Browsing by Author "Chen, Fangzhou"

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    The Effects of Curvature on Turbulent Boundary Layers Over a 3D Bump Geometry: An Experimental Study Using BeVERLI Hill
    Chen, Fangzhou (Virginia Tech, 2025-01-23)
    This thesis presents an experimental investigation of the effects of curvature on turbulent boundary layers using the Benchmark Validation Experiment for RANS and LES Investigations (BEVERLI) Hill setup. The study focuses on analyzing the flow behavior over a three-dimensional bump geometry that incorporates both concave and convex surfaces, with the aim of improving the understanding of the complex interactions among curvature, pressure gradients, and turbulence characteristics. The study examines the mean velocity, Reynolds shear stresses, pressure gradient, turbulence intensity, and pressure coefficient variations in relation to the bump curvature. The results are consistent with prior studies on the destabilizing influence of concave curvature with observations such as increased turbulence intensity, a decrease in mean velocity relative to the free-stream velocity U∞, and higher Reynolds stresses normalized by U2∞ throughout entire turbulent boundary layer, particularly in the near-wall region. Convex curvature results are consistent with prior study as well, which exhibits a stabilizing effect, shown to reduce turbulence intensity, an increase mean velocity relative to the free-stream velocity U∞, and lower Reynolds stresses normalized by U2∞ throughout entire boundary layer. This study also highlights the influence of pressure gradient effect, which acts with the curvature effect, impacts the boundary layer stability. This interaction is observed in amplification of turbulence with increasing of turbulence intensity and boundary layer growth. This stability particularly reflects on the embedded shear layers with inflection points which can create conditions for linear instabilities to grow, thus enhancing coherent turbulent motions. Furthermore, the thesis discusses the challenges in separating the influence of curvature from pressure gradient effects in current model, and proposes future research directions to address this issue. By conducting experiments under controlled pressure gradient flow conditions over concave and convex curvature, researchers can analyze the contributions of curvature effect separately from pressure gradient effect. Alternatively, using a hybrid RANS-LES model, will lead to a more precise understanding of flow dynamics over curved surfaces.