Rotational Flow Through Cascades Part Ii. The Circulation About the Cascade

The variation in circulation about aerofoils in cascade when the approaching stream has a non-uniform velocity is determined by assuming that the secondary flow is confined to the rectangular passages between, and extending downstream from, the blades. The strength of the trailing vortex sheet separating each blade passage is estimated from the secondary flow. From this is deducted the trailing filament circulation, defined in Part I, to give the trailing shed circulation from which the variation in blade circulation can be determined. Measurements of pressure distribution on a cascade of impulse turbine blades confirm experimentally the variation of lift and circulation predicted by the theory. It is shown that the secondary flow tends to cause a stalling of the blades near the wall. A similar behaviour for isolated aerofoils in non-uniform flow is predicted.