Abstract: The 3 D turbulent flows in 90° bends with different cross sections have been analyzed with incompressible,time averaged N-S equation.The capability of k ε turbulence model for predicting the flow field with very strong curvature has been verified by the pipe bend ( R_c/D =0 87) experimental data made by the authors.Calculations of 3 D flow field in a 90° duct bend and a 90° pipe bend are presented.The results show that,before occurrence of the low velocity area formed mainly by the interchange of secondary flows near the inner wall,the mean velocity field predicted by the k ε turbulence model is proved in reasonably good agreement with the experimental data even though the curvature of bends is very strong.But as soon as the above mentioned low velocity area appears,the prediction accuracy of the k ε turbulence model greatly drops down.