Numerical Simulation And Noise Control Of Compressible Cavity Flow

With the requirements of the air transportation industry for silent flight,aviation noise needs to be settled urgently.The contribution of cavity flow to aircraft noise is increasingly prominent,such as landing gear.Therefore,the simulation and control of the cavity flow has attracted the attention in recent years.This paper aims to simulate the flow-induced noise of cavity flow based on high-resolution numerical simulation methods,and perform active and passive control to explore the potential noise reduc-tion mechanism.Firstly,the sensitivity analysis of cavity flow is carried out based on the adjoint method.Secondly,the active control of noise is carried out for the two-dimensional subsonic cavity flow.Finally,passive control based on porous media is carried out for the three-dimensional cavity flow.The details and results of the research are as follows:(1)Firstly,the parameter study of the sensitivity of the cavity flow to the disturbance with different incoming flow conditions is carried out based on adjoint method.In the study of cavity flow control,the position of the highest sensitivity indicates the optimal position for arranging the excitation,and the maximum response of the flow field can be obtained with the smallest input energy.High-resolution DNS of cavity flow with different incoming flow condition,which the Ma ranges from 0.2 to 0.5,Re=3000 and 5000 and momentum thickness ?=1/32.8L and 1/52.8L.Numerical simulation is carried out to analyze the sensitivity of the flow field to the disturbance near the rear corner.The study found that the most sensitive area is mainly concentrated in the development position of the boundary layer,in the upper shear layer of the cavity and near the aft corner.When Ma or Re of the incoming flow increases,the sensitivity amplitude increases,and the sensitive structure of the flow inside cavity becomes complicated.The sensitivity structures upstream of the leading edge of the cavity is located in the boundary layer.When Ma increases,the most sensitive position shifts to the development of boundary layer.However,it is generally close to the leading edge of the cavity,indicating that the control excitation at the leading edge can adapt to a wide range of flow conditions.At the same time,the sensitivity in the cavity is enhanced.When the incoming flow velocity increases to a certain amplitude or the incoming flow boundary layer is too thin,obvious sensitivity distribution appears in the cavity and around the aft corner,and the sensitivity amplitude is even stronger than the upstream of the leading edge.The high sensitivity distribution in the cavity implies that arranging the control excitation in the floor of cavity is also an effective approach to suppress the noise radiated from the rear corner.(2)Based on the sensitivity results,a long-term horizon flow-induced noise control study of unsteady compressible cavity is carried out.A two-dimensional space-time volume force is applied in the boundary layer near the leading edge of the cavity,and the active control of cavity flow with Ma=0.5 and Re=5000 is studied.Firstly,the noise control of the target area that can simultaneously cap-ture noise radiated from the shear layer and the rear corner is performed.The re-sults show that the pressure oscillation distribution in the near-field sound source area has changed,and the noise is suppressed in the overall radiation direction.The maximum drop in sound pressure level is about 2 dB.The flow structure in the cavity does not change significantly based on POD decomposition,but the energy is transferred from the large-scale structure to the smaller structure.At the same time,the control of noise radiated from the rear corner or shear layer are respectively compared.The results show that only controlling the shear layer noise has little effect on the far-field noise,while controlling the noise radiated from rear corner has obvious suppression.The upstream radiation direction can reduce noise by 3 dB,which provides a theoretical basis for active control.(3)Using high-resolution implicit large eddy simulation,the passive noise control of three-dimensional cavity flow is carried out based on porous media.The study found that the pressure fluctuations and radiated noise from the cavity have been substantially suppressed when the solid cavity floor is replaced by a porous media.In order to study the relationship between porosity and flow characteristics,and noise suppression,the influence of four different porosities on the control effect is investigated.For low porosity,the noise reduction effect is better with increasing porosity.The control is best when the porosity is about 11.2%,and the maximum noise reduction is more than 10 dB near the leading edge.As the porosity further increases from 11.2%to 19.27%,the control effect is saturated slightly.The ba-sic flow characteristics are analyzed in detail,and it is found that the porous floor will produce effect of suction and injection,altering the structure of the large-scale recirculation and the shear layer.The control is mainly influenced by the strength of suction effect.POD results show that the controlled shear layer is dominated by small scale structures with lower energy,and the interactions be-tween the shear layer and the recirculation inside the cavity are weakened.The vortex-edge impingement near the rear corner is also mitigated,thus the acous-tic feedback is lower,which decreases the self-sustained oscillations and noise radiation.