Similarity laws of velocity profiles and turbulence characteristics of Couette-Poiseuille turbulent flows

Similarity laws of mean velocity profiles and turbulence characteristics of Couette-Poiseuille turbulent flow (C-P flow) have been studied experimentally. The global parameters of C-P flow are the Reynolds number Re-* and the dimensionless shear stress gradient mu and flow parameter beta. The effects of these parameters on the turbulence structure have also been considered in the wall region and turbulent core region, respectively. In the wall region, the wall law varies greatly with mu but slightly with Re-*. Typically, the additive constant B of the logarithmic law (or Van Driest damping factor A(+)) is shown to depend only on mu. Turbulence characteristics are also strongly influenced by mu, but not much by Re-*. Because the relation lambda = -Re-* holds in plane Poiseuille flow and Re-* has little effect on the similarity laws for C-P flows, the low-Reynolds-number effect on the additive constant and turbulence quantities for plane Poiseuille flow can be attributed to the mu effect. In the turbulent core region, however, there is a great difference in the defect law of the velocity profile and the distribution of turbulence intensity between Poiseuille (P)- and Couette (C)-types flows. For P-type flow, an effective friction velocity mu(e)(*) and a new coordinate eta = y - h(s) are recommended for the universal profile, where y = h(s) = delta(p) is the position of tau = 0 and delta(p) is considered to be appropriate as a characteristic length scale of turbulence. For C-type flow, a different effective friction velocity mu(c)(*) the characteristic length scale 2h and the wall coordinate y are preferred. The turbulence activity away from the wall is extremely high for mu > 0 and low for mu < 0. A strong sweep event plays a dominant role in the Reynolds shear stress when 0 < mu < 50, whereas strong ejection from the near-wall region prevails in the case of negative mu with a small absolute value.