Experimental Investigation On Convection Velocities Of Multi-Scale Structures In Turbulence

The convection velocity in the turbulent boundary layer plans an important role in describing the characteristics of transportation of the momentum, quality and energy in turbulence, serving as a bridge between spatial description and temporal description in the studying of turbulence, and Taylor's frozen hypothesis that we often used is also related to the convection velocities for turbulence. But so far, there is not a definite solution to how to determine the mean convection velocity of turbulent eddy structures in different scales.As to this question, the accurate two-points velocity measurements in turbulent boundary layer over a smooth flat plate was carried out with the IFA300 constant temperature anemometer, two hot-wire probes and two sets of high-accuracy automatically controlled coordinate transverse systems at different Reynolds numbers, different positions from the wall and different longitudinal distance. Time, space & time-space velocity correlations and wavelet analysis were used synthetically to calculate the mean convection velocity of turbulent flows and convection velocities of multi-scale eddy.From the experimental measurement results, the effects to the convection velocity caused by Reynolds numbers, positions beyond to the wall and longitudinal space between two probes were analyzed which aid to make clear the relations between the convection velocity in the different positions beyond the wall and the local mean velocity and the free coming stream velocity. Accordingly, the problems of how to determine convection velocity were analyzed when Taylor frozen hypothesis is used in turbulent boundary layer.