الفصل السادس

6-1.Introduction:
In the previous studies we have discussed and analyzed the ideal performance of turbomachines based largely on one-dimensional frictionless flow assumptions. The actual performance of a turbomachines will differs from the ideal situation because of the occurrence of losses due to fluid dynamic drag, leakage and mechanical friction, for example, the actual performance curve of a centrifugal pump running at constant speed is given in Figure(6-1).
Where the head developed by the pump is shown as a function of delivered volume flow rate. This performance curve differs from the ideal curve shown in Figure (6-2) by the effects of non-uniform velocity distribution (Circulatory flow), the frictional losses in the stationary and moving vanes of the pump, and the separation losses (Turbulence losses) that occur at off-design conditions. As shown in Figure (6-2), at off-design conditions the flow through the pump, and hence the radial velocity differs from that at design, and hence the angle of relative rotor inflow velocity will be different from the blade angle ?1. The ensuing flow separation causes a loss that is proportional to the square of the difference in flow rates, (Q-Qdesign)2. The frictional losses will be proportional to the square of the flow rate Q2, while the