Simplified tunnel correction method

Abstract

Introduction I N wind-tunnel testings, large models relative to the test section size present challenging problems, known as wall effects. In this study, the classical method was used to correct wind-tunnel data for downwash due to the walls, in conjunction with the classical method of blockage correction to account for the increased velocity due to the presence of the model and wake in the test section. The classical method of blockage correction requires the obtaining of factors or constants from published documents that may or may not be available to users of this method. In some cases, this correction method cannot be applied on-line, depending on the test program. This Note presents a simple and effective method of applying blockage corrections to the aerodynamic characteristics of airplane models tested in low-speed wind tunnels with closed test section. The method does not require reference to other documents, and the applicability of the method was experimentally investigated, using two complete airplane models; one with a rectangular wing and the other with a delta wing. The method is suitable for on-line processing. The validity of the correction methods used was examined by comparing the corrected data obtained in a typically large model-to-tunnel size ratio testing environment with those acquired in a near free air testing configuration. Experiments proved the results of this simplified method to be equivalent or superior to those of the classical method.