Investigation On Wave Evolution Mechanisms And Noise Control Methods For Supersonic Cavity Flows

Cavity noise is a common issue suffered by aircraft,rockets,automobiles,high-speed rails,and ships.Under certain inflow and geometrical conditions,the cavity flows is likely to cause periodic pressure oscillations and induce high-energy noise,which will adversely affect structural safety,occupant comfort,and weapon launch.In this study,a research platform for both supersonic cavity flow calculations and experiments is built,the numerical hydraulic analogy visualization method and near-wall moving shock waves recognition algorithm are proposed,the evolution law of different types of waves in cavity flows is analyzed,and the feedback model of cavity pressure oscillations is improved,the impact of moving shock waves on the cavity noises is studied,the transverse baffles control method to suppress the cavity noise is developed and its control effect with different heights and different installation positions is evaluated.The research work of this study mainly includes:(1)The numerical hydraulic analogy visualization method for complex flow field display is proposed.The visualization method is able to display both flow structure and physical field in a single picture,which helps to better understand the flow structure behaviors driven by multi-physics fields in cavity flows.By imitating the visualization principle of hydraulic analogy experiments,a numerical hydraulic analogy visualization algorithm is established,and the display effect of the method in the double Mach reflection flow and Rayleigh-Taylor instability problems is evaluated.Through incorporating other visualization technologies such as contour and texture,the numerical hydraulic analogy is further enchaning its fusion display ability.The improved numerical hydraulic analogy can present flow field information such as flow structure,scalar field,and vector field in a single picture,providing a new visualization method for analyzing the evolution of shock waves and vortices in complex cavity flows.(2)The near-wall moving shock waves recognition algorithm based on the time sequence signal of wall pulsating pressure is developed.The recognition algorithm can accurately identify different types and different strength shock wave structures passing through the measurement points,which is used to analyze the impact of near-wall moving shock waves on surface noises in the cavity flows.Through the analysis of the aerodynamic characteristics of the moving shock waves,a unified near-wall moving shock wave model suitable for plane shock waves and V-shaped shock waves is established.By identifying the steep ascending curves in the pressure response curves,the shock wave information is extracted.By comparing the magnitude of the pressure on both sides of the shock wave,the moving direction of shock wave can be determined.The near-wall moving shock wave recognition algorithm is used to identify the moving shock waves in the cavity flows.The recognition results of single and multiple measurement points show that the algorithm is able to accurately identify shock waves with different types,different intensities and different moving directions.(3)The supersonic cavity flows are simulated using numerical methods,and the development and evolution laws of shock wave,vortex and other flow structures are studied quantitatively.The feedback model of cavity pressure oscillations is improved.The numerical simulations of cavity flows with different Mach numbers and different aspect ratios are carried out,and the numerical methods and solver are validated by comparing with the experimental results.The evolution of different waves during the startup stage and the fully-developed stage is studied respectively.The effects of Ma and L/D on cavity flow oscillations are also studied.Based on previous research,the feedback model of cavity flow oscillation proposed by Tam is further improved.In terms of the initial disturbance generation mechanism,it is found that the anti-clockwise pressure gradient formed by the high pressure from the leading edge of the cavity under the vortex is the main cause of the shocklet.In terms of the disturbance growth mechanism,two mechanisms to accelerate the growth of shocklet,including forcing vortex merging and feedback shock wave interactions,are found.In terms of the feedback shock wave generation mechanism,the shock wave focusing phenomena during the collision between the shocklets and the cavity surfaces is discovered,and the influence of the shock focusing on the formation of the feedback shock is analyzed.(4)The propagation and evolution laws of moving shock waves are investigated using the near-wall moving shock waves recognition algorithm,and the generation mechanism of cavity noise in the context of moving shock waves is revealed.The propagation characteristics of feedback shock waves,front wall reflection shock waves and shocklets are studied,and the increasing trend of cavity noise distribution along the flow direction is explained.Using the near-wall moving shock waves recognition algorithm,the information of shock waves passing through several measurement points is obtained.The causes of local noise increase are analyzed from the perspective of shock intensity and shock superposition effect.The results show that the noise increase at the leading edge of the cavity is mainly due to the collision between the feedback shock waves and the leading edge.The strong noise near the trailing edge of the cavity is mainly caused by the focusing of shocklets.The local noise rise in the middle of the cavity is mainly caused by the collision of high-intensity shocklets and high-intensity feedback shock waves.(5)The transverse baffles control method to suppress the cavity noise is developed.The control effect of the transverse baffles is evaluated through wind-tunnel experiments,and the control mechanism of the transverse baffles is revealed using numerical simulations.The windtunnel experiments of cavity flows at Mach number 2.0 are performed to study the control effects of transverse baffles.The influence of heights and installation positions on the noise control effect of the baffles is evaluated.The experiment results show that the cavity noise is significantly affected by the installation position of the transverse baffle.By adjusting the installation position,the sound pressure level of cavity noise drops by up to 9 d B.The interactions between the baffles and different types of moving shock waves are studied using numerical simulation,and the control mechanisms of the baffles at different installation positions are analyzed.The leading edge baffle reduces cavity noise by effectively interrupting the propagation of the feedback shock.The middle baffle increases cavity noise by generating new feedback waves and enhancing the feedback effects.The trailing edge baffle decrease cavity noise by disturbing the collision of shocklets and the trailing edge and suppressing the intensity of the feedback shock waves.