Momentum and Heat Transport in a Finite-Length-Cylinder Wake

This paper reports an experimental study of the turbulent momentum and heat transport in the wake of a wall-mounted finite-length square cylinder, with the aspect ratio R (= H/d, where H and d are cylinder height and width) chosen to be 3, 5 and 7. All tested cylinder was slightly heated, the temperature difference is about 1°C, so that the temperature can be considered as passive scalar. A moveable three-wire probe (a combination of an X-wire and a clod wire) was used to measure the velocity and temperature fluctuation, at a Reynolds number of 7,300 (based on d and free-stream velocity, U_∞). Measurements were performed at a downstream distance of 10d and different spanwise locations to investigate the effects of R on momentum and heat transport. Measurements were also conducted in a two-dimensional (2D) square cylinder wake to apply a benchmark. It is found that the distributions of time-averaged velocity and temperature are modified in different manners at various spanwise stations in a finite-length cylinder wake. Near the height of free end, time-averaged velocity is increased near the centerline by downwash flow, which entrains high speed fluid into the wake; whereas the mean temperature distribution is not changed significantly. At near the ground plate, the distribution of mean velocity is flattened; while the distribution of mean temperature is concentrated near the centerline. This suggests a more effective transport of momentum than heat near ground plate. Reynolds stresses, temperature variance and heat flux are impaired relative to those of 2D cylinder wake, especially for lateral normal stress. The effects of both downwash flow and boundary layer on the distributions of turbulent statistics become more obvious as R increases from 3 to 7.