Title: Investigation of channels with perforated wall for external boundary layer control

Abstract:

In recent years liquid-infused surfaces (LISs) have become a heavily studied topic due to their broad application range such as self-cleaning, pressure stability and ultra-slippery properties in channel flow. LIS relies on a physiochemical surface coverage with a low viscosity fluid creating an intermediate layer between the flowing fluid and a channel’s surface. Depending on the properties of the infused liquid the LIS is characterized by an effective slip length as the frictional drag that slows down the fluid flow at microscales is reduced. During flow shear forces may cause the partial or complete removal of the infusion liquid layer canceling the desired drag reduction effect. This effect could not be avoided so far due to a missing external access to the infusion layer on the channel’s surface. The main purpose of this study is the development of a technique to achieve active control of the infusion layer. We suggest to partially remove the channel’s surface or replace it by a permeable porous layer to obtain external excess through this surface area by means of an external gas pressure or by refilling the infusion fluid through it. By forming menisci in those open surface areas, the flow condition at the channel’s surface may be affected. As a very first implementation of this concept, we have structured thin stainless-steel sheets by laser ablation to form parallel rectangular slits (see Figure left). These sheets are then installed as one wall of a rectangular channel with the orientation of slits in flow direction. During fluid flow over these sheets, menisci are formed across the open slits establishing a Cassie state. Meniscus stability is improved forming a nanostructure layer on the channel’s surface followed by the depositing of a CF-containing thin film to render the channel’s surface superhydrophobic. CFD-Simulations illustrate the velocity field within and in close proximity to the infusion layer, allowing the numerical characterization of properties such as effective slip-length and frictional drag as well as a comparison of experimental results (see Figure right). First experimental results on the investigation of the flow through such channels and the control of the flow conditions are presented.

Biography:

Ellen Bold received her diploma in 2021 from the Technical University of Kaiserslautern. Since 2021, she is PhD student in the working group “Physics and Technology of Nanostructures” at the Technical University of Kaiserslautern