On the Measurement of Wall-Normal Velocity Derivative in a Turbulent Boundary Layer

摘要

The wall-normal velocity derivative of partial derivative u/partial derivative y is measured in a turbulent boundary layer, down to 2 wall units from the wall, using two parallel hot-wires. The momentum-thickness- and friction-velocity-based Reynolds numbers are 1450 and 584, respectively. The experimental results indicate that partial derivative u/partial derivative y may be captured with an adequate accuracy given a separation (y) of 2 5 Kolmogorov length scales eta between the two parallel hot-wires, slightly different from that (2 eta 4 eta) required for a turbulent channel flow. The surrogate for displays a significant departure in the buffer layer from that in the turbulent channel flow, due to a difference in the large-scale coherent structures between the two flows. The skewness and kurtosis of partial derivative u/partial derivative y differ markedly from their counterparts in a turbulent channel flow, which reflects a difference in the small-scale turbulent structures of the outer region between the two flows.