Experimental Investigation On Drag Reduction Of Surface Coat For Turbulent Gas Pipe Flow

In this paper, coat is applied to the project of gas pipe flow from west to east. Thetechnique of constant temperature anemometry is used to study the mechanism ofdrag reduction for turbulent boundary layer coated on the surface of wall.Mean velocity profile of wall turbulence with different coat boundary has beenfinely measured by IFA300 constant-temperature anemometer and single wire probe.There has some relation between skin friction velocity and the logarithmic law ofmean velocity profile. The skin friction velocity and the shear stress are calculatedthrough fitting the logarithmic law of mean velocity profile. The ability of dragreduction with three kind of coat are studied, which provide experiment bases to theresearch of drag reduction mechanism. In this experiment, each coat has threethickness. Ten flat-plates, including a no-coat flat-plates, are studied with threedifferent Reynold number.The velocity time sequence signal at different vertical locations in a turbulentboundary layer are analyzed by wavelet transform with multi-scale. The scales ofmulti-scale eddy structures are determined by self-correlation function. The coherentstructures are identified by flatness factor based on locally averaged velocity structurefunctions. Phased-average evolution shapes for multi-scale coherent eddy structures inturbulent boundary layer are extracted by this conditional sampling technique. Thedynamic course of multi-scale coherent eddy structures'bursting is researched. Theintermittency features, studied through the probability density function of the waveletcoefficients, are found influenced by multi-scale coherent eddy structures.It is found that coat with drag reduction make the stream-wise mean velocityincreased near the wall region. At the same time the buffer layer is incrassated, andthe log-law region moves upwards. The coat change the distributing of energy, thephased-average evolution shapes and the flatness factor, enhance the coherentstructures, make the flow regular, and work on and control the multi-scale coherenteddy structure in a turbulent boundary layer, in order to reduce the resistance of thewall.In the log-law region, the spraying has no effect on the flow structures.