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Simulation of 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 (Mäteling E., Lemarechal J., Klein C., Puckert D.K., Rist U. (2020) Experimental Investigation of Mixed Convection in Horizontal Channel Flow in Combination with Cylindrical Roughness Elements. In: Dillmann A., Heller G., Krämer E., Wagner C., Tropea C., Jakirli? S. (eds) New Results in Numerical and Experimental Fluid Mechanics XII. DGLR 2018. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 142. Springer, Cham), which visualizes the transition of the laminar boundary layer ahead of the roughness element to a more vertical flow state in its wake through the use of temperature-sensitive paint. The simulations are broken up into two parts. First, a laminar Blasius boundary layer is simulation as the inflow condition ahead of the roughness element. Then, the interaction of the boundary layer with the roughness element is simulated and analyzed. The simulations show the disturbance of the boundary layer by the roughness element and the development of a more complex, vertical wake flow.

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Simulation of 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 (Mäteling E., Lemarechal J., Klein C., Puckert D.K., Rist U. (2020) Experimental Investigation of Mixed Convection in Horizontal Channel Flow in Combination with Cylindrical Roughness Elements. In: Dillmann A., Heller G., Krämer E., Wagner C., Tropea C., Jakirli? S. (eds) New Results in Numerical and Experimental Fluid Mechanics XII. DGLR 2018. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 142. Springer, Cham), which visualizes the transition of the laminar boundary layer ahead of the roughness element to a more vertical flow state in its wake through the use of temperature-sensitive paint. The simulations are broken up into two parts. First, a laminar Blasius boundary layer is simulation as the inflow condition ahead of the roughness element. Then, the interaction of the boundary layer with the roughness element is simulated and analyzed. The simulations show the disturbance of the boundary layer by the roughness element and the development of a more complex, vertical wake flow.