本文選題：空腔流 + 格子玻爾茲曼方法　； 參考：《華中科技大學》2014年碩士論文

【摘要】：氣動噪聲在現(xiàn)今工程和生活實際中處處可見，控制噪聲無論是對工業(yè)實際亦或是日常生活都較為重要。而關于其數(shù)值模擬計算也在近幾十年來逐漸成為熱點，LBM正是其中能夠較好模擬聲波的產(chǎn)生及傳播的方法之一�；诮^熱、等熵假設的D2Q9可以將流體視為微可壓，這使聲傳播模擬成為可能。本文研究主要從以下幾方面進行： 首先模擬多類型空腔流，其中包含方形腔、三角形空腔、半圓形空腔以及梯形空腔。選取含插值的斜邊界外推法處理這幾類含復雜邊界的空腔。改變流速以探究流速變化對各類空腔流場的影響，這些影響主要體現(xiàn)在渦強、渦中心源位置變化及渦數(shù)量等方面。總體而言隨著入流速度的提高，空腔內(nèi)渦流狀態(tài)逐漸向復雜化不穩(wěn)定化發(fā)展，當壁面剪切流達到一定程度時，空腔一般都將于底部或兩側的近壁面處由主渦分化出小渦。 其次，為全面了解聲波傳播特性，對點源、線源的傳播、同頻率與不同頻率點源的合成、不同松弛時間下波的傳播特性以及對多普勒效應進行模擬分析。通過將理論分析解與點源、線源在各時刻的LBM模擬結果對比，初步驗證其計算可行性。對干涉現(xiàn)象的模擬和多普勒現(xiàn)象的計算分析進一步證明了其模擬聲波的準確性，同時，采用不同松弛時間進行模擬，得出松弛時間與流場阻尼正相關，但與聲速無關。 最后，，本文對矩形腔進行了獨立研究，從深長比、入口流速、粘性等角度進行了模擬分析，然后對比相同條件下傳統(tǒng)CFD計算結果，統(tǒng)計二者誤差，結果顯示深長比較大和深長比較小情況下其誤差較低，流速方面，二者誤差隨流速降低而降低。同時，網(wǎng)格技術的模擬說明了其能在一定程度上減少計算耗時。另外，還以LBM監(jiān)測其內(nèi)某些點的聲壓變化，求得其頻譜特性并對比文獻結果，結果證明其聲壓計算值對于各個峰值頻率計算較為準確，說明了LBM對于預測噪聲的準確性。
[Abstract]:Pneumatic noise can be seen everywhere in engineering and daily life nowadays. It is important to control noise both in industry and in daily life. The numerical simulation of LBM has become a hot topic in recent decades, which is one of the methods to simulate the generation and propagation of sound waves. Based on adiabatic, the isentropic D2Q9 can treat the fluid as microcompressible, which makes it possible to simulate acoustic propagation. This paper mainly studies from the following aspects: First, multi-type cavity flow is simulated, including square cavity, triangular cavity, semicircular cavity and trapezoidal cavity. The oblique boundary extrapolation method with interpolation is selected to deal with these kinds of cavity with complex boundary. The effect of velocity variation on the flow field of cavity is investigated by changing the velocity of flow, which is mainly reflected in the vorticity strength, the location change of vortex center source and the number of vortices. In general, with the increase of the inlet velocity, the swirl state in the cavity becomes more and more complex and unstable. When the wall shear flow reaches a certain level, the cavity will generally be separated from the main vortex by the main vortex at the bottom or near the wall of both sides. Secondly, in order to fully understand the characteristics of acoustic wave propagation, the propagation of point source and line source, the synthesis of point source with the same frequency and different frequency, the propagation characteristics of wave at different relaxation time and the Doppler effect are simulated and analyzed. By comparing the theoretical analysis solution with the LBM simulation results of point source and line source at each time, the feasibility of calculation is preliminarily verified. The simulation of the interference phenomenon and the analysis of the Doppler phenomenon further prove the accuracy of the simulated acoustic wave. At the same time, the different relaxation time is used to simulate, and it is found that the relaxation time is positively correlated with the flow field damping, but it is independent of the sound velocity. Finally, an independent study of rectangular cavity is carried out, which is simulated and analyzed from the angles of depth ratio, inlet velocity and viscosity, and then compared with the traditional CFD calculation results under the same conditions, and the errors between the two are calculated. The results show that the error is lower in the case of larger depth ratio and lower depth length ratio, and the error decreases with the decrease of flow velocity. At the same time, the simulation of grid technology shows that it can reduce computational time to some extent. In addition, LBM is used to monitor the variation of sound pressure at some points, and the spectral characteristics are obtained and compared with the results of literature. The results show that the calculated value of sound pressure is more accurate for each peak frequency, which shows the accuracy of LBM in predicting noise.
【學位授予單位】：華中科技大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB53

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本文編號：1795938