Disputation: Petter Vollestad
Doctoral candidate Petter Vollestad at the Department of Mathematics, Faculty of Mathematics and Natural Sciences, is defending the thesis for the degree of Philosophiae Doctor:
Experimental investigations of two-phase flows Dynamics of stratified and particle-laden flows in pipes and flumes
Doctoral candidate Petter Vollestad
The University of Oslo is partially closed. The PhD defence and trial lecture will therefore be partially digital and streamed directly using Zoom. The host of the session will moderate the technicalities while the chair of the defence will moderate the disputation.
Ex auditorio questions: the chair of the defence will invite the audience to ask ex auditorio questions either written or oral. This can be requested by clicking 'Participants -> Raise hand'.
The meeting opens for participation just before the disputation starts, and closes for new participants approximately 15 minutes after the defence has begun.
Submit the request to get access to the thesis
The trial lecture will be prerecorded. The recording of the trial lecture is to be found here 48h before the disputation.
Tittle: "Instability and shear flow: Conditions for instability in a shear flow, and models of wave generation such as sheltering, the Miles and the Phillips models including turbulence."
Main research findings
Airflow above water waves represents a challenging problem, relevant both in air-sea interactions and for multiphase pipe flows. Understanding this interaction is important to accurately predict the exchange of heat, momentum and chemical components between the ocean and atmosphere, important for weather and climate models, and to obtain safe and reliable operation within the petroleum industry.
In the present thesis, optical measurement techniques are used to study the interaction between the phases of stratified gas-liquid flows. While the main focus is on air-water pipe flows, experiments are also performed in a combined wind-wave flume. Wave regimes ranging from regular ‘2D’ to chaotic ‘3D’ waves are analyzed.
3D waves are found to reverse the air-phase secondary flow structures compared with flow over a flat interface, impacting the momentum exchange between the phases. Within the 2D wave regime of air-water pipe flows, small scale wave breaking without air entrainment is found to be a frequent event. The effect of active wave breaking on the overlying airflow is analyzed both in the pipe flow setup and in a wind-wave flume. Results indicate that the geometrical properties of the waves dictate the airflow development, while the state of breaking has a secondary effect.