The leakage flow between the shroud-pump impeller and its housing is simulated with a Navier-Stokes solver. The fluid-structure interactions are modelled with an Arbitrary Lagrangian Eulerian method (ALE). The force components and the rotordynamic coefficients obtained from the numerical simulation are compared to those calculated from measurement. The Navier-Stokes solver is a finite element code, N3S, developed by “Electricité de France”. It solves the Reynolds-averaged Navier-Stokes equations, with a standard k-ε model. The ALE method consists in a calculation of a mesh velocity. A first order approximation provides equations similar to the standard Navier-Stokes equations. Sulzer-pumps has performed measurements. The test installation consists of a test rig, a closed loop with the required components for pressure, temperature, and flow control, and a data acquisition and handling system. This test rig allows the identification of the rotordynamic coefficients of pump rotor components like impeller and annular seals. The dynamic coefficients comparison shows a good prediction of the numerical model, except for the stiffness coefficients. Other functionning conditions have to be tested before to conclude on the ALE model abilities. Although the requiered CPU time to reach the convergence is long, this type of model can be very interesting in the future for such a complicated 3D flow.