利用隱式大渦流紊流模式計算氣動噴流噪音

Abstract

隨著生活品質的提昇，噪音問題越益受到重視，其中又以流體所誘導的氣動噪音最為複雜。本計畫將發展氣動噪音的計算方法用以分析與改善噪音問題。由於計算聲場時，需先計算可壓縮紊流流場以得相關的聲源資訊，因此於本計畫的前期將先發展大渦流(LES)紊流全域流場計算方法，過去的研究多利用顯示紊流模式(explicit turbulence model)為次格點尺度模型(SGS model)。然而此法耗費過多計算時間且應用範圍受限，本研究將發展隱示紊流模式(implicit turbulence model)做為次格點尺度模型，此法不僅撰寫容易，且大幅提升計算效率，適用性更加廣泛。在完成紊流計算方法後，再將流場結果帶入Lighthill方程式的聲源項中以計算氣動噪音的傳遞，藉此分析與改善流場所誘導的氣動噪音問題。 由於上述的困難與不易，本計畫預期兩年完成。第一年，將完成隱示大渦流紊流全域流場計算方法開發。並且在第二年，利用前期所發展的計算方法得到聲源項並帶入Lighthill方程式以計算氣動噪音。

With the improvement of the life quality, the noise induced by aeroacoustic becomes one of the most important and complicated problems of the noise control. The computational methods of the aeroacousitcs used to analyze and improve the noise problems will be developed in this subject. Before resolving the problems of the aeroacoustics, the computational method called large eddy simulation (LES) for compressible turbulence in all speed flows will be developed first. In the previous literatures, the explicit turbulence model was usually used to be a subgrid scale model. However, this kind of models is not efficient and will be limited in practical applications. In order to overcome the problem mention above, the implicit turbulence model for LES which is efficient, easily programmed and wide applications will be developed in the present study. After completing the calculation of turbulence, the results of variable pressure and densities of the fluids obtained by the computational method for compressible turbulence in all speed flows are regarded as a source term in Lighthill equations which are the main governing equations used to resolve the noises induced by the aeroacoustics. Due to the complexity of this subject mentioned above, the project is expected to be the duration of execution of divided two years. First year, the implicit turbulence model for LES will be developed to resolve the compressible turbulence in all speed regions. Second year, use the results obtained by the LES developed in the previous year to resolve the Lighthill equations.