Numerical Study of Unsteady Shock Propagation in a Thermally Choked Flow with the Method of Characteristics

Pee, Xiu Yi; Laurence, Stuart J.

doi:10.2514/6.2021-3544

Cited by 1 publication

(2 citation statements)

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“…HyperTERP is a reflected-shock tunnel capable of operating at a variety of freestream enthalpy and unit Reynolds numbers through modification of the pressure and composition of the driver and driven gases. Although typically used with a Mach-6 free-jet nozzle, HyperTERP was operated with a newly developed Mach-2.8 nozzle and direct-connect test section, as detailed by Pee et al (2021). The propagation speed of the incident shock wave is measured by four PCB 113B26 pressure transducers sampled at 100 kHz.…”

Section: Shock-tunnel Facilitymentioning

confidence: 99%

“…In addition to CO 2 /He mixtures, injection of N 2 is used to ensure that the injection process itself is not responsible for any measured effects, and the injection of pure He is used to examine the effects of mean soundspeed gradients in the boundary layer that would also be present (to a lesser degree) in CO 2 /He mixtures. In each case, the injection timing was adjusted with a variable delay circuit such that the steady plenum pressure of the injector coincided with the steady reservoir pressure in the shock tunnel (Pee, 2021). A typical time trace of the reservoir pressure and injector plenum pressure is shown in Fig.…”

Section: Test Conditionsmentioning

confidence: 99%

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Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Gillespie

Laurence

2023

Preprint

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The effects of vibrational nonequilibrium processes on turbulence-generated acoustic noise were investigated in a Mach-2.8 shock-tunnel facility. Gas mixtures with relevant absorption characteristics were first identified from measurements of attenuation coefficients using a heated acoustic chamber. In the shock-tunnel facility, CO2, N2, He, and He/CO2 mixtures were injected into the lower boundary layer of the flow through a porous plate. A four-point Focused Laser Differential Interferometer (FLDI) positioned above the turbulent boundary layer was used to obtain simultaneous freestream measurements of entropic fluctuations propagating along streamlines and acoustic disturbances along Mach lines. Correlated fluctuations of Mach-line and streamline FLDI signal pairs were analyzed with a cross power spectral density (CPSD). Compared to a boundary layer of pure air, the injection of 30%, 35%, and 40% He/CO2 mixtures resulted in reduced fluctuation powers correlated along a Mach line in the frequency range of 200-800 kHz. Minimal reductions in fluctuation power were found along a streamline, indicating that the vibrationally active gas is affecting acoustic disturbances and not entropic disturbances. A mathematical disturbance model was created to examine the sensitivity of the measured attenuation to acoustic disturbances propagating from the lower boundary layer only. Disturbances were modeled as Gaussian wave packets of finite width, propagating in the streamwise direction and along Mach lines from the four walls of the test section. Modeling the acoustic disturbances from the lower boundary layer with a 15-30% amplitude reduction resulted in amplitude spectral densities and CPSDs that agreed well with the FLDI measurements.

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Section: Shock-tunnel Facilitymentioning

confidence: 99%

Section: Test Conditionsmentioning

confidence: 99%