Drag Reduction: SLIPS
Graduate Student: Matthew Fu
Matt Fu is conducting research into the role of the wall boundary conditions in governing transport from the wall to the free stream. Specifically this research seeks to establish how momentum transport is affected when the "no-slip" boundary condition is replaced with various "slip" boundary conditions. These results hopefully further our understanding of wall-turbulence interaction to better develop passive flow control surfaces to control drag or mixing. The current work utilizes Liquid Infused Surface [LIS], Superhydrophobic Surfaces [SHS] and Slippery Liquid Infused Porous Surfaces [SLIPS], which have been shown to reduce drag through this slip effect, and seeks to model how their surface morphology and lubricant properties affect the magnitude of their effective slip. The resulting models can be validated in a table-top, high shear, channel flow facility outfitted for interchangeable surface slides.
Graduate Student: Yuyang Fan
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.
Turbulent Heat Transfer
Graduate Student: Clayton Byers
Clay is performing research in turbulent boundary layers with temperature as a passive scalar. The investigation utilizes mathematical techniques previously developed for the velocity field, but applied to the temperature field to understand the possible functional forms of the temperature distribution. Analysis also includes the temperature variance, with future work to include the turbulent heat flux parameters. The theory is then applied to experimental results obtained in the Princeton water channel located at the Forrestal campus. The data is collected using the novel nano-scale sensors developed within this lab. In addition, investigation into the nano-scale sensors and their design and characteristics is being conducted, with the goal of maximizing their use and fine tuning their design.
Turbulent Boundary Layer in Compressible Flow
Graduate Student: Katherine Kokmanian
Katherine's interest in compressible flow combined with the important concept of boundary layers has led her to investigate turbulent boundary layer theory in compressible flow. Her objectives include developing a relationship for the velocity and temperature fields using a similar process to that of incompressible flow. After having completed her theoretical work, she will be running experiments in Princeton's hypersonic wind tunnel (Mach 8) with the intent of collapsing her data with the developed theory.
Wind Turbine Aerodynamics
Graduate Student: Mark Miller
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.
Research Assistant: Janik Kiefer
The novel aspect of Mark and Janik'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 Mark and Janik are able to completely match the flow of full-scale wind turbines in a small, laboratory environment. Future work will investigate the Reynolds number dependence of the power and thrust loading on the turbine. In addition, this facility is instrumented with a hot-wire traverse which allows detailed studies of the turbine wake. Such aspects as wake expansion, stability, and turbulence levels under controlled conditions can all be studied. The results of these experiments aim to improve numerical simulations and engineering design codes used for wind turbines.
Large-Eddy Simulations of Wind Tubines
Graduate Student: Tara Nealon
Large-eddy simulation (LES) is a turbulence modeling technique used in computational fluid dynamics (CFD) in order to reduce the high computational costs associated with turbulent flows due to the wide range of scales that exist in these types of flows. In LES, a low-pass filter is applied to the Navier-Stokes equations in order to use these equations to compute only the effects of the larger scales. The effects of scales smaller than the cut-off filter width are then modeled instead of directly computed in order to capture the transfer of energy between scales. In order to properly simulate wind turbines, a turbulence model must be applied since turbine wakes are turbulent. In order to simplify the simulations, wind turbines can be modeled using an actuator line model (ALM), in which turbine blades are represented as rotating lines of points where the effects of the blades on the flow are computed. Tara is currently collaborating with a group at Johns Hopkins University led by Charles Meneveau in order to increase the accuracy of LES of wind turbine models by comparing the results obtained from Mark and Janik's experiment with the results obtained by modeling the same turbine using the LES code.