relative roughness 是专指管壁粗糙凸起高度(绝对粗糙度)ε与管子内径D的比值，即ε/D，是无因次数。
实验结果表明当壁面粗糙度超过1%时摩擦系数随着壁面相对粗糙度的增加而增加。
The friction factor obtained from the experiments increases with the surface roughness increase when the relative roughness is greater 1%.
若流线型物体表面的摩擦阻力系数仅为相对粗糙度的函数，则形状阻力系数与雷诺数无关。
Since if the frictional resistance coefficient is a function of relative roughness, then the form resistance coefficient is independent of the Reynolds number.
对于不同粗糙程度的壁面，在同一流量条件下的糙率系数会随着相对粗糙度的增大而增大。
The roughness coefficient increases when the relative roughness of the surface becomes larger under the same condition of discharge.
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