Centrifugal compressors cover a very large range of applications, from powers of a few watts to those of several megawatts. These compressors are used in gas turbines, turbochargers for cars and helicopter engines. Even though the maximum mass flows are lower than those produced by axial machines, the compression rates per stage are on the contrary very much higher (10 to 2 greater than those for axial compressors). Today, the efficiency of these machines exceeds 90%. However, because of changes in curvatures and technological effects, the flow that develops in these compressors is particularly complex. The interactions between the moving rotor and the diffuser cause unsteady phenomena that are not always well understood. Recourse to numerical simulation for analyzing these mechanisms may then well prove to be essential.
A joint Onera, Turbomeca and LMFA research program is aimed at improving the understanding of the flow in a high speed and high compression rate centrifugal compressor. The measurements taken by the LMFA were compared with the numerical results obtained by the Turbomachinery team using a 3D Navier-Stokes simulation (elsA code). The calculation clearly showed up the flow's topology in the clearance zone (fig. 1). This study also demonstrated how the results from a numerical simulation can complete the experimental data by providing information about areas where measurement is impossible.
Figure 1 : visualization of the streamlines in the clearance (3D computation)
