Supersonic Impinging Jets Research Articles

503 超音速衝突噴流の自励振動に及ぼす半円形プレートの影響(流体工学III)

503 超音速衝突噴流の自励振動に及ぼす半円形プレートの影響(流体工学III)

503 半円形プレートが超音速衝突噴流の自励振動の特性に及ぼす影響(流体工学IX)

503 半円形プレートが超音速衝突噴流の自励振動の特性に及ぼす影響(流体工学IX)

Active and Adaptive Control of Supersonic Impinging Jets

The behavior of supersonic impinging jets is dominated by a feedback loop due to the coupling between the fluid and acoustic fields. This leads to many adverse effects when such flows occur in short takeoff and vertical landing aircraft, such as a significant increase in the noise level, very high unsteady loads on the nearby structures, and an appreciable loss in lifting during hover. In earlier studies, it was demonstrated that by using supersonic microjets one could disrupt the feedback loop that leads to substantial reductions in the aforementioned adverse effects. However, the effectiveness of control was found to be strongly dependent on the ground plane distances and the jet-operating conditions. The effect of various microjet control parameters are investigated in some detail to identify their influence on control efficiency and additional insight is provided on the physical mechanism behind this control method. Parameters studied include microjet angle, microjet pressure, and the use of microtabs instead of microjets. These results indicate that by choosing appropriate control parameters it should be possible to devise a control strategy that produces optimal control for the entire operating range of conditions of the supersonic impinging jet. Moreover, the experimental results provide convincing evidence of the generation of significant streamwise vorticity by the activation microjets. It is postulated that the generation of streamwise vorticity and its evolution in the jet flow might be one of the main physical phenomena responsible for the reduction of flow unsteadiness in impinging jets.

Laser reflection method for determination of shear stress in low density transitional flows

The details of laser reflection method (LRM) for the determination of shear stress in low density transitional flows are presented. The method is employed to determine the shear stress due to impingement of a low density supersonic free jet issuing out from a convergent divergent nozzle on a flat plate. The plate is smeared with a thin oil film and kept parallel to the nozzle axis. For a thin oil film moving under the action of aerodynamic boundary layer, the shear stress at the air–oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope generated by the shear force is done using a position sensing detector (PSD). The thinning rate of the oil film is directly measured which is the major advantage of the LRM. From the oil film slope history, calculation of the shear stress is done using a three-point formula. The range of Knudsen numbers investigated is from 0.028 to 0.516. Pressure ratio across the nozzle varied from 3,500 to 8,500 giving highly under expanded free jets. The measured values of shear, in the overlapping region of experimental parameters, show fair agreement with those obtained by force balance method and laser interferometric method.

An experimental study of the oscillatory flow structure of tone-producing supersonic impinging jets

An experimental investigation into the structure of a supersonic jet impinging on a large plate is presented. Digital particle image velocimetry (DPIV), shadowgraph photography and acoustic measurements are used to understand the relationship between the unsteady jet structure and the production of tones for nozzle-to-plate spacings between 1 and 5 nozzle exit diameters at a nozzle–pressure ratio equal to 4. Results indicate that the instability of the jet depends on the location of the plate in the shock cell structure of the corresponding free jet and the strength of the standoff shock wave, rather than on the occurrence of recirculation zones in the impingement region. Phase-locked studies show streamwise displacements of the stand-off shock wave, a moving recirculation zone in the subsonic flow in front of the plate, and significant oscillations of both the compression and expansion regions in the peripheral supersonic flow when tones are produced. Sound is shown to be generated by periodic pulsing of the wall jet boundary resulting from periodic motion of the flow in the impingement and near-wall regions of the flow.

410 超音速不足膨張衝突噴流の自励振動に及ぼす半円形プレートの影響(OS4-3 高速流れと衝撃波現象の基礎と応用(非定常流れ),OS4 高速流れと衝撃波現象の基礎と応用,オーガナイズドセッション)

410 超音速不足膨張衝突噴流の自励振動に及ぼす半円形プレートの影響(OS4-3 高速流れと衝撃波現象の基礎と応用(非定常流れ),OS4 高速流れと衝撃波現象の基礎と応用,オーガナイズドセッション)

CHARACTERISTICS OF OSCILLATION FREQUENCY CAUSED BY SUPERSONIC IMPINGING JET(Impinging Jet)

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition, namely the pressure ratio in the flow field, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flow field and the mechanism of oscillation have to be more cleared to control the oscillation. This paper aims to clear the characteristic of oscillation frequency, pressure fluctuation on the surface of cylindrical body and the control of self-induced flow oscillation during the impingement with the cylindrical body. The numerical and experimental investigations were carried out using the TVD method and discussed.

