| With the continuous improvement of economic level,car ownership in China has grown rapidly,and consumers have made higher demands on car safety and comfort.Driving with the windows open produces low frequency and high intensity buffeting noise,which can easily tire the driver.Although every automobile company spends a lot of money on buffeting noise control research every year,the existing control schemes still have many shortcomings,such as poor effect and great influence on vehicle styling.In recent years,the dielectric barrier discharge plasma actuator(DBDPA)has become a research focus in the field of flow control due to its advantages of simple structure,fast response and little influence on vehicle styling,and has shown a good effect in flow control.Therefore,based on the active flow control technology of DBD-PA,this paper applied the method of combining numerical simulation and wind tunnel test,and introduced interval optimization algorithm to study the active control of vehicle buffeting noise.The main research contents are as follows:First,based on the back-step flow,the advantages of Omega vortex identification method compared to the commonly used vorticity method and velocity gradient tensor method were analyzed in terms of resistance to shear interference and sensitivity to threshold change.In the simulation study of buffeting noise,the Omega method clearly captured the process of vortex generation,shedding,development and breakdown from the leading edge of the opening,which accurately revealed the mechanism of the flow field in the generation of buffeting noise and provided analysis basis for studying the characteristics of buffeting noise and the influence mechanisms of various factors.Second,to study the mechanism of cavity buffeting noise,wind tunnel tests of cavity buffeting noise at different wind speeds were carried out.Then,the characteristic of cavity buffeting noise was simulated and analyzed,and the flow field characteristics of cavity opening region were extracted based on the proper orthogonal decomposition(POD)method.The wind tunnel tests and simulation analysis showed that: the cavity buffeting noise was mainly due to the periodic vortex shedding caused by the instability of the free shear layer at the opening,which led to periodic pressure pulsation in the cavity,and it was the result of the combined effect of acoustic feedback mechanism and Helmholtz resonance mechanism.POD analysis results showed that: the first three modes were the dominant large-scale flow structures in the flow field,accounting for79.9% of the energy of the flow field,which could reconstruct the main flow structure characteristics and morphology in the opening region;the first two modes represented the shear layer oscillation and shedding vortex structure in the opening region,which had the same single dominant frequency as the buffeting frequency and the third mode represented the flow structure invading into the cavity;the high-order modes were small-scale flow structures in the cavity with low energy,which had little influence on the characteristics and morphology of the flow field;POD analysis results further verified the mechanism of buffeting noise generation.Third,the influence mechanism of the thickness and turbulence of the incoming flow boundary layer on the characteristics of buffeting noise was analyzed.The results showed that: as the thickness of the incoming flow boundary layer increased,the stability of the free shear layer was effectively improved,the effect of Helmholtz resonance and feedback mechanism was weakened,and the buffeting noise gradually decreased;with the increase of the turbulence of the incoming flow boundary layer by adding bosses,the quasi-resonance phenomenon disappeared,the vortex scale at the opening decreased and the shear layer oscillation was far away from the cavity,which effectively weakened the feedback mechanism and decreased the buffeting noise;the error between simulation and experimental results was the comprehensive influence of the difference in thickness and turbulence of the incoming flow boundary layer,and the difference in thickness was the main reason.In addition,the influence of the opening size and volume of the cavity on the characteristics of buffeting noise was also studied.Fourth,by studying experimentally the breakdown characteristics of DBD-PA,the breakdown voltage regression model was established and the influence of actuator parameters on breakdown voltage was analyzed based on the regression model,which provided guidance for the selection of sample space for DBD-PA parameter optimization.The results showed that: the fitted regression model had good accuracy and could be used as a model to predict the breakdown voltage;the frequency had the greatest influence on the breakdown voltage,followed by the length and the electrode gap;the interaction between the electrode gap and frequency,as well as between the frequency and length also had a great influence on the breakdown voltage.Fifth,based on the orthogonal experimental design and RBF neural network approximation model,interval optimization algorithm was introduced to optimize the parameters of the actuator,which improved the excitation performance of the actuator and achieved adjustable excitation intensity.Based on the established regression model,the sample points were generated by orthogonal array method,and the PIV test was carried out in a windless environment;the variance analysis of the orthogonal experiment results showed that the influence of the excitation voltage on the performance of the actuator was highly significant,the electrode gap had a certain influence,and the influence of the rest parameters was not significant;based on the orthogonal experiment results,the RBF neural network approximate model was established;taking the excitation voltage as the uncertainty variable,the optimal parameter combination of the certainty variables was obtained by using the interval optimization algorithm: the electrode gap was 0mm,the upper electrode width was13 mm,the lower electrode width was 20 mm,the frequency was 8.6k Hz.At different excitation voltages,the induced maximum wind speed increased by about 0.52m/s on average,and the ratio of increase was about 17.7%.Sixth,the Shyy model was modified based on the interval optimization results,and the control mechanism of the spanwise DBD plasma actuator(SDBD-PA)and DBD vortex generator(DBD-VG)on the near wall flow of the plate was studied.The results showed that: the forward and reverse arrangement of SDBD-PA mainly had obvious acceleration and deceleration effects on the near wall flow field respectively,and the control effect increased with the increase of the excitation voltage and the thickness of the incoming flow boundary layer;two groups of SDBD-PA in parallel could greatly improve the control effect;a small-scale single streamwise vortex near the wall was induced by the coupling between DBD-VG and incoming flow,effectively improving the kinetic energy of the boundary layer fluid;as the excitation voltage increased,the scale of the streamwise vortex became larger and the displacement of the vortex center increased;the thickness of the incoming boundary layer also had a certain influence on the displacement of the vortex center.Seventh,ten different layout forms of DBD-PA were designed to actively control the cavity buffeting noise,and the interval optimization algorithm was used to find the best layout form,which was then applied to control the buffeting noise of the Ahmed model.The results of active control of cavity buffeting noise showed that: SDBD-PA had good control effect,and the overall control effect of the reverse layout was better than that of the forward layout,and the control effect decreased in turn when the layout position was in the front,rear and oblique;when DBD-VG was placed in the front,there was basically no control effect,and when DBD-VG was placed in the rear,there was a certain control effect;when DBD-VG was longer,the control effect was better;the results of the interval optimization algorithm showed that at different speeds,the reverse-front-SDBD-PA in the spanwise actuator achieved the best equalization control effect,the average noise reduction was 5.26 d B and the maximum noise reduction was7.48 d B;the long-rear-DBD-VG in the vortex generator achieved the best equalization control effect,the average noise reduction was 4.42 d B and the maximum noise reduction was 5.79 d B.In the buffeting noise active control of Ahmed model,the maximum noise reduction of reverse-front-SDBD-PA was 5.86 d B,while the maximum noise reduction of long-rear-DBD-VG was 5.39 d B.In this paper,through numerical simulation and wind tunnel test,DBD-PA active flow control technology was used to effectively control vehicle buffeting noise,which provided a new idea and technical method for vehicle buffeting noise control. |
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