Experiments on the flow past a rotating cylinder

Abstract

Parts 1 -3. In 1925 the writer made a series of measurements of the direction and velocity of the air throughout the field about a rotating cylinder. The resulting velocity contours and streamlines were published at the time, but later the data were worked upto give the distribution of vorticity throughout the field. This was found by graphically differentiating the components of the velocity. Fig. 1 shows the observed air directions and Fig. 2 the vorticity values. The results of calculating the circulation round various contours in this field is shown in Fig. 3. It is seen that there is no very marked change in the circulation outside a contour of about twice the area of the cylinder section. It will also be seen that there is no circulation in the wake as a whole. The upper part contains positive vorticity and the lower an equal amount of (more concentrated) negative. This is in accordance with Prandtl's idea that a state of balance has been attained in the production of positive and negative eddying above and below. The circulation corresponding to the actual lift on this cylinder is about 16 ft./sec. The discrepancy is only apparent as the larger figure obtained in Fig. 3 refers to the centre section, where the lift is 15-20 per cent. greater than the mean as measured on the balance (see R. & M. 1082). As these experiments gave no information regarding the conditions close to the surface of the cylinder, a series of measurements in the boundary layer was made in 1927. These experiments are described in Parts 2 and 3.