Effect of Wind-Tunnel Walls on the Drag of a Sphere

The wind-tunnel wall interference effect on the drag and base pressure coefficients is investigated experimentally in the range of Reynolds-number independence. The drag results of Achenbach for large blockage ratios are also included, thus covering a range of blockage ratio between 6.3 to 83.9 percent. The measured drag is corrected using blockage correction formulas for three-dimensional flow obtained by the method of images and the analytical equation of Maskell. The results given by Maskell’s method are found to be under-corrected by up to 20 percent and the method of images is totally inadequate. Replacing the blockage factor, ε, in Maskell’s equation by an empirically determined value improved the corrections considerably.