單腔消音器之流場與氣動力噪音分析

Abstract

本文主要在探討氣流流經單腔消音器時，氣流場壓力變動所產生之噪音。文中使用有限體積法離散控制方程式，之後以分離式求解法，逐一求解各變量代數方程組，並採用雷諾平均法(RANS)配合Rk-ε紊流模式求解紊流流場。為了累積分析經驗及瞭解氣流對消音器性能的影響，文中首先針對穩態均勻流通過二維單腔消音器的部分進行研究，探討在不同入流速度下，改變消音器之幾何尺寸，包括長度、半徑、入出口延伸管長及入出口位置等，其氣流所產生之總噪音量。在進行三維單腔消音器模擬之前，文中先針對特定三種單腔消音器進行模擬，同時與車廠實驗數據做對照與校正，以驗證分析之正確性。結果顯示，入出口靜壓差之模擬與實驗數據呈現定性關係。爾後，便以此模擬模式為基礎，進行三維單腔消音器之紊流噪音分析。本文在聲場分析中，採用以Lighthill聲學類比理論為基礎之寬頻帶噪音模式(Broadband Noise Source Model, BNS)模擬氣流在消音器內部產生之噪音，使用Proudman與Curle方程式計算每單位體積聲音輸出功率與表面聲功率。文中以氣流產生之噪音總量作為比較的指標，分析二維及三維單腔消音器在不同入流速度與不同幾何參數的情形下，氣流音對消音器消音性能的影響，期作為消音器設計改善的參考依據。

The purpose of this research is to investigate the simple chamber noise which is induced by pressure variation in the turbulent flow. The SIMPLE algorithm with finite volume based scheme was used in this numerical analysis, and Reynolds Averaged Navier-Stokes equations combine with Rk-ε turbulent model are used to solve the turbulent flow. In order to establish the analysis experiences and understand the effect of flow induced noise on the performance of a muffler, uniform flow passes through a 2D muffler is analyzed firstly. The influences of flow velocities and the parameters, such as length, radius, inlet/outlet extended pipe length and so on, on the turbulence noise generation are discussed. Three specific mufflers are simulated, and are compared with the experimental datum to verify the accuracy before starting 3D muffler analysis. The result of simulation and experiment datum show that they have qualitative relationship. Therefore, 3D muffler is analyzed according to this model. For the sound field analysis, the flow induced noise in the interior of a muffler is computed by the Broadband Noise Source (BNS) model. Proudman’s and Curle’s formula were used to evaluate acoustic power per unit volume and surface acoustic power. In this study, we focus on the total aerodynamic noise generated when the fluid pass through a muffler, and analyze different flow velocities and the parameters to understand how the aerodynamic noise is generated. Hoping that this study would improve muffler’s performance.