Abstract
Porous materials fixed on and downstream the cylinder can reach a much better effect in suppressing wall pressure fluctuations. In the present paper, numerical comparative studies have been conducted to investigate passive control of flow past a cylinder surface, in which three schemes with different porous treatments are applied to compare their pros and cons. The results show all of the three schemes of porous materials increase the time-averaged flow drag and reduce fluctuations of lift and drag forces. It can be concluded the velocity gradient reduction inside the boundary layer and the vortex shedding delay through porous coating, as well as reverse transition from turbulent vortex shedding into laminar through porous treatment downstream the cylinder, are main flow control mechanisms of porous materials. These mechanisms all reduce fluctuations of lift and drag fluctuations, but have a distinct effect on the features of wake evolution, such as the wake width and length as well as the fluctuating components of the flow velocity. In addition, the wake evolution is highly affected by the location of porous materials.
Highlights
Various techniques have been developed to control the flow past a circular cylinder, aiming at reducing flow drag, suppressing pressure fluctuations and associated noise and controlling alternating vortex shedding and associated wake evolution
Flow inside the porous regions is simulated by combining the LES with the volumeaverage method (VAM) [23], where an extra source term is added on the right-hand side of the momentum equation to describe the additional pressure gradient ∇ p through the porous material
The total flow drag Dtotal consists of pressure drag Dp and friction drag Df acting on the cylinder surface, which expressed by: where p and τ are theisstatic pressure and friction shear stress acting on the shear and πD ⋅ ⋅ dθ
Summary
Flow past bluff bodies have been paid much attention due to wide existence of these phenomena in various applications, such as water flowing and wind blowing past bridges and islands, air past aircraft landing gears, automobiles and high-speed trains. A classic feature of turbulent flow past bluff bodies is alternating vortex shedding, which is highly correlated to the following three aspects: flow drag, wall pressure fluctuations and downstream wake. Various techniques have been developed to control the flow past a circular cylinder, aiming at reducing flow drag, suppressing pressure fluctuations and associated noise and controlling alternating vortex shedding and associated wake evolution. Recent numerical study of Hu et al [10] reveals that a partial circumferential porous coating can reach a better effect in reducing flow drag and noise compared with the full coating scheme. Numerical studies will reveal that a combination of porous materials fixed on and downstream the cylinder can reach a much better effect in suppressing wall pressure fluctuations.
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