Supersonic Impinging Jets Research Articles

Interaction of Shocks and Vortices in a Highly Underexpanded Supersonic Impinging Jet

A large eddy simulation of a highly underexpanded supersonic jet impinging on a large plate is reported. The Favre filtered compressible Navier–Stokes equations in cylindrical coordinates have been solved by using a finite difference method. The large eddy simulation code employs a fifth-order weighted essentially nonoscillatory scheme known asWENO for the convective fluxes, a fourth-order centered difference approach for the viscous fluxes, and a four-stage third-order strong-stability-preserving Runge–Kutta technique in time. The numerical simulation successfully captures the shockwave structure in the jet plume and vortex structureswith different scales in the inner and outer shear layers. The evolution of annular shock waves and the vortex in the inner shear layer has been observed. Under the impact of the inner and outer shear layers, the interlacing vortex structures in the wall jet are formed. From this simulation, it can be concluded that the generation and disappearance of the annular shock arise from the actions of theMach disk, the oblique shock wave, vortices in the inner shear layer, and the impinging plate, all combined.

Particle image velocimetry study of the impinging height effect on the overexpanded supersonic impinging free jet of Ma = 1.754. Part 2: detailed velocity distribution

In this article, the flowfield of an overexpanded axisymmetric supersonic impinging jet with exit Mach number 1.754 is studied using particle image velocimetry. In particular, the influence of the impinging height on the detailed flowfield velocity distributions has been investigated. The velocity distribution precisely indicates where the Mach disk and the plate shock are generated. With the increasing impinging height, the plate shock position is found to move away from the impinging wall, until it reaches the maximum of 0.767 D for the dimensionless impinging height of Z/ D = 2.5. With a further increasing of the impinging height, the plate shock moves back to the impinging wall. Furthermore, the shape, position, as well as size of the stagnation bubble zone can also be deduced from the velocity distribution. According to the time-averaged flowfield result, the velocity coefficient of the radial wall jet is found to be as high as 0.8146, which is critical to the ground erosion problem in the application. It indicated that although the radial velocity appeared to be supersonic in the instantaneous result in Part I [Xu J, Lin C and Sha J. Particle image velocimetry study of the impinging height effect on the overexpanded supersonic impinging free jet of Ma = 1.754. Part I: global coherent structure. Proc IMechE, Part G: J Aerospace Engineering 2012; 226(1): 64–73.], it is high subsonic in the mean result in this part. This disagreement is due to the intrinsic highly unsteady nature of the flow under investigation. The vorticity isopleths demonstrate that the stagnation bubble and the recirculating flow are formed due to the impingement of the nozzle inner shear layer of the main jet.

819 超音速不足膨張衝突噴流の自励振動による圧力変動の数値解析(0S.2 圧縮性流れの基礎と応用4)

819 超音速不足膨張衝突噴流の自励振動による圧力変動の数値解析(0S.2 圧縮性流れの基礎と応用4)

814 非平衡凝縮を伴う超音速衝突噴流特性に関する数値的研究(0S.2 圧縮性流れの基礎と応用3)

814 非平衡凝縮を伴う超音速衝突噴流特性に関する数値的研究(0S.2 圧縮性流れの基礎と応用3)

A Computational Fluid Dynamics Model of Shrouded Supersonic Jet Impingement on a Water Surface

A Computational Fluid Dynamics Model of Shrouded Supersonic Jet Impingement on a Water Surface

Particle image velocimetry study of the impinging height effect on an overexpanded supersonic impinging free jet at Ma = 1.754. Part 1: global coherent structure

Results of an experimental study of an overexpanded axisymmetric supersonic impinging jet at Mach 1.754 with particle image velocimetry (PIV) are presented in this article. The focus of Part I is on the influence of the impinging height on the global coherent flow structure, while in Part II the detailed velocity magnitude, both axial and radial, as well as the position variation of the plate shock will be presented. The PIV results clearly demonstrate the formation of the stagnation bubble as well as the presence of the recirculating flow in it. When the impinging height reaches five times the nozzle exit diameter, the stagnation bubble disappears, which is thought to be the result of the increase in the thickness of the shear layer of the main jet and consequently the decrease in the difference of the stagnation pressure between the centre of the stagnation zone and the impinging point of the main jet shear layer. The comparison between instantaneous and mean PIV measurements demonstrates that there exists highly unsteady behaviour of the impinging jet. The shock wave structure and the unsteady entraining vortex of the nozzle jet and the wall jet are all clearly recorded by PIV. All these results are crucial to understand the effects of the impinging height on the global flowfield coherent structure of the overexpanded axisymmetric supersonic jet impingement.