超音速衝突噴流による自励振動の周波数スペクトルの遷移(流体工学VII)

超音速衝突噴流による自励振動の周波数スペクトルの遷移(流体工学VII)

Control of Supersonic Impinging Jet Flows Using Supersonic Microjets

Supersonic impinging jets, such as those occurring in the next generation of short takeoff and vertical landing aircraft, generate a highly oscillatory e ow with very high unsteady loads on the nearby aircraft structures and the landing surfaces. These high-pressure and acoustic loads are also accompanied by a dramatic loss in lift during hover.Previousstudies of supersonic impinging jets suggestthatthehighly unsteady behavioroftheimpinging jets is due to a feedback loop between the e uid and acoustic e elds, which leads to these adverse effects. A unique active control technique was attempted with the aim of disrupting the feedback loop, diminishing the e ow unsteadiness, and ultimatelyreducing theadverseeffectsofthise ow.Flowcontrolwasimplementedbyplacingacirculararray of 400-πm-diamsupersonicmicrojetsaroundtheperipheryofthemainjet.Thiscontrolapproachwasverysuccessful in disrupting the feedback loop in that the activation of the microjets led to dramatic reductions in the lift loss (40%), unsteady pressure loads (11 dB), and near-e eld noise (8 dB). This relatively simple and highly effective control technique makes it a suitable candidate for implementation in practical aircraft systems. NUNDERSTANDINGoftheimpingingjete owe eld isnecessary for the design of efe cient short takeoff and vertical landing (STOVL) aircraft. When such STOVL aircraft are operating in hovermode,thatis,in closeproximityto theground,thedownwardpointing lift jets produce high-speed, hot e ow that impinges on the landing surface and generates the direct lift force. It is well known that in this cone guration several e ow-induced effects can emerge, which substantially diminish the performance of the aircraft. In particular, a signie cant lift loss can be induced due to e ow entrainment bytheliftingjetsfromtheambientenvironmentinthe vicinityofthe airframe. Other adverse phenomena include severe ground erosion on the landing surface and hot gas ingestion into the engine inlets. In addition, the impinging e owe eld usually generates signie cantly highernoiselevelsrelativetothatofafreejetoperatingundersimilar conditions. Increased overall sound pressure levels (OASPL) associated with the high-speed impinging jets can pose an environment pollution problem and adversely affect the integrity of structural elements in the vicinity of the nozzle exhaust due to acoustic loading. Moreover, the noise and the highly unsteady pressure e eld are frequently dominated by high-amplitude discrete tones, which may match the resonant frequencies of the aircraft panels, thus further exacerbating the sonic fatigue problem. These problems become more pronounced when the impinging jets are supersonic, the operating regime of the STOVL version of the future joint strike e ghter. In addition, the presence of multiple impinging jets can potentially further aggravate these effects due to the strong coupling between the jets and the emergence of an upward-moving fountain e ow e owing opposite to the lift jets. 1 A

511 垂直平板に衝突する不足膨張噴流の自励振動に及ぼす平板の大きさの影響

511 垂直平板に衝突する不足膨張噴流の自励振動に及ぼす平板の大きさの影響

310 超音速不足膨張衝突噴流の自励振動に及ぼす圧力比と距離の影響

310 超音速不足膨張衝突噴流の自励振動に及ぼす圧力比と距離の影響

Distributions of Recovery Temperature on Flat Plate by Underexpanded Supersonic Impinging Jet

An experimental investigation has been conducted on the impingement of underexpanded, axisymmetric, and supersonic jets on a flat plate. The surface pressure and the adiabatic wall temperature distributions on the flat plate have been measured in detail at small nozzle-to-plate distances. The influences of the pressure ratio, the exit Mach number, the nozzle-to-plate distance, and the impinging angle have been considered. The surface pressure and the adiabatic wall temperature distributions on the flat plate for supersonic jet impingement are affected significantly by the nozzle-to-plate distance and the existence of a stagnation bubble in the central region

Experimental and Computational Investigation of Supersonic Impinging Jets

The results of an experimental and computational study of a moderately underexpanded axisymmetric supersonicjetissuingfroma convergingnozzleand impingingonagroundplanearepresented.Thegoalofthisworkisto develop a better understanding oftheimpinging jet e owe eld, which is of signie cantpracticalinterestbecause of its presence in short takeoff and vertical landing (STOVL)aircraft during hover as well as in other aerospace-related and industrial applications. Theexperimental measurementsinclude e ow visualization, surface-pressuredistributions,and velocitye elddataobtained using particleimagevelocimetry (PIV).Theexperimentaldata,especially the velocity e eld measurements, were used to verify theaccuracy of computational predictions. Computational results obtained using two differentturbulencemodels produced almost identical results. Comparisons with experimental results reveal that both models capture the signie cant features of this complex e ow and were in remarkably good agreement with the experimental data for the primary test case. The experiments and computations both revealed the presence of the impingement zone stagnation bubble, which contains low velocity recirculating e ow. Other features, including the complex shock structure and the high-speed radial wall jet, were also found to be very similar. The ability to measure and predictaccurately theimpinging jetbehavior, especially neartheground plane, is critical because these are regions with very high mean shear, thermal loads, and unsteady pressure forces, which contribute directly to the problem of ground erosion in STOVL applications.

