For streamlined objects in laminar flow, the drag is dominated by friction drag. To counteract this, the boundary condition of the object can be changed to introduce an apparent slip on the surface. A number of approaches have been proposed for introducing surface slip to reduce drag and viscous resistance in fluid flows. This work investigates a novel approach to providing slip via fluid entrapment in a perforated domain embedded in the surface. The fluid entrapment system uses a cavity underneath the domain to allow entrapment of fluid of the same type, or supply air to the surface perforations in the case of gas entrapment in a liquid flow. Either case provides a fluid at the surface perforations and relaxes the no-slip condition. As a model case, fluid entrapment is used for flow over a flat plate with the perforated domain at various downstream locations. Flow over the flat plate is provided by a miniature water tunnel (cross section 5cm x 7cm). Velocity profiles were measured using Particle Image Velocimetry (PIV) of the flow across the top of the two-dimensional (2-D) perforated surface at a Reynolds number (Re) in the range of 4,000-6,000. Using this method, the boundary layer profiles for a flat plate with air entrapment were analyzed and compared with the results from a solid, control flat plate and a flat plate with water entrapment. The results show slip flow at the surface for the air entrapment and water entrapment cases, with the air entrapment case showing higher measured slip flow, in terms of both slip length and slip velocity, than the water entrapment case.
Dr. Paul Krueger
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Hays, Abigail, "Effect of Surface Fluid Entrapment in a Laminar Flat Plate Boundary Layer" (2023). Mechanical Engineering Research Theses and Dissertations. 56.