運用可滲透表面轉換計算螺槳流場噪音

Abstract

本文係經由雷諾平均方程(RANS)的軟體計算出的暫態螺槳流場作為發出聲壓訊號的聲源，分別使用Ffowcs Williams-Hawkings(FW-H)聲波方程式計算螺槳葉片表面上所產生的噪音及可滲透表面轉換 (Porous Formulation)定義一圓柱發聲體包覆螺槳及周圍流場所產生的噪音，定義兩個不同的表面函數計算出聲壓值。其中，使用了有限差分法（Finite Difference Method）與數值積分法取代了方程式中的偏微分項與積分。為了驗證程式碼的可靠性，本文以點源流建立了假想的無黏流場函數代入FW-H聲波方程中，以驗證數值方法的準確性。再將所取得的暫態螺槳流場資料使用勢流理論中的鏡像法(Method of Images)建立自由液面的邊界條件，並使用可滲透表面轉換式模擬出螺槳在水下對於遠場觀測點所造成的聲壓變化。

The objective of this thesis is to simulate the acoustic pressure field of a marine propeller. The unsteady flow field of a marine propeller is generated by RANS. Two methods are used for calculating acoustic pressure in this thesis, fowcs Williams-Hawkings (FW-H) analogy and Porous Formulation. The differential terms and integrals in the formulations are approximated by Finite difference and numerical integration. At beginning, this thesis uses an inviscid function generated by a point source to verify the method based on FW-H. At last, this thesis uses the method of images in the Potential theory to set up a free surface boundary condition, and uses Porous Formulation to calculate sound pressure of an underwater marine propeller.