输气管道壁面涂料减阻机理的实验研究

EXPERIMENT OF SURFACE COATING DRAG REDUCTION MECHANISM IN GAS TRANSPORTATION PIPE

用IFA-300热线风速仪以高于对应最小湍流时间尺度的分辨率精细测量了风洞中不同壁面涂料的管道湍流边界层不同法向位置流向速度分量的时间序列信号,利用湍流边界层近壁区域对数律平均速度剖面与壁面摩擦速度、流体黏性系数等内尺度物理量的关系和壁面摩擦速度与壁面摩擦切应力的关系,在准确测量湍流边界层近壁区域对数律平均速度剖面的基础上,间接测量湍流边界层的壁面摩擦阻力．对不同壁面涂料的壁湍流脉动速度信号用子波分析进行多尺度分解,用子波系数的瞬时强度因子和平坦因子检测管道湍流边界层中的多尺度相干结构,提取不同尺度相干结构的条件相位平均波形,对比研究输气管道壁面涂料的减阻机理．

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 meanvelocity 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.