On the Energy Transfer in Centrifugal Compressors

In the layout and calculation of centrifugal compressors there are still considerable uncertainties when it comes to the theoretical determination of energy transfer from the impeller to the flowing medium and to the subsequent energy conversion in the diffuser. These problems arise particularly where compressor stage design with high pressure ratios and mass flow rates are concerned. A solution to these questions can presumably be found only through a physically balanced interpretation of the extremely complex flow mechanisms in the impeller. Since purely theoretical methods have hardly led to any reliable conclusions concerning the criteria of flow separation in the impeller or the secondary character of the impeller flow, there is still little knowledge about the creation of the jet-and-wake zones in the impeller and their decay (associated with large losses) in the connected diffuser. In studying the energy conversion process in the stage as a whole, great attention has to be devoted to the effects of the momentum exchange directly downstream the impeller. Hence the only possible way of solving these problems seems to be specific experimentation. For high flow velocities, this necessitates a special nonsteady measuring technique which also gives information about the relative flow in the rotating impeller.