Takeo Okunuki

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

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.

A Study on Ablation Behavior of Spherical Ice Piece in Hypersonic Flow

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.

Visualization movie analysis of acoustic phenomena of a supersonic jet and Its comparison with intensity vectors

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.

Near-field acoustical array measurements of an impinging supersonic jet

Behavior of a piece of water ice was experimentally observed in flows of the hypersonic wind tunnel at Mach number 7. The wind tunnel tests of ice pieces were performed at the hypersonic wind tunnel in Kashiwa campus, The University of Tokyo. A series of the spatial phenomena consisting of melting in the stagnation region, flow of melted ice (water) over the ice surface, re-freezing, and so on and the temporal process from surface melting to fragmentation are clearly observed. From the snapshots, the shape change of icy body is measured and the volume of icy body is estimated. The volume of icy body at the front part decreases almost linearly although the curvature of front part changes. On the other hand, the volume of icy body at refrozen part increases. The total volume loss rate is increase with the increase in stagnation temperature. The temperature of icy body is also measured and it shows that the effect of latent have an important role to decide the body temperature.

Experimental and computational investigation of supersonic cavity flows

The authors have studied the acoustic wave from an unheated, Mach 1.8 ideally expanded jet by using the acoustic intensity vector measurement and analysis of high-speed schlieren visualization movies (for example, the Fourier transform and wavelet-based conditional sampling). Both these techniques reveal the characteristics of the acoustic wave, such as the propagation direction and location of a source region. These techniques have their own advantages: the quantitative data can be obtained by using the acoustic intensity vector measurement, whereas the acoustic field including a close region to the jet can be visualized with high spatial resolution by using the Schlieren movie analysis. Therefore, their comparison is a meaningful approach to understand the acoustic phenomenon. This presentation compares these two techniques and describes what can be discussed with their comparison, considering the advantage and disadvantage of each measurement technique.

Numerical Analysis of Flapping Wing

Impingement significantly alters the rocket plume in the near-launch pad environment, which in turn affects the acoustic radiation. Prior laboratory measurements of an unheated, Mach 1.8 ideally expanded jet impinging on 45-degree inclined flat plate were carried out using a microphone that was moved within a relatively dense grid [Akamine et al., AIAA J. 53, 2061–2067 (2015)]. A multi-institution collaboration by the authors was begun in order to conduct array measurements of the acoustic radiation from both impinging and free jets. Measurements comprised a total of 42 measurement channels located within 40 nozzle diameters. An array of two-dimensional microphone probes was placed so as to examine the transition from the hydrodynamic near field to the acoustic radiation. A scanning linear array of microphones and a stationary polar array were also designed to enable beamforming, cross correlation, and partial field decomposition. This paper describes the jet facility, experiment design, and initial analy...