純粋ポアズイユ, 純粋クエットおよびクエット・ポアズイユ型バックステップ乱流の回復域の平均速度分布

Mean velocity profiles in velocity recovery region of pure Poiseuille, pure Couette and Couette-Poiseuille type turbulent channel flows over a backward-facing step are measured and investigated experimentally. The flows are turbulent channel flows between moving and step-side stationary walls with different non-dimensional upstream pressure gradients β0 (flow type parameter). The channel expansion ratio is 1.50. The upstream flows are fully developed pure Poiseuille (β0=-1), pure Couette (β0=0) and Couette-Poiseuille (β0=-0.5) turbulence plane channel flows. The reattachment region is specified by tuft visualization method. The central point of the reattachment region is less dependent on β0. Velocity profiles are measured by hot-wire anemometry for the flows at Reτ0=300, where Reτ0 is the Reynolds number based on the friction velocity and channel half width at the upstream flow. The logarithmic law of velocity is observed even for sections just after the reattachment region. The additive constant appeared in the logarithmic law decreases with increase of β0. The half power law is formed at the beginning of the recovery region for the flows with β0=-0.5 and 0, while it is not observed for the flow with β0=-1.