開水路流れにおける乱れの空間構造について (4)

Abstract

The time-space structure of turbulence is characterized by the spatial extentsion of turbulenceand convection process with main flow. Through the turbulence measurement by hot-filmflowmeters at multi-points, these characteristics in a free surface shear flow are investigated bymeans of techniques of time-space correlation coefficient and spectral function.The experimental results obtained are as follows; 1) The spatial scale of turbulencenear the free surface is larger than that near the bed and the ratio of longitudinal, lateraland vertical scale at the half depth is 10: (2～4): (3～4). 2) The phase of turbulence nearthe free surface is in advance of that near the bed, while the phase lag of turbulence measuredat two points separated laterally is negligible. 3) The convection velocity is almost sameas the local mean velocity and independent of the frequency. 4) The Lagrangian time scalewhich is normalized with the depth, mean velocity and friction velocity depends only on therelative depth. 5) The longitudinal coherency may be represented by the power law offrequency.