High-blockage corrections for circular arcs at transitional Reynolds numbers

Abstract

Model-scale testing might suffer from blockage effects due to the finite dimensions of the test section. Measurements must be corrected to predict the forces that would have been measured in unconfined conditions. Blockage corrections are well-established for streamlined and bluff bodies, while more data is needed to develop corrections for bodies that generate both high lift and large wakes. In this work, towing tank and water tunnel tests of two-dimensional circular arcs are employed to develop a correction for a blockage ratio, i.e. the ratio of the frontal area of the geometry to the cross-sectional area of the test section, up to 0.2477. Experiments are conducted at positive incidences between the ideal angle of attack and deep-stall at transitional Reynolds numbers from 53 530 to 218 000. The results show that a linear blockage correction can be devised for the whole range of tested blockage ratios. Furthermore, the critical angle of attack and Reynolds number at which the force crisis occurs is independent of the blockage ratio. These results may allow extending the range of model sizes that can be tested in water and wind tunnels and may contribute to the accurate accounting of blockage effects at transitional Reynolds number conditions.