Heat transfer from the stagnation area of a heated cylinder at ReD = 140,000 affected by free-stream turbulence

The effect of free-stream grid-turbulence on the flow around and heat transfer from the stagnation region of a circular cylinder was studied using direct numerical simulations (DNS). Simulations with and without free-stream fluctuations were carried out at a Reynolds number of ReD = 140,000 (based on the inflow velocity and the cylinder diameter D), which is in the higher subcritical range. A splitter plate was introduced behind the cylinder to counteract the formation of a vortex street. To resolve the flow up to 746.5 million grid points were employed. Compared to the fully laminar simulation, the addition of Tu = 30% grid turbulence at the inflow plane was found to lead to an increase in heat transfer at the stagnation line of the cylinder of 66%. A very good agreement was obtained with the correlations of Dullenkopf and Mayle [K. Dullenkopf, R. Mayle, The effects of incident turbulence and moving wakes on laminar heat transfer in gas turbines, ASME J. Turbomach. 116 (1994) 23–28; K. Dullenkopf, R. Mayle, An account of free-stream-turbulence length scale on laminar heat transfer, ASME J. Turbomach. 117 (1995) 401–406].