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A Simulation Study of the Flow Over a Roughness Element

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A design focus of transportation systems is the reduction of aerodynamic drag forces in order to increase overall energy efficiency. An important component of such work is the transition of laminar to turbulent flows in the boundary layers developing on the vehicles? surfaces. Laminar flows generally result in lower drag forces and higher energy efficiency, but turbulent boundary layers can improve the stability of lift forces generated by airfoils. The laminar to turbulent transition occurs naturally in boundary layers, but the flow can also be tripped to become turbulent by surface roughness, imperfections, or protrusions. This study considers the flow around a cylindrical roughness element under laminar inflow conditions. The simulations aim to reproduce an experiment performed at the German Aerospace Center, which visualizes the transition of the laminar boundary layer ahead of the roughness element to a more vortical flow state in its wake through the use of temperature-sensitive paint. The simulation consists of a Blasius boundary formation ahead of the roughness element and an interaction of the boundary layer with the roughness element. The simulations show the disturbance of the boundary layer by the roughness element and the development of a more complex, vortical wake flow downstream. The analyzed velocity profiles and temperature variations compare with data provided by the German Aerospace Center, with next steps including the comparison of wall shear profiles in order to confirm an accurate simulation model.

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A Simulation Study of the Flow Over a Roughness Element

A design focus of transportation systems is the reduction of aerodynamic drag forces in order to increase overall energy efficiency. An important component of such work is the transition of laminar to turbulent flows in the boundary layers developing on the vehicles? surfaces. Laminar flows generally result in lower drag forces and higher energy efficiency, but turbulent boundary layers can improve the stability of lift forces generated by airfoils. The laminar to turbulent transition occurs naturally in boundary layers, but the flow can also be tripped to become turbulent by surface roughness, imperfections, or protrusions. This study considers the flow around a cylindrical roughness element under laminar inflow conditions. The simulations aim to reproduce an experiment performed at the German Aerospace Center, which visualizes the transition of the laminar boundary layer ahead of the roughness element to a more vortical flow state in its wake through the use of temperature-sensitive paint. The simulation consists of a Blasius boundary formation ahead of the roughness element and an interaction of the boundary layer with the roughness element. The simulations show the disturbance of the boundary layer by the roughness element and the development of a more complex, vortical wake flow downstream. The analyzed velocity profiles and temperature variations compare with data provided by the German Aerospace Center, with next steps including the comparison of wall shear profiles in order to confirm an accurate simulation model.