Effect of corner radius on flow topology and heat transfer from free oscillating tandem cylinders at low Reynolds number

Flow-induced vibration (FIV) on two tandem cylinders with forced convection is numerically investigated at a constant Re = 150. Elastically mounted cylinder with four different values of corner radii (r* = r/R: r = radius of fillet; R = radius of circle) = 0 (square cylinder), 0.25, 0.75, and 1 (circular cylinder) with two spacing ratio ( L / D) = 4 and 2 is studied. Transverse oscillations are generated from the cylinder having non-dimensional mass ( m *) = 10. The structural damping coefficient is assigned a zero value with varying reduced velocity U r = 2 - 10. The two-dimensional incompressible Navier-Stokes and energy equations are solved together with Newton's second law governing the motion of the cylinders. Both cylinders' surfaces are maintained at a higher constant temperature of T * = 1, and incoming flow is set to be at T * = 0 with Prandtl number (Pr) = 0.7. The effect of r* and L / D is observed on the flow structure and FIV parameters. Flow characteristics at L / D = 4 such as steady flow, reattachment, and unsteady flow are examined. A "shift " in vibrational amplitude is noted from r* = 1 and 0.75 to r* = 0 and 0.5, respectively. The downstream cylinder ( D C) experiences a hike in vibration amplitude due to the impingement of vortex shedding from the upstream cylinder ( U C). r* = 1 has 18.1% higher vibrational amplitude than r* = 0 at their respective lock-in regimes for D C. For L / D = 2, vortices from upstream and downstream cylinders interact to form C(2S) and 2S types of vortex shedding. Different regimes, such as single body, reattachment, and co-shedding, have been observed while changing L / D. r* = 0.75 results in 13.3% higher oscillation amplitude as compared to r* = 0.5 for D C. The average Nusselt number ( N u avg) strongly depends on flow topology, corner radius, and vibrational amplitude A / D. At low L / D, heat transfer from the downstream cylinder is plummeted due to rolling of shear layers over the cylinder. There is a significant change in N u avg due to higher vibration; for example, increase in 10.71% change is observed from U r = 2 to U r = 6 for r*=1 and L / D = 4. Corner radii also alter the N u avg as a decrease in 27.39% from r* = 1 to r* = 0 at U r = 10 and L / D = 4 ( U C).