Research Interests
Dr. Bohl’s research interests are in the development and application of new diagnostic techniques for measurement of fluid flows. His technical interests include: unsteady aerodynamics, vortex dynamics, multiphase flow fields, and the release and dispersion of volatile/hazardous chemicals.
Development of Optical Diagnostic Tools
Diagnostic tools are critical for an experimentalist. The scope and complexity of the problems being investigated are ever increasing. It is, therefore, imperative that the tools used to study these problems also evolve. The development of optical diagnostic tools like Particle Image Velocimetry (PIV) and Molecular Tagging Velocimetry (MTV) has revolutionized experimental fluid dynamics. These techniques allow for simultaneous measurements over a region in a flow field which in turn allows the experimentalist to observe instantaneous flow structures. Dr. Bohl’s research involves the development and advancement of optical techniques for the measurement of fluid flows. He has been an integral part of the multidisciplinary team that developed a novel optical velocimetry technique know as Molecular Tagging Velocimetry, expanding the technique to include stereoscopic measurements and quantification of fluid temperature.
Dynamic Stall
When a lifting surface is placed at a sufficiently high angle of attack (AOA), the fluid flow on the low pressure surface separates causing loss of lift and stall. Static stall typically happens at relatively small angles depending on the shape of the airfoil. It has been shown, however, that for surfaces that are undergoing dynamic pitching, the angle at which the lifting surface stalls is considerably higher. This phenomenon is known as dynamic stall. When dynamic stall is encountered, the loss of lift is abrupt resulting in nearly instantaneous loss of lift.
Dr. Bohl’s research group is active in the investigation and quantification of the flow field around airfoils undergoing dynamic stall. The goals of this work are to understand the effects of pitch rate, aspect ratio and tip conditions of the process of dynamic stall and to develop control strategies to mitigate the effects of dynamic stall. Additionally, Dr. Bohl has been investigating the hydrodynamics of airfoils modified based on the flippers of humpback whales. In recent years engineers have begun to utilize the natural world as inspiration for engineering solutions. Humpback whales are recognized for their high degree of maneuverability given their body size. The leading edges of the humpback whale’s control surfaces (i.e. its flippers) are characterized leading edge protrusions, or tubercles. Studies of the static lift and drag characteristics of airfoils modeled after the humpback whale’s flipper have shown that at angles of attack past the onset of static stall the bio-inspired airfoil showed better performance by “softening” the stall characteristics. It was inferred that the tubercles were inhibiting large scale separation along the low pressure surface. Because Humpback whales use their flippers for dynamic control when swimming and hunting, which are characterized by rapid changes in orientation, Dr. Bohl is investigating the possibility that these bio-adaptations are passive mechanisms for delaying or controlling dynamic stall.
Release and Dispersion of Hazardous Materials
The potential hazards of the transportation of chemicals via rail, road and sea are becoming of interest to many governmental agencies and first responders. This interest is being driven by recent accidents, the increased volume of transportation and because of domestic/international threats. As recent rail accidents have shown, the accidental release of hazardous chemicals can have a significant impact both from loss of life and economic loss standpoints. In the event of a release, protection of the public from these hazards requires real time analysis. Computational simulations are widely used for this analysis; however the key in an emergency is the speed at which the hazard assessment can be made.
Reduced order models are computational codes that simplify the governing equations to gain speed at the expense of not fully accounting for the chemistry and physics of a flow field. Instead these techniques rely on experimentally derived parameters and/or correlations which simulate the physics and chemistry. In many cases the chemicals of interest are highly volatile and/or caustic. They may undergo rapid changes in particle/droplet conditions (e.g. size, shape, state, etc.) due to evaporation, droplet interaction, phase changes, etc. These chemicals pose a difficult problem for low order models as the droplet physics are not well understood and so cannot be adequately modeled. Further, these chemicals are difficult to measure using traditional aerosol sampling techniques due to their caustic nature and the likelihood of changing properties due to physical sampling. Both new techniques to measure the aerosol dynamics and data from controlled experiments are critically needed to develop and validate these computational models.
Flow Induced by Plasma Discharge
Plasmas formed directly in and contacting a liquid are a powerful source of reactive radicals, ions and electrons. Because of their high reactivity, these species have been used to purify drinking water, sterilize food, create new materials, and for applications in plasma medicine. As an example, to purify contaminated water, using only electricity, plasmas split liquid water into powerful radicals and create electrons which are capable of completely destroying toxic molecules. For an environmental group of pollutants with carcinogenic properties called perfluorinated compounds, plasmas have been shown to be the only technology available capable of completely destroying these compounds. Therefore, the development of a plasma-based technology that will rapidly degrade contaminants of emerging concern before they are released into rivers and drinking water supply networks is essential for improving the quality of life.
The goal of this collaborative research project is to quantify the physical and chemical processes occurring at plasma-liquid interfaces. The project combines plasma chemistry and bulk liquid chemistry measurements with fluid dynamic investigations and molecular dynamics simulations to investigate transport mechanisms of plasma excited species and ions across the interface and quantify the interrelationship of these with the bulk liquid. Two specific goals this multidisciplinary approach will achieve are: (1) Correlation of the bulk liquid transport processes with the plasma-liquid interface dynamics and (2) Determination of the significance of the plasma excited species transport in the kinetics of interfacial chemical processes. The central approach for achieving these goals lies in identifying degradation mechanisms of several organic compounds of environmental and biological importance and applying Particle Image Velocimetry (PIV) and Laser-Induced Fluorescence (LIF) imaging to understand the role bulk transport processes play in the dynamics at the interface.