The motivation to setting three-dimensional eddy-resolving computations of turbulent flow in annual ax ial-radial diffusers is given. The results of numerical simulation of separated flow in an annual axial-radial diffuser previously studied experimentally are presented. Using the ANSYS FLUENT package, numerical solutions have been obtained on the basis of the Reynolds-averaged Navier-Stokes equations using different turbulence models, as well as with the Detached Eddy Simulation method. Possibilities of the applied methods for the diffuser efficiency prediction are evaluated by means of comparison of the calculated and experimental data. It has been shown that the loss values calculated by RANS at Re = 1,8×105 are the clos est to the experimental ones in case of the Spalart-Allmaras turbulence model. For this Reynolds number the calculation results produced by the IDDES method and the RANS approach almost coincide. At higher Re values the IDDES method predicts smaller loss values, as compared with RANS.