Microflow-based control of near-wall fluctuations for large viscous drag reduction |
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Authors: | Jovan Jovanovi? Bettina Frohnapfel Rubitha Srikantharajah Djordje Jovanovi? Hermann Lienhart Antonio Delgado |
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Affiliation: | 1.Institute of Fluid Mechanics,Friedrich-Alexander University Erlangen-Nuremberg,Erlangen,Germany;2.Center of Smart Interfaces,Technische Universit?t Darmstadt,Darmstadt,Germany |
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Abstract: | The stabilizing effect of microgroove surface morphology on viscous drag reduction was studied experimentally in the inlet
region of a plane channel flow. The stabilization is thought to be due to the ability of a microgrooved surface pattern to
suppress the velocity fluctuations in the spanwise direction on a restricted portion of the wetted surface, which prevents
vorticity development at the wall and consequently across the entire flow field. This smart microflow control strategy, which
works successfully only under very particular circumstances, was implemented in a microgroove-modified channel flow in which
the front part has a microgrooved surface topology. The results of pressure drop measurements indicate that microgrooved surfaces
can effectively stabilize laminar boundary layer development, leading to a significant reduction in the viscous drag. In the
rear flat part of the microgroove-modified channel test section, a maximum drag reduction of DR @ 35%{\rm DR\simeq 35\%} was measured. This corresponds to an overall drag reduction of DR @ 16%{\rm DR\simeq 16\%} at a length Reynolds number of Rex @ 106.Re_x\simeq 10^6. The drag reduction effect persisted in a narrow range of flow velocities and for the reported experimental conditions corresponds
to microgroove dimensions between 1.5 and 2.5 viscous length-scales. |
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