Three different applications of high-speed near-resonantly enhanced shearing interferometry to visualise and investigate
hypersonic wake flows are described. In the present application, two axisymmetric objects, a sphere and a model of a
planetary entry vehicle, are placed in a Mach 10 shock tunnel flow. The influence of different mounting structures on the
wake flow of the entry vehicle is demonstrated. Planar laser induced fluorescence (PLIF) thermometry is used as an
additional tool to monitor base flow temperatures. The unsteadiness of the wake flow of the sphere is compared to the
flow unsteadiness around the entry-probe. The velocity in selected parts of the wake flow field is also determined with
the help of a time-resolved time-of-flight method.
An investigation of flow establishment behind two blunt bodies, a circular cylinder and a 45° half-angle blunted-cone was conducted. Unlike previous studies which relied solely on surface measurements, the present study combines these with unique high-speed visualisation to image the establishment of the flow structure in the base region. Test flows were generated using a free-piston shock tunnel at a nominal Mach number of 10. The freestream unit Reynolds numbers considered were 3.02x105/m and 1.17x106/m at total enthalpies of 13.35MJ/kg and 3.94MJ/kg, respectively. In general, the experiments showed that it takes longer to establish steady heat flux than pressure. The circular cylinder data showed that the near wake had a slight Reynolds number effect, where the size of the near wake was smaller for the high enthalpy flow condition. The blunted-cone data showed that the heat flux and pressures reached steady states in the near wake at similar times for both high and low enthalpy conditions.
This paper describes the application of the free flight technique to determine the aerodynamic coefficients of a model for
the flow conditions produced in a shock tunnel. Sting-based force measurement techniques either lack the required
temporal response or are restricted to large complex models. Additionally the free flight technique removes the flow
interference produced by the sting that is present for these other techniques. Shock tunnel test flows present two major
challenges to the practical implementation of the free flight technique. These are the millisecond-order duration of the
test flows and the spatial and temporal nonuniformity of these flows. These challenges are overcome by the combination
of an ultra-high speed digital video camera to record the trajectory, with spatial and temporal mapping of the test flow
conditions. Use of a lightweight model ensures sufficient motion during the test time. The technique is demonstrated
using the simple case of drag measurement on a spherical model, free flown in a Mach 10 shock tunnel condition.
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