低雷诺数下椭圆翼型层流分离研究

通过采用计算流体力学方法对不同相对厚度的椭圆翼型在低雷诺数范围下进行了数值模拟，研究了椭圆翼型在低雷诺数下的层流分离现象及流场结构.结果表明:在低雷诺数下，薄椭圆翼型在小攻角时前缘出现层流分离泡是其具有高的升力系数及升阻比的原因，随厚度的增加，前缘层流分离泡逐渐消失，在后缘形成时均小泡.随着雷诺数升高，薄椭圆翼型时均分离泡都出现在前缘，但外形缩小，而在较低雷诺数下，薄椭圆翼型小攻角时没有发生转捩再附现象；同时层流分离泡的出现也对翼型后缘分离涡的尺寸和位置产生了重要影响.相对厚度和雷诺数通过影响椭圆翼型上表面层流分离泡的尺寸、位置以及后缘分离涡的形态结构，进而改变了气动特性.

Study on Laminar Flow Separation of Elliptic Airfoils at Low Reynolds Numbers

The different relative thickness of elliptic airfoils was simulated to study the laminar flow separation and the structure of flow field in the range of low Reynolds numbers by the method of computational fluid dynamics. The results showed that a leading-edge separation bubble forms on the thin elliptical airfoil at low Reynolds numbers， which accounts for high lift coefficient and lift-drag ratio at a small angle of attack. The laminar separation bubbles gradually disappear at the leading edge and appear at the trailing edge with the increase of relative thickness. The size of the leading-edge separation bubbles of the thin elliptic airfoil gradually reduces with the increase of Reynolds numbers. However， the phenomenon of transition and reattachment disappears at lower Reynolds numbers; at the same time， the size and position of the vortex at the trailing edges of the airfoil are also greatly affected by the appearance of laminar separation bubbles. The relative thickness and Reynolds number change the aerodynamic characteristics by influencing the size and position of laminar separation bubbles on the upper surface of the elliptic airfoil and the structure of separation vortex at the trailing edge.