Drag reduction and interface stability of a ferrofluid film in turbulent channel flow

Drag reduction and interface stability of a ferrofluid film in turbulent channel flow

The research explores the interfacial instability of ferrofluid films in plane channel flow, where the upper wall is coated by a film of ferrofluid held in place by external permanent magnets aligned with the mean flow direction. Key applications of ferrofluid layer for drag reduction include mechanical (seals, bearings) and biomedical (drug delivery, MRI) fields. The study focuses on the effects of static magnetic fields on drag reduction and stability of the main flow. Under certain turbulent flow conditions, the interface between the two fluids may develop unstable traveling waves, which can finally lead to the detachment of the ferrofluid film. The purposes of the present research are to determine the stability conditions of the interface, to analyze the drag reduction mechanisms, and to numerically describe flow within the ferrofluid film. Different approaches, namely linear stability analysis, laboratory experiments and numerical simulations, are adopted.

The research goals are following:

1. determining the flow conditions at which the interface becomes wavy and subsequently unstable by means of linear stability analysis

2. verifying experimentally the mathematical results and determining the limits of the linear stability analysis,

3. investigating the origin of drag reduction either associated with the slip condition at the ferrofluid interface and with the effect of progressive waves.

4. describing numerically the flow within the ferrofluid film which cannot be observed optically because of the ferrofluid opacity.

Different approaches, namely linear stability analysis, laboratory experiments and numerical simulations, are adopted.