PO Box 5725
Potsdam, NY 13699-5725
B.S., University of Connecticut (1992)
M.S., Michigan State University (1996)
Ph.D., Michigan State University (2002)
ES330 - Fluid Mechanics
AE/ME 427 - Design of Propulsion Systems
Dr. Bohl's research interests are in the development and application of new diagnostic techniques for measurement of fluid flows. His background includes: unsteady aerodynamics, flow control, low Reynolds number mixing, spill and dispersion of volatile chemicals and dynamics of energetic materials.
Molecular Tagging Velocimetry (MTV)
In order to better understand the dynamics of fluid systems measurement techniques must be developed to visualize the flow fields. MTV is a whole field optical measurement technique that relies upon molecules that are premixed in the fluid medium that can emit light when excited by photons at the proper wave length. In this technique the patterns are written into the flow medium. Two images are taken during the lifetime of the molecule displacement of the small fluid region is determined via image correlation techniques. The velocity fields are determined knowing the displacement and time between the images.
The above images are a MTV image pair from a vortex ring impinging on a wall. The velocity vectors are the resultant velocity field from the images. (Gendrich et al. 1997)
Stall on lifting surfaces is a fundamental phenomenon in aero and hydrodynamics. In this work the physics of dynamic stall will be investigated experimentally. The goals of the work are two fold. First, dynamic stall will be investigated for finite aspect ratio (i.e. 3-D) lifting surfaces. These results will be compared to published results for infinite (i.e. 2-D) lifting surfaces so that the differences in the flow dynamics, which are not currently well understood, can be described. Second, bio-inspired hydrodynamic shapes will be investigated to ascertain their potential as passive control mechanisms to delay the onset of dynamic stall. The overall goal of the study is to develop an understanding of dynamic stall so that control strategies can be developed and applied to technical problems.
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. While dynamic stall has been investigated in the past for 2-D lifting surfaces there is considerably less work on dynamic stall for 3-D cases. The limited results show that the onset of dynamic stall is delayed for 3-D lifting surfaces compared to 2-D surfaces, though the maximum normal force is reduced. The results are suggestive that there is a change in the structure of the dynamic stall vortex on the 3-D wing due to end effects of the wing. The first objective of the proposed work is to investigate the change in structure of the dynamic stall physics for 3-D lifting surfaces.
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, the PI of the current work hypothesizes that the leading edge protrusions will act to delay the onset of dynamic stall. The second goal of the proposed work is to investigate bio-inspired lifting surfaces for the purpose of delaying of dynamic stall.
Solar Thermal Systems
As human kind searches for renewable/sustainable energy sources Solar Thermal Systems will play an ever increasing role. These systems utilize incident sunlight to create heated fluids. The energy from these heated fluids can be used to provide Domestic Hot Water (DHW) and space heating, but can also be used to provide cooling. Dr. Bohl is a member of the Solar Thermal Consortium which developed a roadmap for the adoption of ST technologies in New York State.
Heat Transfer Control
The coupling of heat transfer and friction are of critical concern in many engineering processes. Considerable amounts of energy are expended to overcome viscous drag. Viscous losses affect both external flows, such as those experienced by aircraft, ships, submarines, and internal flows, such as those found in pipelines, cooling systems, and even in the cardiovascular system. The use of small scale protrusions, known as riblets, on the solid surface for drag control has been well studied. These riblets have found application as boundary layer control devices that reduce skin friction. Another effect they have, that has received much less attention, is the potential to change the heat transfer coefficient. Limited research has shown that riblets can either increase or decrease heat transfer rates. The coupling of these two effects (i.e. drag and heat transfer) via riblets is unknown. We are investigating the relationship between the velocity and temperature fields in turbulent flows near surfaces with riblets to better understand the mechanisms that control heat transfer rates.
Mixing is typically caused by large scale motions in flows associated with turbulence. In the processing of polymers the small scale motions are not available because of the high viscosity of these materials. In this case mixing is a result of large scale stirring action. The quality of the final product is highly dependent upon the homogeneity of the mixture. Currently there is interest in understanding the underlying physics of mixing at low Reynolds number so that more efficient mixing processes can be developed. We are applying optical measurement techniques such as Particle Image Velocimetry (PIV) to these flows to map out the velocity and mixing fields.
The images show the measured vorticity and mixing fields in a simple batch mixer. Motion is driven by the rotation of a flat blade shown by the purple line. Re = 109.
- D.G. Bohl, N. Santitissadeeekorn, A. Mehta and E. Bollt, "Characterization of Mixing Using Experimentally Derived Velocity Fields and Lagrangian Coherent Structures in a Simple Paddle Mixer," Submitted physics of Fluids (July 2010).
- J. Ke and D.G. Bohl, "Effect of Experimental Parameters and Image Noise on the Error Levels in Simultaneous Velocity and Temperature Measurements Using Molecular Tagging Velocimetry/Thermometry (MTV/T)," Accepted Experiments in Fluids (July 2010).
- D.G. Bohl and M.M. Koochesfahani, "MTV Measurements of the Vortical Field in the Wake of an Airfoil Oscillating at High Reduced Frequency," Journal of Fluid Mechanics, Vol. 620, pp. 63-88 (2009).
- N. Santitissadeekorn, D.G. Bohl and E. Bollt, "Analysis and Modeling of an Experimental Device by Finite-Time Lyapunov Exponent Method," Journal of Bifurcation and Chaos, Vol. 19, No. 3 (2009).
