Large-eddy simulations of 90° pipe bend flows

Oscillatory phenomena in separated turbulent flows through 90 degrees pipe bends are numerically investigated using large-eddy simulations. Curvature ratios of one and three pipe diameters are considered and the Reynolds numbers range from 5000 up to 27 000. The analysis of the simulations shows that the results are in good agreement with the experimental data. Spectra of the overall forces exhibit a distinct peak in the high-frequency range, related to vortex shedding at the inner side of the bends, and show a low-frequency oscillation at higher Reynolds numbers, which is due to an alternating domination of one of the Dean vortices. The Strouhal number of the low-frequency oscillation matches the so-called swirl switching frequency earlier found in experimental measurements.