Aerodynamic design of three-dimensional contraction for low-speed wind tunnel

This study presents a systematic parametric investigation aimed at optimizing the contraction design for a large low-speed wind tunnel. The numerical study is undertaken by relating the geometric and performance parameters of a contraction nozzle to satisfy a certain set of design criteria. The Computational Fluid Dynamics (CFD) simulations were performed in ANSYS Fluent by solving the Reynolds Averaged Navier-Stokes (RANS) approach coupled with the Shear Stress Transport (SST) k-ω turbulence model. Contraction design charts were developed for three different test section flow speeds (10 m/s, 25 m/s, and 75 m/s). The range of geometrical parameters explored includes contraction length (L/D) from 0.8 to 1.6, match point location (X) from 0.2 to 0.8, and polynomial power factors ( n 1 and n 2 ) ranging from 3 to 9. An optimal combination of these parameters effectively prevents boundary layer flow separation around the entrance, while also minimizing boundary layer thickness and velocity field nonuniformity downstream of the exit. Notably, transitioning from a square-to-rectangular cross-section to an octagon-to-octagon cross-section significantly enhances the flow quality in the test section. The contraction with an octagonal cross-section, characterized by n 1 = 3, n 2 = 6, L/D = 1.02, and X = 0.575, meets all design criteria and is proposed as the optimal choice for a large low-speed wind tunnel with a contraction ratio (CR) of 9.