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Seminars and Colloquia


Particles and Fields in Partial-differential-equation Models for Fluid and Superfluid Turbulence 
Mon, Aug 31, 2020,   04:00 PM at WEBINAR

Prof. Rahul Pandit
Indian Institute of Science Bangalore

Many natural and laboratory flows and industrial processes involve the advection of particles, bubbles, and droplets by turbulent flows in fluids or superfluids. The first part of this talk gives an overview of our studies of the statistical properties of particles and fields in such flows. These studies use extensive direct numerical simulations (DNSs) of partial-differential-equation (PDE) models for fluids and superfluids and some stochastic PDEs; we augment our DNSs with theoretical analyses of simple models. In particular, we investigate the statistical properties of tracer and heavy inertial particles in turbulent fluids and superfluids by using, respectively, the Navier-Stokes (NS) and Hall-Vinen-Bekharevich-Khalatnikov (HVBK) PDEs. Our studies elucidate (a) the first-passage-time problem in such turbulent flows (with potential applications to the spreading of viruses), (b) the statistical properties of particle trajectories, such as their persistence-time statistics,  (c) the characterization of the irreversibility of superfluid turbulentce, and (d) multiscaling in statistically homogeneous and isotropic superfluid turbulence. The second part of this talk begins with the Gross-Pitaevskii description of a superfluid; we add Newtoniain gravity by considering the Gross-Pitaevskii-Poisson equation (GPPE), which we then solve by extensive DNSs  to elucidate the phase transition from a tenuous Bose gas, at high temperatures, to a condensed bosonic compact object at low temperatures; we introduce temperature by using a Fourier-truncated GPPE. Furthermore, we show that, if we add a crust potential and rotation to this GPPE, we get a minimal model for a pulsar-type condensed object that shows dynamical glitches which exhibit self-organized-critical behaviour of the  type that has been observed in several experimental studies of pulsar glitches 


This talk is based principally on the PhD thesis of my student, Akhilesh Kumar Verma; The first-passage studies have been carried out in collaboration with Akshay Bhatnagar and Dhrubaditya Mitra (NORDITA Stockholm); the work on the HVBK equation have been carried out jointly with Vishwanath Shukla (IIT, Kharagpur) and Abhik Basu (SINP, Kolkata); the investigations of the GPPE have been conducted along with Marc Brachet (ENS, Paris).


IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.
Topic: Physics Colloquium - Prof. Rahul Pandit, IISc, Bangalore
Time: Aug 31, 2020 04:00 PM India
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