Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and direct numerical simulation

Abstract

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels were conducted by means of a slender wedge probe and direct numerical simulation. The study comprises comparative tunnel noise measurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shock tunnel. Surface pressure fluctuations were measured over a wide range of frequencies and test conditions including harsh test environments not accessible to measurement techniques such as pitot probes and hot-wire anemometry. A good agreement was found between normalized pitot pressure fluctuations converted into normalized static pressure fluctuations and the wedge probe readings. Quantitative results of the tunnel noise are provided in frequency ranges relevant for hypersonic boundary layer transition. In combination with the experimental studies, direct numerical simulations of the leading-edge receptivity to fast and slow acoustic waves were performed for the slender wedge probe at conditions corresponding to the experimental free-stream conditions. The receptivity to fast acoustic waves was found to be characterized by an early amplification of the induced fast mode. For slow acoustic waves an initial decay was found close to the leading edge. At all Mach numbers, and for all considered frequencies, the leading-edge receptivity to fast acoustic waves was found to be higher than the receptivity to slow acoustic waves. Further, the effect of inclination angles of the acoustic wave with respect to the flow direction was investigated. An inclination angle was found to increase the response on the wave-facing surface of the probe and decrease the response on the opposite surface for fast acoustic waves. A frequency-dependent response was found for slow acoustic waves. The combined numerical and experimental approach in the present study confirmed the previous suggestion that the slow acoustic wave is the dominant acoustic mode in noisy hypersonic wind tunnels.

Receptivity to Freestream Acoustic Noise in Hypersonic Flow over a Generic Forebody

“…works [28,31,34], as described in Section I. Moreover, in the work of Wagner et al [48] low frequencies (below 100 kHz) were found to have a significant effect on the response to slow acoustic waves, which was more amplified compared to the higher frequencies. Figures 13 and 14 show the time-averaged surface heat flux (in kW/m 2 ) for fast and slow acoustic waves respectively.…”

“…[47] and Wagner et al [48], aimed at investigating the noise characteristics in the environment of hypersonic wind tunnels.…”

Transition mechanisms in cross-flow-dominated hypersonic flows with free-stream acoustic noise

“…The geometry consists of a cylinder-wedge shaped wall boundary, with a nondimensional nose radius of R = 1 and a half-wedge angle of 4 • , based on the wedge probe investigated in Wagner et al (2018). The main dimensions (normalised with the nose radius) of the three-dimensional computational domain, shown in figure 1(a), are L x = 1000 along the x-axis, L y = 352 along the y-axis and L z = 55 along the z-axis.…”

“…For the specific case of hypersonic wind tunnels, it is known from previous studies, e.g. Duan et al (2014), Wagner et al (2018) and Cerminara et al (2019), that slow acoustic waves are likely to be the most dominant acoustic disturbance radiated from the turbulent boundary layer on the nozzle wall. This does not mean, however, that fast modes are not of interest.…”

“…We present DNS of the complete transition process in unswept and swept configurations. The simulations start from acoustic free-stream disturbance, which are known to be the dominant type of disturbance in hypersonic wind tunnels, as reported by previous experimental works (Schneider 2001(Schneider , 2008(Schneider , 2015Masutti et al 2012;Parziale, Shepherd & Hornung 2014), and more recently confirmed by the numerical study of Duan, Choudhari & Wu (2014) and the combined experimental-numerical study of Wagner et al (2018). Simulations are carried out for fast and slow acoustic disturbances as well as for two different amplitudes to identify key nonlinear aspects.…”