Simulation of the flow past a model in the closed test section of a low-speed wind tunnel and in the free stream

Abstract

The flow around a model in the closed test section of a low-speed wind tunnel has been analyzed in 2D approximation. As the contour of the nozzle, test section, and diffuser, the contour of the T-324 wind tunnel, of the Khristianovich Institute of Theoretical and Applied Mechanics (ITAM SB RAS, Novosibirsk), in its symmetry plane was adopted. A comparison of experimental with calculated data on the distribution of velocities and dynamic pressures in the test section is given. The effect due to the sizes of a model installed in the test section on the values of the aerodynamic coefficients of the model is analyzed. As the aerodynamic model, the NASA0012 airfoil and the circular cylinder were considered. For the airfoil chord length b = 20 % of nozzle height, the values of the aerodynamic coefficients of the airfoil in the free stream and in the test section proved to be close to each other up to the angle of attack a = 7°, which configuration corresponds to blockage-factor value ξ ≈ 7 %. The obtained data are indicative of the expedience of taking into account, in choosing the model scale, not only the degree of flow passage area blockage by the model but, also, the length of the well-streamlined model. In the case of a strongly blunted body with a high drag-coefficient value, the admissible blockage factor ξ may reach a value of 10 %.