FLUID MECHANICS TUTORIAL No.8A WATER （流体力学教程No.8A水）.pdfVIP

FLUID MECHANICS TUTORIAL No.8A WATER TURBINES When you have completed this tutorial you should be able to • Explain the significance of specific speed to turbine selection. • Explain the general principles of Pelton Wheels Kaplan Turbines Francis Turbine • Construct blade vector diagrams for moving vanes for a Pelton Wheels and a Francis Turbine • Deduce formulae for power and efficiency for turbines. • Solve numerical problems for a Pelton Wheels and a Francis Turbine ©D.J.Dunn freestudy.co.uk 1 1. INTRODUCTION A water turbine is a device for converting water (fluid) power into shaft (mechanical) power. A pump is a device for converting shaft power into water power. Two basic categories of machines are the rotary type and the reciprocating type. Reciprocating motors are quite common in power hydraulics but the rotary principle is universally used for large power devices such as on hydroelectric systems. Large pumps are usually of the rotary type but reciprocating pumps are used for smaller applications. 1.1 THE SPECIFIC SPEED FOR VARIOUS TYPES OF TURBINES The power P of any rotary hydraulic machine (pump or motor) depends upon the density ρ , the speed N, the characteristic diameter D, the head change ∆H, the volume flow rate Q and the gravitational constant g. The general equation is: P = f(ρ, N, D, ∆H, Q, g) It is normal to consider g∆H as one quantity. P = f{ρ, N, D, (g ∆H),Q} There are 6 quantities and 3 dimensions so there are three dimensionless groups Π , Π and