Conditional Sampling Analysis of Acoustic Phenomena from a Supersonic Jet Impinging on an Inclined Flat Plate

Effect of Nozzle–Plate Distance on Acoustic Phenomena from Supersonic Impinging Jet

“…The acoustic waves (ii) are radiated from the impingement region and propagate in a direction almost perpendicular to the inclined flat plate. This suggestion of Nonomura et al [10] was consistent with the observations of subsequent studies involving similar impinging jets, such as the numerical simulations of Tsutsumi et al [12,13], Brehm et al [14], and Nonomura et al [15] and the experimental works of Worden et al [16,17] and Akamine et al [18,19]. For example, Akamine et al [19] experimentally observed the complicated acoustic waves around the impinging jet, which corresponded to the Mach waves (i) from the free-jet region and acoustic waves (ii) from the impingement region, as shown in the schlieren image in Fig.…”

“…The extracted results depend on the location of the microphone and target frequency. The location of the microphone was r∕D 40 and θ 75 deg, at which a high OASPL was observed for both the shorter and longer nozzle-plate distances (5D and 15D, respectively), as mentioned in [19] and shown in Fig. 6.…”

“…This motivated us to apply an extraction technique to these raw movies. In this study, the acoustic-triggered conditional sampling technique using the wavelet transform proposed by Akamine et al [19] was employed. This technique is an extension of the conditional sampling such as Moore [22], Camussi and Guj [23], and Guj et al [24] and differs from the other methods that involve the use of the wavelet transform, such as the wavelet filtering by Cavalieri et al [25] and Koenig et al [26] and the method for detecting the periods of noise generation by Hileman et al [27] and Kastner et al [28].…”

“…Understanding of the effects of the nozzle-plate distance is important not only for elucidating the noise generation mechanisms of an ideally expanded jet impinging on an inclined flat plate but also for predicting the acoustic noise field around the ascending launch vehicle. Comparisons of the characteristics of the acoustic fields of various nozzle-plate distances have been presented by Nonomura et al [10] (5 and 10 nozzle-exit diameters), Worden et al [16,17] (ranging from 2 to 12 nozzle-exit diameters), and Akamine et al [19] (5 and 15 nozzle-exit diameters). Akamine et al [19] found an interesting feature; the overall sound pressure level (OASPL) was higher in a part of the upstream region (in the direction approximately 75 deg from the inclined flat plate) in the case of the greater nozzleplate distance.…”

“…In addition to the sound pressure level (SPL) measurement, schlieren visualization movies with high spatial resolution are made to observe the complicated phenomena around the source region. An acoustictriggered conditional sampling technique [19] is applied to these movies to extract phenomena that correlate to the targeted intermittent acoustic wave. Furthermore, a ray tracing of acoustic intensity vectors [21] is introduced to estimate the propagation region of the Mach waves (i) from the free-jet region.…”