Seite - 1567 - in Book of Full Papers - Symposium Hydro Engineering

3. FLOW REGIME OBSERVATION 3.1. FLOW REGIMES IN CONTRACTION SECTION As demonstrated in Figure 2, the flow upstream of the STED remained in an open channel condition, with a flat free surface and hydrostatic pressure distribution. Then due to the effects of the side wall contraction, the flow contracted transversely and extended longitudinally when passing through the STED. Figure 3 shows that, the shock waves on both side collided at the center line. The water surface profile no longer remained flat along the contraction section. The flow in the contraction section was affected by two factors, upstream of the shock wave intersection, i.e. the friction effect caused by the roughness of the side wall and the turbulence inertia effect caused by large vortex. Considering the distance from the inlet of the contraction section to the shock wave intersection point is rather short, the friction effects that caused by the small vortex in the boundary layer of the flow could be ignored. On the other hand, the force acted on the contracted side walls that caused by the inertial impact of the high-speed incoming flow would bring about rapid shock waves (a special form of hydraulic jump). After the shock waves intersected, the turbulence kept growing. As the side walls contracted continuously, the flow depth increased and the velocity decreased, then the inertial effects of the flow reduced accordingly. Large vortexes in the flow constantly split into small vortexes, due to the limitation of the side walls. As a result, large vortexes and small vortexes coexisted in the flow, whereas the turbulence inertia effects caused by large vortexes still played a dominant role in this section. Upstream of the shock wave intersection, the water-surface curve near the center line of the STED raised slowly, while the water-surface curves near the side wall raised rapidly. The cross section of the flow presented an ‘U’ shape. Downstream of the shock waves intersection, the water-surface curves near the side wall kept rising, while the water-surface curve near the center line raised sharply, and got above of that near the side wall, due to the collision of the shock wave flow. A ‘W’ shaped cross section of the flow appeared. Moreover, part of the water detached from the main flow, then ejected out in the form of scattering, with high inclined initial velocity above the main flow. That was how the water wings formed. Fig. 2 Overall flow regime in STED 1567