Dynamics of tandem cylinders in the vicinity of a plane moving wall

• Early onset of co-shedding for gap ratio = 0.5 for tandem cylinders with near-wall.
• Parallel double-vortex row arrangement in co-shedding regime at e/D=0.5e/D=0.5.
• Inviscid Kármán stability analysis of parallel vortex double-rows.
• Gradual recovery of tandem freestream dynamics from gap ratio=3ratio=3–5.0.
• Enhanced unsteady fluctuations in force signals of downstream cylinder.

We present dynamics of the flow around two cylinders in a tandem configuration along a moving plane wall. A spectral element method is employed to perform the simulations with high accuracy at Reynolds number Re=200Re=200. A moving wall with no-slip boundary is considered rather than a stationary wall to avoid the confusing interaction of the wall boundary layer and thus focus completely on the influence of wall proximity effects on the force and wake dynamics. The influence of the moving wall with gap ratio e/D=0.2e/D=0.2–5.0 and longitudinal center-to-center separation L/D=1.5−8.0L/D=1.5−8.0 on the unsteady force dynamics is examined for the two cylinder configuration. Through detailed analysis of the flow field dynamics, we observe early transition from reattachment to co-shedding behavior. At co-shedding separation distances, the combined wake interference and wall proximity effects lead to a parallel double-row of vortices for the tandem cylinders at Re=200Re=200 for e/D=0.5e/D=0.5. For a longitudinal separation of 4D, the ratio of the street width h to distance between two adjacent vortices in the same row l is in good agreement with that obtained from inviscid theory. Finally, we provide detailed flow visualizations, Strouhal number and force coefficient trends and investigate recovery of freestream behavior as the tandem cylinder configuration of varying L/D is gradually distanced further from the moving plane wall.