Mechanism of acoustic radiation from Supersonic Jets Impinging to Inclined Flat Plates

Acoustic wave radiated from supersonic cold jets impinging to inclined flat-plates is investigated numerically with the help of the experimental work. This type of acoustic generation is important for estimating and minimizing the acoustic loading of launch vehicle at lift-off. Through the study on the 45-degree-inclined flat plate located 5 D downstream from the nozzle exit, two noise sources are found to be generated due to the jet impingement: (1) interaction between the vortex of the jet shear-layer and the shock waves appearing at the jet impingement region and at the downstream region, (2) the Mach wave radiated from the large-scale vortex structure of the flow downstream of the plate. The former is similar to the broadband shock-associated noise. Those features are clearly confirmed by applying the proper orthogonal decomposition analysis to the numerical result. Prediction accuracy of 5 dB in far-field OASPL is obtained in the current numerical technique.

Aeroacoustic Waves Generated from a Supersonic Jet Impinging on an Inclined Flat Plate

This paper presents a computational study of the flow and flow-induced acoustic fields of a supersonic jet impinging on an inclined flat plate. For the numerical simulations, we solved three-dimensional compressible Navier-Stokes equations with a modified weighted compact nonlinear scheme. We analyzed the simulation results mainly from the viewpoint of the acoustic emission and propagation mechanism, and we investigated the acoustic field characteristics such as directivity, their spectra, and acoustic wave source positions. The acoustic fields indicate that there are at least three types of acoustic waves in all the cases considered in the study: (i) Mach waves generated from the shear layer of the main jet, (ii) acoustic waves generated from the impingement region, and (iii) Mach waves generated from the shear layer of the supersonic flow downstream of the jet impingement. The indication of the second type of wave (ii) is important because the commonly used empirical method for the estimation of the acoustic waves from a rocket plume does not consider such acoustic waves. We also discussed the effects of nozzle-plate distance and temperature on the second type of acoustic waves (ii).

Effect of plate position and size for self-induced flow oscillation of underexpanded supersonic jet impinging on perpendicular plate

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, 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 flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.

Relationship between vortex and sound in under-expanded supersonic impinging jets

SUMMARY The study of an under-expanded supersonic jet impinging on a flat plate by using large-eddy simulation is reported. A third-order upwind compact difference and a fourth-order symmetric compact scheme are employed to discretize the nondimensional axisymmetric compressible Favre-filtered Navier–Stokes equations in space, whereas the third-order Runge–Kutta method with the total variation diminishing property is adopted to deal with the temporal discretization. The numerical simulation successfully captures the shock wave and vortex structures with different scales in the flow field. Waves with high and low frequencies traveling forward and reflecting back, and sound sources in different locations can be observed. By comparison with the frequency of the impinging tone from the experiment, it can be deduced that the change of pressure and swirling strength in the shear layer, pressure change on the impinging plate, and vortex merging in the jet shear layer are interdependent with the impinging tone. The effects of nozzle lip thickness on the impinging jet flow field have been investigated. The results show that the values of pressure fluctuation and vortex swirling strength in the shear layer near the nozzle have an extremum with the variation of the nozzle lip thickness. The results provide a theoretical foundation for the design of supersonic nozzles. Copyright © 2011 John Wiley & Sons, Ltd.

Density Field Measurements of a Supersonic Impinging Jet with Microjet Control

Density Field Measurements of a Supersonic Impinging Jet with Microjet Control

Explosive erosion during the Phoenix landing exposes subsurface water on Mars

While steady thruster jets caused only modest surface erosion during previous spacecraft landings on the Moon and Mars, the pulsed jets from the Phoenix spacecraft led to extensive alteration of its landing site on the martian arctic, exposed a large fraction of the subsurface water ice under the lander, and led to the discovery of evidence for liquid saline water on Mars. Here we report the discovery of the ‘explosive erosion’ process that led to this extensive erosion. We show that the impingement of supersonic pulsed jets fluidizes porous soils and forms cyclic shock waves which propagate through the soil and produce erosion rates more than an order of magnitude larger than that of other jet-induced processes. The understanding of ‘explosive erosion’ allows the calculation of bulk physical properties of the soils altered by it, provides insight into a new behavior of granular flow at extreme conditions and explains the rapid alteration of the Phoenix landing site’s ground morphology at the northern arctic plains of Mars.

