Masahito Akamine

Acoustic Phenomena from Correctly Expanded Supersonic Jet Impinging on Inclined Plate

PAYLOAD vibration due to acoustic waves from the exhaust plume is a significant problem during the liftoff of a launch vehicle. These acoustic waves are considered to be caused by jet impingement on the ground or on the flame deflector at the launch pad, as well as being from the free jet region. The ground slope or flame deflector profiles are therefore considered to affect the intensity and characteristics of this acoustic phenomenon, but design principles to suppress acoustic wave generation have not yet been established, because the generation mechanisms of the acoustic waves from the jet impingement have not been sufficiently clarified. Therefore, this study investigates the acoustic phenomena from a correctly expanded supersonic jet impinging on an inclined flat plate, through experiments conducted using a jet facility. The flow field of a supersonic jet impinging on a solid surface has been examined in many previous studies. For example, the fundamental flow structure was described by Donaldson and Snedecker [1]. From their experiments using an underexpanded jet impinging on a perpendicular or inclined plate at various angles, the flow structure was explained as being composed of three regions with different flow regimes: the free jet, impingement, and wall jet regions. The free jet region is minimally affected by the jet impingement, and its flow structure is similar to that of a free jet, as regard the potential core and supersonic shear layers. Next, the jet impinges on the plate, yielding a recirculation flow in the impingement region while, finally, the jet flows along the plate surface in the wall jet region. Carling and Hunt [2] experimentally discussed the flow field of a correctly expanded jet impinging on a perpendicular plate, and observed a series of expansion, recompression, and, in some cases, shock waves on the plate surface. As for an underexpanded jet impinging on an inclined plate, complicated shock structure in the impingement regionwas observed in the experiments of Lamont and Hunt [3], and in the calculations of Kim and Chang [4]. This structure is composed of plate shocks (i.e., standoff shocks) with additional tail shocks around the plate shocks. Nakai et al. [5] experimentally classified this structure into four types under various plate angle, nozzle–plate distance, and pressure ratio conditions. Moreover, a detailed numerical description of this shock structure was given by McIlroy and Fujii [6]. As for the investigation of the related acoustic phenomena, most previous studies have focused on discrete tone noise. The acoustic characteristics and the related perpendicular jet impingement flow phenomena were discussed in experimental studies (e.g., [7,8]) and recent numerical works (e.g., [9,10]), while, also, Risborg and Soria [11] discussed the acoustic feedback loop of an underexpanded jet impinging on an inclined plate by visualizing acoustic waves. As for studies on the acoustic phenomena from a correctly expanded supersonic jet impinging on an inclined plate, the subject that is examined in the present study, several numerical reports can be found, such as [12–14]. These studies were conducted to investigate the acoustic phenomena during the liftoff of a launch vehicle, and also discussed the acoustic and flow fields, which contain complex shock structures in the impingement region. In particular, the results of these studies revealed that there exist two types of acoustic waves: the Mach waves from the supersonic turbulent wall jet, and the acoustic waves propagating in an approximately perpendicular direction to the plate. The acoustic field under various impingement conditions was also calculated by Nonomura et al. [14] and Honda et al. [15] but, on the other hand, only [16] can be found as an experimental study of these phenomena. They measured noise from Mj 1.5 correctly expanded jets impinging on inclined plates at two fixed locations, mainly focusing on the noise environment of an aircraft carrier deck. They successfully revealed the influence of the nozzle–plate distance and the jet temperature on the sound pressure level (SPL), whereas they also noted that further investigations, such as spatial distribution of SPL, localization of the source region, and optical measurements, may be useful to fully characterize the acoustic and flow properties. As described above, these acoustic phenomena have been investigated numerically in detail, but discussion based on experimental data is currently lacking. Detailed experimental results are indispensable to a discussion of acoustic phenomena, because a limitation in the frequency range of the spectra obtained by numerical analyses exists. Therefore, the objective of the present study is to study the characteristics of the acoustic waves from a correctly expanded supersonic jet impinging on the inclined plate experimentally. To achieve this, the acoustic waves from the impinging jet are measured using a microphone at a jet facility. The waves are then visualized using the schlieren method, and their propagation directions, spectra, and the extent of the source region are discussed in this study.After an evaluation of the accuracy of the SPLmeasurement and confirmation of the jet profile (described in Sec. II.D.), an overview of the acoustic field based on the results of the SPL measurements and schlieren visualization is presented inSec. III.A. Then, the spectra of the acoustic waves are discussed in Sec. III.B. Finally, the extent of the source region of the acoustic waves is discussed using the SPL distributions and a schlieren visualization movie analysis, in Sec. III.C. Received 26 September 2014; revision received 4 November 2014; accepted for publication4November 2014; published online 28 January 2015. Copyright© 2014byMasahitoAkamine. Published by theAmerican Institute of Aeronautics and Astronautics, Inc., with permission. Copies of this paper may be made for personal or internal use, on condition that the copier pay the

