By-pass transition and re-laminarization – Two sides of the same coin

Name of the Speaker:  Prof. Garry Brown, Dept. of Mechanical and Aerospace Engineering, Princeton University

Title: By-pass transition and re-laminarization – Two sides of the same coin

Date & Time: Wednesday, 13 February 2019, 4:00 – 5:00 PM

Venue: Auditorium, Department of Aerospace Engineering, IISc, Bangalore

Abstract:

Transition and re-laminarization are good examples of the complexity of many technologically important flows for which predictions from the physics are needed.  Two routes to ‘transition’ for a laminar boundary layer are well-known: one, the classical route via amplifying Tollmien-Schlichting (T-S) instability waves (and the onset and merging of ‘turbulent spots’), the other, ‘By-pass’ transition, (a description coined by Morkovin for the absence of amplifying T-S waves). Boundary layer transition has been identified with a rapid increase in wall shear stress (and heat-transfer) but details of the actual mechanisms by which the wall shear stress increases have been elusive.  The talk will describe new insights into ‘roughness induced transition’, (characteristic of Bypass transition).  In particular it will describe from a vorticity point of view a final phase which leads to chaotic vorticity (characteristic of turbulence) and a rapid increase in the shear stress at the wall in the absence of any 2D T-S waves.  The unravelling of what occurs is based on the vorticity transport near the wall (which was elucidated initially by numerical studies of turbulent channel flow).  A similar point of view, but applied to the ‘opposite side of the same coin’, namely, ‘re-laminarization’ has allowed new insights into why re-laminarization occurs in a spatial turbulent boundary layer subject to a highly favourable pressure gradient.  It has also been found not to occur in a temporal, boundary layer (Rayleigh flow) having the same initial  and subject to a rapid acceleration of the plate (also a source of spanwise vorticity), which is comparable with the acceleration of the free stream flow in the spatial case.  The reason for the different behavior is described and readily appreciated

Speaker:

Prof. Garry Brown is the Emeritus Robert Porter Patterson Professor of Engineering at Princeton University. He received a first class Honors Degree in Engineering from the University of Adelaide in 1964, was awarded a Rhodes scholarship, completed his D.Phil at Oxford and was then a research fellow/senior research fellow at GALCIT, Caltech. In 1971 he returned to the University of Adelaide and in 1978 returned to Caltech as full professor. He was asked to serve as Director of the Australian Aeronautical Research Laboratory and held this position from 1981-1990 after which he joined the faculty at Princeton, serving as Chair of the Department of Mechanical and Aerospace Engineering from 1990 to 1998. His best known work is in the study of turbulence. Fifty years after the inception of the Journal of Fluid Mechanics, his 1974 paper with Professor Roshko “On density effects and large structure in turbulent mixing layers,” was the most frequently cited paper in the history of the journal. After joining Princeton he explored new research horizons while continuing his abiding interest in turbulence. In 2016 he was the Clark Millikan Visiting Professor at Caltech and taught a course with Professor Roshko and in 2017 he was the Satish Dhawan Visiting professor at the Indian Institute of Science in Bangalore where he also taught a course on turbulent shear flows. He has also made significant contributions, as a consultant in Australia and to the American aerospace industry, that include the root cause of extreme propeller-induced-vibration of the Lysaght Enterprise, the root cause of failure and redesign of the solid rocket motor for the Titan IV, the cause of early failure and development of the thrust-vectoring system for AIM-9X and the resolution of critical issues for Tactical Tomahawk and for the Standard Missile-3 Programs. He played a leading role in the failure investigation and redesign of early air-cooled test cells for the after-burning F100 engine. He is a Fellow of the Institution of Engineers of Australia, Fellow of the American Physical Society, and a Fellow of the AIAA

ALL ARE WELCOME

High Tea @ 5 PM

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P.S. The distinguished lecture series is COMPULSORY for all students (both M.Tech and Ph.D.) of the AE department.

Date/Time
Date(s) - 13/02/2019
4:00 pm - 5:00 pm

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