| NSF Org: |
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems |
| Recipient: |
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| Initial Amendment Date: | December 6, 2021 |
| Latest Amendment Date: | December 6, 2021 |
| Award Number: | 2152596 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Ron Joslin
rjoslin@nsf.gov (703)292-7030 CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems ENG Directorate for Engineering |
| Start Date: | December 15, 2021 |
| End Date: | November 30, 2024 (Estimated) |
| Total Intended Award Amount: | $266,011.00 |
| Total Awarded Amount to Date: | $266,011.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
3112 LEE BUILDING COLLEGE PARK MD US 20742-5100 (301)405-6269 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
3112 LEE BLDG 7809 Regents Drive College Park MD US 20742-1800 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
CFS-Combustion & Fire Systems, FD-Fluid Dynamics |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
This project was inspired by the discovery and ongoing study of the blue whirl, an apparent breakdown mode of a fire whirl in which it unexpectedly transitions to a small and seemingly benign blue flame. The blue whirl produces no soot and minimal pollutants, suggesting optimal burning and a potential source of clean energy. Creating a blue whirl without having to pass through the fire whirl state would enable a safe and clean form of hydrocarbon combustion that could be used in combustors, for propulsion, or for controlled burns (e.g., oil spill clean-up). More broadly, because vortex breakdown occurs in a wide variety of applications, a better understanding and ability to control and predict its dynamics has broad implications for many fluid dynamics systems affected by this instability. Controlling vortex breakdown would enable higher force production and enhance aerodynamic stability on wings and blades ranging from small-scale micro air vehicles to large-scale wind turbines, as well as more robust pump operation in cooling and emergency operations. This project aims to characterize and quantify the process of vortex breakdown in an incompressible non-reacting flow, and to identify mechanisms by which breakdown might be controlled via a new type of experiment wherein energy (in the form of heat) is introduced into the core of a vortex flow.
The objective of this project is to experimentally demonstrate the effect of heat injection on vortex breakdown in a non-reacting incompressible flow, and to evaluate the parameter space over which heat addition has a measurable effect on the breakdown process and final state of the flow. A new type of vortex breakdown experiment will be developed to enable time-resolved velocity field measurements in a swirling flow with variable temperature (and thereby density) gradients. Complementary numerical simulations (performed by collaborators X. Zhang and E. Oran) will provide guidance in the development of the experimental facility and test matrix, and will make it possible to explore regions of the parameter space not easily achieved in the laboratory. Results from these experiments will include quantitative time-resolved measurements of the changes in flow structure during the process of vortex breakdown, with and without heat injection. The proposed experiments are expected to provide new physical insight into the process and mechanisms of vortex breakdown to inform theories and scaling laws, allowing for a generalization of the results gained here towards new methods of vortex control.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Vortex breakdown occurs in many flow applications such as weather, aerodynamics, swirl combustors, and more. When it occurs, it introduces an unsteadiness that is often undesired and may be catastrophic. While vortex breakdown has been previously investigated extensively, much of this work was performed some time ago and researchers often struggled to efficiently quantify and characterize these flows due to the flow’s sensitivity to intrusive probes. As such, there is no real consensus regarding the breakdown process and the evolution of the resulting flow structures. Recently, researchers in the field of reacting flows have discovered the blue whirl, a silent and efficient flame that they believe is a mode of vortex breakdown. It has been suggested that there exist mechanisms of flow control, perhaps via heat addition or extraction, that may stabilize or prevent the formation of this flame structure. The current work uses modern time-resolved and non-intrusive flow measurement techniques to investigate vortex breakdown at high temporal and spatial resolution than have previously been possible.
Results from the current work demonstrate the effect of heat addition at the inflow of a standing vortex on the onset and behavior of breakdown modes. Smoke flow visualization experiments were preformed to identify the effects of heating and swirl rate on standing vortex flows. Decreasing the incoming swirl was found to delay or fully suppress the formation of a bubble-mode vortex breakdown. Increasing the inlet temperature had a similar effect, likely due at least in part to buoyancy effects on the flow, increasing the axial velocity thus reducing the effective swirl. 3D Particle Tracking Velocimetry was used to obtain time-resolved flow fields of the vortex flow and breakdown with and without heating. Individual velocity profiles and velocity fields are reported, showing that flow behavior is dependent on much smaller flow scales than have previously been studied.
Last Modified: 04/25/2025
Modified by: Anya Jones
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