Supersonic Cavity Flow Research Articles

A modified blending function for zonal hybrid Reynolds-averaged Navier—Stokes/large-eddy simulation methodology

A modified blending function for zonal hybrid Reynolds averaged Navier—Stokes/large eddy simulation (RANS/LES) methodology was developed using an empirical analogy from Menter k—ω shear stress transport (SST) turbulent model (Menter, 1994) to predict complex turbulent flows. Tests of slot jet in supersonic flow and supersonic flow over compression—expansion ramp was conducted and prediction of separations was well improved when certain model constant was forced on the traditional blending function (Baurle et al., 2003). Analysis based on calculations of flat plate boundary layer demonstrated that an efficient empirical constant could be used in blending function and boundary layer could be well calculated without heavy contamination of RANS on wake region. Validation of the modified zonal hybrid RANS/LES approach for slot jet in supersonic flow, supersonic flow over compression—expansion ramp, supersonic flow over backward facing step, and supersonic cavity flow was conducted. The simulated results showed that the modified blending function performs well on complex turbulent flows. Deficiencies of traditional hybrid zonal RANS/LES method in over-prediction of separations associated with adverse pressure gradient flows were favourably improved.

An investigation into supersonic shallow swept cavity flows

AbstractAn experimental investigation was conducted to determine the flow characteristics of shallow swept cavities at a free-stream Mach number of 2. The investigation described herein focused on obtaining information on both time-averaged and time-dependent flow features. The data consisted of steady and unsteady pressure measurements as well as some surface oil and schlieren flow visualisation. The effective length-to-depth ratiosl/dof cavities investigated ranged between 5·65 and 8 for shallow ‘open’ cavities and between 11·31 and 16 for ‘closed’ cavities. The cavity sweep angles were 0°, 15° and 45°. The results of the swept cavities, when compared to the datum cases of the straight (0°) cavities, showed some distinct differences. With regard to time-averaged flow characteristics, in an open swept cavity (5·65 <l/d< 8), the flow displayed quasi-open flow behaviour, distorted by the spanwise cross flow within the cavity. In the case of the closed swept cavity (11·31 <l/d< 16), flow features resembling the ‘closed’ to ‘transitional closed’ cavity flow types were seen to exist simultaneously across the span. Unsteady pressure data indicated that for an open cavity at 15° sweep angle, the discrete frequencies observed were similar to those of a straight open cavity. In contrast to this, at 45° sweep angle, the frequencies were broadband with no discrete frequency across the cavity length. For the closed cavity, the frequencies were all broadband irrespective of the sweep angle. The investigation also showed that the influence of the sweep angle on the pressure drag of the cavity strongly depends on the type of cavity flow: a sweep angle increase from 0° to 45° approximately doubled the pressure drag for an open cavity, while it led to a drag reduction of about 37% for the closed cavity.

Passive Control Techniques to Alleviate Supersonic Cavity Flow Oscillation

The effectiveness of two passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow was investigated numerically. The control devices suggested in the present study include a triangular bump and a subcavity installed near the leading edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the subcavity compared with the bump or blowing, and a larger subcavity leads to better control performance.

Three-dimensional effects of supersonic cavity flow due to the variation of cavity aspect and width ratios

Unlike the steady closed-type supersonic cavity flow, open-type cavity flow is divided into internal and external flows by turbulent shear layer. The cavity flow may cause resonance phenomena due to pressure oscillation, depending on the cavity geometry and the flow conditions. These phenomena may induce noise generation, structural damage, and aerodynamic instability. In this research, the flow characteristics of three-dimensional supersonic cavity flow of Mach number 1.5 were analyzed with the variations of aspect ratio and width ratio. Three-dimensional unsteady compressible Reynolds-averaged Navier-Stokes (RANS) equations were used with a turbulence model. For numerical calculations, the 4th-order Runge-Kutta method and the FVS method with van Leer’s flux limiter were applied. The numerical calculations were performed by using a parallel processing program with 16 CPUs. The sound pressure level (SPL) spectra of pressure variations were analyzed at the point of cavity leading edge. The correlation of pressure distribution (CPD) was also analyzed for the propagation of dominant oscillation pressure waves with respect to the reference point of the cavity leading edge. The dominant oscillation frequency was compared with the oscillation modes of Rossiter’s formula. Oscillation Mode 2 appeared as a dominant oscillation frequency regardless of the aspect ratio of cavity in the two-dimensional flow. Oscillation Modes1 and 2 appeared in three-dimensional cavities of small aspect ratios. However, as the aspect or the width ratio increases, only the mode 2 or 3 frequency appeared as a dominant oscillation frequency.

