Title：Predicting and Damping of Thermoacoustic Instabilities

Reporter：Dr. Dong Yang

Imperial College London

Time：December 25 (Tuesday) 2018，14:00-16:00 pm

Location：A-459 , Lee Shau Kee Building of Science and Technolog （李兆基科技大楼 A-459 ）

Abstract

Thermoacoustic instabilities (or “combustion instabilities”) come from the positive feedback between acoustics and unsteady combustion; unsteady combustion generates acoustic waves which propagate within the combustor, being reflected by the boundaries and further disturb the flame to generate more acoustics. Due to the compactness and very intensive heat release in aero-engine or land-based gas turbine combustors, this coupling can generate catastrophically large pressure oscillations – it is one of the main challenges for designing modern low-emission combustors. Numerically predicting thermoacoustic instabilities is difficult since it requires resolving couplings across very different scales (acoustics, turbulence and combustion). Full-scale experiments are extremely expensive but lab-scale rig does not capture all key physics. This is especially challenging when real annular combustors with 10 to 20 burners are considered. A state-of-the-art methodology is to combine analytical treatments of acoustics and numerical/experimental treatments of flames in a network sense to capture the coupling. Evidence will be given for the first time to show how such method can predict different types of thermoacoustic modes in annular combustors. To damp thermoacoustic instabilities, acoustic dampers, such as Helmholtz resonators, perforated liners/plates, are important tools used by all main aero-engine and land-based gas turbine companies (such as Rolls-Royce, Siemens, GE and Mitsubishi). These dampers rely on circular holes with mean bias flow to transfer acoustic energy into vortex energy which is finally dissipated by viscosity; accurately predicting this energy conversion is of key importance -- a new theoretical model which greatly extends the capability of widely used classical models will be presented. Finally, a systematic optimization (based on adjoint sensitivity analysis) of many acoustic dampers targeting many thermoacoustic modes is presented.

Brief Biography

Dr. Dong Yang is a Research Associate at Imperial College London. He got his first and Master’s degrees from Tsinghua University, and his PhD in 2017 from Imperial College London with a thesis “The acoustics of short circular holes and their damping of thermoacoustic oscillations” wining the Osborne Reynolds Award 2017 Oral Presentation Finalist--top six best PhDs in Fluid Mechanics in the UK. His research in hole acoustics and thermoacoustic damping has made significant impact in the acoustic damping and thermoacoustic community. He has been invited by many leading companies such as Rolls-Royce, Siemens to give talks on thermoacoustic damping. He is an organizer of the 23rd International Congress on Acoustics, and reviewer for Journal of Sound and Vibration, AIAA Journal, Applied Acoustics, Journal of Engineering for Gas Turbines and Power etc.