Joint MECH-CHBE Special Speaker Seminar Mar 31

Title: A statistical approach for fast and reliable prediction of room-scale airborne viral contagion

Time and Date: Friday, March 31st, from 3:00pm – 4:00pm

Location: CHBE 102 (2360 East Mall)


The risk of airborne viral contagion in indoor spaces is a multidisciplinary problem involving a wide range of parameters. From a fluid mechanics perspective, the problem of infectivity can be divided into an ejection-scale problem and a room-scale problem. The ejection-scale problem aims to answer the question of what range of droplet sizes remain airborne as a result of expiration activities of a sick person. A theoretical framework was developed to answer this question and validated with high-fidelity simulations. It is shown that the risk of infection is heightened when the droplet evaporation rate is fast, i.e., under hot and dry ambient conditions.

The room-scale problem is then considered to examine the probability of contagion on a longer time scale. Well-mixed models have been used extensively to solve the problem of infectivity at the room-scale. However, it is reasonable to expect that a perfectly well-mixed state cannot be achieved at any realistic level of ventilation. We test the robustness of the well-mixed theory at four levels. Results show that the well-mixed theory is accurate in predicting the viral concentration only when averaged over the entire room. The prediction could be substantially off at separation distances under 2m and over 6 m. A simple correction function is introduced to account for departure from the well-mixed theory. Based on this accurate and rapid predictions can be made that are applicable for a wide range of ventilation conditions (ACH, filtration, etc), wide range of ejection activities (breathing, speaking, singing), for any source-sink separation distance. This framework can also be used to answer questions such as if higher air-change-per-hour (ACH) always better?


Portrait of Dr. S. Balachandar.

Professor Balachandar is currently the William F. Powers Professor in the Department of Mechanical and Aerospace Engineering at the University of Florida. From 2005 to 2011, he was the Chairman of the department. Under his leadership, the department grew rapidly from 42 to 54 faculty. He is the inaugural Director of the Herbert Wertheim College of Engineering Institute for Computational Engineering (ICE) and under his leadership the Institute has established the graduate certificate program in Scientific Computing.

Professor Balachandar’s expertise is in computational multiphase flow, direct and large eddy simulations of transitional, turbulent flows, and integrated multiphysics simulations of complex problems. He has contributed to the understanding of thermal convection in the earth’s mantle, the structure of bluff body wakes and their effect on the dynamics of small particles, the dynamics of vortices in wall turbulence, and the theory of two-phase flow, including the equilibrium Euler formulation for dispersion force. Professor Balachandar is a fellow of the American Physical Society and the American Society of Mechanical Engineers.

Professor Balachandar received the Francois Naftali Frenkiel Award from the American Physical Society Division of Fluid Dynamics in 1996 and the Arnold O. Beckman Award and the University Scholar Award from the University of Illinois.