Scalar Plumes and Mosquito Orientation
Host-seeking female mosquitoes utilize a variety of sensory cues to locate potential hosts. In addition to visual cues, these signals include CO2, volatile skin emanations, humidity, and thermal cues, each of which can be considered as passive scalars in the environment, primarily distributed by local flow conditions. The behavior of host-seeking female mosquito vectors can be more thoroughly understood by simulating the natural features of the environment through which they navigate. In order to bridge between laboratory findings and the natural, ecologically relevant setting, a unique active flow modulation system consisting of a grid of independently operated paddles was developed. Unlike static grids that generate turbulence within a predefined range of scales, an active grid imposes variable and controllable turbulent structures onto the moving air by synchronized rotation of the paddles at specified frequencies.
This research focuses on designing and manufacturing MEMS devices for turbulence measurements (both scalars and vectors). Conventional sensors suffer from limited spacial and temporal resolutions in high Reynolds number flows or in the near-wall regions of wall-bounded flows. Development of MEMS technology enables mass-production of smaller sensors that can improve sensing resolutions as well as to probe regions of interest that conventional technology could not reach. Yuyang is currently developing MEMS hot- and cold-wires for more accurate turbulence velocity and temperature measurements, as well as sensors to measure humidity in gaseous environment.
Wind Turbine Wakes
With the newest wind turbines reaching 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 the interplay of the three important non-dimensional numbers, namely the Reynolds number, Tip Speed Ratio, and the Mach number. In traditional, small-scale wind tunnels these three parameters are impossible to match with the full-scale values.
The novel aspect of Alex's work in the Hultmark lab involves using a high-pressure wind tunnel in which the density can be varied, and thus the Reynolds number can be adjusted independently of the Tip Speed Ratio. With this facility, Alex is able to completely match the flow of full-scale wind turbines in a small, laboratory environment. In addition, this facility is instrumented with a hot-wire traverse which allows detailed studies of the turbine wake. Future work will involve studying the effects of tip speed ratio and turbulent inflow using a grid on turbine wake evolution.
Supersonic Flow past a Cylinder
Madeline Vorenkamp is studying the wake oscillations characteristic of a supersonic flow past a cylinder. Specifically, she is working to correlate the Strouhal number of the wake to various characteristic dimensions of the flow. High speed Schlieren videos are taken, using a Phantom V2020 camera on loan from Professor Luc Deike, at 200,000 fps. The image sequences are then processed using Fourier analyses.