Calculation Methods for the Determination of Blade Excitation Due to Suction Elbows in Centrifugal Compressors

Experimental investigations on a single stage centrifugal compressor showed that asymmetric suction elbows can cause unacceptable blade vibrations. For turbocharger applications it is important to assess this issue in an early design phase. Although computational methods are known to estimate the influence of the asymmetric flow structure on referring blade vibration resonance by means of unsteady CFD and FE vibration analysis, those are not suitable for the design process, as they are too time and CPU consuming. Thus, the focus of this project is to define a procedure which determines the blade excitation by simplified models that can easily be integrated into the compressor design loop. For the evaluation of blade excitation due to asymmetric incoming flow, the flow fields at the inlet of the impeller using calculation methods of varying accuracy are compared. The potential energy of the harmonic blade excitations at the inlet of the impeller at different axial and radial positions is determined and evaluated by Fast Fourier Transform analysis over the circumference. The flow field of the unsteady calculation acts as a reference, since it was used to reproduce the measured blade vibrations in an accurate way in [1]. The blade excitation potential due to asymmetric incoming flow is examined by means of several steady CFD calculations, each differing in the model resolution. It is shown that the potential blade vibration excitation due to suction elbows or asymmetric aspiration ports is accurately determined by a standard steady-state calculation and therefore the computational effort can be minimized.Copyright © 2009 by ASME