Optimization of contraction cone length in an open-circuit wind tunnel

Abstract

The studies in the literature mostly focus on the curvature of the contraction cone, while research regarding the impact of contraction length on flow characteristics is limited. This study aims to determine the optimal length of the contraction cone, which ensures uniform flow at the outlet section, considering the wall shear factor. Four contraction cones of varying lengths were designed based on the hydraulic radius of the inlet. Numerical analysis was conducted to obtain static pressure and velocity distributions for the designed geometries. It was observed that wind tunnels designed with contraction cone lengths 2, 3, and 3.5 times the inlet hydraulic radius exhibited similar flow patterns. However, a longer contraction curve minimizes flow disturbances and turbulence, thereby enhancing flow uniformity and steadiness, while thicker boundary layers result from increased wall shears due to boundary layer growth. Consequently, it was concluded that a wind tunnel configured with a contraction cone length of 2 times the inlet hydraulic radius (square contraction cone) is the optimal choice, considering the combined effects of wall shear and flow uniformity.