Influence of wall proximity on flow around two tandem circular cylinders

An experimental study was conducted to investigate the flow around two tandem cylinders placed near and parallel to a plane wall. The Reynolds number based on the cylinder diameter (D) was 6300. The cylinder centre-to-centre spacing ratio (L*=L/D) was varied from 1.5 to 6, and the gap-height-to-cylinder-diameter ratio (G* =G/D) from 0.15 to 2. The flow fields were measured using Particle Image Velocimetry (PIV), in conjunction with measurements of fluid dynamic forces (drag and lift) on the downstream cylinder using load cell. The flow strongly depends on the combined value of G* and L*. With reference to G*, the flow could be classified as vortex-shedding suppression regime (G* < 0.3), intermediate-gap regime (0.3 < G* < 1) where vortex shedding occurs but is influenced by wall proximity, and large-gap regime (G* > 1) where the wall influence becomes negligible. Similarly, three categories can be identified as a function of L*, namely, extended-body regime 1 < L* < 2, reattachment regime at 2 < L* < 4, and impinging regime at L* > 4. Variations of dynamic drag and lift coefficients, spectra, Strouhal numbers, and Reynolds shear stress are also presented to characterize the different flow regimes in the G*-L* plane. (C) 2014 Elsevier Ltd. All rights reserved.