The measurement of ground effect using a fixed ground board in a wind tunnel

Abstract

An experimental and theoretical investigation is made of the method of determining the effect of ground proximity in a wind tunnel using a fixed board to represent the ground. The influence which the boundary layer on the fixed ground board has on the flow about the model has been determined from overall force measurements on three models of aspect ratios 1.6, 3 and 8 and the twodimensional configuration has been solved theoretically. These measurements and calculations show that the boundary layer influence is most significant at the lower aspect ratios and for these configurations an experimental procedure is proposed which enables this influence upon the data to be eliminated. The form of the threedimensional boundary layer which grows on a fixed ground board beneath a low aspect ratio model is discussed and the reason for its influence upon the model explained. A brief discussion of the form of the threedimensiona! boundary layer which will grow on a runway as an aircraft passes by is given and the case of infinite aspect ratio (twodimensional flow) has been analysed theoretically.