Effect of the shape of the transition section on head losses in intakes of a pumped-storage station

Abstract

1. In intakes of the upper reservoirs of pumped-storage stations for straight variants and for layouts with bends (R=4dc) the coefficients of head losses in the pump operating regime are 2–3 times greater than in the turbine. 2. The experimental value of the coefficient of head losses ξplexy, taking into account losses in the intake proper and in the bend located behind it, in the pump regime, as a rule, differs substantially from the sum ξplexy=0+ξt.b.calc of the experimental value of the coefficient of losses of a straight intake and coefficient of head losses in the bend calculated by the recommendations given in the literature. This is due to the fact that the bend affects the value of losses in elements of the intake located above it. Therefore, a reliable value of the resistance coefficient of an intake with a bend in the pump regime can be obtained only experimentally. In the turbine operating regime the coefficients ξtlexy and ξtlexy=0+ ξt.b.calc for intakes with a bend differ among themselves by less than 12%. 3. Intakes with various degrees of expansion and transition section 2 from a circle to a rectangle (b=1.67dc, h=dc) located between the bend and intake proper have smaller head losses than intakes with transition section 1 from a circle to a square (b=h=dc) for all angles of turn of the bend (γ=0–90°) both in the pump and in the turbine regimes. 4. In intakes with transition section 1 (b=h=dc) in the pump regime the total losses, including also the losses in the bend, increase with increase of γ of the bend. In more extensive intakes with transition section 2 (b=1.67dc, h=dc) straight layouts (γ=0) have minimum losses; in the presence of a bend with γ=25° and γ=90° the coefficients of head losses are practically the same and, on average, are 45% greater than when γ=0, and when γ=60° are 4.5–10.5% less than when γ=25 and 90°. 5. In intakes with bends (R=4dc) of rectangular section (b=1.67dc, h=dc) with an area 2.12 times greater than the area of the conduit and transition 2 located between the conduit and bend, in the pump regime the coefficient of head losses are 1.4–1.5 times less than in intakes with bends of circular section (d=dc) for all investigated angles of turn of the bend. 6. In the turbine operating regime the total coefficients of head losses increase with increase of the angle of turn of the bend.