Effects of end plates and blockage of structural members on drag forces

Abstract

The aerostatic and aerodynamic characteristics of structural members were investigated using two-dimensional wind tunnel tests. In these tests problems occur owing to the effects of end plates and blockage. End plates are used to produce two-dimensional flow around models. There is an optimum size for end plates, because the degree of the two-dimensional characteristics of the air flow depends on the size of the end plates. The required condition for the end plates was determined by measurement of the wind velocity distributions and base pressures around the testing body in relation to the formation of the wake. It is concluded that the required dimensions of the end plates can be determined on the basis of Kármáns theory of vortex streets. In practice, the diameter of the end plate should be larger than 8.5 times the model depth. On changing the blockage ratio with end plates of a constant size, the aerostatic forces change significantly. This is the result of the combined effects of end plates and blockage.