Experimental Study on Acoustic Phenomena of Supersonic Jet Impinging on Inclined Flat Plate

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Experimental validation of acoustic intensity bandwidth extension by phase unwrapping

10.00 in correspondence with the CCC. *Graduate Student, Department of Advanced Energy. Student Member AIAA. Ph.D. Student, Department of Advanced Energy; currently at IHI Corporation. Associate Professor, Department of Advanced Energy. Member AIAA. Associate Professor, Department of Aeronautics and Astronautics. Senior Member AIAA. Senior Engineer, Department of Aeronautics and Astronautics. **Engineer, JAXA’s Engineering Digital Innovation (JEDI) Center. Member AIAA.

Near-field spatial variation in similarity spectra decomposition of a Mach 1.8 laboratory-scale jet

Acoustic and flow fields of a Mj = 1.8 correctly-expanded jet impinging on a 45○ inclined flat plate are investigated experimentally. In the experiments, microphone measurement, Schlieren visualization, and wall static pressure measurement on the inclined plate surface are conducted for different nozzle-plate distances. When the nozzle-plate distance is 5D, two types of acoustic waves, whose characteristics are different in propagation directions, spectra, and source locations, are observed. One propagates in the 30○ direction from the inclined plate surface, and the other propagates in the 75○ direction. When the nozzleplate distance is varied, the change of the intensities of those two types of acoustic waves is observed, and the correlation between the acoustic waves and the shock structures of the flow field is discussed.

Characterization of Supersonic Laboratory-Scale Jet Noise with Vector Acoustic Intensity

The phase and amplitude gradient estimator (PAGE) method for active acoustic intensity uses pairwise microphone transfer functions to obtain the phase gradient, which improves the calculation bandwidth over the traditional weighted quadspectral method. Additionally, for broadband sources, the PAGE theory indicates that the transfer function phase can be unwrapped to further extend the usable frequency range to beyond the spatial Nyquist frequency. Here, two experiments demonstrate intensity bandwidth extension by more than an order of magnitude using phase unwrapping. First, plane-wave tube results show accurate one-dimensional intensity calculations with the microphones separated by five wavelengths, 30 times the traditional limit. Second, two-dimensional measurements of a laboratory-scale jet with a four-microphone probe yield physically reasonable calculations at frequencies 15 times the traditional limit.

Laser optical measurement of acoustic phenomena in the near field of a supersonic jet using 2-D position sensitive detector

The primary source of supersonic jet noise originates from the interaction of the turbulent flow with the ambient air. Tam et al. [AIAA Paper 96-1716 (1996)], proposed similarity spectra for a two-source model corresponding to omnidirectional fine-scale turbulence structures (FSS) and directional large-scale turbulent structures (LSS). These empirical similarity spectra agree reasonably with angular variation in mid and far-field spectra of both military and laboratory-scale jets. Near-field measurements of an ideally expanded, Mach 1.8 laboratory-scale jet from the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo were analyzed. Similarity spectra decompositions adequately describe the turbulent mixing noise as close as 10 jet diameters. Neglecting the effect of the hydrodynamic field, the LSS spectrum provides consistent fits at 15°-40° from the jet axis. A combination of LSS and FSS spectra match the measured spectra at 45°-55°. FSS spectrum matches the spectra at angles greater than 60°, except very close to the nozzle exit plane where there is an overprediction at high frequencies. Comparison of near and mid-field locations may provide insights into propagation radials.The primary source of supersonic jet noise originates from the interaction of the turbulent flow with the ambient air. Tam et al. [AIAA Paper 96-1716 (1996)], proposed similarity spectra for a two-source model corresponding to omnidirectional fine-scale turbulence structures (FSS) and directional large-scale turbulent structures (LSS). These empirical similarity spectra agree reasonably with angular variation in mid and far-field spectra of both military and laboratory-scale jets. Near-field measurements of an ideally expanded, Mach 1.8 laboratory-scale jet from the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo were analyzed. Similarity spectra decompositions adequately describe the turbulent mixing noise as close as 10 jet diameters. Neglecting the effect of the hydrodynamic field, the LSS spectrum provides consistent fits at 15°-40° from the jet axis. A combination of LSS and FSS spectra match the measured spectra at 45°-55°. FSS spectrum matches the spectra at an...

