Rotation Rate Influence on Flow Around Porous Media Coated Circular Cylinders

Experimental rotation effects on flow past cylinders have been observed. The cylinders have the porous media coatings (PMC) named PMC۱, PMC۲, PMC۳ and PMC۴. For the range of rotation rates, including α = ۰.۵۲, α = ۱.۰۵ and α = ۱.۵۷, the flow characteristics have been presented at a Reynolds number of Re = ۲۵۰۰. In comparison with the experimental results for stationary cases (α = ۰), the zones with lower streamwise velocity values became closer to the bodies as the rotation rates were enhanced. The maximum wake displacements have been obtained as ۱.۸D for the circular cylinder with no coating. For coated cylinders, these are ۱.۹D, ۱.۹D, ۱.۷D and ۱.۹۵D for the PMC۱, PMC۲, PMC۳ and PMC۴, respectively. For the same reason, the cross-stream velocity components also approached the circular cylinders. However, asymmetrical distributions for flow patterns have been attained. For this reason, the lower values for cross-stream velocity became more dominant in the wake. Moreover, separated flows were obviously seen by velocity fluctuations. The interaction of separated and wake flows induced these fluctuations. Wake lengths have been reduced compared to those of the cases with no rotation. The highest percentage for wake length reduction has been obtained as ۹۲.۹% by α = ۱.۰۵ for the bare cylinder. The maximum reductions have been attained as ۸۹.۷% by α = ۱.۰۵ for PMC۱, ۹۶.۳% by α = ۱.۰۵ for PMC۲, ۸۵.۷% by α = ۱.۵۷ for PMC۳ and ۹۰% by α = ۱.۰۵ for PMC۴. The experimental results have also been presented for turbulence values. The highest turbulence kinetic energy value, ۰.۲۳۶, has been obtained at α = ۱.۰۵ for the bare cylinder. These values are ۰.۲۷۱ at α = ۰.۵۲ for the PMC۱, ۰.۲۷۱ at α = ۱.۰۵ for PMC۲, ۰.۲۴۵ at α = ۱.۰۵ for the PMC۳ and ۰.۲۱۷ at α = ۰.۵۲ for the PMC۴. As with the flow patterns, the induction by surface coating has been clearly observed through the augmentation of α values. Since surface movement for coating has also been seen for these situations, boundary layer thickness values have been reduced.

کلیدواژه ها:

Flow control ، Particle Image Velocimetry (PIV) Porous media coated cylinder ، Reynolds number ، Rotation rate