An investigation of wall interference blockage in the twisted flow wind tunnel at the University of Auckland

Abstract

Consulta en la Biblioteca ETSI Industriales (8145)

[EN] To get improved agreement between wind tunnel results and full-scale performance, the Yacht Research Unit (YRU) desires to investigate the blockage effect of the TFWT. To do this, different models of various sizes were tested in the wind tunnel and the results of these tests have been compared with theoretical results. The models used were scale models of yachts with solid sails, and scaled airfoils of different sizes (same aspect ratio) placed at various angles to the flow with the test section both open and closed. Steady pressure distributions over the stationary wings were investigated. In order to confirm these results data from the Langley Transonic Cryogenic Tunnel is used as well. In the second part of the investigation, the lift and drag coefficients were measured on two different sized NACA 0015 and a NACA 0012 airfoils, modified with split flaps to check that we were getting the same range of lift and drag coefficients as in the published literature blockage, and to see how increased blockage modified the results in both open jet and closed test section configurations. Finally, a modification in the walls of the test section of the wind tunnel was performed in order to improve the flow quality of the wind tunnel. By comparing the results given by the measurements and the mapping of the dynamic pressure, it is possible to argue in favor or against this modification. Besides, a 2D simplification of the TFWT was calculated with CFD for a qualitative study of the patterns of the flow. It was found that the results obtained with the slotted walls test section were closer to the closed test section results than to the open test section results. It was also found that the pressure surrounding the test section as a result of the warehouse housing of the TFWT magnifies the expected over-expansion of the flow in the open test section and therefore the difference between this and the measurements in the closed and slotted test section. Thus it is finally recommended that slotted walls be installed as a first step to improve the TFWT quality.