A large-eddy simulation (LES) study is undertaken to explore the complex flow of developing turbulent flow through stationary and rotating U-ducts with strong curvature. Three flow cases are investigated: stationary (non-rotating), positive and negative rotational cases. Stationary and positive rotational cases are shown to have similar flow characteristics in terms of the mean velocity variations, although the predicted separation zone is nearly doubled in size for positive rotational case. Unlike the positive rotation for which the laminarization effects are observed, turbulence is significantly enhanced for the negative rotation mainly due to the existence of strong secondary flow. Turbulence is found to be highly anisotropic throughout the duct apart from the far downstream regions of the bend for the negative rotational case. The stress strain relation seems to be completely invalid in the U-duct apart from the bend region. Copyright (C) 2009 John Wiley & Sons, Ltd.