Second- and third-order longitudinal velocity structure functions in a fully developed turbulent channel flow

Second-and third-order moments of temporal increments of the longitudinal velocity fluctuation have been measured using hot wires in a fury developed turbulent channel flow and analyzed using values of the mean energy dissipation rate inferred from direct numerical simulation data for the same flow and Reynolds numbers. The results indicate that dissipative range scales approach isotropy relatively rapidly when the mean shear is negligible. For larger inertial range type scales, the approach is slower. The rate at which isotropy is approached seems slower for third-order than second-order structure functions. This rate depends more on the mean shear than on the turbulent Reynolds number. Two-point laser Doppler anemometry measurements provide reasonable support for the use of Taylor's hypothesis, at least outside the buffer region. (C) 1997 American Institute of Physics.