The far wake behind cylinders at hypersonic speeds. Part I: Flowfield

Abstract

The flowfield in the wake of circular cylinders was studies experimentally at a Mach number of 6 to a distance of 2400 diam downstream. In the Reynolds number range considered (Re_d ≈ 300-4000), the inner wake stemming from the cylinder boundary layer is laminar and loses its identity within 60 diam, so that only the outer wake caused by the bow shock is of importance. The flowfield was defined experimentally by Pitot pressure, static pressure, and mean-flow hot-wire measurements. Experiments show that the outer wake can be considered inviscid in the first 100 diam but viscosity is essential thereafter. Within a certain region the experimental results compare well with laminar linear theory but the wake profiles do not become similar within 2400 diam. In one case (Re_d ≈ 960), rapid deviations from steady laminar behavior were observed beyond x/d = 1600, indicating breakdown of this flow because of strong nonlinear instabilities that increase "the effective diffusivity." The stability problem of these wakes is considered in Pt. II of this study (to be published in AIAA Journal).

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