Lifting multi-blade flows with interaction

Planar flow past multiple successive blades and wakes is studied for nearly aligned configurations with normal non-symmetry inducing lift. The typical blade lies relatively near the centreline of the oncoming wake from the pr eceding blade. The central motion over a wide parameter range is in condens ed periodic boundary layers and wakes with fixed displacement, buried withi n surrounding incident shear flow. This is accompanied, however, by streamw ise jumps in the pressure, velocity and mass flux, across the leading edge of each blade, a new and surprising feature which is supported by the combi nation of incident shears and a solid surface and which is related to the n ormal flow through the multi-blade system. The leading-edge jumps are requi red in order to satisfy the equi-pressure condition at the trailing edge. C omputational results include separating flows and show the lift and drag, a nd these are followed by a short-blade analysis which captures the main flo w properties explicitly. The results agree qualitatively with experiments a nd direct simulations for rotor blade flows. The jump feature also extends for example to a single blade immersed in the relatively large wake of an u pstream blade.