Drag Reduction of High Altitude Airships by Active Boundary Layer Control : Cusp Effect

抄録

The aerodynamic characteristics of station-keeping airships at high Reynolds numbers were examined. The boundary layer flow developed on the hull surface was sucked in by an axial flow fan through a slot located at the rear part of the airship and the sucked-in gas was blown out as a jet. Two models, one with and one without a cusp attached to the inlet of the suction slot, were designed to validate the effects of the cusp. The flow field near the inlet, in particular the pressure on the hull surface, was measured by varying the suction flow rate. We obtained the form drag data by integrating the pressure distribution in a wide range of Reynolds numbers and of suction flow rates. Taking into account the jet thrust and the calculated friction drag, we determined the total drag and evaluated the role of the cusp. It has been found that the effects of the cusp are significant and responsible for reducing the drag.