Control of High-Temperature Supersonic Impinging Jets Using Microjets

The flowfield associated with supersonic impinging jets has been of interest to both engineers and researchers for some time due to its wide range of practical applications and its complex nature from a fundamental fluid dynamic point of view. An example of supersonic impinging jets occurs in short takeoff and vertical landing aircraft, for which the highly oscillatory flowfield and the associated acoustic loads are also accompanied by a dramatic loss in lift during hover, severe ground erosion of the landing surface, and hot gas ingestion into the engine inlets. Another characteristic feature of this flowfield is an intensive heat transfer between the jet and the impingement surface. In the past we have examined impinging jets and their control using microjets at cold conditions; the present study is a step toward examining this flowfield and the effectiveness of microjet control at increasingly realistic thermal conditions. An ideally expanded, Mach 1.5 primary jet issuing from an axisymmetric nozzle was heated up to a stagnation temperature of ∼500 K. Mean and unsteady temperature and pressure measurements were obtained on a lift plate representative of the undersurface of an aircraft and on the ground plane over a range of nozzle-to-plate distances (representing aircraft hover conditions). In addition, near-field noise was also measured using a microphone. The velocity field of the impinging jet for both cold and hot conditions was mapped using particle image velocimetry. Our results show that the temperature recovery factor at the stagnation point on the ground plane is strongly dependent on the temperature ratio and nozzle-to-plate distance, similar to observations in subsonic impinging jets. The hover lift loss for hot jets is much higher than for cold jets, nearly 75% of the primary jet thrust at small nozzle-to-plate distances. The pressure fluctuations generated by hot impinging jets are also substantially higher than their cold counterparts. As in cold jets, pressure and noise spectra for hot jets show discrete, high-amplitude acoustic tones (generally known as impinging tones) at frequencies varying with jet temperature. The activation of microjet control shows a substantial reduction in pressure fluctuations both in terms of overall sound pressure levels (up to 20 dB on the ground plane and 15 dB on the lift plate) and the attenuation of discrete, high-amplitude impinging tones (up to 32 dB). High-temperature peaks were observed in the temperature spectra at frequencies corresponding to impingement tones in the pressure and noise spectra; these were also substantially attenuated with microjet control. As much as 50% of the lift loss was recovered by using control for hot jets at smaller nozzle-to-plate distances. In general, the results provide evidence of the feasibility of using this active control approach under increasingly realistic conditions to achieve desired reductions in noise, unsteady pressures, and thermal loads.

0609 超音速衝突噴流の自励振動の周波数と衝撃波構造との関係(OS6-3 超音速流と衝撃波,オーガナイズドセッション)

0609 超音速衝突噴流の自励振動の周波数と衝撃波構造との関係(OS6-3 超音速流と衝撃波,オーガナイズドセッション)

Experimental study of physical mechanisms in the control of supersonic impinging jets using microjets

Supersonic impinging jet(s) inherently produce a highly unsteady flow field. The occurrence of such flows leads to many adverse effects for short take-off and vertical landing (STOVL) aircraft such as: a significant increase in the noise level, very high unsteady loads on nearby structures and an appreciable loss in lift during hover. In prior studies, we have demonstrated that arrays of microjets, appropriately placed near the nozzle exit, effectively disrupt the feedback loop inherent in impinging jet flows. In these studies, the effectiveness of the control was found to be strongly dependent on a number of geometric and flow parameters, such as the impingement plane distance, microjet orientation and jet operating conditions. In this paper, the effects of some of these parameters that appear to determine control efficiency are examined and some of the fundamental mechanisms behind this control approach are explored. Through comprehensive two- and three-component velocity (and vorticity) field measurements it has been clearly demonstrated that the activation of microjets leads to a local thickening of the jet shear layer, near the nozzle exit, making it more stable and less receptive to disturbances. Furthermore, microjets generate strong streamwise vorticity in the form of well-organized, counter-rotating vortex pairs. This increase in streamwise vorticity is concomitant with a reduction in the azimuthal vorticity of the primary jet. Based on these results and a simplified analysis of vorticity transport, it is suggested that the generation of these streamwise vortices is mainly a result of the redirection of the azimuthal vorticity by vorticity tilting and stretching mechanisms. The emergence of these longitudinal structures weakens the large-scale axisymmetric structures in the jet shear layer while introducing substantial three-dimensionality into the flow. Together, these factors lead to the attenuation of the feedback loop and a significant reduction of flow unsteadiness.

