A study of turbulent heat transfer in curved pipes by numerical simulation

Turbulent heat transfer in curved pipes was studied by numerical simulation. Two curvatures delta (pipe radius a / curvature radius c) were considered, 0.1 and 0.3; results were also obtainedfor a straight pipe (delta=0) for comparison purposes. A tract of pipe 5 diameters in length was chosen as the computational domain and was discretized by finite volume multiblock structured grids of ~5.3x10^6 hexahedral cells. Fully developed conditions were assumed; the friction velocity Reynolds number was 500, corresponding to bulk Reynolds numbersbetween 12 630 and ~17 350 according to the curvature, while the Prandtl number was 0.86.Simulations were protracted for 20 LETOT’s a/utau; the last 10 LETOT’s were used to compute first and second order time statistics, including rms fluctuating temperature andturbulent heat fluxes.In curved pipes, time averaged results exhibited Dean circulation and a strong velocity and temperature stratification in the radial direction. Turbulence and heat transfer were strongly asymmetric, with higher values near the outer pipe bend. In the outer region, counter-gradient heat transport by turbulent fluxes was observed. For a given friction velocity Reynolds number, overall turbulence levels were lower than in a straight pipe; nevertheless, heat transfer rates were larger due to the curvature-induced modifications ofthe mean flow and temperature fields.