FY2022 Annual Report

Fluid Mechanics Unit
Professor Pinaki Chakraborty



We studied landfalling hurricanes, dynamic boundary-layer flows, and turbulent Taylor-Couette flows.

1. Staff

  • Pinaki Chakraborty, Professor
  • Tapan Sabuwala, Group Leader
  • Julio Manuel Barros Junior, Staff Scientist
  • Kalale Chola, Postdoctoral Scholar
  • Vishnu Ravindran, Postdoctoral Scholar
  • Christian Butcher, Research Unit Technician
  • Florian Fritsch, Research Unit Technician
  • Yuna Hattori, Ph.D. Student
  • Hanley Andrean, Ph.D. Student
  • Tomoe Owan, Research Unit Administrator

2. Collaborations

2.1 Theory of spectral link in turbulent flows

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Gustavo Gioia, OIST

2.2 Turbulent Rayleigh-Taylor instability

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Marco Rosti, OIST
    • Professor Gustavo Gioia, OIST

2.3 Turbulent Taylor-Couette flows

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Gustavo Gioia, OIST


3. Activities and Findings

3.1 Testing the robustness of the climatic signal in the decay of landfalling hurricanes

In previous work (Li and Chakraborty, Nature, 2020), we showed that a warmer climate results in a slower decay of hurricanes past landfall. There, we analyzed field data of the intensity decay of North Atlantic landfalling hurricanes between 1967 and 2018. We have now conducted additional robustness tests of this analysis. This includes analyzing the data at different levels of coarse-graining: from event-level and hurricane-season-averaged data (which use no smoothing) to multi-year smoothed data. Further, we tested the influence of additional factors on the decay. Our analysis showed that the slowdown of decay and its relationship with a warming climate (encapsulated via the sea-surface temperature) are robust results. Our results are reported in L. Li and P. Chakraborty, Reply to: Landfalling hurricanes track modes and decay. Nature, vol. 606, E12-E15, 2022

3.2 Boundary-layer flow over a dynamic boundary

In a vertical soap-film channel, the falling film induces flow in the surrounding air, confined to a thin boundary layer adjacent to the film. In turn, the flowing air exerts a frictional drag on the falling film. Thus, the film flow and airflow are dynamically coupled. We carried out experiments to measure the film flow and the airflow. For the former, we used the standard technique of Laser Doppler Velocimetry. For measuring the airflow, we adapted the technique of super-resolution Particle Image Velocimetry, wherein we simultaneously resolved high shear and high velocities. Our experiments are the first to measure airflow induced by a soap film.

3.3 Friction in rough-walled, turbulent Taylor-Couette flows

Friction in rough-walled, turbulent pipe flows has long been investigated. A storied instance is Nikuradse's classic experiment from 1933, which continues to shape our current understanding of turbulent flows over rough walls. In contrast to pipe flows, friction in rough-walled, turbulent Taylor-Coeutte flows has received scant attention. We have modified the OIST Taylor-Couette setup to measure friction in rough-walled Taylor-Couette flows. One distinctive feature of our experiments is that the roughness is of a single lengthscale, echoing the single-lengthscale roughness of Nikuradse's experiment.  This research is conducted in close collaboration with the Continuum Physics Unit.

4. Publications

4.1 Journals

  1. L. Li and P. Chakraborty. 2022. Reply to: Landfalling hurricanes track modes and decay. Nature, vol. 606, E12-E15. PDF

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

  1. C. Butcher, An all-composing, all-choreographing CD system for LabVIEW, The Independent Graphical Developer Conference 2022, Amsterdam, Netherlands, September 2022.
  2. K. Chola and P. Chakraborty. 2022. Symmetry analysis of the turbulent dissipation rate. Annual Meeting of American Physical Society – Division of Fluid Dynamics (APS–DFD), Indianapolis, November 2022 (Virtual Meeting).
  3. Y. Hattori, K. Chola, J. Barros Jr., C. Butcher, R. Cerbus, and P. Chakraborty. 2022. Boundary- layer flow of air induced by a falling soap film. Annual Meeting APS–DFD, Indianapolis, November 2022 (Virtual Meeting).

5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

6. Meetings and Events

6.1 The New Physics of Fluids

  • Date: January 13, 2023
  • Venue: OIST Campus Lab1
  • Speaker: Prof. Alan Jeffrey Giacomin (Queen's University)

6.2 The 100-Eyes Particle Image Velocimetry and Thermometry Using a Mirror Array

  • Date: March 15, 2023
  • Venue: OIST Campus Lab1
  • Speaker: Prof. Jun Sakakibara (Meiji University)

7. Other

Nothing to report.