Direct numerical simulation of a turbulent 90º bend pipe flow

Direct numerical simulation (DNS) has been performed for a spatially develop- ing 90 bend pipe ow to investigate the unsteady ow motions downstream of the bend. A recycling method is implemented to generate a fully-developed turbulent in ow condition. The Reynolds number of the pipe ow is ReD = 5300 and the bend curvature is = 0:4. A long straight pipe section (40D) is attached in the downstream of the bend to allow the ow to develop. Flow oscillations downstream of the bend are measured using several methods, and the corresponding oscillation frequencies are estimated. It is found that di erent characteristic frequencies are obtained from various ow measurements. The stagnation point movement and single-point velocity measurements may not be good measures to determine the swirl-switching frequency. The oscillations of the lateral pressure force on the pipe wall and half-sided mass ow rate are proposed to be a more unambiguous measure of the unsteady ow motions downstream of the bend