Level-educed Wavepacket Representation of Mach 1.8 Laboratory-Scale Jet Noise

A new method for the calculation of vector acoustic intensity from pressure microphone measurements has been applied to the aeroacoustic source characterization of an unheated, Mach 1.8 laboratory-scale jet. Because of the ability to unwrap the phase of the transfer functions between microphone pairs in the measurement of a radiating, broadband source, physically meaningful near-field intensity vectors are calculated up to the maximum analysis frequency of 32 kHz. The new intensity method is used to obtain a detailed description of the sound energy flow near the jet. The resulting intensity vectors have been used with a raytracing technique to identify the dominant source region over a broad range of frequencies. Additional aeroacoustics analyses provide insight into the frequency-dependent characteristics of jet noise radiation, including the nature of the hydrodynamic field and the transition between the principal lobe and sideline radiation.

Frequency-dependent jet noise source localization using cross-correlation between near and far-field microphone arrays

Acoustic measurement close to noise sources is significant to understand the generation mechanisms of jet noise. Microphones are generally used for the acoustic measurement, but they may disturb the flow and acoustic fields when they are used in the near field of a jet. In this study, an optical measurement method using a laser and 2-D position sensitive detector (PSD) is proposed for the acoustic measurement in the near field. In this method, 2-D PSD detects the angle and direction of the refraction of the laser path by acoustic wave passing, so that the propagating direction, as well as the acoustic intensity, is expected to be measured by this method. To discuss its validity, this method was applied to the acoustic measurement of a correctly expanded supersonic jet. In this experiment, microphone measurement was also carried out simultaneously, and cross correlation between the signals of these two measurements is discussed. Also, the measured spectra and propagating directions for different frequencies are compared with those of the acoustic intensity vector measurement.Acoustic measurement close to noise sources is significant to understand the generation mechanisms of jet noise. Microphones are generally used for the acoustic measurement, but they may disturb the flow and acoustic fields when they are used in the near field of a jet. In this study, an optical measurement method using a laser and 2-D position sensitive detector (PSD) is proposed for the acoustic measurement in the near field. In this method, 2-D PSD detects the angle and direction of the refraction of the laser path by acoustic wave passing, so that the propagating direction, as well as the acoustic intensity, is expected to be measured by this method. To discuss its validity, this method was applied to the acoustic measurement of a correctly expanded supersonic jet. In this experiment, microphone measurement was also carried out simultaneously, and cross correlation between the signals of these two measurements is discussed. Also, the measured spectra and propagating directions for different frequencie...

Calculating the frequency-dependent apparent source location using peak cross-correlation between near-field and far-field microphone arrays

The search for an equivalent acoustic source model for high-speed jet noise has recently focused on wavepacket representations. A wavepacket is defined as a spatially extended source with an axial amplitude distribution that grows, saturates and decays, an axial phase relationship that produces directional noise, and correlation lengths longer than the integral length scales of the turbulent structures. This definition of a wavepacket has the same characteristics as the large-scale turbulent mixing noise; if the turbulent mixing noise can be isolated, the associate equivalent acoustic wavepacket—defined as a pressure fluctuation on a cylinder around the jet nozzle—can be found. An estimate of the frequencydependent, spatial variation in the large-scale turbulent mixing noise comes from a similarity spectra decomposition of the measured autospectral density, which in turn leads to data-educed wavenumber axial spectra associated with the frequency-dependent equivalent wavepackets. This wavepacket eduction technique has been applied to acoustical measurements of an unheated, Mach 1.8 jet in the near and far fields. At both locations, the resulting frequency-dependent, data-educed wavenumber spectra exhibit different types of self-similarity for low and high frequency regimes that become apparent when the axial wavenumber is scaled by the acoustic wavenumber, with a transition band between the two regimes. As expected, the data-educed wavenumber spectra can be used to predict field levels in the dominant radiation lobe. Addition of an uncorrelated source distribution, derived from the similarity spectra decomposition associated with the fine-scale turbulent mixing noise, creates a model that accounts for the sideline levels. This field-prediction ability of the wavepacket-plus-uncorrelated-distribution model is tested using the near and far field measurements. When predicting the field at the other location, the model’s average error is less than 2 dB for St = 0.04-0.25 but increases for larger St because the apparent directivity changes from near to far field, likely due to the frequency dependence of the extended source region.

Experimental study of plate-angle effects on acoustic phenomena from a supersonic jet impinging on an inclined flat plate

The apparent acoustic source region of jet noise varies as a function of frequency. In this study, the variation of the apparent maximum source location with frequency is considered for an ideally expanded, unheated, Mach-1.8 jet with exit diameter of 20 mm. In this study, the source location is ascertained for one-third octave bands by evaluating peak cross-correlation between near-field linear microphone arrays at three sideline distances and a far-field microphone arc. The impact of the hydrodynamic field on correlation results is considered. Source locations determined by these means are compared with intensity analyses for the same jet [K. L. Gee et al., AIAA Paper 2017-3519 (2017)]. Correlational methods together with filtering can provide a straightforward measure of the acoustic origin as a function of frequency and thus inform optimal microphone array layout for specific frequency regimes.