Susumu Teramoto

Experimental verification of the feasibility of a 100 W class micro-scale gas turbine at an impeller diameter of 10 mm

The feasibility of a 100 W class micro-scale gas turbine with a centrifugal impeller of 10 mm diameter has been studied by experimentally verifying the four major component performance requirements found from cycle analysis. The rotor is required to rotate at 870 000 rpm to generate the compressor pressure ratio 3, and it has successfully been achieved by using hydroinertia gas bearings. A compressor efficiency higher than that required by the target cycle has been measured. After correcting the effect of the heat leakage, approximately 65% of the compressor adiabatic efficiency is estimated to be achievable. The combustor has achieved stable self-sustained combustion at a combustion efficiency higher than 99.9%. The heat conduction analysis based on measured data showed that it is possible to keep the compressor below 170 °C when the turbine inlet temperature is 1050 °C. All four requirements are proven to be achievable, and hence, the feasibility of the micro-scale gas turbine at an impeller of 10 mm diameter has successfully been proven at component level.

Large-Eddy Simulation of Transitional Boundary Layer with Impinging Shock Wave

The transition of a boundary layer on a flat plate with an impinging shock wave is studied numerically by compressible large-eddy simulation using a hybrid compact/Roe scheme. The numerical code is verified by comparison with experimental observations of shock wave/turbulent boundary-layer interaction and then applied for the analysis of shock wave/transitional boundary-layer interaction. The simulation provides accurate results with respect to the location of reattachment and the boundary-layer properties downstream of reattachment. Large-scale coherent structures such as longitudinal vortex pairs, low-speed streaks, and hairpin vortices are identified in the transitional region, and it is revealed that these coherent structures play important roles in the transition. Thus, it is important to resolve these structures adequately to obtain an accurate prediction of the reattachment point. The subsequent breakdown of these coherent structures have smaller length scales, and resolving the breakdown requires much finer grid resolution. However, the influence of underresolution of breakdown on the downstream flowfield can be largely ignored under the conditions examined. Large-eddy simulation is, therefore, useful for the qualitative analysis of flowfields involving a supersonic transitional boundary layer.

Numerical Analysis of Dynamic Stability of a Reentry Capsule at Transonic Speeds

Dynamic stability of a reentry capsule in transonic speeds is discussed. An unsteady flowfield around the capsule under the forced pitching oscillation in the transonic flow of M = 1.3 is numerically simulated based on the three-dimensional thin-layer Navier-Stokes equations. The numerical result reveals that the dynamic instability is caused by the phase delay of the base pressure. It is also found that the base pressure, the recompression shock wave, and the wake behind the recompression shock wave all oscillate with the same delay time. The flow mechanism is proposed based on the idea that the phase delay of the base pressure is caused by a feedback loop of the flowfield behind the capsule. This flow mechanism reasonably explains the features observed in the present numerical simulation, as well as the experimental fact that the dynamic instability occurs at very low reduced frequencies.

Mechanism of Dynamic Instability of a Reentry Capsule at Transonic Speeds

A blunt and short reentry capsule tends to be dynamically unstable at transonic speeds, attributed primarily to the delay of base pressure. In the present study the flowfield around a capsule under forced pitching oscillation is numerically simulated, and the results are compared with that around the capsule at a fixed pitch angle. The two flowfields are found to be essentially the same except for a delay in the base pressure in the oscillating case. Detailed flow analysis reveals that impingement of reverse flow behind the capsule determines the base pressure distribution, and the behavior of the reverse flow is governed by the vortex structure behind the capsule. The vortex structure is composed of a ring vortex and a pair of longitudinal vortices, and the interaction between the longitudinal vortices and the flowfield near the neck point defines the flowfield behind the capsule

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

Clustering Effects on Performance and Heating of a Linear Aerospike Nozzle

Numerical and experimental investigations are conducted to identify the key aspects of the flowfield that effects the performance and heating of a linear aeropsike nozzle with clustered modules. The flowfield near the linear aerospike nozzle surface is characterized by the viscid-inviscid interaction between the jet and boundary layer over the nozzle. Whereas, the off-surface flowfield exhibits the inviscid features of the jet from the rectangular-exit module and the interaction between the jets from neighboring modules. The correlation between the flow mechanism and clustering effects on the performance and heating was analyzed, based on the knowledge of the flowfield. It is revealed that the major part of the performance loss results in the shock loss due to the inviscid jet interaction in the offsurface flowfield. On the other hand, the heat-flux distribution over the linear aerospike nozzle stems from the viscid-inviscid interaction near the nozzle surface.

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

Acoustic Generation Mechanism of a Supersonic Jet Impinging on Deflectors

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

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

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.

Structure of Underexpanded Jets from Square Nozzles

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.