Large-scale structure evolution in axisymmetric, compressible free-shear layers

This paper is a description of work-in-progress. It describes Sandia`s program to study the basic fluid mechanics of large-scale mixing in unbounded, compressible, turbulent flows, specifically, the turbulent mixing of an axisymmetric compressible helium jet in a parallel, coflowing compressible air freestream. Both jet and freestream velocities are variable over a broad range, providing a wide range mixing layer Reynolds number. Although the convective Mach number, M{sub c}, range is currently limited by the present nozzle design to values of 0.6 and below, straightforward nozzle design changes would permit a wide range of convective Mach number, to well in excess of 1.0. The use of helium allows simulation of a hot jet due to the large density difference, and also aids in obtaining optical flow visualization via schlieren due to the large density gradient in the mixing layer. The work comprises a blend of analysis, experiment, and direct numerical simulation (DNS). There the authors discuss only the analytical and experimental efforts to observe and describe the evolution of the large-scale structures. The DNS work, used to compute local two-point velocity correlation data, will be discussed elsewhere.