FY2016 Annual Report

Fluid Mechanics Unit
Associate 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,  Associate Professor
  • Rory Cerbus,  Postdoctoral Scholar
  • Christian Butcher,  Research Unit Technician
  • Yuna Hattori,  PhD Student
  • Lin Li,  PhD Student
  • William Powell,  PhD Student
  • Kaori Egashira,  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 Ballistic segregation on asteroid Itokawa

  • Type of collaboration: Scientific collaboration
  • Researchers:
    • Professor Troy Shinbrot, Rutgers University
    • Dr. Tapan Sabuwala, OIST

2.3 Granular cratering

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

2.4 Experiments on turbulent pipe flows

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

2.5 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 Robustness of Janus spectra in two-dimensional flows

We have shown earlier that decaying two-dimensional (2D) turbulence in the presence of mean shear exhibits a species of turbulent spectra that has never before been observed or predicted theoretically: the Janus spectra. Here, the streamwise and transverse fluctuations behave as two mutually-independent turbulent fields of disparate dynamics that are concurrently active within the flow. Their attendant spectral exponents, surprisingly, are the same as the isotropic ones from the classical 2D turbulent cascades. Using soap-film experiments, we established that the Janus spectra is a robust phenomenon -- it can be realized for a wide range of forcing conditions.

3.2 Ballistic segregation under ultra-low gravity

In research carried out in FY2015, we proposed that the unexpected size segregation seen on the asteroid Itokawa, where regions populated almost entirely by small pebbles are separated in space from regions consisting only of larger boulders, is caused by the novel mechanism of ballistic segregation. Our experiments and simulations demonstrating this phenomenon were conducted under Earth's gravity. We conducted simulations of ballistic segregation under Itokawa's gravity -- which is smaller than Earth's gravity by five orders of magnitude -- and showed that the effect of ballistic segregation becomes even more pronounced. Our results suggest that ballistic segregation plays a dominant role in shaping the surfaces of Itokawa and rubble-pile asteroids in general.

3.3 Surface topography and granular cratering

We have continued experiments and simulations to study how surface topography shapes the ejecta in granular cratering. Our preliminary results suggest that surface topography might be the key to unveiling the mystery of the long-elusive crater ray system -- the set of long, radial, streaks of ejecta that fan out from a crater, like spokes on a wheel.

3.4 Fluid friction in transitional pipe flows

Osborne Reynolds's seminal experiments from 1883 reported three distinct states of flow in a pipe: laminar, turbulent, and a transitional state that lies in between laminar and turbulent states. As a quantitative signature of the flow states, Reynolds measured the flow friction, f, as a function of the dimensionless flow velocity (now known as the Reynolds number, Re). The f vs. Re diagram acts as a state diagram: the different states of flow occupy distinct regions in the diagram. Using experiments and direct numerical simulations, we study the f vs. Re behavior for the transitional state which has remained perplexing ever since Reynolds's work. Our preliminary results suggest that the conventional measure of f in the transitional state is misleading as it averages the values over two distinct states: the laminar and turbulent states.

3.5 Experiments on turbulent Taylor-Couette flows

We have continued development of the OIST Taylor-Couette experiment. We have coupled the experimental setup with a chiller unit that is located outside the building. The purpose of this chiller is to cool the working fluid in the setup. This is done via a coolant fluid that circulates between the chiller and the top and bottom plates of the Taylor-Couette cylinders. To monitor the temperature of the working fluid, we have installed many resistance thermometers inside the inner cylinder (in all three sections). We have also designed and procured rough inner cylinders with geometrically-similar roughness which are spread over a hexagonal lattice.

 

4. Publications

4.1 Journals

  1. C-C. Liu, R. Cerbus, and P. Chakraborty. 2016. Janus spectra in two-dimensional flows. Physical Review Letters,  vol. 117,  article 114502. 

     

  2. Shinbrot, T., Sabuwala, T., Siu, M., Chakraborty, P. 2017. Size Sorting on the Rubble-Pile Asteroid Itokawa. Physical Review Letters, vol. 118, PP.111101, DOI10.1103/PhysRevLett.118.111101.

