PhD Defense - Sijo GEORGE - LHEEA/ED SPI

Committee

Reviewer: Elie Rivoalen Professeur des universités, LMR, INSA de Rouen
Reviewer: Xavier Amandolese MCF HDR, LMSSC, CNAM Paris
Examinator: Marie- Laure Gobert MCF, INSA, Val de Loire
Examinator: Jacques-André Astolfi Professeur des universités, IRENav, Ecole Navale de Brest
Examinator: David Le Touzé Professeur des universités, LHEEA, Centrale Nantes
Supervisor: Antoine DUCOIN, Maître de Conférences HDR, LHEEA, Centrale Nantes

Protocole

The thesis defense will take place as usual. The president of the jury will open the defense, followed by a 45-minute presentation. The president will then allow the jury members to ask questions, one by one. After this session, the jury will retire to a separate conference room for discussion; the main conference room will remain open to the public (cameras/microphones allowed). The committee will then return to the main room to announce its decision. Afterwards, the room will remain open for a general discussion where, depending on the result, we will be able to congratulate Zhenrong.

Visioconference

The thesis defense will take place on Zoom:
https://ec-nantes.zoom.us/j/91862022724
Code de la réunion : 91862022724

The defense will start at 14:00 am, the videoconference will be open from 13:30 am so that you can test your connection.
In order to lighten the bandwidth, all participants will be asked to switch off their camera and microphone throughout the presentation. Finally, we thank you to connect around 13:45 am or earlier in order to have time to manage any technical problems before starting the defense. Thanks to all of you!

Abstract

The laminar to turbulent transition induced vibration over a NACA66 hydrofoil at Re =450000 is investigated in this thesis. DNS is used to simulate the 3D incompressible boundary layer flow, and it is coupled with a freely pitching hydrofoil. An implicit coupling is developed within the fluid solverNek5000. A number of cases are performed to validate this method, which lead to study the transition-induced vibration. Then, a parametric study consisting of two forced and three free oscillations allowed analyzing the interactions between the vibration and the boundary layer transitional flow. A set of specific non-dimensional parameters are set, which aim at characterize the fluid structure interactions in such flow regime. From the boundary layer flow analysis, it was observed that the spatial location of the transition point is proportional to the amplitude of pitch, velocity, and frequency ratio. The generation of TS waves (the first stage of laminar to turbulent transition) is also influenced by vibrations. It was also observed that the spanwise wavelength of coherent structures (so called “hairpin” structures” that form downstream of the TS waves) is proportional to the displacement thickness. The spatial advancement of the transition point reduces the amplitude of periodic pressure fluctuations in the transition regime. In addition, the length of the transition region is increased. Finally, a multi-scaled frequency response is observed due to the enhanced interaction between transition and pitch oscillation when the transition and natural frequencies are close to each other. The study suggests that in this case, the fluid structure interaction tends to disturb the spatio-temporal behavior of laminar to turbulent transition. Although it has to be confirmed, this phenomenon has already identified experimentally through measurements performed at the Naval Academy Research Institute (IRENav) in hydrodynamic tunnel for a higher Reynolds number case.