February 6, 2023: Bharathram Ganapathisubramani

February 6, 2023
9:15 a.m.
Room: 310 Kelly Hall
Bharathram Ganapahisubramani, University of Southhampton
Faculty Host: Dr. William Devenport

"Rough makes going tough!  Turbulent flows over rough surfaces"

Abstract:  Turbulent flows over rough surfaces are ubiquitous in engineering/natural systems and their impact on these systems cannot be understated. On one hand, roughness is responsible for over 90% of the skin-friction drag in shipping applications and therefore a major source of inefficiency. On the other hand, roughness can improve mixing efficiency or thermal characteristics leading to better performance of heat exchangers, combustors etc. Despite its significance, we are unable to reliably predict the influence of roughness on turbulent flows. The development of new ways to predict and harness the influence of rough walls could be a major pathway to realizing some of our Net Zero goals. In most flow applications, surface roughness can be characterized as homogeneous or heterogeneous roughness based on the scale(s) of spatial variations of the roughness relative to the length scales of the flow developing over them. In this talk, I will present work carried out in our group to understand the effects of spatial characteristics of roughness on turbulent boundary layers. I will start with the experimental work performed over different types of homogeneous rough surfaces such as bio-fouled ship hulls, commercially available surfaces, and urban-type roughness. I will elaborate on how we can develop “surface-specific” Moody diagrams that can predict the drag incurred by such surfaces. I will then discuss the effects of surface roughness heterogeneity and its influence on the characteristics of the turbulent flow over it. The focus will specifically be on spanwise heterogeneity where we have examined the impact of different topographical heterogeneities (from smooth ridges to multiscale roughness) on wall-turbulence. Results including flow topology, skin-friction drag variations as well as preliminary attempts at modelling the flow over these heterogeneous surfaces will be presented. I will conclude with an outlook towards developing data-driven predictions of turbulent flows over rough surfaces.

Bio:  Bharath Ganapathisubramani is a Professor of Experimental Fluid Mechanics in the Department of Aeronautics and Astronautics at the University of Southampton. His research interests are in aerodynamics and propulsion relevant to transportation and energy generation. He completed his undergraduate degree in Naval Architecture and Ocean Engineering at the Indian Institute of Technology-Madras. He moved to the University of Minnesota in the US where he secured his Masters and PhD in Aerospace Engineering. He was then a postdoctoral research fellow at the University of Texas at Austin in the Centre for Aeromechanics research. He moved to the UK as a Lecturer (Assistant Professor) in the Department of Aeronautics at Imperial College London. He has been in Southampton since 2010, first as Senior Lecturer (Associate Professor) and then as a Professor. He currently serves as an Associate Editor for Experiments in Fluids and Flow. He is a Fellow of Data-Centric Engineering at the Alan Turing Institute, A Fellow of the Royal Aeronautical Society, and an Associate Fellow of AIAA.