AN EXPERIMENTAL INVESTIGATION OF INTERFERENCE EFFECTS FOR HIGH BLOCKAGE BLUFF-BODIES IN A SLOTTED-WALL WIND-TUNNEL TEST SECTION

This paper reports on an experimental investigation of interference ef fects when large area and large volume bluff bodies are tested in wind tunnels having longitudinally slotted test-section sidewalls and ceil ing and a solid groundplane. Open area ratios of 30% and 45% were util ized. Three body shapes were tested at zero yaw and pitch angle: flat plates normal to the flow, sharp edged elongated blocks and elongated blocks with rounded edges. Maximum area-blockages and relative body vo lumes were substantially larger than previously tested values. Drag co efficients ranged from 0.25 to 1.2. Interference effects were small to moderate up to very high values of area blockage; 0.36 was the maximu m value tested. Interference effects, when they occurred, could be asc ribed to wall constraint or to upstream and downstream effects due to proximity of the test-section entry and exit. Proximity effects can pr obably be eliminated by use of adequate test section length. Guideline s are suggested. The results indicate that certain body types are more susceptible to wall effects. Guidelines regarding acceptable area-blo ckage limits are suggested.