Research Interests

Active turbulence

Classical-high Reynolds number turbulence is characterised by strong non-linear interactions with a well-separated inertial range and celebrated Kolmogorov’s (K41) scaling laws. Active matter (living and non-living) is comprised of self-propelled entities, having the ability to convert chemical/ambient energy into directed motion. In general, at high enough concentration, these active systems (e.g., dense bacterial suspensions, microtubule networks) organize themselves into complex patterns characterized by collective behaviour, hydrodynamic instabilities, enhanced fluid mixing etc. These low Reynolds number flow patterns qualitatively resemble the high Reynolds number turbulent patterns, hence termed as active turbulence. The complete physical understanding and governing scaling laws behind active turbulence are quite unclear. I am interested in studying various types of active matter, corresponding non-equilibrium hydrodynamic models and hydrodynamic instabilities based on their symmetry, swimming mechanism and the nature of momentum conservation and exploring universal characteristics in terms of spectral scaling laws etc.

Classical turbulence in simple and active binary fluids

Binary fluid is a two-component fluid ranging from a mixture of two incompressible fluids e.g. oil and water to complex fluids such as active fluids. Simple binary fluids contain microstructures such as droplets and sharp interfaces while active fluid contains living microorganisms or nonliving self-propelled rods or entities. The dynamics of binary fluid can be described by a composition field (describing the chemical composition of two fluids) and by a mean velocity. Sharp variation in composition filed across interfaces generates diffusion currents which in turn drive the velocity field by exerting feedback stress. Below the critical temperature, binary fluid flow stabilizes by phase separation via coarsening or domain growth. For active binary fluid, this phase separation arises from purely repulsive interactions among the active particles but through density dependent self-propelled velocities termed as motility-induced-phase-separation (MIPS). In the presence of high Reynolds number - classical turbulence the phase-separation got arrested. We are interested to study the effect of turbulence on coarsening, spectral energy transfers and scaling laws in terms of exact laws of the cascading invariants and direct numerical simulations etc.

Here are the tiles of my main ongoing research work :

  1. Study of Energy transfer in simple and active binary fluid turbulence in terms of exact scaling relations and numerical investigations

  2. Active turbulence: Experimental study of pattern formation by dense bacterial suspensions

SOTA_NANDITA_PMRF.pdf

Publications

  • Energy transfer in simple and active binary fluid turbulence - a false friend of incompressible MHD turbulence,
Nandita Pan and Supratik Banerjee, arXiv preprint arXiv:2206.12782