Fluid dynamic turbulence is one of the most challenging computational physics problems because of the extremely wide range of time and space scales involved, the strong nonlinearity of the governing equations, and the many practical and important applications. While most linear fluid instabilities are well understood, the nonlinear interactions among them makes even the relatively simple limit of homogeneous isotropic turbulence difficult to treat physically, mathematically, and computationally. Turbulence is modeled computationally by a two-stage bootstrap process. The first stage, direct numerical simulation, attempts to resolve the relevant physical time and space scales but its application is limited to diffusive flows with a relatively small Reynolds number (Re). Using direct numerical simulation to provide a database, in turn, allows calibration of phenomenological turbulence models for engineering applications. Large eddy simulation incorporates a form of turbulence modeling applicable when the large-scale flows of interest are intrinsically time dependent, thus throwing common statistical models into question. A promising approach to large eddy simulation involves the use of high-resolution monotone computational fluid dynamics algorithms such as flux-corrected transport or the piecewise parabolic method which have intrinsic subgrid turbulence models coupled naturally to the resolved scales in the computed flow. The physical considerations underlying and evidence supporting this monotone integrated large eddy simulation approach are discussed.

New insights into large eddy simulation

Supersonic jets, particularly shock-containing jets, often exhibit high-intensity, discrete-frequency acoustic tones. These tones are the signature of an aeroacoustic resonance loop established by ...

https://journals.sagepub.com/doi/pdf/10.1177/1475472X19834521

Aeroacoustic resonance and self-excitation in screeching and impinging supersonic jets – A review:

Noise generation mechanisms for a perfectly expanded supersonic Mach number turbulent jet impinging on a inclined plate are investigated for a Reynolds number of employing a large-eddy simulation. Excellent comparisons with experimental acoustic far-field measurements and pressure measurements on the impingement plate are obtained. Two local maxima are identified in the far-field overall sound pressure levels in the and observer directions, which are associated with different noise generation mechanisms. The peak frequencies in the spectra with Strouhal numbers of for and for match the experimental measurements. The jet-impingement region generates pressure waves that propagate predominantly in the observer direction. The noise generation in this region is attributed to vortex stretching and tearing during shear-layer impingement, and shock oscillations that are induced by the motion of downstream convected vortical flow structures. The second peak in the overall sound pressure distribution at is associated with noise sources located in the wall jet. The noise generation in the wall jet is associated with supersonically convecting large-scale coherent flow structures that also interact with tail shocks in the wall jet causing large localized pressure fluctuations. Strongly coherent flow structures are identified by applying proper orthogonal decomposition (POD) to the unsteady flow field. The frequency characteristics of the most energetic POD modes are distinctly different based on which energy norm is chosen. The most energetic entropy-based POD modes contain a peak frequency of approximately , while the most energetic turbulent kinetic-energy-based POD modes appear to be dominated by lower-frequency content. The causality method, based on Lighthill’s acoustic analogy, is used to link the acoustic noise signature to the relevant physical mechanisms in the source region. A differentiation is made between the application of normalized and non-normalized cross-correlation functions for noise source identification and characterization.

Noise generation mechanisms for a supersonic jet impinging on an inclined plate

Large-eddy simulations are performed using high-fidelity numerical schemes developed for turbulence simulations and computational aeroacoustics to study near-ideally expanded and tone-producing supersonic jets vertically impinging on a large flat plate. The simulations compute the complex interaction of the supersonic jet with the flat impingement plane and directly provide the noise generated by this interaction. Two jet-operating temperatures, which correspond to isothermal and heated conditions, are considered in the simulations. The simulation results from both cases are examined to investigate the intense tonal noise generation arising from the jet impingement. The comparisons between the simulation results and the corresponding experimental measurements generally show a reasonable agreement and provide credibility to the quality of the simulation predictions. The simulations reveal important details about the problem of interest, which are not observable from the experiments. A dynamic mode decompos...

