Large Eddy effect on Turbulent Heat Transfer Analyzed by Correlations between Heat flux and Velocity Fluctuations

为了阐明紊流换热性能的机理，人们进行了许多研究。在这些研究中，大多数都没有研究空间湍流运动与输运通量之间的关系。本文通过测量射流中输运通量与速度波动之间的相互关系，研究了冲击射流中大涡运动结构对冲击板的传热、传质和剪切应力的影响。从相互关系的时空分布可以追溯大涡的运动和崩塌。在换热情况下，用LDV测量速度场，用自制热流密度传感器测量板上的热流密度。采用电化学方法测定了剪切应力和传质系数。影响热通量的大涡流在射流中运动，其运动速度与射流的平均速度相当。而在传质情况下，在质量通量测点附近存在自相关结构。这种结构是由扩散边界的存在引起的。为了弄清结构，数值分析了质量通量、热流通量和切应力边界层对边界层外速度波动的响应。理论结果表明，自相关结构只存在于传质过程中。这一趋势与实验结果完全吻合。

Many researches to clarify the mechanism of turbulent heat transfer performance have been carried out.In the most of these researches, the relations between the turblent motions in space and the transported flux have not been studied. In this research, the structures of large eddy motion in the impinging jet, which strongly affect the heat transfer, the mass transfer and the shear stress on the impinged plate, were investigated by measuring the cross-correlations between the transported fluxes and the velocity fluctuation in the jet. The movement and collapse of the large eddies can be traced from the time and space distributions of the cross-correlation. In the case of heat transfer, the velocity field were measured by LDV, and the heat flux on the plate were measured by a hand-made heat flux sensor. To measure the shear stress and the mass transfer coefficient, electro-chemical method were used. The large eddies affecting on the heat flux moved in jet whose moving speed was quite same as the mean velocity of the jet. However, in the case of mass transfer, the auto-correlative structure was existed near the measuring point of the mass flux. This structure was caused by the existence of the diffusion boundary. In order to clarify the structure, the responses of the mass flux, the heat flux and the shear stress boundary layeto the velocity fluctuation outside of the boundary layer were numerically analyzed. The theoretical results showed that the existence of the auto-correlative structure only for the mass transfer. This tendency accurately agreed with the experunental results.