Computational Analysis of Diffuser Performance for Subsonic Aerodynamic Research Laboratory Wind Tunnel

Abstract

Improving the efficiency of the Air Force Subsonic Aerodynamic Research Laboratory (SARL) wind tunnel with the use of alternative diffuser geometries is investigated. A previous analysis of head losses throughout the tunnel has shown that approximately thirty percent of losses through the tunnel occurred at the exit of the tunnel (Britcher, 2011). In the present work, two separate diffuser geometries, identified after precursory calculations made using SolidWorks, were computationally evaluated using the ANSYS FLUENT CFD code to determine their efficiency improvement with respect to the original tunnel geometry and with respect to each other. Computations were made on the full scale model of the fan duct and the diffuser sections with an average inlet velocity of sixty meters per second, using both uniform and fully developed velocity profiles at the entrance of the fan duct since the velocity profile in the SARL tunnel is not known. The results indicate that a 3.5° half-apex angle conical diffuser followed with tubular and annular conical section with dividers results in the least total pressure loss. The calculated percent head loss reductions for this diffuser geometry range from 14.9% to 20.9% over the existing SARL diffuser geometry. For the entire SARL tunnel, this corresponds to a substantial 5.2% to 7.3% efficiency improvement.