The laminar-turbulent transition of an unsteady turbulent channel flow
报告人:
Prof. Shuisheng He
Professor, Chair in Thermofluids and Head of the Thermofluids Subject Group of the Department of Mechanical Engineering at the University of Sheffield
报告时间:
2014-07-15 09:30
报告地点:
热能工程系系馆第一会议室
主办单位:
热能工程系
简介:
Abstract Ever since the publication of the pioneering work by Osborne Reynolds in 1883 defining the concept of laminar and turbulent flows, the subject has remained a central theme of research in fluid mechanics due to its fundamental importance to the subject and its relevance to many engineering applications and the natural world. It is probably one of the most fundamental concepts that the flow in a pipe is laminar when the Reynolds number is below around 2300 and turbulent when the Re is higher. In this talk, we will present a radically new perspective of the laminar/turbulent flow and will show that the many turbulent-to-turbulent transient processes are in fact laminar-turbulent transition. We will present experimental evidence as well as DNS simulations to demonstrate that, following an increase of flow rate from an initially turbulent flow, the new flow will be re-established itself as a result of laminar-turbulent transition due to instability, rather than progressively evolving from the initial turbulent flow to a new one. The transient process is characterised by the appearance of elongated streamwise streaks followed by generation of turbulent spots which are typical of bypass transition processes. This new understanding leads to new interpretation of the statistics of transient flows and could have profound implications in the understanding and prediction of many unsteady flows encountered in practice, and lead to the development of new strategies for turbulence control, all of which are yet to be explored.
Bio of the Speaker: Professor Shuisheng He is a Chair in Thermofluids and Head of the Thermofluids Subject Group of the Department of Mechanical Engineering at the University of Sheffield. He received his BSc and MSc from Huazhong University of Science and Technology of China and his PhD from the University of Manchester of the UK. He has spent over three years with British Energy (now EDF Energy) as a reactor thermal hydraulics analyst, before starting an academic career with Robert Gordon University, later the University of Aberdeen and since 2011, the University of Sheffield. Professor He’s research focuses on non-equilibrium turbulence, including unsteady and buoyancy-influence flows, nuclear thermal hydraulics, and computational fluids dynamics using RANS and DNS. He is a Member of UK EPSRC Review College, member of UK Turbulence Consortium and Follow of the Institute of Mechanical Engineers.
