Experimental and numerical investigation of the movement of liquids between two plane-parallel plates under flow, gravity and mechanical vibrations

• Applicant: Professor Dr.-Ing. Uwe Janoske
• Subject Area: Mechanical Process Engineering ; Fluid Mechanics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565308393

In technical applications, e.g. in the channels of fuel cells or in gaps in which liquid can lead to corrosion, liquid droplets are present that wet both walls of the channel. There is currently no understanding of the movement of droplets wetting both sides in channels with plane-parallel walls under the influence of aerodynamic forces, the gravitational field as well as superposed mechanical vibrations. Previous investigations for the case of parallel walls are limited to the forced movement of droplets at low Reynolds numbers in a Hele-Shaw configuration. Preliminary investigations have shown different patterns of movement of the droplet under aerodynamic flow (sliding, bursting, movement as a droplet wetting one side). As part of the experimental investigations, shadowgraph-technique and particle image velocimetry (PIV) are used to identify the regimes for different properties of the channel walls (contact angle) both with incident flow and with superimposition of a differently orientated gravitational direction. Due to the coupling of the channel with an electrodynamical shaker, different amplitudes and frequencies can be adjusted. The direction of the vibration is in flow direction as well as perpendicular. The regimes of the droplet movement are represented as a function of dimensionless numbers, which are based on operating, geometry and material data. The evaluation of the shadowgraph-technique is used to characterise the wetting and movement behaviour of the droplet, while the PIV measurement is used to analyse the associated flow field. In parallel, numerical investigations are carried out for selected operating points using a coupled volume-of-fluid model (VoF), which is combined with a feed-back deceleration approach to describe the contact angle hysteresis. The experimental and numerical investigations are used to derive detailed analyses of the movement behaviour of double-sided wetting droplets between two plane-parallel plates. The aim is to gain a fundamental understanding of the mechanisms that lead to the different regimes. Dimensionless numbers allow the estimation of the regimes. The validated numerical model can reliably calculate the behaviour in similar configurations. By using the theoretical knowledge gained in this project, the superposition of additional forces may lead to new applications controlling the movement of liquids to reduce corrosion effects, flooding, etc. in small gaps.

• DFG Programme: Research Grants