FY2018 Annual Report

Fluid Mechanics Unit
Professor Pinaki Chakraborty

 

Abstract

The Fluid Mechanics unit pursued research on turbulent flows, atmospheric flows, planetary flows, and granular flows, and continued to develop a joint fluid mechanics--continuum physics laboratory.

1. Staff

  • Pinaki Chakraborty,  Professor
  • Julio Manuel Barros Junior,  Staff Scientist
  • Rory Cerbus,  Staff Scientist
  • Tinihau Meuel,  Postdoctoral Scholar
  • Christian Butcher,  Research Unit Technician
  • Yuna Hattori,  PhD Student
  • Lin Li,  PhD Student
  • William Powell,  PhD 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 Granular cratering

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Gustavo Gioia, OIST
    • Dr. Tapan Sabuwala, OIST

2.3 Experiments on turbulent pipe flows

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Gustavo Gioia, OIST
    • Jun Sakakibara, Meiji University, Japan

2.4 Experiments on Taylor-Couette flows

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Dr. Yasuo Higashi, OIST
    • Professor Gustavo Gioia, OIST

3. Activities and Findings

3.1 Frictional drag in two-dimensional turbulent flow over rough walls

The scaling of the frictional drag in three-dimensional (3D) turbulent flows over rough walls is governed by the well-known Strickler scaling law. Although known for over a century and used in legions of applications, this law had remained purely an empirical law until the last decade. The spectral theory of frictional drag showed that the frictional drag over rough walls is but inextricably linked to the spectral exponent of turbulence. Its prediction for 3D turbulence is the famous Strickler law, but, the theory implies, if the spectral exponent changes, so would the Strickler law. To test this prediction, we turn to two-dimensional turbulent flows with enstrophy cascade whose spectral exponent is disparate from that of the energy cascade of 3D turbulence. To that end, in collaborative work with the University of Bordeaux, we are conducting experiments in a soap-film channel where the channel walls are rough.

3.2 Small-scale universality in transitional pipe flows

Kolmogorov's postulate of "small-scale university" furnishes an extraordinary insight into the complexity of turbulent flows. Building on this postulate, Kolmogorov predicted universal statistics for the small scales of turbulent flows, irrespective of the particular flow. Over the past half century, these predictions have been verified by legions of experiments and computational simulations. These verification efforts have focused on ideal conditions (meaning, homogeneous and isotropic flows at very high Reynolds numbers) because Kolmogorov assumed that these conditions would be needed for the postulate to hold. These stringent restrictions suggest that that Kolmogorov's theory is unfortunately only valid for a small subset of flows. Using experiments and simulations that span a wide range of Reynolds number, we show, for the first time, that Kolmogorov’s predictions are valid in a flow with no apparent ties to Kolmogorov’s ideal flow: transitional pipe flow, which is a relatively low Reynolds number and inhomogeneous (segmented along the flow direction and fully circumscribed by walls) flow. Our results not only extend the universality of Kolmogorov’s framework beyond expectation, but also establish a link between transitional pipe flow and Kolmogorovian turbulence.

3.3 A new model to predict impactor diameter in rayed craters

A central question in planetary geology is: what was the diameter of the impactor that formed a given crater? Current models that predict the impactor diameter rely on a number of ill-constrained parameters, which can translate to large variations in the predicted value. Building on our research on granular cratering, we propose a new and simple model to predict the impactor diameter. Specifically, we use the geometric model that we developed in FY2017, which model links the number of prominent rays in a rayed crater to the crater diameter and the target surface topography. By knowing the number of prominent rays and surface topography, we predict the impactor diameter. We test this model on a number of lunar craters. Our predictions, which rely only on geometry, are in good accord with the corresponding best estimates from current models.

