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Low-Speed Wind Tunnel

Optimizing Spray

The U.S. Environmental Protection Agency will now accept and review results from spray drift experiments in the University of Dayton Low-Speed Wind Tunnel.

According to assistant professor and lab director, Sidaard Gunasekaran, "With our facility, clients can test nozzle, pressure and tank mixture for applying treatments, and use the data to accurately predict the drift potential in the field."

sid-windtunnel.jpgDuring testing, the wind tunnel is set to 15 miles per hour and the sprayer is set to the EPA-approved pressure for the mixture and nozzle being tested. The droplet size information is used to understand the drift potential of each test combination.

Adverse Effects of Lift-Induced Drag

Adverse effects of lift-induced drag on the aerodynamic efficiency of aircraft are well known. Lift-induced drag is generated as a byproduct of downwash from the wingtip vortices. We explored the flow physics associated with wingtip vortex core axial flow transformation from wake-like (velocity less-than the freestream) to jet-like (velocity greater-than the freestream) behavior in the vicinity of the maximum lift to drag ratio (L/D) lift condition.

Particle Image Velocimetry (PIV) experiments were performed at the University of Dayton Low-Speed Wind Tunnel in the near wake of an AR 6 wing with a Clark-Y airfoil to investigate the characteristics of the wingtip vortex at angles of attack ranging from 2° and 8°. Results showed changes in the velocity distributions in the vortex inner and outer cores. Vorticity and exergy distributions indicated the existence of the wake-like to jet-like transformation in the range of 4° to 6° angle of attack. This range corresponds with the maximum L/D angle of attack of the Clark-Y tested. A relationship between the vortex core axial velocity profile changeover and the angle of attack at maximum L/D was identified. Improved understanding of this relationship could be extended not only to improve aircraft performance through the reduction of lift induced drag, but also to air vehicle performance in off-design cruise conditions.

Errors in Off-Axis Loading
Significant, repeatable errors can result when loading off-the-shelf 6-component force transducers at relatively short distances off-axis. A number of permutations of off-axis loading were investigated to better elucidate the cause of the error. The magnitude of the measurement error provides substantial incentive to produce an independent sensor interaction matrix when test circumstances dictate similar off balance center loading.

Wind Tunnel Blockage Corrections

An investigation into wake and solid blockage effects of vertical axis wind turbines (VAWTs) in closed test-section wind tunnel testing is described. Static wall pressures have been used to derive velocity increments along wind tunnel test section which in turn are applied to provide evidence of wake interference characteristics of rotating bodies interacting within this spatially restricted domain. Vertical-axis wind turbines present a unique aerodynamic obstruction in wind tunnel testing, whose blockage effects have not yet extensively investigated. The flowfield surrounding these wind turbines is asymmetric, periodic, unsteady, separated and highly turbulent. Static pressure measurements are taken along a test-section sidewall to provide a pressure signature of the test models under varying rotor tip-speed ratios (freestream conditions and model RPMs). Wake characteristics and VAWT performance produced by the same vertical-axis wind turbine concept tested at different physical scales and in two different wind tunnels are investigated in an attempt to provide some guidance on the scaling of the combined effects on blockage. This investigation provides evidence of the effects of large wall interactions and wake propagation caused by these models at well below generally accepted standard blockage figures.

Post-Stall Performance Improvement
Inspired by birds’ covert feathers, previous research has shown that artificial self-deployable flaps placed on the suction surface of wings can act as a passive boundary layer flow control mechanism improving post-stall wing lift performance by as much as 15%. Parametric variations are performed in this study, to investigate the range of effectiveness of these artificial flaps.Subsequent experiments and complementary XFoil investigations revealed that each wing will respond differently to the placement of the artificial feathers depending on the wing’s stall characteristics, boundary layer thickness, and pressure distribution

Low-Speed Wind Tunnel, Dr. Sidaard Gunasekaran, Director

Kettering Laboratories
300 College Park
Dayton, Ohio 45469