- D.G. Bohl, R. Lee and E. Palmero, "Break-Up and Performance of Reactive Materials," D.G. Bohl, R. Lee, E. Palmero, "Break-Up and Performance of Reactive Materials", JANNAF Journal, Vol. 1 (May 2008).
- D.G. Bohl, "Experimental Investigate of the Fluid Motion in a Batch Mixer Driven by a Flat Plate Impeller," Journal of Fluids Engineering, Vol. 149, No.6, pp.137-146 (2007).
- D.G. Bohl and G. Jackson, "Experimental Study of the Spill and Vaporization of a Volatile Liquid," Journal of Hazardous Materials, Vol. 140, No. 1-2, pp. 117-128 (2007).
- D.G. Bohl and R.J. Volino, "Experiments With Three Dimensional Passive Flow Control Devices on Low Pressure Turbine Airfoils," Journal of Turbo Machinery, Vol. 128, pp. 251-260 (April 2006).
- D.G. Bohl and M.M. Koochesfahani, "MTV Measurements of Axial Flow in a Concentrated Vortex Core," Physics of Fluids, Vol. 16, No. 11. pp. 4185-4191 (2004).
- D.G.Bohl, "Experimental Study of the 2-D and 3-D Structure of a Concentrated Line Vortex Array," Michigan State University, Doctoral Dissertation (2002).
- D.G.Bohl, M.M.Koochesfahani and B.J.Olson, "Development of Stereoscopic Molecular Tagging Velocimetry," Experiments in Fluids, Vol. 30, No.3, pp 302-308 (2001).
- D.G.Bohl and J.F.Foss, "Near Exit Plane Effects Caused by Primary-Plus-Secondary Tabs," AIAA Journal, Vol. 37, No.2, pp.192-201 (1999).
Selected Conference Proceedings
- J. Kehs, D.G. Bohl, G. Ahmadi and B. Tavakoli, "Experimental Study of Airflow Around the Syracuse COE Building", Proceedings of FEDSM2009, ASME 2009 Fluids Engineering Division Summer Meeting, Vail, CO August 2-5, 2009.
- B. Tavakoli, G. Ahmadi, D.G. Bohl and J. Kehs, "Computational Modeling of Airflow and Particulate Pollutant Transport Around the Syracuse COE Building", Proceedings of FEDSM2009, ASME 2009 Fluids Engineering Division Summer Meeting, Vail, CO August 2-5, 2009.
- S.E. Powers, B. Brydges, P. Turner, G. Gotham, J.J. Carroll and D.G. Bohl "Successful Institutionalization of a K-12 - University STEM Partnership Program", Proceedings of the 115th Annual ASEE Conference & Exposition, Pittsburgh PA, June, 2008.
- R.J. Lee, K.E. Newman, D.T. Knutson, N. M. McGregor and D.G. Bohl, "Combined Air Blast and Quasi-Static Overpressure Assessment for Pressed Aluminized Explosives", Proceedings of the 13th International Detonation Symposium, Norfolk, VA, July 23-28 (2006).
- D.G. Bohl and R.J. Lee, "Study of the Break-Up and Impact of a Metal/Polymer Composite Material in a Two-Step Process", Proceedings of the 37th International ICT Conference, Karlsruhe, Germany, June 27-30, 2006.
- R.J. Lee, W. Mock, J.R. Carney, W.H. Holt, G.I. Pangilinan, R.M. Gamache, J.M. Boteler, D.G. Bohl, J. Drotar and G.W. Lawrence, "Reactive Materials Studies", Proceedings of the 14th APS Topical Conference on Shock Compression of Condensed Matter, Baltimore, MD (July 31-August 5, 2005).
- R.J. Volino and D.G. Bohl, "Structure of Oscillating Vortex Generator Jets", Proceedings of the 4th International Symposium on Turbulence and Shear Flow Phenomena, Williamsburg, VA (June 27-29, 2005).
- D.G. Bohl and R.J. Volino, "Experiments With Three Dimensional Passive Flow Control Devices on Low Pressure Turbine Airfoils", Proceedings of ASME Turbo Expo 2005, Paper GT2005-68969, Reno, NV (June 6-9, 2005).
- R.J. Volino, D.G. Bohl, "Separated Flow Transition Mechanism and Prediction with High and Low Freestream Turbulence Under Low Pressure Turbine Conditions", Proceedings of ASME Turbo Expo 2004, Paper GT2004-53360, Vienna, Austria (June 14-17, 2004).
- D.G. Bohl and M.M. Koochesfahani, "MTV Measurements of the Flow Structure Downstream of an Oscillating Airfoil", AIAA-Paper 2003-4017 (2003).
- D.G. Bohl and M.M. Koochesfahani, "MTV Measurements of Axial Flow in Concentrated Vortex Cores", AIAA-Paper 2003-0425 (2003).
- M.M. Koochesfahani and D.G. Bohl, "Molecular Tagging Visualization and Velocimetry of the Flow at the Trailing Edge of an Oscillating Airfoil", Proceedings of the 10th International Symposium on Flow Visualization, Kyoto Japan (August 26-29, 2002).
- C. Somerton, D. Bohl, M. Crimp, "Development of an Engineering Teaching Certificate Program", Proceedings of the ASEE 2000 Spring Conference North Central Section, Michigan State University, East Lansing, MI (March 30-April 1, 2000).
- C.P. Gendrich, D.G. Bohl, M.M and Koochesfahani, "Whole-Field Measurement of Unsteady Separation in a Vortex Ring/Wall Interaction", AIAA Paper 97-1780 (1997).