ＬＩＦ法を用いた超音速キャビティ流れの温度振動場の可視化

ＬＩＦ法を用いた超音速キャビティ流れの温度振動場の可視化

Aeroacoustic Computations Using a High-Order Shock-Capturing Scheme

For aeroacoustic computations in the supersonic regime, it is necessary to use a numerical scheme that can represent shock waves without generating spurious numerical oscillations. The centered schemes that are usually used with success in the subsonic case, combined with a selective filtering, will generally oscillate in the presence of discontinuities. A new class of shock-capturing schemes, the one-step monotonicity-preserving schemes, combine the high accuracy and the nonoscillating property. It is thus a good candidate for supersonic aeroacoustic applications. The good spectral properties of these schemes are illustrated in the scalar linear case. Results of aeroacoustic test problems for the Euler and Navier-Stokes equations are compared with a dispersion-relation-preserving scheme. The application to a supersonic cavity flow, which induces a complex pattern of moving shocks, shows that the one-step monotonicity-preserving schemes capture the moving discontinuities without spurious oscillations and preserve a high accuracy at the same time.

416 サブキャビティを有する超音速キャビティ流れのパッシブコントロール(1)(OS4-4 高速流れと衝撃波現象の解明と制御,OS4 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

416 サブキャビティを有する超音速キャビティ流れのパッシブコントロール(1)(OS4-4 高速流れと衝撃波現象の解明と制御,OS4 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

Self-Excited Supersonic Cavity Flow Instabilities as Aerodynamic Noise Sources

A turbulent cavity flow at Mach 1.5 and 2.5 is modelled to study the flow instability and the associated aerodynamic noise generation. The short-time averaged Navier-Stokes equations, coupled with a k – ω turbulence model, are solved to predict the large-scale time-dependent flow. Values of the cavity wall pressure, drag, streamwise velocity and density are in good in agreement with past measurements and the results of other computations. The noise generation physics of the unsteady flow is addressed by estimating the noise source strength in a Lighthill acoustic analogy. The time-dependent flow predictions highlighted the upstream and downstream cavity edges as areas of large flow unsteadiness. The same areas are identified by the acoustic analogy as the dominant noise source regions in this flow.

Supersonic Cavity Flows and Their Control

A detailed experimental study of supersonic, Mach 2, flow over a three-dimensional cavity was conducted using shadowgraph visualization, unsteady surface pressure measurements, and particle image velocimetry. Large-scale structures in the cavity shear layer and visible disturbances inside the cavity were clearly observed. A large recirculation zone and high-speed reverse flow was revealed in the cavity. In addition, supersonic microjets were used at the leading edge to suppress flow unsteadiness within the cavity. With a minimal mass flux (blowing coefficient B c = 0.0015), the activation of microjets led to reductions of up to 20 dB in the amplitudes of cavity tones and of more than 9 dB in the overall sound pressure levels. The microjet injection also modified the cavity mixing layer and resulted in a significant reduction in the flow unsteadiness inside the cavity as revealed by the shadowgraphs and the velocity-field measurements.

A Numerical Study on Passive Control of Cavity Induced Pressure Oscillations in Two-Dimensional Supersonic Flow

A computational study has been conducted to evaluate a passive control technique of suppressing intense pressure oscillations in a cavity with supersonic free stream flow. A porous surface with a sub-cavity fitted at the leading edge wall of an open square cavity at Mach number 1.83 at the cavity entrance was investigated for that purpose. The introduction of these control devices helped to alter the oscillating shear layer in a favorable way so that some of the undesirable effects resulting from supersonic cavity flows were eliminated. The results also showed that the resultant amount of attenuation of pressure oscillations was dependent on the porosity, the size of perforation of the Porous surface, and on the sub-cavity.

Cavity Flows in a Scramjet Engine by the Space-Time Conservation and Solution Element Method

Numerical simulation of supersonic flows over open cavities in the setting of a dual-mode ramjet/scramjet engine are reported. To calculate the unsteady cavity flows, we employ the space-time conservation element and solution element (CESE) method, a novel numerical method based on a unified treatment of space and time for calculation of flux balance. Supersonic cavity flows with and without fuel injection are studied to understand the mechanisms of mixing enhancement and flame holding by cavities. Without injection, numerical results compared favorably with the experimental data for dominant frequencies and time-averaged pressure coefficients inside the cavities. With an upstream injection, the flow oscillations are drastically suppressed

数値シミュレーションによる超音速キャビティ流れの三次元非定常挙動の解明(S26-1 高速流れと衝撃波現象の基礎と応用その1,S26 高速流れと衝撃波現象の基礎と応用)

Three-dimensional unsteady behaviors of a supersonic cavity flow are investigated by the numerical simulation based on the Navier-Stokes equations; The resulting time-dependent solutions are phase-averaged on the dominant frequency. As a result, the standing wave in the cavity and vortex-shedding are found to be highly three-dimensional.

