Direct numerical simulation of turbulent heat transfer in curved pipes

Fully developed turbulent convective heat transfer in curved pipes was investigated by Direct Numerical Simulation for a friction velocity Reynolds number of 500, yielding bulk Reynolds numbers between 12 630 and ~17 350 according to the curvature (pipe radius/curvature radius). Three different curvatures were compared, i.e. 0 (straight pipe), 0.1 and 0.3. The Prandtl number was 0.86. The computational domain was a tract of pipe 5 diameters in length. A finite volume method was used, with multiblock structured grids of ~5.3x10E6 hexahedral volumes. Simulations were typically protracted for 20 LETOT’s starting from coarse-grid results. Results were post-processed to compute first and second order time statistics, including rms fluctuating temperature and turbulent heat fluxes, on a cross section of the pipe. In curved pipes, time-mean 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. Overall turbulence levels were lower than in a straight pipe