| With the rapid development of society and the gradual improvement of people’s living standards,car sales are rising year by year.The accompanying problems of ride safety and ride comfort have attracted widespread attention from consumers.When the window is opened during vehicle driving,strong buffeting noise will be generated,which is a kind of flow excited resonance phenomenon with low frequency and high intensity,which will cause a lot of negative effects on the occupants.At present,the existing buffeting noise control methods are mainly passive control methods.There are few active control studies,and there are still many defects in the existing control schemes.Therefore,given the advantages of dielectric barrier discharge(DBD)plasma exciter such as fast response,light weight,stable control effect and convenient installation,and that they have demonstrated excellent control performance in the flow control area,in this paper,the DBD plasma actuator has been applied to the control of automobile buffeting noise,and a complete modal analysis method based on proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)is established to explore the generation mechanism and control mechanism of vehicle buffeting noise.The main research contents are as follows:Firstly,the parameters of Shyy model are modified to reduce errors caused by empirical parameters of the model.Based on the measurement results of static ion wind test,the formula of volume force is derived according to the law of conservation of momentum,and then the volume force distribution under each reference excitation voltage is obtained.Then,multi-objective optimization of Shyy model is carried out.The peak velocity and peak volume force are taken as target variables to calibrate the shape control parameters and charge density of Shyy model.After the experimental scheme is generated by the optimal Latin hypercube design,the radial basis founction(RBF)neural network approximation model is established based on the experimental results.Finally,a non-dominant sorting genetic algorithm with elite strategy(NSGA-Ⅱ)is used to obtain the optimal parameter combination.Finally,the boundary of the model is determined,and the relationship between the model charge density ρ rand the peak value of the excitation voltage V(pp) is obtained:ρ=5.819×ln(V(pp)+4.5)-12.302.The optimized model has better computational accuracy.Secondly,the modified Shyy model is used to control the buffeting noise actively.By arranging different types of actuators on the leading edge of the cavity,the noise reduction effect of cavity buffeting noise is achieved to varying degrees.The control effect of 45°direction excitation is the best,and the peak sound pressure level can be reduced by 20.28 dB.The control effect of horizontal reverse excitation,vertical excitation and horizontal forward excitation decreases successively,which are 16.5 dB,11.37 dB and 2.73 dB respectively.Then,the POD method is applied to the velocity field analysis in the cavity opening region.The results show that when the horizontal forward actuator is turned on,the K-H type vortex in the shear layer rolls up earlier under the action of the excitation source,and develops into a low-frequency large-scale vortex structure to dominate the flow field,reducing the impact frequency of the shedding vortex and the cavity trailing edge;when the horizontal reverse actuator acts,the thickness of shear layer increases greatly,the position of velocity pulsation amplitude increases,and the free shear layer oscillates away from the cavity opening.And when the horizontal excitation is applied,the energy proportion of the first three modes of flow field decreases,and the modal energy transfers to the higher order mode.When the vertical actuator is turned on,the radial shear stress in the shear layer is weakened,the rolling up of the K-H type vortex is suppressed,and the generation of the discrete vortex is delayed;when the 45°direction excitation is applied,the stability of the free shear layer is increased,and the acoustic wave radiated by the interaction between the incoming flow and the trailing edge corner of the cavity opening is weakened.Both of the two excitation methods transfer the modal energy to the first and higher order modes.This flow control method based on DBD plasma transfers the main mode frequency of the flow field to the low frequency and high frequency away from the buffeting frequency.While reducing the cavity resonance,it suppresses the self-excited oscillation feedback mechanism of the cavity and reduces the cavity buffeting noise.Finally,in order to analyze the spatio-temporal evolution characteristics of the main motion features of the flow field from the dynamic level,the dynamic mode decomposition(DMD)method was applied to the velocity field under different conditions in the cavity opening region.The results show that:the modal coefficients of the first three modes all show periodic changes with time,indicating that DMD can accurately capture the shedding vortex structure in the shear layer region.Under the action of the excitation source,the diverging mode of the original cavity flow changes to the convergent mode,which increases the stability of the flow field in the dynamic sense.At the same time,the excitation effect of the actuator also changes the growth rate and structural frequency of the main modes and realizes the flow control of the open cavity flow.At the same time,according to the periodic variation characteristics of DMD modal coefficients,the phase analysis of the flow field in each working condition is carried out,and the velocity field is reconstructed according to the first three main modes.The influence of small-scale vortices and background noise is filtered,and the main vortex structures that dominate the temporal evolution characteristics of the flow field are obtained.The generation,development and dissipation process of the main vortex structures moving downstream can be clearly observed from the temporal evolution cloud diagram of vortex intensity. |
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