     

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

  1. Cerbus, R., Liu, C., Sakakibara, J., Gioia, G., Chakraborty, P., The mean velocity profile in turbulent slugs, RIMS International Project Research 2016, Fluid Dynamics of Near-Wall Turbulence, Kyoto, Japan, June 21 (2016).
  2. Zhang, D., Gioia, G., Chakraborty, P., Macroscopic non-universality in turbulent plane-Couette flows, RIMS International Project Research 2016, Fluid Dynamics of Near-Wall Turbulence, Kyoto, Japan, June 21 (2016).
  3. Zhang, D., Gioia, G., Chakraborty, P., Spectral link for the mean velocity profile in the atmospheric boundary layer, 69th Annual Meeting of the APS Division of Fluid Dynamics, Portland, Oregon, USA, November 21 (2016).
  4. Cerbus, R., Liu, C., Gioia, G., Chakraborty, P., Turbulence in Reynolds' flashes, 69th Annual Meeting of the APS Division of Fluid Dynamics, Portland, Oregon, USA, November 22 (2016).
  5. Cerbus, R., Liu, C., Chakraborty, P., Janus spectra: cascades without local isotropy, 69th Annual Meeting of the APS Division of Fluid Dynamics, Portland, Oregon, USA, November 22 (2016).
  6. Cerbus, R., Liu, C., Sakakibara, J., Gioia, G., Chakraborty, P., Energy cascade in transitional pipe flows, Dynamics Days Asia-Pacific (DDAP), Hongkong, December 17 (2016).
  7. Cerbus, R., Energy cascade in transitional pipe flows, University of Tokyo, Japan, March 3 (2017)

5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

6. Meetings and Events

6.1 Short Courses

(1) Introduction to Compressible Flows

  • Date: December 21st & 22nd , 2016
  • Venue: OIST Campus Lab3
  • Speaker: Dr. Emile Touber (Imperial College London)

(2) Short Course on Impact Cratering

  • Date: January 18th & 20th, 2017
  • Venue: OIST Campus, Lab3 & Center building 
  • Speaker: Professor H. J. Melosh(Distinguished Professor of Earth, Atmospheric and Planetary Science, Purdue University, USA)

6.2 Seminars

(1) Boundary layer transition beneath free-stream turbulence: Linear precursors of nonlinear breakdown

  • Date: June 10th, 2016
  • Venue: OIST Campus Lab1
  • Speaker: Prof. Tamer A. Zaki (Johns Hopkins University)

(2) Experimental Studies on Multiphase Flow for Improved Engineering Systems

  • Date: August 12th, 2016
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Shuichiro Miwa (Division of Energy and Environmental Systems, Graduate School of Engineering, Hokkaido University)

(3) Effects of dissolved gases in the dispersion of carbon nanotubes in water

  • Date: December 9th, 2016
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. C.K. Chan (Institute of Physics, Academia Sinica, Taiwan)

(4) Boundary layer fluctuations and their effects on mean and variance temperature profiles in turbulent Rayleigh-Bénard convection

  • Date: December 9th, 2016
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Penger Tong (Hong Kong University of Science and Technology)

(5) Planetary Smashups:  From the Moon’s Origin to the Dino’s Demise

  • Date: January 17th, 2017
  • Venue: OIST Campus, Center building 
  • Speaker: Professor H. J. Melosh(Distinguished Professor of Earth, Atmospheric and Planetary Science, Purdue University, USA)

(6) Micro-size multiphase fluid dynamics in the human lung: Airway reopening strategies and roles of pulmonary surfactant

  • Date: March 14th, 2017
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Eiichiro Yamaguchi (Tulane University, USA)

(7) Integral wall-model for Large Eddy Simulations and analytical roughness models for turbulent flows over rough surfaces at high Reynolds numbers

  • Date: March 21st, 2017
  • Venue: OIST Campus Center building
  • Speaker: Prof. Charles Meneveau (Johns Hopkins University)

(8) Universality of oscillating boiling in Leidenfrost transition

  • Date: March 24th, 2017
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Tuan Tran (Nanyang Technological University)

(9) Reversal of a large-scale flow in a randomly forced two-dimensional turbulence in a square domain

  • Date: March 27th, 2017
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Takeshi Matsumoto (Department of physics, Kyoto University)

(10) SO(3) decomposition: case studies as an end-user

  • Date: March 28th, 2017
  • Venue: OIST Campus Lab1 
  • Speaker: Prof. Takeshi Matsumoto (Department of physics, Kyoto University)

7. Other

Nothing to report.