EXPERIMENT OF SURFACE COATING DRAG REDUCTION MECHANISM IN GAS TRANSPORTATION PIPE

The velocity time sequence at different verticallocations in a turbulent pipe flow with different surface coating wascarefully measured by IFA300 constant-temperature anemometer with a resolutionhigher than the frequency with respect to Kolmogorov dissipative scale.A method is put forward to calculate the skin friction velocity by means ofnonlinear iteration, in order to achieve a non-perturbed or micro-perturbedmeasurement of wall shear stress. The relationship among some inner-scalephysical parameters, e.g., the mean-velocity profile, skin friction velocityand fluid dynamics viscosity, and the relationship between skin frictionvelocity and skin friction shear stress were used in accuratelycalculating the skin friction drag based on the precise measurement of logarithmicmean-velocity profile in the near wall region of turbulent boundary layer.The velocity signals were decomposed into multi-scale eddy structures bywavelet transform. A conditional sampling technique for the multi-scale coherenteddy structure detection from the simultaneous turbulent field wasintroduced using the multi-scale instantaneous intensity factor and multi-scaleflatness factor of wavelet coefficients. Coherent eddy structures fordifferent scales were extracted by this technique and the mechanism ofsurface coating drag reduction is investigated for gas transportationof turbulent pipe flow.