Simulation of Tonal Noise Generation by Supersonic Impinging Jets

Subscale model tests and a numerical investigation are performed to predict and attenuate the acoustic level of the Epsilon launch vehicle at liftoff. Requirements for the subscale model test to predict a full-scale acoustic environment are investigated, and then the scale size of the model test is set at 1/42. The launch pads employed herein are designed to attenuate reflection of the Mach wave radiated from the free jet and the acoustic wave due to the jet’s impinging on the flame deflector. When comparing the acoustic result taken at the fairing location with that at three different altitudes, 9De, 14De, and 22De, where De represents the nozzle exit diameter, the acoustic level observed at 14De is the highest and exceeds the design requirement at all frequencies. It is revealed from the numerical analysis that the reflection of Mach waves radiating from the free jet within the flame path is the dominant acoustic source. A front cover is attached to the vertical flame path to shield the Mach wave radiat...

Study on Acoustic Prediction and Reduction of Epsilon Launch Vehicle at Liftoff

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 $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 1533-385X/15 and $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.

Acoustic Phenomena from Correctly Expanded Supersonic Jet Impinging on Inclined Plate

Numerical simulation of a supersonic jet impinging to a 45-degree-inclined flat plate is conducted to reveal the correlation between hydrodynamic structure and the acoustic field. This type of acoustic generation is of interest for lift-off acoustics of launch vehicles. Through the conditional sampling, it is clarified that acoustic wave overarching the plate shock and the 1st tail shock is an onset of the acoustic wave generated near the impingement region. This result implies that the acoustic wave generated near the impingement region is formed by the interaction of turbulent structure of the jet shear layer with the plate and the tail shock waves. Preliminary numerical study is then conducted to analyze the effect of deflector shape on the plate and the tail shock waves and resulting acoustic level of launch vehicle. It turns out that magnitude of the plate shock and acoustic level around the vehicle are attenuated by employing steeply inclined flat plate. While, a tail-shock-free deflector with 45-degree initial inclination is designed to avoid formation of the tail shocks. It is found that the tail-shock-free deflector is compact in size to redirect the jet horizontally, but the acoustic level near the vehicle is almost the same with the 45-degree-inclined flat plate. The results obtained in this study shed light on deflector design criteria based on acoustic point of view.

Acoustic generation mechanism of a supersonic jet impinging on deflectors

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.

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

Acoustics radiated from a M=1.8 ideally-expanded jet impinging on a 45 degree-inclined flat plate is investigated numerically with the help of the experimental work. Validation of computational method and grid convergence study are conducted firstly. Result of the free jet is satisfactory, while the present study overestimates the noise level of the impinging jet by 5 dB in OASPL. Based on the numerical technique validated here, mechanism of acoustics is analyzed. In addition to the well-known free-jet noise sources such as the Mach wave and the fine-scale turbulent mixing noise, additional two noise sources are found; 1) interaction between the shock waves and the vortex of the shear layer, 2) the Mach wave radiated from the jet flowing on the inclined plate. The former is similar to the shockassociated noise, and the OASPL plot at far-filed shows omni-directional feature. These two waves are also observed in the present experiment.

Numerical Study on Acoustic Radiation from a Supersonic Jet Impinging to an Inclined Plate

For the prediction and reduction of acoustic loading of launch vehicle at lift-off, acoustic wave radiated from ideally-expanded supersonic cold jets impinging to an 45-degree-inclined flat-plate, representative of a flame deflector, located 5D downstream from the nozzle exit is investigated numerically with the help of the experimental work. It turns out that dominant noise source is classified into three types: (i) the Mach wave radiation from free jet before the impingement, (ii) the acoustic wave generated from the impingement region, and (iii) another Mach wave radiation from supersonic wall jet after the impingement. Those features are clearly observed by applying the Proper Orthogonal Decomposition (POD) analysis to the numerical results. Comparing with the experimental result conducted in this study, prediction accuracy of 5 dB in OASPL is obtained in the current numerical simulation.

https://iccfd.org/iccfd7/assets/pdf/papers/ICCFD7-3104_paper.pdf

Yuta Nakanishi

Papers

Acoustic Phenomena from Correctly Expanded Supersonic Jet Impinging on Inclined Plate

Acoustic generation mechanism of a supersonic jet impinging on deflectors

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

Numerical Study on Acoustic Radiation from a Supersonic Jet Impinging to an Inclined Plate

Analysis of Acoustic Wave from Supersonic Jets Impinging to an Inclined Flat Plate