VIVEK N. PRAKASH
  • Home
  • Research
  • Videos
  • Media

Research

Picture
                                                                                                            Organismal Biophysics
                                                                                                             Hydrodynamics of swimming versus feeding in starfish larvae

        Here, we study the ciliary bands of starfish larvae, and discover a beautiful pattern of             slowly-evolving vortices that surrounds the swimming animals.  Quantitative                           experiments and modeling demonstrate that these vortices create a physical tradeoff           between feeding and swimming in heterogenous environments, which manifests as               distinct flow patterns or "eigenstrokes" representing each behavior---potentially                     implicating neuronal control of cilia. This quantitative interplay between larval form               and hydrodynamic function generalizes to other invertebrates, and illustrates the                   potential effects of active boundary conditions in other biological systems.

      Publications:

      W. Gilpin, Vivek N. Prakash, and M. Prakash,
      Vortex arrays and entangled cilia underly the feeding vs. swimming            
      tradeoff in sea star larvae
     
Nature Physics, 13, 380-386 (2017) [web link]

      W. Gilpin, Vivek N. Prakash, and M. Prakash
     
Flowtrace: simple visualization of coherent structures in biological fluid 
    flows, 
Journal of Experimental Biology, 220, 3411-3418 (2017)
​                                                                                                            [web link] 
[biorXiv preprint]
                                                                                                             Download Flowtrace here: www.flowtrace.org


Picture
   Fluid Mechanics - multiphase flows
  
Energy spectra in turbulent bubbly flows

      We conduct experiments in a turbulent bubbly flow to study the nature of the transition       between the classical -5/3 energy spectrum scaling for a single-phase turbulent flow             and the -3 scaling for a swarm of bubbles rising in a quiescent liquid and of bubble-               dominated turbulence. The energy spectra are found to follow the -3 scaling at length           scales smaller than the size of the bubbles for bubbly flows. This -3 spectrum                         scaling holds not only in the well-established case of pseudoturbulence, but surprisingly       in all cases where bubbles are present in the system (b > 0). Therefore, it is a                         generic feature of turbulent bubbly flows.


     Publication:
     Vivek N. Prakash, J. M. Mercado, L. van Wijngaarden, E. Mancilla,
     Y. Tagawa, D. Lohse, and C. Sun
                                                                                                            Energy spectra in turbulent bubbly flows
​                                                                                                            Journal of Fluid Mechanics, 791, 174-190 (2016)


Picture
   Fluid Mechanics -
   Particle-laden turbulent flows

    Buoyant spheres in turbulence

      Particles suspended in turbulent flows are affected by the turbulence and at the same         time act back on the flow. The resulting coupling can give rise to rich variability in their         dynamics. Here we report experimental results from an investigation of finite-sized               buoyant spheres in turbulence. We find that even a marginal reduction in the particle’s         density from that of the fluid can result in strong modification of its dynamics. We                 find that the particle acceleration variance increases with size. We trace this reversed           trend back to the growing contribution from wake-induced forces, unaccounted for in           current particle models in turbulence. Our findings highlight the need for improved               multiphysics based models that account for particle wake effects for a                                     faithful representation of buoyant sphere dynamics in turbulence.

    Publication:
    V. Mathai, Vivek N. Prakash, J. Brons, C. Sun and D. Lohse
    Wake-driven dynamics of finite-sized buoyant spheres in turbulence
​                                                                                                           Physical Review Letters, 115, 124501 (2015)


Picture
   
    Fluid Mechanics -
   Particle-laden turbulent flows

    Finite-sized bubbles in turbulence

     We report results of the first systematic Lagrangian experimental investigation in a previously             unexplored regime of very light (air bubbles in water) and large (D/eta) particles in turbulence.             Using a traversing camera setup and particle tracking, we study the Lagrangian acceleration                 statistics of 3mm diameter (D) bubbles in a water tunnel with nearly homogeneous and isotropic         turbulence generated by an active grid. The experiments reveal that gravity increases the                     acceleration variance and reduces the intermittency of the probability density function (PDF) in           the vertical direction. Moreover, the experimental acceleration PDF shows a substantial                       reduction of intermittency at growing size ratios, in contrast with neutrally buoyant or heavy                 particles. 

