Analytical and numerical investigations on active and passive flow controls by Tamás Józsa (Oxford)

Duration: 42 mins 6 secs

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Description:	Talk given by Dr Tamás Józsa (Institute of Biomedical Engineering, University of Oxford) at Aerodynamics and Flight Mechanics group, University of Southampton on 4 December 2019, as part of the Southampton/AFM seminar series.


Created:	2019-12-10 11:39
Collection:	UKFN_Southampton_AFM
Publisher:	University of Cambridge
Copyright:	Dr Tamás Józsa
Language:	eng (English)


Abstract:	Moving fluids through channels and vehicles through fluids dissipates 25% of the energy used in industrial and commercial environments. Turbulent friction drag contributes as much as ≈50%, ≈90%, and ≈100% to the fluid mechanical losses of airliners, marine vehicles, and pipe networks, respectively. Therefore, taming turbulence by introducing a practical friction drag reduction technique would have a positive global impact. Designing a wall deformed by the fluid forces, which reduces the friction drag acting on the surface, has challenged the fluid dynamics community for more than sixty years. The seminar aims to introduce the audience to friction drag reduction in turbulent boundary layers based on actuated (active) and deformable (passive) walls. Modelling techniques will be presented that allow us to gain insight into the fascinating world of fluid motions manipulated by in-plane flow controls. So far compliant wall research targeted characterising pressure-driven surfaces with wall-normal deformation response. By comparison, this seminar focuses on wall-shear-stress-driven surfaces promoting in-plane wall fluctuations. The interaction between fully turbulent incompressible channel flows and in-plane deforming coatings was investigated using Direct Numerical Simulations (DNS) and analytical calculations. The results highlight that a surface, driven by the streamwise wall shear stress fluctuations to deform solely in the streamwise direction, can reduce the turbulent friction drag by approximately 4%. These are the first simulations showing evidence of a drag reduction mechanism that can be sustained by surface motions without an external energy source.

Abstract:

Moving fluids through channels and vehicles through fluids dissipates 25% of the energy used in industrial and commercial environments. Turbulent friction drag contributes as much as ≈50%, ≈90%, and ≈100% to the fluid mechanical losses of airliners, marine vehicles, and pipe networks, respectively. Therefore, taming turbulence by introducing a practical friction drag reduction technique would have a positive global impact. Designing a wall deformed by the fluid forces, which reduces the friction drag acting on the surface, has challenged the fluid dynamics community for more than sixty years. The seminar aims to introduce the audience to friction drag reduction in turbulent boundary layers based on actuated (active) and deformable (passive) walls. Modelling techniques will be presented that allow us to gain insight into the fascinating world of fluid motions manipulated by in-plane flow controls. So far compliant wall research targeted characterising pressure-driven surfaces with wall-normal deformation response. By comparison, this seminar focuses on wall-shear-stress-driven surfaces promoting in-plane wall fluctuations. The interaction between fully turbulent incompressible channel flows and in-plane deforming coatings was investigated using Direct Numerical Simulations (DNS) and analytical calculations. The results highlight that a surface, driven by the streamwise wall shear stress fluctuations to deform solely in the streamwise direction, can reduce the turbulent friction drag by approximately 4%. These are the first simulations showing evidence of a drag reduction mechanism that can be sustained by surface motions without an external energy source.

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