EXPERIMENT OF SURFACE COATING DRAG REDUCTION MECHANISM IN GAS TRANSPORTATION PIPE
输气管道壁面涂料减阻机理的实验研究

The velocity time sequence at different vertical locations in a turbulent pipe flow with different surface coating was carefully measured by IFA300 constant-temperature anemometer with a resolution higher than the frequency with respect to Kolmogorov dissipative scale. A method is put forward to calculate the skin friction velocity by means of nonlinear iteration, in order to achieve a non-perturbed or micro-perturbed measurement of wall shear stress. The relationship among some inner-scale physical parameters, e.g., the mean-velocity profile, skin friction velocity and fluid dynamics viscosity, and the relationship between skin friction velocity and skin friction shear stress were used in accurately calculating the skin friction drag based on the precise measurement of logarithmic mean-velocity profile in the near wall region of turbulent boundary layer. The velocity signals were decomposed into multi-scale eddy structures by wavelet transform. A conditional sampling technique for the multi-scale coherent eddy structure detection from the simultaneous turbulent field was introduced using the multi-scale instantaneous intensity factor and multi-scale flatness factor of wavelet coefficients. Coherent eddy structures for different scales were extracted by this technique and the mechanism of surface coating drag reduction is investigated for gas transportation of turbulent pipe flow.