큰 받음각을 갖는 익형주위의 비정상류에 대한 수치해석;와동의 생성 및 소멸과정과 실속특성

Abstract

An incompressible Navier-Stokes procedure for two-dimensional airfoils in unsteady motion has been developed. Using conformal mapping, the computational grid is generated to be orthogonal and, also, congruent to the streamlines, to keep the equations simple and to minimize the false diffusion. The method is second-order accurate as the QUICK scheme is adopted for the discretization of the convective derivatives. Once the code had been verified through calculations for the driven-cavity flow and the oscillatory flow about a cylinder, the method is applied to solve the flow about an impulsively started airfoil at various angles of attack for Re=1000. After an initial transient period, the flow either approaches to the steady limit or becomes periodic and exhibits the formation and breakaway of many, large and small, vortices, especially on the suction side. At α=25°, the flow is still periodic, but the flow in each cycle is much more complex. These phenomena as well as the observations made on the initial flow behavior and the unsteady separation are discussed in the paper.