The Experimental Investigation On Detection And Control Of Multi-scale Structures'Intermittency In Turbulent Boundary Layer

In order to learn about the effect of local heating on the wall affecting on multi-scale structures in turbulent boundary layer ,a group of longitudinal heating wires are laid on the flat-plate. Before and after heating up ,the longitudinal velocity time sequence at different vertical locations in a flat-plate turbulent boundary layer are finely measured by IFA300 with resolution higher than Kolmogorov scale. A comparative study has been performed on the statistical characteristics such as energy distribution, occurring probability and relative intension of multi-scale coherent eddy structure at different Reynold quantities and vertical locations in a flat-plate turbulent boundary layer before and after heating up.An analysis has been carried out to reveal that turbulent multi-scale structures are controlled by wall longitudinal eddy and therefore the friction is reduced .Dissipative ,Taylor , shear and integral scale are calculated ,and the relationship between them and vertical locations in turbulent boundary layer are obtained.The turbulent fluctuation velocity signals are analyzed for multi-scale structure decomposition by wavelet transform.Space length of multi-scale eddy structure are gained by self-correlation method.Finaly,the relationship between scale parameter of wavelet transform and dissipative ,Taylor, shear and integral scale are studied.Through the present study, the velocity structure function based on locally averaged turbulent structure is proved to agree with Harr wavelet transform.The new concept of instantaneous intensity factor and instantaneous flatness factor based on wavelet coefficients together with sampling schemes for multi-scale coherent eddy structures are represented in this paper.Moreover phased-average evolution shapes for multi-scale coherent eddy structures in turbulent boundary layer are extracted and the dynamic course of the burst of multi-scale coherent eddy structures is researched. The experiment study reveals that the coherent eddy structure picked up at different scales share similar shape and they are responsible for the intermittency and the anomalous scaling law in the turbulent boundary layer .