B131 数値シミュレーションによる超音速キャビティ流れの三次元振動現象の可視化

Three-dimensional unsteady behaviors of a supersonic cavity flow are investigated by the numerical simulation based on the Navier-Stokes equations. The resulting time-dependent solutions are phase-averaged on a dominant frequency. As a result, the standing wave in the cavity and vortex shedding from the leading edge are found to be highly three-dimensional.

超音速キャビティ流れに及ぼす形状と主流マッハ数の影響

超音速キャビティ流れに及ぼす形状と主流マッハ数の影響

Effects of Three Types of Control Devices on Closed-Type Supersonic Cavity Flows

Three types of devices were tested for their effects in reducing the strong adverse pressure gradient in a closed-type cavity with a depth of 8 mm and length-to-depth ratio of 15. The first type of control device consisted of embedding arrays of tubes longitudinally along the two sides of the cavity. It sought to move the high-pressure air at the recompression wake to the separation wake by creating a passage. The second type of control device consisted of installing a baffle plate laterally near the shock impingement line or the mid-part of the cavity floor. It aimed at changing the wave structure of the cavity flow through interfering with the reattaching or reattached boundary layer. With the third type of control device, we tried to increase the base pressure by supplementing external fluid with downstream blowing through side-holes along a lateral tube placed at the front corner of the cavity. Of the three types of control devices, the installation of tubes along the two sidewalls of the cavity was found to be the most effective in reducing adverse pressure gradient along the cavity centerline. Of the four combinations of plates installed laterally on the cavity floor, the 4-mm-high plate installed near the middle of the cavity was found to be the most effective. The relative ineffectiveness of downstream blowing near the cavity front corner is believed to be a result of the low blowing rate.

A Theoretical Study on the Mechanism of Supersonic Cavity Flow Oscillations

A Theoretical Study on the Mechanism of Supersonic Cavity Flow Oscillations

Experimental Investigation on the Mechanism of Flow-Type Changes in Supersonic Cavity Flows.

Compressible flows over cavities with a series value of length-to-depth ratio (L⁄D) were investigated experimentally, with the objective being to elucidate the mechanism of the transition of types of cavity flows as their L⁄D increases or decreases. For open-type cavity flows, the freedom of backflow inside the cavity is found to be crucial in smoothing out adverse pressure gradient. The spreading of the shear layer and its gradual approach toward the cavity floor as L⁄D increases tend to suppress the freedom of backflow, causing the cavity flow to change from the open-type to the transitional-type. For closed-type cavity flows, the finite thickness of the upstream boundary layer leads to the presence of three kinds of characteristic lengths that correspond to the recirculation region, the deflection of the main flow and the recovery or the abrupt rise of the pressure, respectively. The compression fans at the foot of the impingement and the exit shock waves will approach each other well in advance of the possible merge of the vertices of the conventionally defined separation and recompression wakes. As the L⁄D of a closed cavity decreases, the reattached boundary layer on the mid-portion of the cavity floor will have less developing distance, thus it will be more susceptible to adverse pressure gradient and prone to separation. For the present two-dimensional cavity models, the critical values of L⁄D were found to be about 10 and 14 for the transition of cavity flows from the open- to the transitional-type and from the transitional- to the closed-type, respectively. The sum of the pressure lengths at the front and rear wakes agrees remarkably well with the second critical L⁄D.

Some Thoughts on the Mechanism of Supersonic Cavity Flow Oscillations

Some Thoughts on the Mechanism of Supersonic Cavity Flow Oscillations

Some Thoughts on the Mechanism of Supersonic Cavity Flow Oscillations

Some Thoughts on the Mechanism of Supersonic Cavity Flow Oscillations

A Measurement of Disturbance Propagation in High-Speed Flow by a Laser Induced Fluorescence Method(Application to a Supersonic Cavity Flow).

A method for measuring propagation of disturbance in a high-speed flow has been developed by using a laser induced fluorescence (LIF) technique. A cross correlation function between the time-dependent LIF signal and a pressure sensor signal at a reference point enables to measure a propagation speed of disturbance. Through a bandpass filter, the speed of disturbance with a particular frequency can he obtained. A feature of disturbance propagation can be grasped by drawing maps for the cross-correlation coefficients on a space at successive delay-times and making an animation. The method was applied to a supersonic flow over a rectangular cavity with length to depth ratio of 2, to elucidate feedback mechanisms of self sustaining flow oscillation with several dominant frequencies.