Interactive flow past multiple blades and wakes

Periodic flows past multiple blades and wakes aligned or nearly aligned in the streamwise direction are studied for high Reynolds number. The interact ion between the blade and wake sections of the flow, and the inner-outer vi scous-inviscid interaction, lead to an elliptic problem requiring the solut ion of the boundary-layer equations together with a pressure-displacement r elation which extends over the whole period. This is solved computationally , with the results showing in particular cases of boundary-layer separation from the blades. The results also lead to an analysis for blades of short streamwise extent compared with the inter-blade distance, an arrangement of practical relevance to rotorcraft. Both the numerical and the analytical a pproaches yield the result that viscous effects cause an abrupt reduction o f pressure over the blade, balancing a gradual pressure growth throughout t he wake.