4. Publications

4.1 Journals

  1. Sabuwala, T., Butcher, C., Gioia, G., Chakraborty, P. (2018) Ray Systems in Granular Cratering. PHYSICAL REVIEW LETTERS, vol. 120, 264501-1 to 264501-5, DOI: https://doi.org/10.1103/PhysRevLett.120.264501

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

  1. Butcher, C., Wachno, O., Evolving from Quick Coding to Good Architecture and Clean Code, NI Week 2018, Austin, Texas, US, May 23 (2018)
  2. Gioia, G., Cerbus, R., Liu, C., Chakraborty, P., Kolmogorovian turbulence in transitional pipe flows, Kyoto University, Kyoto, Japan, July 19 (2018)
  3. Cerbus, R., Li, L., Sakakibara, J., Gioia, G., Chakraborty, P., Slug flows in transitional pipes, Kyoto University, Kyoto, Japan, July 19 (2018)
  4. Sabuwala, T., Powell, W., Ray systems in granular cratering, Granular Matter Gordon Research Conference, Stonehill College in Easton, MA, USA, July 24 (2018)
  5. Butcher, C., API Design Choices, GDevCon, Cambridge, UK, September 5 (2018)
  6. Chakraborty, P., Cerbus, R., Liu, C., Gioia, G., The states of flow in transitional pipes, University of Tokyo, Japan, November 1 (2018)
  7. Li, L., Symmetry breaking in supercell thunderstorms, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 18 (2018)
  8. Hattori, Y., Measurements of air drag on two-dimensional soap-film flow, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 19 (2018)
  9. Cerbus, R., The turbulent flow in a slug, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 19 (2018)
  10. Butcher, C., Ray Systems in Granular Cratering, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 19 (2018)
  11. Barros, J. M., Spectral structure of small scales in turbulent Taylor-Couette flows, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 20 (2018)
  12. Cerbus, R., The turbulent flow in a slug, Meiji University, December 5 (2018)
  13. Chakraborty, P., Sabuwala, T., Butcher C., Gioia, G. How the Moon got its rays, University of Bordeaux, France, December 11 (2018)
  14. Cerbus, R., The turbulent flow in a slug, University of Bordeaux, Bordeaux, France, December 12 (2018)
  15. Chakraborty, P., The states of flow in transitional pipes, Fluid flows, from Graphene to planet atmosphere, Weizmann Institute of Science, Israel, December 17 (2018)
  16. Cerbus, R., Transitional and fully-turbulent pipe flows, Fluid flows, from Graphene to planet atmosphere, Weizmann Institute of Science, Israel, December 17 (2018)
  17. Chakraborty, P., Cerbus, R., Liu, C., Gioia, G., The states of flow in transitional pipes, University of Illinois at Urbana-Champaign, IL, USA, February 1 (2019)
  18. Chakraborty, P., Gioia, G., Goldenfeld, N., Goldburg, W., Kellay, H., The spectral link in turbulent friction drag, Stanford University, CA, USA, February 5 (2019)
  19. Cerbus, R., The transition to turbulence in short pipes, 74th Meeting of the Japanese Physical Society, Kyusyu University, Fukuoka, Japan

 

Video Poster

  1. Sabuwala, T., Butcher, C., Gioia, G., Chakraborty, P., V0043: Ray Systems in Granular Cratering, American Physical Society Division of Fluid Dynamics Meeting 2018, Atlanta, Georgia, USA, November 18-20 (2018), DOI: https://doi.org/10.1103/APS.DFD.2018.GFM.V0043

 

5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

6. Meetings and Events

6.1 Mini-workshop

  • Date: June 29, 2018
  • Venue: OIST Campus Lab1
    • Improving tropical cyclone forecasts with aircraft missions, Prof. Kosuke Ito (University of the Ryukyus)
    • Double Warm-Core Structure of Typhoon Lan(2017) as observed through upper-tropospheric aircraft reconnaissance during T-PARCⅡ, Prof. Hiroyuki Yamada (University of the Ryukyus)
    • Ray systems in granular cratering, Dr. Tapan Sabuwala (OIST)

6.2 Seminars

1. Vapor-Induced Attraction of Floating Droplets

  • Date: January 16, 2019
  • Venue: OIST Campus Lab3
  • Speaker: Prof. Tuan Tran (Nanyang Technological University)

 

2. Extreme Waves: Deterministic Modelling and Experimental Validations

  • Date: February 22, 2019
  • Venue: OIST Campus Lab3
  • Speaker: Prof. Amin Chabchoub (The University of Sydney)

 

3. Impact response of granular materials: From the origin of the universe to catastrophic asteroid strikes

  • Date: : March 20, 2019
  • Venue: OIST Campus Lab1
  • Speaker: Prof. Xiang Cheng (University of Minnesota)

7. Other

Nothing to report.