喷嘴长宽比和雷诺数对旋流冷却流动与传热特性的影响

Effects of Jet Nozzle Aspect Ratio and Reynolds Number on Flow and Heat Transfer Characteristics of Vortex Cooling

针对叶片前缘冷却流动与传热问题,建立了合理的旋流腔冷却结构。通过求解三维稳态RANS方程和标准k-ω湍流模型,数值分析了喷嘴长宽比和雷诺数对旋流冷却流动和传热的影响。基于数值计算结果对无量纲传热系数Nu、喷嘴长宽比Car和雷诺数Re进行方程拟合,得到旋流冷却的传热关联式。结果表明:冷气从喷嘴进口切向射入旋流腔并形成高速旋流,显著增强换热;随着喷嘴长宽比从0.2增大到9,旋流外区面积、冷气速度和冷气湍流动能先减小后增大,冷气压力系数先增大后减小;在大喷嘴长宽比时,Nu沿旋流腔周向和轴向的分布较为均匀;随着雷诺数的增大,冷气在旋流腔中的流动结构不变,而冷气速度、湍流动能、压力系数和壁面Nu均显著增大;平均Nu随着雷诺数的增大而显著增大,随着喷嘴长宽比的增大先减小然后增大;传热关联式与数值计算结果的误差在10%以内,可以准确预测旋流冷却的换热系数。

A proper vortex chamber structure is established in terms of blade leading edge cooling.The influence of jet nozzle aspect ratio and Reynolds number on flow field and heat transfer characteristics of vortex cooling is numerically analyzed by means of 3-D steady RANS equations coupled with standard k-ωturbulence model.Based on numerical data,the heat transfer correlations are summarized with respect to the Nusselt number,jet nozzle aspect ratio and Reynolds number.Results show that high speed rotational flow is formed by the impingement air,thus the heat transfer intensity is significantly enhanced. When jet nozzle aspect ratio increases from 0.2to 9,the outer rotation region,air speed and turbulence kinetic energy decrease at first and then increase,while the static pressure ratio increases at first and then decreases.A larger jet nozzle aspect ratio results in more uniform Nusselt number distribution in the circumferential and axial direction.An increase in Reynolds number leads to pronounced increases in air speed,turbulence kinetic energy,static pressure ratio and wall Nusselt number.However,the flow characteristics are not sensitive to Reynolds number.The globally averaged Nusselt number increases as Reynolds number increases,but decreases at first and then increasesas jet nozzle aspect ratio increases.The heat transfer correlation can be used to accurately predict the vortex cooling heat transfer coefficient with a deviation less than 10%.