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.
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.
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 3.02x10<sup>5</sup>/m and 1.17x10<sup>6</sup>/m at total enthalpies of 13.3<sup>5</sup>MJ/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.
The early evolution of laser-induced plasma explosions has been investigated by means of a high-speed time-resolved
schlieren visualisation. Images were obtained with a high-speed video camera yielding frame rates of up to 1 million
frames per second at a frame resolution of 312 by 260 pixels. With this setup it was possible to resolve the temporal
development of the ionised plasma kernel and its associated shock wave. The plasma is formed by focusing a pulsed
ruby laser beam, with pulse energies of up to 4.5 J. The time-resolved visual data have been used to yield shock speeds,
from which, together with direct energy measurements, one can determine the portion of energy released by the plasma
explosion to drive the shock. Shock sphericity as well as plasma growth and emission lifetimes have also been evaluated.
The location of longest emission lifetime was found to change as a function of laser pulse energy: for high energy pulses,
the longest-living plasma luminosity was located ahead of the focal spot, i.e. closer to the laser source, while with lower
energy pulses the longest-living plasma luminosity was located behind the focal spot. This behaviour was also observed
for double-pulsed plasma explosions, when a second laser pulse was generated with a delay time of 50 μs. The
experiments show that for single pulses, more than 50 percent of the laser energy is expended in generating the shock