EFFECTS OF LARGE BLOCKAGE IN WIND-TUNNEL TESTING

Wind tunnels play an integral role in the aerodynamic development and refinement of virtually all airplanes and of numerous ground vehicles. Their advantage lies in the ability to generate a variety of conditions in terms of airspeed, angles of attack, and sideslip in a well-controlled environment. Test conditions are independent of atmospheric changes and testing equipment is abundant and stationary, compared to some of the limitations during a flight test of an instrumented airplane. However, the fact that a model is being confined into a limited-size environment brings to light the first and most important conflict. One side of this conflict emerges from the need to reduce the operating costs of the testing facility. This requirement translates to a reduction in test-section size and drive power. In addition, as the windtunnel size increases, environmental difficulties may arise and some full-scale facilities must be placed in isolated research centers, at a safe distance from residential areas. The other side of the conflict is rooted in the need to increase model size to facilitate accessibility, while at the same time keep tunnel boundaries “sufficiently” far from the model. Furthermore, circumstances may occasionally require the testing of models that are larger than intended by the designers of a particular facility. And there always must be a compromise between model designers wishing to test the largest possible model and the available wind-tunnel facility with an existing test section. © 1995 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.