analysis partially with experimental research。 Nevertheless; these fruitful results
83
remain with inconsistencies in both theory and practice。
Firstly; for a definite shear stress
? o = ? hJ; the effect of wall roughness is
assumed to be only limited to a shallow region of viscous sublayer adjacent to the
wall; while the velocity distribution in the turbulent core is assumed to be identical
for all conditions of flow。
Secondly; assumption has been made that the turbulent core velocity curve u~y
joins abruptly the viscous film straight line at the point of depth y = δ=11。6? /u* ;
where u* is the shear velocity and ? ; the kinematic viscosity。 This is far from truth
as shown by many recent velocity measurements close to the boundary (1) 。 The slopes
du
of velocity gradients
dy
for the two regimes are radically different。
Thirdly; in puting the average velocity by summation; the effect of flow
within the range y
小提示:按 回车 [Enter] 键 返回书目,按 ← 键 返回上一页, 按 → 键 进入下一页。
赞一下
添加书签加入书架