Performance of the tolerant tunnel for bluff body testing

A new passive form of low-boundary-correction wind tunnel test section is under development. In the version designed for testing two-dimensional bluff bodies the two boundaries opposite the model under test consists of arrays of evenly spaced airfoils at zero incidence. The spacing is selected so that the outer streamlines of the test section flow can pass into an outer plenum and return to the test section downstream, in such a way that the overall streamline pattern closely approximates the corresponding free-air pattern. The design is passive in that a fixed optimized boundary configuration is used for all sizes and shapes of test model. The theoretical background of the design is described, and experimental pressure distributions are presented for several sizes each of normal flat plates, circular cylinders, and circular cylinders with splitter plates, over a range of boundary airfoil spacings. It is shown that a single optimal spacing exists for which the pressure distributions for all sizes of each bluff body shape collapse onto or very close to appropriate reference curves representing unconfined flow conditions.