Testing the Efficacy of Micro Vortex Generator Geometries on Boundary Layer Separation Mitigation

This paper investigates the performance of custom designed vortex generators (VGs) with respect to airfoil aerodynamics. The research was carried out by an undergraduate student enrolled in an independent study that took place over the summer semester. The student applied basic fluid mechanics principles to solve an existing practical problem: mitigation of boundary layer separation. Vortex Generators are passive devices located near the trailing edge of an airfoil to aid in aerodynamics. They energize the flow by adding turbulence thus delaying the separation of the boundary layer. Apart from the size, the shape of the vortex generator is critical in evaluating the efficacy. While several studies on VG size exists, the effect of VG shape on boundary layer separation has not been extensively studied. First, the base airfoil NACA 4414 was numerically investigated using the commercially available software ANSYS FLUENT. The lift coefficient at various angles of attack and the stall angle were identified for a Reynolds Number of 2x10^5. This was then compared to experimentally available data in the literature and the numerical setup was verified. The chord length of the airfoil was 100 mm while the stall angle of attack was 14 deg. A grid independence study was also done to identify an optimal mesh size. Following this, two custom VG shapes (Modified Trapezoidal and Delta Wing) were tested. Both design concepts were based on basic fluid mechanics principles. For each VG shape, a parametric study was conducted where the height, thickness, axial chord location, inter-spacing, rotation, and angle of incidence were varied to identify the best performing configuration. For the Modified Trapezoidal, a tab/no-tab setup was also considered. A Modified Trapezoidal configuration was identified as optimal. This configuration had no effect on lift coefficient till 10 deg. angle of attack. However, beyond this angle, there was a marked increase in lift, and the stall angle was delayed to 18 deg. While the Delta Wing configuration did not provide positive results, strong vortices were present. Further modifications could be done to utilize these vortices by aligning them in the desired manner. It is believed that such a VG design could also be used on fins to improve heat transfer performance in heat exchangers.