Experimental investigation of a diffuser for use in skydiving vertical wind tunnel

Abstract

Diffusers are vital components of vertical wind tunnels. In this experimental study, the velocity distribution, pressure recovery coefficient, turbulence intensity, and flow separation of a 1:13 model of a diffuser with an octagonal inlet and square outlet for use in the skydiving vertical wind tunnel have been investigated. The experiments were carried out both in suction and blowing flow modes. Results showed no significant pressure loss and separation in the diffuser under study. Also, the pressure loss results were compared with the results obtained using semi-empirical correlations for a diffuser with a circular inlet and square outlet, which is geometrically the closest to the diffuser under consideration in the present work. It was observed that to correctly predict the pressure loss in the model diffuser using the semi-empirical correlations, the diffuser big-angle plane of 10.66° should be used in these correlations instead of the equivalent cone angle. Besides, if the effect of the non-uniformity of the velocity in the diffuser is not considered in the determination of the pressure loss, a significant error will incur in determining the pressure loss coefficient.