The connection between sound production and jet structure of the supersonic impinging jet.

An experimental investigation into the sound-producing characteristics of moderately and highly underexpanded supersonic impinging jets exhausting from a round convergent nozzle is presented. The production of large plate tones by impingement on a square plate with a side dimension equal to 12 nozzle exit diameters is studied using random and phase-locked shadowgraph photography. Discrete frequency sound is produced in the near-wall region of the jet when a Mach disk occurs upstream of the standoff shock wave. Tones cease when the plate distance is approximately 2.2 free-jet cell lengths and the first and second shock waves are located in the free-jet positions. The production of impulsive sound appears to be associated with the collapse of the standoff shock wave during a portion of the oscillation cycle. Results from unsteady plate-pressure measurements indicate that plane-wave motion occurs in the impingement region and a secondary pressure maximum is observed on the plate adjacent to the flow region where sound appears to originate.

レーザ蛍光法による超音速矩形衝突噴流自励振動サイクルの可視化

Feedback mechanism of self-sustained oscillation in supersonic impinging jets is studied experimentally by using a laser-induced fluorescence (LIF) technique. Phase velocities of disturbances in the flow field are obtained from a time-dependent cross-correlation function between a pressure sensor signal at a reference point and the LIF signal. A feature of disturbance propagation can be visualized by drawing maps for the cross-correlation coefficients on a plane at successive delay-times and making an animation. The discrete frequencies appeared near the neutral wave frequencies proposed by Tam and symmetric and asymmetric modes of the neutral wave were observed corresponding to his theory.

A Study on Fundamental Properties of PSP in Low Pressure Region.

Recently pressure sensitive paint (PSP) has actively developed to measure continuous distribution of the surface pressure. However, the pressure range has been limited above 1 Torr (133.3 Pa) and there is no application to lower pressure range because the pressure sensitivity seems to be not so high in that range. In this study, we apply three types of PSP [two types are composed by organic dye and polymer (luminophore/binder) ; PtOEP/GP 197 and PtTFPP/poly (TMSP), and another one is Bath-Ru adsorbed on anodized aluminum] to the rarefied gas flow mainly lower than 1 Torr and examine those fundamental properties, such as pressure/temperature sensitivity and time response of luminescence and so on, leading to selection of the most suitable PSP among them for the low pressure range. Finally, the pressure distribution of the surface on which a low density supersonic free jet impinges is measured by the PSP.

低密度気体中におけるPSPの評価と応用

Recently pressure sensitive paint (PSP) has actively developed to measure continuous distribution of the surface pressure. However, the pressure range has been limited above 1 Torr (133.3 Pa) and there is no application to lower pressure range because the pressure sensitivity seems to be not so high in that range. In this study, we apply three types of PSP [two types are composed by organic dye and polymer (luminophore/binder); PtOEP/GP197 and PtTFPP/poly(TMSP), and another one is Bath-Ru adsorbed on anodized aluminum] to the rarefied gas flow mainly lower than 1 Torr and examine those fundamental properties, such as pressure/temperature sensitivity and time response of luminescence and so on, leading to selection if the most suitable PSP among them for the low pressure range. Finally, the pressure distribution of the surface on which a low density supersonic free jet impinges measured by the PSP

802 不足膨張衝突噴流の自励振動による圧力変動と振動周波数の特性

802 不足膨張衝突噴流の自励振動による圧力変動と振動周波数の特性

Experimental and computational investigation of supersonic impinging jets

The results of an experimental and computational study of a moderately underexpanded axisymmetric supersonic jet issuing from a converging nozzle and impinging on a ground plane are presented. The goal of this work is to develop a better understanding of the impinging jet flowfield, which is of significant practical interest because of its presence in short takeoff and vertical landing (STOVL) aircraft during hover as well as in other aerospace-related and industrial applications. The experimental measurements include flow visualization, surface-pressure distributions, and velocity field data obtained using particle image velocimetry (PIV). The experimental data, especially the velocity field measurements, were used to verify the accuracy of computational predictions. Computational results obtained using two different turbulence models produced almost identical results

704 垂直平板に干渉する超音速不足膨張噴流により形成される流れ場の特性

704 垂直平板に干渉する超音速不足膨張噴流により形成される流れ場の特性