PhD Offer
Turbulent Drag and Drag Reduction
There are significant gaps in the fundamental understanding of turbulent flows. Two aspects of such flows have been the subjects of extensive, but separate, research efforts: their macroscopic properties and their turbulent spectrum. The macroscopic properties of turbulent flows are essential to design hydraulic structures and water-treatment plants, to assess the hazards associated with floods and hurricanes, to evaluate the environmental effects of water-borne pollutants and organic matter. The key properties of interest for practical purposes are the frictional drag experienced by a flow past a wall and the mean velocity profile of the flow in a pipeline. The turbulent energy spectrum of the velocity fluctuations on the other hand is representative of the small-scale statistics of the flow and has universal features as remarked by Kolmogorov decades ago. The link, if any, between these two strands has remained unexplored. This link plays a fundamental role in statistical mechanics where macroscopic quantities are determined by the fluctuations but has no precedent in turbulence. Only recently has experimental and theoretical work begun to focus on trying to unravel the nature of this missing link in turbulence with emphasis on the common and economically interesting case of friction drag in turbulent flows in pipes and channels. Linking these two strands of turbulence represents a major step and opens new possibilities in controlling the macroscopic response through tuning the statistical properties of turbulent flows, notably by using additives such as polymers, surfactants, or air bubbles. The present project will contribute to this endeavor and, in particular, to the long-standing issue of turbulent drag reduction by polymers.
This project concerns the interplay between fluctuations and macroscopic drag in a system developed in our laboratory using soap film channels of large dimensions. Work on both smooth channels and rough channels will be essential to determine the main ingredients of turbulent drag and its link to the nature of the fluctuations. An important part of the project will concern drag reduction by polymers. Different types of polymers will be used depending on their flexibility and length. State of the art Particle tracking and Laser Doppler velocimetry will be used to characterize the velocity and stress fields of turbulent flows in such channels both with and without the addition of drag reducing agents. The work is coupled to Direct Numerical Simulations carried out in our Partner’s Lab, IMB of the University of Bordeaux.
Note : Ce travail se fera dans le contexte de l'ANR collaborative LIFT en collaboration avec P. Fischer de l’IMB de l’Uinversité de Bordeaux. Le travail de thèse se fera sous la direction de H. Kellay, J. F. Boudet et T. Barois dans le groupe Instabilités et Turbulence de l'équipe Matière Molle et Biophysique du Laboratoire Ondes et Matière d'Aquitaine (UMR 5798 CNRS/U. Bordeaux) situé sur le campus de Talence de l'université de Bordeaux.
Related Publications from the group :
A. Vilquin et al. Science Advances, 2021
Contact :
hamid.kellay@u-bordeaux.fr
Interested candidates should send their CV, a letter of motivation, and contact information of two or more references.