以聲學類比方法預測螺槳噪音

Abstract

本文係以經由雷諾平均方程(RANS)的軟體計算出的螺槳流場作為發出聲壓訊號的聲源，並為了使其有時間上的變化，將場點上的速度、壓力旋轉平移以模擬出螺槳在流場中推進的效果，再使用Ffowcs Williams-Hawking(FW-H)聲學類比的演算法對其進行計算。其中，使用了有限差分法(Finite Difference Method)與數值積分法取代了FW-H聲波方程中的微分項與積分。為了驗證演算法的可靠性，本文以點源流建立了假想的無黏流場函數代入演算法中，以驗證數值方法的準確性。在計算螺槳流場引起的聲壓時，將計算螺槳在流場中旋轉時場點上聲源強度的分布，以探討與螺槳流場的聲壓變化的關係，並討論聲壓在近場與遠場之間的差異。

The objective of this thesis is to simulate the acoustic pressure field of a marine propeller. The flow field of a marine propeller is generated by software based on RANS. The method for calculating acoustic pressure used in this thesis is based on Ffowcs Williams-Hawking(FW-H) analogy. The partial differential and integral terms in FW-H acoustic wave equation are substituted with Finite difference method and Numerical integration. Besides, this thesis uses an inviscid flow field function generated by point source to verify the method reliability based on FW-H. When calculating the acoustic pressure of marine propeller, the relationship between sound pressure and distribution of sound source strength is investigated. The difference of sound pressure for far field and near field is discussed.