Experimental study on laminar flow over two confined isothermal cylinders in tandem during mixed convection

An experimental investigation of laminar aiding and opposing mixed convection is carried out using particle image velocimetry (PIV) to assess the thermal effects on the wake of two isothermal cylinders of equal diameter in tandem array placed horizontally and confined inside a vertical closed-loop downward rectangular water channel. The buoyancy effect on the flow distributions are revealed for flow conditions with Reynolds number based on cylinder diameter of Re = 100 and 200, blockage ratio of BR = D/H = 0.3, aspect ratio of AR = W/D = 5, pitch-to-diameter ratio of σ=L/D = 3, and values of the buoyancy parameter (Richardson number) in the range −1≤Ri≤ 3. In this work, the interference effects on the complex flow features are presented in the form of mean and instantaneous contours of velocity and vorticity. In addition, separation angles, wake structure, recirculation bubble lengths, time traces of velocity fluctuation, Strouhal number and vortex shedding modes of the two-cylinder system are obtained as a function of the Richardson number. In this arrangement, the results indicate that the effects of the Reynolds number are very pronounced, and that the vortex shedding patterns exhibit a strong dependence on Ri. We also show the modulation effect of the channel walls on the three-dimensional flow under varying thermal buoyancy, and the results reported herein demonstrate how the flow structure, wake behavior and vortex shedding pattern are entirely different from that behind a single circular cylinder under wall confinement and thermal effects.