# Priya Subramanian

# Short-bio

Priya Subramanian completed her Bachelor degree in Aeronautical Engineering in 2004 from Madras University. She then completed her doctorate at the Department of Aerospace Engineering, IIT Madras in 2012 in the group of Prof. R. I Sujith. Her PhD focused on the interaction between acoustics and premixed flames which can lead to thermoacoustic instabilities in rockets, aero-engines and gas turbines. Since her doctorate, she has been a PostDoc in the MPRG of Dr. Tobias Schneider and works in the areas of pattern formation in transitional flows, emergent dynamics in elastic squirmers along with continuing her investigation into the nonlinear dynamics of thermoacoustic systems.

# Research interests

## Spatio-temporal patterns in Inclined Layer Convection

The rich variety of spatio-temporal patterns observed in the inclined layer convection (ILC) system range from linearly unstable (buoyancy-driven instabilities) to a linearly stable (shear-driven instabilities) system with variation of the inclination angle. This feature will be exploited with tools such as amplitude equations to understand the mechanism of patterm formation.

In the figures above, we see the comparison of temperature field generated using a Galerkin stability analysis (in color) with observed patterns of shear-domainted instability in experiments (in grey scale). Regions of red color in the simulation result and bright regions in the experimental results indicate regions of temperature fluctuations higher than the mean temperature profile. Results are for cases just above the linear threshold of instability.

We observe from this comparison that the pattern generated using two of the least stable eigenmodes (as predicted from the Galerkin stable analysis) is very similar to the patterns observed in experiments (Daniels, 2002). Coupled with new experimental investigations in the Bodenschatz group and results from numerical continuation of the ILC system, we look to explain the multitude of patterns observed in the ILC with emphasis on the chosen wavelengths and orientation of the patterns to the direction of mean flow.

## Emergent dynamics of active elastic swimmers

Active systems such as bacterial suspensions and ciliary beds are intrinsically out of equilibrium and show rich, self-organized dynamics. We are interested in a subset of these systems which exhibit elasticity as well as activity, such as systems consisting of connected self-propelled (active) colloids.

Above we observe the shapes of the filament for different end conditions (Chelakkot et al. 2012). For the clamped case, we observe the shapes over one cycle (asymmetry due to noise) and in the right, a self-contracting, stably beating long filament. For the pivoted end, we observe rotating filaments similar to those observed in motility assays. Building on these studies, we are currently exploring the use of linked active colloids to form synthetic mimics of cilia and to understand the interactions between many filaments which leads to different modes of collective behavior as observed below.

## Patterns in transitional shear flows

Regions of turbulence co-exist with laminar flows to create patterns in transitional shear flows. Such patterns have been observed both in experiments (Prigent et al.) and in simulations (Tuckerman & Barkley). We seek to identify invariant solutions of the flow that make up basic elements of such transitional patterns. Coherent structures have been identified in many fluid flows such as plane Couette flow, pipe flow, etc. In the figure below, we see an invariant periodic solution that is tilted at an angle of 26 degrees to the direction of motion.

Localised structures in non-tilted flows are reflected as 'snaking' behavior in their bifurcation diagrams. We seek to obtain localised coherent structures in tilted flows that display an oblique angle to the direction of mean flow. With this approach we look forward to understanding the occurrence of observed transitional tilted patterns.

# Publications

Subramanian, P., Mariappan, S., Sujith, R. I. & Wahi. P.

Bifurcation analysis of thermoacoustic instability in Rijke tube.

International Journal of Spray and Combustion Dynamics. 2(4):325–356. 2010.

Subramanian, P. & Sujith, R.I.

Non-normality & internal flame dynamics in premixed flame-acoustic interaction.

Journal of Fluid Mechanics. 679: 315-342. 2011.

Subramanian, P., Sujith, R. I. & Wahi, P.

Subcritical bifurcation and bistability in thermoacoustic systems,

Journal of Fluid Mechanics. 715: 210-238. 2013.

Blumenthal, R. S., Subramanian, P., Sujith, R. I., & Polifke, W.,

Novel Perspectives on the Dynamics of Premixed Flames.

Combustion & Flame. 160: 1215-1224. 2013.

Agharkar, P., Subramanian, P., Kaisare, N. S. & Sujith, R. I.

Thermoacoustic instabilities in a ducted premixed flame: reduced order models & control.

Combustion Science and Technology. 185, 920. 2013.