Flow Structure behind Spanwise Pin Array in Supersonic Flow

Abstract

This work focused on the experimental characterization of a complex flow structure behind a cross-flow array of cylindrical pins installed on the wall of a supersonic duct. This geometry simulates several common gas dynamic configurations, such as a supersonic mixer, a turbulence-generating grid, or, to some extent, a grid fin. In this work, the instrumentation employed is essentially non-intrusive, including spanwise integrating techniques such as (1) fast schlieren visualization and (2) Shack–Hartmann wavefront sensors; and planar techniques, namely (3) acetone Mie scattering and (4) acetone planar laser-induced fluorescence. An analysis of the data acquired by these complementary methods allowed the reconstruction of a three-dimensional portrait of supersonic flow interactions with a discrete pin array, including the shock wave structure, forefront separation zone, shock-induced separation zone, shear layer, and the mixing zone behind the pins. The main objective of this activity was to use various visualization techniques to acquire essential details of a complex compressible flow in a wide range of temporal–spatial scales. Particularly, a fine structure in the supersonic shear layer generated by the pin tips was captured by a Mie scattering technique. Based on the available publications, such structures have not been previously identified or discussed. Another potential outcome of this work is that the details revealed could be utilized for adequate code validation in numerical simulations.