Asymmetric Solid–Liquid Two-Phase Flow around a NACA0012 Cascade in Sediment-Laden Flow

Abstract

Sediment abrasion may cause the removal of material and efficiency loss to hydraulic machinery (hydro-turbine, pump, etc.), which may worsen the internal flow and endanger the safe operation of the machines. As abrasion is caused by the impact of sediment on the solid surface, the movement of particles determines the wear intensity. To understand the wear mechanism of hydraulic machinery, the motion characteristics of the asymmetric solid–liquid two-phase flow in a sediment-laden flow around NACA0012 cascades were studied. The laser particle imaging velocimetry (PIV) method was used to measure the flow of quartz particles with median diameters d50 of 82.7 μm, 65.9 μm, and 31.8 μm near the wall of cascades at an impact angle of 10° in a Venturi circuit. The flow characteristics and velocity slip between solid and liquid phases, as well as the effects of particle size and the Reynolds number on velocity slip, were analyzed. The results showed that: (1) the flow is asymmetrically distributed in front of the cascade’s leading edge at a 10° impact angle, and there is strong velocity slip between solid and liquid phases; (2) under the influence of particle inertia, the velocity of the solid phase is higher than that of the liquid phase in the deceleration stage, while the velocity of the solid phase is lower than that of liquid phase in the acceleration stage; (3) in the process of approaching the leading edge, the velocity difference between the solid and liquid phase increases by about 10% and the angle difference increases by about 8.8°.

PIV experimental study on water-sediment two-phase flow in NACA0012 cascade

“…The cascade consists of five NACA0012 foils with a chord length of 100 mm and a pitch of 40 mm. The test section is a rectangular section with a size of 200mm × 30mm, and the flow impact angle is 10° [13].…”

“…After calculating 100 instantaneous velocity fields at each test point, the instantaneous velocity field is averaged to obtain the average velocity distribution within 1 s. The zone near the leading edge of the foil which has a great influence on the wear is taken as the key area. The flow is divided into two areas, the upstream zone and the near wall zone, corresponding to the dividing lines x 1 ~ x 3 of -8.0mm, -0.8mm and 0.8mm as shown in Figure 5 from refence [13]. The velocity distribution in the near-wall zone is obtained by extracting the velocity along the vertical direction near the leading edge.…”