Experimental investigations on the V/STOL tunnel at NASA/Langley Research Center

The flow characteristics of the V/STOL tunnel were investigated. The results show an interaction between tunnel components. The flow around the tunnel circuit gradually deteriorated with increasing distance from the testing area. The flow in the first diffuser was still satisfactory at the beginning of the circuit, while at the end of the circuit, the flow approaching the contraction became entirely unsatisfactory. Deterioration of flow was due largely to turning the stream around the corners, with the resulting flow distortion affecting the diffusers downstream. The large end of the last diffuser stalled on one side and nearly stalled the flow at the tip of the fan. It was found that these adverse flow characteristics reduce the flow quality and the efficiency of the tunnel.