A Study of Leading Edge Shapes for the Front Duct of a Dual Ducted Fan Vehicle

An experimental investigation was undertaken in an effort to redesign the leading edge of the front duct for dual ducted fan vehicles. Two different shapes are evaluated. The first is a typical blunt nose shape seen on most ducted fan vehicles. This is to serve as a baseline for other shapes that are tested. The second shape is an extended nose, which forms a more streamlined shape. Flow visualization via a smoke wire is performed for qualitative data. Flow velocity within the front duct is then examined with the use of a 5-hole pitot probe, kiel probe, and hot wire. The lift and drag of the vehicle are measured with the use of a force and moment balance. Separation over the front lip of the baseline model is made evident by both the flow visualization and flow measurements. Flow separation is still apparent with the streamlined nose when flow visualization is performed. However, flow velocity measurements reveal higher velocities in the forward portion of the front fan; a 50% increase is measured at the lowest advance ratio. This suggests decreased separated flow with the streamlined nose. Examining the lift and drag of the two shapes showed very little change. Only at a pitch of -10 degrees, a rotor RPM of 8000, and a forward velocity of 20 m/s did the streamlined nose show an improvement in lift. Any changes in drag are small enough to be neglected.