Investigation of the influence of different rotor components on the axial impeller tip clearance at different operating points

This work examines a radial turbo-compressor for a high-temperature heat pump (HTHP) with steam as the working medium. The given boundary conditions result in very small blade heights for the impellers. It is therefore necessary to minimize the gap between the impeller and housing in order to ensure the lowest possible gap flow. It is to be expected that even small deviations towards a larger gap have a major negative impact on the performance of the compressor. Nevertheless, a collision must also be avoided. In order to find efficient and reliable impeller designs an automated optimization is performed considering aerodynamic as well structural aspects (Schaffrath et al., 2022). However, the optimal impeller design represents the so-called hot geometry under operating conditions, for the manufacturing process this geometry have to be transformed into the so-called cold geometry (Schaffrath et al., 2023). Due to the necessary quality of detail in the gap maintenance, the question arises as to whether it is sufficient to execute the hot-to-cold transformation exclusively on the impeller and whether there is a significant influence of the other components of the rotating system. The FE simulation is used to compare the maximum axial deformation values between the design of the single impeller and the entire rotating system. The result shows a deviation in axial deformation of more than 50% compared to the result of the ”hot-to-cold transformation” (H2C) used in optimization process chain. This shows that the single impeller calculation is not sufficient to precisely achieve the gap on which the CFD design is based.