Rear Wall Of Cavity Research Articles

Numerical study of gas–solid two-phase flow and erosion in a cavity with a slope

Gate valve is mainly used to turn on or turn off the pipeline in pneumatic conveying. When the gate valve is fully open, the particles are easy to collide with the cavity rear wall and enter into the cavity, resulting in particles’ accumulation in the cavity. The particles in cavity will accumulate between the cavity bottom and the flashboard bottom wall and prevent the gate from turning off normally. Meanwhile, the particles’ collision with cavity rear wall will cause serious erosion. Both the particles’ accumulation and erosion will cause the poor sealing of the gate valve, further resulting in the leakage of the pipeline system. To reduce the particles’ accumulation in cavity and erosion on cavity when the gate valve is fully open, we simplify the gate valve into a cavity structure and study it. We find that adding a slope upstream the cavity can effectively reduce the particles’ accumulation in the cavity and the erosion on the cavity rear wall. In this work, Eulerian–Lagrangian method in commercial code (FLUENT) was used to study the gas–solid two-phase flow and erosion characteristics of a cavity with a slope. The particle distribution shows that the particles with Stokes number St = 1.3 and St = 13 cannot enter the cavity due to the slope, but the particles with St = 0.13 enter the cavity following the gas. For St = 13, the particles collide with the wall many times in the ideal cavity. Erosion results show that the slope can transfer the erosion on cavity rear wall to the slope and reduce the maximum erosion rate of the wall near the cavity to some degrees.

Effect of cavity rear wall modifications on pressure fluctuations at supersonic speed

Experiments were carried out to assess the effect of rear face geometrical modifications of a wall mounted rectangular cavity on pressure fluctuations at supersonic speed. Initially, tests were conducted on a base cavity of length to depth ratio of 3.6, in a 50 × 100 mm at a Mach number of 2, and a Reynolds number of 2 × 106 based on cavity length. Geometrical modifications to the rear face of the base cavity in the form of single ramp, double ramp and partial ramp circle were done to study their acoustic emission characteristics. Oil flow images revealed the complex nature of the flow inside the cavities. Time resolved flow visualization revealed attenuation of receptive interaction at the cavity leading edge, and minimized mass flux into the cavity by adopting these modifications. Unsteady measurements indicated reduction in the peak tones, broadband levels, and coherence. Among the modified geometries, double ramp configuration significantly reduced the overall sound pressure levels and the fluctuating pressures of the order of 10 dB and 50% respectively.

Spatial structural characteristics of a combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity

A hybrid large eddy simulation (LES)/assumed subgrid probability density function (PDF) closure model was employed to investigate the structural characteristics of the combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity. The wall pressure distribution from numerical simulation was compared with experimental data, and the numerical results are in good agreement with the experimental data. The spatial distribution characteristics of combustion heat release in the flow field are obtained from the simulation results. The reaction heat release zone is mainly distributed in the cavity. The cavity shear layer forms a concentrated reaction zone that produces a large amount of chemical heat release, thus further maintaining local stable combustion and forming a flame base. The front part of the cavity shear layer has the highest temperature in the whole flow field. There is still excess fuel reaching the cavity rear wall and producing a certain intensity of reaction. In addition, a dispersed small flame intermittently forms in the downstream near-wall region. The premixed combustion mode dominates the cavity recirculation zone, while the combustion in the downstream region evidently shows a non-premixed mode.

Flow characteristics of Axisymmetric Cavity Rear Wall Divergence Angle in a Scramjet Combustor

Non-reacting experimental study was performed on a rear wall angled cavity actuated supersonic flow of Mach 1.5 from a convergent divergent nozzle using a blowdown wind tunnel test setup. Ten different model combinations of double angled rear wall cavities is preferred for the study of improvements in the geometrical design of the combustor. Flow field properties of various cavity geometries were analyzed based on the key parameters like, wall static pressures, stagnation pressure loss to the flow and qualitative mixing of flow using momentum flux distribution. The static pressure is found to decrease inside the combustor with a decrease in the secondary dual rear wall angle below 90 degrees whereas value increases at the rear wall OWING to oscillation and recompression of shear layers inside the cavity region. In addition, the decrement in primary rear wall angle, an enhancement in mixing profile and a reduction in stagnation pressure loss are also observed.

Effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor

This paper reports a numerical investigation on the effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor with a single rear-wall-expansion cavity. The numerical solver and the LES methods were validated against available experimental data and the numerical results were shown in good agreement with the experiments. Effect of the cavity rear wall height on the non-reacting flow fields was then investigated. It was found that the vertical flow velocity of the region located right after the expansion wave starting from the cavity leading edge was increased significantly towards the cavity when lowering the rear wall height, leading to an enhanced fuel entrainment into the cavity. Subsequently, at a larger cavity expansion ratio, the mixture inside the cavity became more fuel-rich, giving rise to a deteriorated mixing environment. In addition, the cavity recirculation zone was further compressed and the turbulent flow and scalar dissipation inside the cavity would be enhanced, which were likely the reason causing the ignition failures and poor flame stabilizations. An optimal cavity expansion ratio for the maximum fuel entrainment was found in the present rig.

Investigation on flow oscillation modes and aero-acoustics generation mechanism in cavity

Unsteady flow and multi-scale vortex transformation inside a cavity of L/D = 6 (ratio of length to depth) at Ma = 0.9 and 1.5 were studied using the numerical simulation method of modified delayed detached eddy simulation (DDES) in this paper. Aero-acoustic characteristics for the cavity at same flow conditions were obtained by the numerical method and 0.6 m by 0.6 m transonic and supersonic wind-tunnel experiments. The analysis on the computational and experimental results indicates that some vortex generates from flow separation in shear-layer over the cavity, and the vortex moves from forward to downward of the cavity at some velocity, and impingement of the vortex and the rear-wall of the cavity occurs. Some sound waves spread abroad to the cavity fore-wall, which induces some new vortex generation, and the vortex sheds, moves and impinges on the cavity rear-wall. New sound waves occur. The research results indicate that sound wave feedback created by the impingement of the shedding-vortices and rear cavity face leads to flow oscillations and noise generation inside the cavity. Analysis on aero-acoustic characteristics inside the cavity is feasible. The simulated self-sustained flow-oscillation modes and peak sound pressure on typical frequencies inside the cavity agree well with Rossiter’s and Heller’s predicated results. Moreover, the peak sound pressure occurs in the first and second flow-oscillation modes and most of sound energy focuses on the low-frequency region. Compared with subsonic speed (Ma = 0.9), aerodynamic noise is more intense at Ma = 1.5, which is induced by compression wave or shock wave in near region of fore and rear cavity face.

Large Eddy Simulation of the flame stabilization process in a scramjet combustor with rearwall-expansion cavity

Large Eddy Simulation (LES) was employed to study the flame stabilization process in a hydrogen fueled scramjet combustor with a rearwall-expansion cavity. The numerical solver was first validated for a reactive flow, the scramjet combustor with rearwall-expansion cavity case, and the numerical results were shown in good agreement with the available experimental data. Effects of different cavity configurations and equivalence ratios on the flame stabilization process were then studied. It was found that during the combustion process, the most concentrated heat release regions are all located near the cavity rear wall. Besides, the majority of heat release regions are existed in the supersonic zones and attached to the sonic lines. The flame distribution in the combustor is sensitive to the equivalence ratio, and a thin flame would be formed when further decreasing the equivalence ratio. At the same equivalence ratio, the cavity with lower rear wall will delay the occurrence of chemical reaction and form a more concentrated and intense heat release region downstream the cavity, which will accelerate the chemical reaction and also achieve a sufficient combustion in the combustor. For the rearwall-expansion cavity, both the cavity configuration and equivalence ratio should be combined to optimize the flame stabilization process in the combustor.

Experimental investigation of the effect of small-obstacle-induced vortex sheet on the separated flow in cavity

In the present paper, we report results of an experimental study of the influence which a vortex-generating element installed upstream of the main obstacle has on the separated flow and heat transfer in a cross-flow cavitytrench. The element was a small cross-flow rib whose height was an order of magnitude smaller than the depth of the cavity. In the experiments, the variable parameters were the angle of inclination of the frontal and rear walls of the cavity, the rib height, and the rib-to-cavity distance. It is shown that the introduction of additional vortical perturbations into the recirculation zone leads to a substantial modification of both the vortex production process and the distributions of pressure and heat-transfer coefficients. Optimal height of the mini-turbulizer and its optimal location are defined by the fall of the re-attachment point of mini-rib-generated flow onto the rear wall of cavity. In the latter situation, the maximal value of the heat-transfer coefficient increases as compared to the case with no vortex generator used, the increase amounting to 30 %.