|Soutenance à l’EM : plan|
Unsteady dynamics of corner separation in a linear compressor cascade
- Rob MILLER - Professeur, Cambridge University, UK, Rapporteur
- Dario PASTRONE - Professeur, Politecnico di Torino, IT, Rapporteur
- Ivana VINKOVIC - Professeure, Université Lyon I, FR, Examinatrice
- Pavlos ZACHOS - Professeur, Cranfield University, UK, Examinateur
- Xavier OTTAVY - Chargé de recherche, École Centrale de Lyon, FR, Directeur de thèse
This work focuses on the study of the corner separation phenomenon in turbomachinery. Usually, this particular three-dimensional separation appears in the junction between the blade and the endwall of compressor blade rows, with consequent impacts on the efficiency and the stability of the machine. Whereas time averaged characteristics of the separation are well known from the past, its unsteady nature is not yet completely understood.
Even if improvements in CFD methods start to permit the correct simulation of the corner separation unsteadiness, computational costs remain too high and experimental investigations are essential to gain further physical insight.
The study presented in this work was carried out in a subsonic linear cascade in order to isolate the separation unsteadiness. Time resolved PIV and synchronized unsteady pressure measurements (Fig.1) show the intermittent nature of the flow, which switches between two statistically preferred states in a bistable fashion (Fig.2), called bimodal behavior. Correlations and POD modal decomposition draw the picture of a self-sustained instability intrinsic to the diffusing nature of the inter-blade passage.
Finally, the interaction between adjacent separations is elucidated by time-resolved total pressure measurements in multiple blade passages.