Pulsed microjet control of supersonic impinging jets via low-frequency excitation

Several fluid flow problems related to propulsion and power generation exhibit strong acoustic resonances. Produced due to interactions of the acoustics with other underlying unsteady mechanisms such as unsteady heat release or shear flow instability, these resonances manifest as large and sustained pressure oscillations. Active control of such resonances has been shown to be highly effective, resulting in a dramatic reduction in the acoustic resonances using a very small fraction of the system energy. In this paper, a specific fluid flow problem is discussed, that of supersonic impinging jets, and the control of the acoustic resonances that are produced by these jets, via detailed experimental investigations. The actuator used for active control consists of a pulsed microjet, by which it is shown that in a scaled supersonic experimental facility acoustic resonances can be reduced, utilizing a fraction of the mass flowrate needed with a steady microjet. Several parameters related to pulsed injection are varied to evaluate their impact on the resonances, and it is found that duty cycle and pulsing frequency have the most dominant effect on the jet noise as well as on the overall flow field. System identification based models of the uncontrolled and controlled jet are derived to explain the results obtained. The effect of low-frequency pulsing on resonance suppression is explained via the introduction of a controller in the closed-loop whose parameters vary non-linearly with the pulsing parameters.

Effect of Energy Pulse on 3-D Edney IV Interaction

This study investigates the effect of energy deposition on pressure and thermal loads generated by an Edney IV interaction. This complex supersonic jet impingement problem is formed by the intersection of an oblique shock generated by a 15-deg wedge with a Mach 3.45 bow shock in front of a 0.0254-m diam sphere. The full three-dimensional Reynolds-averaged Navier-Stokes equations are solved with the k-w turbulence model. Mesh-resolved simulations show that surface pressure without energy addition is in good agreement with experiments. The peak value is 1.8 times that observed without the impinging shock. Results from a grid resolution study confirm that the surface pressure is less sensitive than the heat flux. For flow control, a spherical energy pulse with a volume of 3 mm 3 and energy of 283 mJ is deposited upstream of the primary triple point. The unsteady interaction of the energy spot and its induced blast wave with the oblique shock, the distorted bow shock, and the impinging supersonic jet is elucidated in the context of the lensing phenomenon. The simulations indicate significant impact of the energy deposition on the surface pressure and heat flux. The instantaneous surface pressure and heat flux rise when the blast wave and high-energy spot hit the surface and fall when the expansion waves reach the surface. However, the overall integrated stress and thermal loads are reduced, mainly due to the effect of the expansion waves.

Characteristics of Supersonic Impinging Moist Air Jets

Supersonic impinging Jets, such as those occurring in the space launch vehicle systems, multi-stage rocket separation, jet-engine exhaust impingement, terrestrial rocket launch, and in the next generation short take off and vertical landing (STOL) aircraft, generate a highly oscillatory flow with very high unsteady loads on the near by structures and the landing surfaces. These high-pressure and acoustic loads are also accompanied by a dramatic loss in lift during aircraft hover. Previous studies of supersonic impinging jets suggest that the highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid And acoustic fields, which leads to these adverse effects, In actual supersonic jet flow, usually the working gas nu be condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur in the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation, In the present study, characteristics of under-expanded axisymmetric supersonic impinging moist air jets on a vertical flat plate were investigated numerically.

Flowfield and Noise Characteristics of Twin Supersonic Impinging Jets

A way of controlling the acoustic and aerodynamic characteristics of ideally expanded impinging twin jets has been proposed. As a means of control, microjets were used at the nozzle exit. The effect of the controlling method on the flowfield and acoustic field was investigated. Particle image velocimetry was used as the main tool for flowfield diagnostics

An unsteady, moving mesh CFD simulation for Harrier hot-gas ingestion control analysis

Hot gas ingestion (HGI) can be a problematic feature of short take-off vertical landing (STOVL) aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows.A flow solver has been developed to include a suitable linear mesh deformation technique for the descending aircraft configuration. The code has been applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. This has enabled an understanding of the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake.This paper presents three sets of CFD results. First a validation exercise shows predicted results from the twin-jet with intake in crossflow test-case. This is an unsteady Reynolds averaged Navier Stokes (URANS) solution for a static geometry (there is no moving mesh). This allows comparison with experiment. Secondly, a full descent phase URANS Spalart-Allmaras (SA) turbulence model calculation is done on an 8·5m cell mesh for half the flow domain of the Harrier model and test-rig without dams/strakes. This shows how the HGI flow mechanisms affect the engine intake temperature profiles, for the case where there are no flow control methods on the underside of the aircraft. Thirdly, the full descent phase URANS SA turbulence model calculation is done on a 22·4m cell mesh for the full flow domain of the Harrier model and test-rig, with the dam/strake geometry included in the structured mesh region.