    Publication:
    Vivek N. Prakash, Y. Tagawa, E. Calzavarini, J. M. Mercado, F. Toschi, D. Lohse,
​    and C. Sun
​    How gravity and size affect the acceleration statistics of bubbles in turbulence
    New Journal of Physics, 14, 105017, (2012)


Picture
   
   Fluid Mechanics -
   Particle-laden turbulent flows

    Micro-bubbles in turbulence

     We study the Lagrangian velocity and acceleration statistics of light particles (microbubbles in              water) in homogeneous isotropic turbulence. Micro-bubbles with a diameter of 340 μm are                dispersed in a turbulent water tunnel operated at Taylor-Reynolds numbers (Reλ) ranging from          160 to 265. We reconstruct the bubble trajectories by employing 3D Lagrangian particle tracking        experiments. It is found that the probability density functions (PDFs) of microbubble acceleration        show a highly non-Gaussian behavior with flatness values in the range 23 to 30. These                          acceleration PDFs show a higher intermittency compared to tracers and heavy particles in wind          tunnel experiments. 

    Publication:
    J. M. Mercado*, Vivek N. Prakash*, Y. Tagawa, C. Sun, and D. Lohse
    Lagrangian statistics of light particles in Turbulence
    Physics of Fluids, 24, 055106 (2012)
    (*Equal authorship)


Picture
   Fluid Mechanics -
   Particle-laden turbulent flows

    3D Voronoi analysis to study inertial particle clustering in turbulence

      A 3D Voronoi analysis is used to quantify the clustering of inertial particles in homogeneous isotropic               turbulence using data sets from numerics in the point particle limit and one experimental data set. We           study the clustering behaviour at different density ratios, particle response times and Reynolds                         numbers. The p.d.f.s of the Voronoi cell volumes of light and heavy particles show different behaviour             from that of randomly distributed particles, i.e. fluid tracers, implying that clustering is present. Light                 particles show maximum clustering for St around 1–2 for both Reynolds numbers. The                                       Lagrangian temporal autocorrelation function of Voronoi volumes shows that the clustering of light                 particles lasts much longer than that of heavy or neutrally buoyant particles.


​     Publication:
     Y. Tagawa, J. M. Mercado, Vivek N. Prakash, E. Calzavarini, C. Sun, and D. Lohse
     Three-dimensional Lagrangian Voronoi analysis for clustering of particles and                                                                                                        bubbles in turbulence
                                                                                    Journal of Fluid Mechanics, 693, 201-215 (2012)


Picture
   
   Fluid Mechanics -
   Particle-laden turbulent flows

    3D Voronoi analysis to study clustering of freely rising bubbles  

    We investigate the clustering morphology of a swarm of freely rising                                deformable bubbles. A 3D Voronoi analysis enables us to distinguish                              quantitatively between two typical preferential clustering configurations: a                    regular lattice arrangement and irregular clustering. The bubble data are                      obtained from DNS using the front-tracking method. It is found that the bubble            deformation, represented by the aspect ratio , plays a significant role in                          determining which type of clustering is realized: nearly spherical bubbles form a          regular lattice arrangement, while more deformed bubbles show irregular                    clustering. 

​
​     Publication:
     Y. Tagawa, I. Roghair, Vivek N. Prakash, M. van Sint Annaland,
     H. Kuipers, C. Sun, and D. Lohse
​     The clustering morphology of freely rising deformable bubbles
     Journal of Fluid Mechanics, 721, R2 (2013)


Picture
                                                                                         Fluid Mechanics - Convection
    Plume structure in Mantle convection

    We have conducted laboratory experiments to model important  aspects of mantle convection. We focus on the role of the viscosity    ratio, U (between the ambient fluid and the plume fluid) in determining  the plume structure and dynamics. In our experiments, we are able to  capture geophysical convection regimes relevant to mantle convection  both for hot spots (when U > 1) and plate subduction (when U < 1)  regimes. The LIF technique is used for flow visualization and  characterizing the plume structures. The convection is driven by  compositional buoyancy generated by the perfusion of lighter fluid          across a permeable mesh.

  Publication:
  Vivek N. Prakash, K. R. Sreenivas, and J. H. Arakeri
  The role of viscosity contrast on plume structure in                   laboratory modeling of mantle convection
  Chemical Engineering Science, 158, 245-256 (2017) 

Location

Thank you for visiting !

(C) 2016 Vivek N. Prakash. All Rights Reserved.

Contact ME

  • Home
  • Research
  • Videos
  • Media