Novel design and experimental validation of a contraction nozzle for aerodynamic measurements in a subsonic wind tunnel

A novel design for a contraction nozzle, based on a logarithmic profile, is presented and developed to enhance aerodynamic measurements in a low-speed wind tunnel. The improvements obtained with this new proposal are validated, both, numerically and experimentally. As a starting point, four different wind tunnel contraction profiles were firstly considered and tested using the Computational Fluid Dynamics (CFD) package ANSYS FLUENT®. Both polynomial, due to its classical inclusion for wind tunnels, and logarithmic profiles, due to its expected enhancement, have been studied in terms of avoidance of separation of the boundary layer, procurement of a maximum level of exit-flow uniformity, and minimum turbulence levels at the outlet. Numerical comparison between obtained results shows the benefits of the new logarithmic profile developed by the authors, which was finally employed to construct the nozzle. To characterize its real performance, intensive experimental measurements have been conducted using pressure transducers and both single and dual hot wire anemometry. The pressure coefficient along the nozzle sidewall reveals an optimal evolution, matching perfectly with the theoretical design. In addition, low levels of turbulence and high flow uniformity is confirmed at the nozzle discharge. Turbulence intensities below 0.7% are obtained for the whole range of velocities available in the wind tunnel, and even practically constant uniform flow is obtained for all the traverses tested for validation. These indicators conclude that the contraction designed with the new profile is a good enhancing of the wind tunnel benefits.