2018 Fiscal Year Annual Research Report
Flow instabilities in intersecting geometries
| Project/Area Number |
17J00412
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
BURSHTEIN Noa Batia 沖縄科学技術大学院大学, 科学技術研究科, 特別研究員(DC1)
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| Project Period (FY) |
2017-04-26 – 2020-03-31
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| Keywords | Vortex dynamics / Vortex confinment / Flow instability / Intersecting geometries |
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| Outline of Annual Research Achievements |
This year we have published 2 papers in well known scientific journals. I presented this work in 2 international and 1 domestic conferences.
This past year we have focused on the confinement effect on the onset of symmetry breaking in intersecting geometries.
As we increase the aspect ratio of the cross section of the cross-slot geometry we observe that the critical value in which symmetry breaking occurs is reduced. Our time dependent experiments show that as we impose Reynolds numbers that are close to the critical point, the transition will slow down.
In our well controlled experimental system we found that we can induce merging and splitting of vortices by simply changing the Reynolds numbers of the imposed flow. Vortex dynamics is important in many fields, especially in aerodynamics and turbulent flows.
In our dynamic experiments we found that the merging and splitting of vortices are exponential processes with a rate that depends on the imposed Reynolds number. We show that the confinement of vortices changes the very mechanism in which the merger and splitting process occur.
Additionally, we show that for high aspect ratios where vortices are less confined (confinement is determined by the depth of the geometry), the vortex merging process is faster than the process of vortex splitting. Yet for low aspect ratio where the vortices are highly confined, the merging process is slower than the splitting process. This can be explained by the proximity of the walls that stabilize the flow and act against the vorticity intensification.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project is advancing though with the new collaboration in ESPCI the direction of the research has slightly shifted, yet the preliminary results show a promising direction.
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| Strategy for Future Research Activity |
Currently we are exploring high Reynolds number flow within the cross-slot geometry. Initial observations reveal that at a critical Reynolds number the flow becomes unsteady and periodic with a specific frequency that depends on the aspect ratio. The periodic flow occurs for a certain Reynolds number range. Increasing the Reynolds number to higher values results in an unsteady and a-periodic flow that can be described as chaotic. Our collaborators are currently performing numerical simulations to support our findings.
During my internship at the PMMH lab at ESPCI (Paris, France), we are studying the interaction between large spherical particles (80 micrometers diameter polystyrene particles, ~8% of channels width) and the vortex flow in the cross-slot geometry. Initial observations reveal that for a Newtonian fluid the particles will be evenly distributed in the flow field. This is seen for a symmetric flow field as well as for an asymmetric vortex flow (the particles swirl inside the vortical structure). When adding polymer solution (4MD Polyethylene glycol) at a concentration of 100 ppm, the particles will also be evenly distributed in a symmetric flow field. However, once symmetry breaks and a vortex is formed, the particles will flow around the vortex and will not be able to swirl through the vortical structure. Further experiments will be done this year.
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