冲击射流流动换热超大涡模拟研究

Very-Large Eddy Simulation of Impinging Jet Flow and Heat Transfer

为了准确预测发动机热端部件中广泛采用的冲击射流冷却复杂的流动和换热特性,发展了基于BSL k-ω模型的超大涡模拟(VLES)高精度模拟方法,并对高雷诺数Re=4×104,两种不同射流距离2和6的单孔冲击射流及三孔冲击射流这一经典的流动传热问题进行三维非稳态高精度数值计算。同时,将分离涡方法(DDES)和k-ωSST,RNG,Transition SST三种RANS方法的数值模拟和开发的超大涡模拟(VLES)方法进行对比。研究表明,VLES方法均能够准确捕捉冲击射流流场的复杂非稳态流动及传热特征,包括自由射流区、壁面射流区小尺度涡系和大尺度湍流结构的演化和破碎,同时冲击壁面的换热系数计算结果与实验值吻合较好。DDES方法未能准确捕捉流场复杂的小尺度湍流结构,壁面换热计算结果与实验值差异较大。RANS方法计算的换热结果与实验数据差异最大,基本未能预测到壁面换热特性。在相同的计算网格和计算方法下,VLES方法计算结果优于DDES方法,DDES方法一般好于RANS方法。这表明新开发的VLES方法能够准确地计算冲击射流相关的流动及换热问题。

To accurately predict the complex flow and heat transfer characteristics of impinging jet,which is widely used in the cooling for aero-engine hot components,in the present study,a new high-fidelity numerical method,named as very-large eddy simulation(VLES),is developed based on the BSL k-ωturbulence model.It is applied to the high-fidelity numerical simulations of the three-dimensional unsteady turbulent flow and heat transfer of a classical configuration,including a single impinging jet at high Reynolds number Re=4×104 with two different jet distances of 2 and 6,and the case with three impinging jets.At the same time,the numerical simulation results by delayed detached eddy simulation(DDES)and RANS method including k-ωSST,RNG and transition SST models are compared to those by the newly developed VLES method.The results show that the developed VLES method can accurately capture the complex unsteady flow and heat transfer characteristics of impinging jet,including the evolution and breakup of the small-scale vortex and large-scale turbulent structures at free jet and wall jet zones.It is found that the calculated heat transfer coefficient of the impinging wall via VLES is in good agreement with the experimental data.However,the performance of DDES and RANS method is unsatisfactory because DDES method fails to accurately capture the complex unsteady turbulent small-scale structure in the flow field,and their predictions of the heat transfer coefficients are quite different from the experimental data.The difference of wall heat transfer between the predictions from RANS method and the experiments is largest among all the models,meaning that the wall surface heat transfer is not well predicted.Under the same computational grids and numerical conditions,the results of VLES method are significantly better than DDES method,and DDES method is generally better than the RANS method.It confirms that the present VLES method can accurately predict the flow and heat transfer characteristics associated with impinging jet.