A pulsed jet for generation of turbulent spots in a mach 6 boundary layer
Hypersonic vehicles operate in an environment with a high level of boundary-layer pressure fluctuations. The largest of these fluctuations are due to the intermittent passage of turbulent spots within the transition region, and can be sufficiently large to affect internal components of the vehicle. In order to better predict these flow variations, a turbulent spot model could be used. The boundary layer on the Boeing/ AFOSR Mach 6 Quiet Tunnel nozzle-wall provided a convenient location for studying the statistical properties of turbulent spots in a hypersonic boundary layer, including growth rates, convection velocities, and pressure-fluctuation intensities. A valve system was developed to inject a transverse jet of air into the nozzle-wall boundary layer in an attempt to generate controlled spots. The resulting perturbations were characterized. The pressure fluctuations were measured on the tunnel centerline downstream of the perturber. Pressure traces and spectra were examined to determine the effectiveness of the perturber system. The initial perturber system produced disturbances with a duration that was too long. A reduction in perturbation duration was achieved through modification of the perturber electronics. Physical modifications were also made to the valve, with mixed success. The perturbations were of a longer duration and higher initial amplitude than perturbations generated using a pulsed glow perturber in previous studies in the Boeing/AFOSR Mach-6 Quiet Tunnel, including fully turbulent perturbations at the maximum quiet freestream Reynolds number. Inconsistent alignment of the perturber became the largest difficulty in using the device. A new method of aligning the valve was developed. A more effective means of maintaining the alignment during transfer from the alignment tool to the nozzle wall is necessary. Additional reductions to the perturbation duration could be possible by optimizing the geometry of the passage through the nozzle wall. Presently, the perturber requires further refinement prior to use as a tool for generating repeatable turbulent spots.
Schneider, Purdue University.
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