基于超大涡模拟的翼端间隙流湍流特性与损失机理分析

Very Large Eddy Simulation Analysis of Turbulent Flow Characteristic and Mechanisms for Turbulent Loss in Hydrofoil Tip Clearance Flows

摘要:

为探明不同翼端间隙条件下水翼端部间隙区湍流特征及间隙湍流损失机理，以NACA0009型钝尾缘水翼为研究对象，采用基于SST k-ω湍流模型的超大涡模拟方法，分析了间隙宽度τ（分别为0.1c和0.02c）和翼端倒圆半径r（分别为0，0.5%c和1%c）对间隙区涡系结构、湍流雷诺应力、湍动能和湍流损失的影响。结果表明，不同间隙条件下，间隙流动的雷诺应力分布与间隙涡系分布趋于一致，以法向正应力〈v′v′〉和展向正应力〈w′w′〉为主。大间隙下（τ=0.1c），湍动能和雷诺应力主要分布在间隙分离涡区域，速度梯度〈v〉/z和雷诺应力〈w′w′〉主导间隙分离涡区域的湍动能生成，随翼端倒圆半径增加，间隙湍流损失因间隙区雷诺应力的显著减小而降低；小间隙下（τ=0.02c），间隙端壁边界层在间隙泄漏涡的强卷吸作用下形成诱导涡，间隙区湍流损失主要产生于间隙泄漏涡和诱导涡区域内，随翼端倒圆半径增大而增大，其原因是主导诱导涡湍动能生成的雷诺应力〈v′v′〉与速度梯度〈v〉/y和主导间隙泄漏涡湍动能生成的〈v′w′〉与(〈v〉/z+〈w〉/y)均随翼端倒圆半径增加而增大。

Abstract:

The tip-leakage flows over an NACA0009 blunt trailing edge hydrofoil with different tip gap width (τ=0.1c and 0.02c, c is hydrofoil chord length) and tip edge rounding (rounding radius r=0, 0.5%c and 1%c) were studied by using SST k-ω turbulent model based very large eddy simulation (VLES) with particular emphasis on understanding the turbulence characteristics and the underlying mechanisms for turbulent loss in the vicinity of the tip gap. Systematic and detailed analysis of the vortex structures, Reynolds stresses, turbulent kinetic energy and tip clearance turbulent loss was made around the hydrofoil with a stationary endwall. Results showed that the Reynolds stress distributions in the tip gap region were consistent with the distributions of the tip clearance vortices, and the magnitude of the normal stresses 〈v′v′〉and 〈w′w′〉 around the tip gap vortices were larger than that of other Reynolds stress components. For the gap τ=0.1c, turbulent kinetic energy and Reynolds stresses of the tip clearance flow were found to be concentrated in the tip separated vortex (TSV) region, the velocity gradient 〈v〉/z and the spanwise normal stress 〈w′w′〉dominated the generation of turbulent kinetic energy in the TSV region; as the tip rounding radius increased, the significant decrease of the Reynolds stresses resulted in a reduction of the tip clearance turbulent loss. For gap size of 0.02c, the strong entrainment of the tip leakage vortex (TLV) on the end-wall boundary layer induced the formation of an induced vortex (IV), which rotated opposite to the TLV. The tip clearance turbulent loss mainly occurred in the TLV and IV regions for the smaller tip gap cases, and its magnitude was increased with the increase of the rounding radius. The underlying mechanism for this tendency was that enlarging the tip clearance increased the normal Reynolds stress 〈v′v′〉 and the velocity gradient 〈v〉/y, which dominated the production of turbulent kinetic energy in the IV region; and it also led to an increase of the Reynolds shear stress 〈v′w′〉 and velocity gradient 〈v〉/z+〈w〉/y), which dominated the generation of turbulent kinetic energy in the TLV region.