二維均勻流及剪流流經正方阻塊之數值分析

Abstract

本論文主要探討二維非穩態的流場中，流體流經一方形阻塊，數值方法使用有限體積法(FVM)來離散，使用隱式非疊代的PISO法，即Pressure-Implicit with Splitting of Operators，來求解暫態的流體方程式。當中分別探討了均勻流及剪力流兩種不同的入口條件；於剪力流的條件下分別以3：1及3：2兩種速度比，以及從入口邊界到方形阻塊之間以 6和 10不同的單位長度加以比較， 探討的雷諾數範圍從50 到500。結果發現到，在入口速度較高的速度比之下，會產生較低的Strouhal 頻率；而在整個流場當中都是負的渦度所主導下卻發現，負的渦度耗散還比正的渦度耗散還要迅速；在剪力流的案例中，舉升力是指向速度較快的那一方。

The two-dimensional unsteady flow field over a square cylinder has been numerically predicted by finite volume method (FVM) with a non-iterative method PISO, standing for Pressure-Implicit with Splitting of Operators, solving implicitly discretised time-dependent fluid equations. The uniform and the shear free stream were considered. The shear flow was studied with two different velocity ratio 3:1 and 3:2 as well as two different distances 6 and 10 in unit length between the square cylinder and the inlet boundary of the computational domain while Reynolds number was in the range from 50 to 500. The higher velocity ratio of free stream brings the lower Strouhal frequency. The negative vortices dissipate more rapidly then the positive ones do even thought the negative background dominates. The direction of lifting force is pointing to the faster free stream side of the shear flow cases.