Fluctuating pressure calculation induced by axial flow trough mixing grid

Computational Fluid Dynamics (CFD) simulations is used with the STARCCM software to calculate fluctuating fluid forces acting on the rods induced by the mixing vanes. The results presented show that the fluid force acting on the rod is mostly due to the fluid pressure. This force can be decomposed into a mean part and a fluctuating part. The fluctuating force decays along the rod but show some coherence length depending on the frequency. This has to be accounted for in the definition of the fluid force acting on a rod. The structural code results gives an estimation of the fretting wear damage of the rod. The comparison of the present results with the reduced spectra used in the structural code show that the reduced spectra definition could be improved to be closer to the reality, in order to finally have a better estimation of the fretting wear.