Measurement of Flow Perturbation Spectra in Mach 4.5 Corner Separation Zone

Abstract

Characterization of the M 4.5 flow over a flat-plate model with a 30 deg compression ramp was performed with low-enthalpy (T 0 300 K) and high-enthalpy (T 0 800-1250 K) flow conditions for a wide range of unit Reynolds numbers (Re l 4 ⋅ 10 5 − 1 ⋅ 10 7 m −1). Three measurement techniques were employed to measure the frequency spectrum of flow perturbations: a high-frequency Shack-Hartmann wavefront sensor (aerooptical method), highfrequency PCB™ pressure sensors, and a laser differential interferometer. The magnitude and frequency of flow oscillations measured by all three methods provide comprehensive and complementary results in determining spectra of gas disturbances within the flow. Of these measurement methods, the Shack-Hartmann wavefront sensor is shown to be the most suitable tool for analysis of the high-speed flow. Aerooptical measurements detect modification to the flow structure when plasma actuation is employed or when Re l is varied. In this work, flow characterization by the Shack-Hartmann sensor at individual points over the ramp has shown three flow regimes depending on the unit Reynolds number: turbulent, transitional, and laminar. At higher Re l , the freestream disturbances become strong enough to significantly affect the perturbations in the boundary-layer and the separation zone on the compression ramp. Frequency spectrum measurements during high-frequency plasma actuation (F 100 kHz) indicate amplification of the perturbations from the natural state that occur over the separation region.

Rapid control of force/momentum on a model ramp by quasi-DC plasma

“…A different approach for plasma-based control of a supersonic inlet was employed in [16,17] where the pulse-periodic arc plasma was used to control the SW reflection. Recently, several exper imental efforts were performed to control the flowfield within a compression surface configuration at higher Mach numbers, M = 4.5 and 7, by means of different electrical discharges, such as shallow cavity discharge [18], and DC discharge [19,20]. In the first case, there was found a significant modification in the spectra of flow perturbations in a corner separation zone.…”

Experimental investigation into the effects of shock waves on Shack-Hartmann wavefront sensor measurements

“…[1][2][3][4] In a broad sense, this interaction of light with turbulent aerodynamic flows is called the aero-optics problem. [5][6][7][8][9] In the recent past there has been significant research into the aero-optics problem across a wide range of flow regimes including subsonic, [10][11][12][13][14][15] supersonic, 16,17 and hypersonic 18,19 flows.…”

Plasma-Assisted Control of Supersonic Flow over a Compression Ramp

“…In [13][14][15][16] and other publications, the plasma-based technique and the mechanisms of the plasma-flow interaction were examined in supersonic flow. It was found that the near-surface electric discharge is well applicable for the purposes of the modification of surface pressure distribution, flow field pattern, and shock wave formation.…”