RESEARCH PROJECTS

Dynamic Stall

Dynamic stall is an unsteady aerodynamic phenomenon that occurs when an airfoil undergoes a pitching or heaving motion. It is associated with the formation and convection of a vortex from the surface of an airfoil. This phenomenon is still not completely understood due to the complex, non-linear physics of the boundary layer. Victoria is studying the effects of chord Reynolds number (Re), wing three-dimensionality, airfoil shape, and airfoil kinematics on an airfoil undergoing dynamic stall in the variable-density High Reynolds number Test Facility (HRTF). By scaling pressure instead of velocity, the experiments bypass compressibility and time-scale challenges faced by unsteady aerodynamic studies in traditional wind tunnels operating at high Re and atmospheric pressure. Her findings are pertinent to large and small-scale aeronautics, wind energy, and biological flows.

Under natural conditions, many flying insects locate resources vital to survival and reproduction by responding to, and tracking, plumes of scalar cues present in their surroundings (e.g. odors, humidity, temperature, carbon dioxide). The spatio-temporal distribution of the scalar field is a function of turbulence and unsteadiness, that introduce a large range of length and time scales into the flow present in the atmospheric boundary layer (ABL) or in-built environments. Yet, we know very little about the behavioral strategies by which insects accomplish this remarkable feat under the turbulent conditions characteristic of natural habitats. Much of our current understanding of the insect behavioral mechanisms come from no-flow, limited flow, or laminar-flow wind tunnel experiments. Addressing this limitation would have several important implications, including deployment of optimized distraction strategies and innovative tracking strategies for autonomous vehicles in hazardous environments. We are measuring the flow conditions correlated with mosquito activity with an in-house very-large scale bubble velocimetry through field measurements at the Salt lake City Mosquito Abatement District at Utah. In order to reproduce these conditions for controlled wind tunnel studies, a novel, cost-effective turbulence generating grid is under development.

As modern wind turbines continue to grow to sizes of nearly 200 meters in diameter, it becomes increasingly difficult to perform computer simulations or laboratory experiments which match all of the governing parameters simultaneously. Prior work has been limited by tradeoffs inherent in the three important non-dimensional numbers for wind-turbine aerodynamics, namely the Reynolds number, tip-speed ratio, and Mach number. In traditional small-scale wind tunnels, these three parameters are impossible to match with the full-scale values. Researchers in the Hultmark lab are using a high-pressure wind tunnel in which the density can be varied, such that the Reynolds number can be adjusted independently of the tip-speed ratio. With this facility, they are able to match the flow physics of full-scale wind turbines in controlled laboratory conditions. The facility is instrumented with a hot-wire traverse which allows detailed studies of the turbine wake. Topics of investigation include the dynamics and wake structure of yaw-misaligned turbines, differences between actuator-disc and turbine wake profiles, and the effects of dynamic induction control on wake recovery.

Prior work in the Princeton superpipe has been limited to pipe flow measurements. With Ian's work, an axisymmetric body of revolution that traverses in the streamline direction has been added to the centerline of the superpipe. His research involves studying how Reynolds number, pressure gradients, streamline convergence/divergence, and streamline curvature affect turbulence. Ian is also looking at how Reynolds number affects wake development and recovery.