of the turbulent region is defined by means of Pitot-pressure profiles measured at several streamwise locations. A compressibility-effect parameter is defined that correlates and unifies the experimental results. It is the Mach number in a coordinate system convecting with the velocity of the dominant waves and structures of the shear layer, called here the convective Mach number. It happens to have nearly the same value for each stream. I n the current experiments, it ranges from 0 to 1.9. The correlations of the growth rate with convective Mach number fall approximately onto one curve when the growth rate is normalized by its incompressible value at the same velocity and density ratios. The normalized growth rate, which is unity for incompressible flow, decreases rapidly with increasing convective Mach number, reaching an asymptotic vaue of about 0.2 for supersonic convective Mach numbers.

Experimental and numerical investigation of the turbulent wake flow of a generic space launcher configuration

“…It can be seen that compared to the boundary layer, when shedding from the base shoulder, the coherent structures in the shear layer start increasing in size and merge with neighboring structures (region (ii) in Fig. 14a), which is similar to the formation of Brown Roshko-like structures [31,32] due to a density gradient between the outer §ow and the recirculation area. Note that this fact was already (Fig.…”

Measurements in the annular shear layer of high subsonic and under-expanded round jets

“…The importance of high Mach number shear layers was signalled by its being selected as a test case for turbulence modelling at one of the first international conferences on this topic in the 1970s (Birch and Eggers 1972). Most of the fundamental research has to date focussed on planar shear layers, with the classical experimental data of Papamoschou and Roshko (1988) documenting the significant reduction in shear layer growth rate due to compressibility effects. This reduction was correlated best against the convective Mach number-the Mach number in a frame of reference moving with the speed (U C ) of the dominant instability waves (or any other disturbances, e.g.…”

“…For mixing where both streams are pressure-matched and have the same specific heat ratio, the isentropic model suggested by Papamoschou and Roshko (1988) leads to a speed-of-sound weighted average for U C :…”

Compressible effects on a temporal direct numerical simulation

“…This global effect has been observed by many authors (Papamoschou and Roshko 1988) (Elliott and Samimy 1990) (Papamoschou 1989), but no convincing explanation has been given. This growth rate reduction causes the stabilization of the flow in supersonic regime (Sarkar 1995).Thus, it was also observed (Clemens and Mungal 1992) (Lele 1994) that the large-scale organised structures play different role as Mach number increases.…”

“…To characacterize the compressibility effects a convective Mach number M c has been introduced by Papamoschou&Roshko (Papamoschou and Roshko 1988) based on previous Bogdanoff work (Bogdanoff 1983). Recent experiments (Clemens and Mungal 1995) revealed changes in turbulence statistics and typical eddy structure which becomes strongly three dimensional for convective Mach number greater than 0.6.…”