EFFECT OF BEARING POSITION ON THE VIBRATION RESPONSE FOR ROTOR–BEARING–FAN SYSTEM USING FLUID STRUCTURE INTERACTION (FSI)

Abstract

This paper presents a theoretical and experimental study to investigate the effect of the bearing position on the vibration response of a centrifugal fan – rotor – bearing system. The theoretical analysis includes fluid – structure interaction (FSI) analysis. ANSYS Parametric Design Language (APDL) was used for this purpose. The interaction between the two fields typically takes place at the boundary of the model solution (the fluid – structure interface on the fan impeller), where the results of one field are passed to other field as a load. This load is already sensitive to dynamic pressure pulsation developed either as a part of normal fan operation or as a result of abnormal structure dynamic or aerodynamic un stabile conditions. The experimental work is done on a test rig designed and constructed at the workshop of Baghdad – South Steam Power Plant. A single – stage centrifugal fan impeller is driven by a motor through coupling and driving rotor. The rotor is supported by two journal bearings, where the axial position of one of them is controlled by means of sliding mechanism and control circuit. The test rig is equipped with multisensory system for measuring the essential experimental parameters. The results indicated distinguished bearing positions at which the response is so high. These positions must be taken into account to avoid the higher response of vibration. The values of the stiffness and damping coefficients are fluctuating along the span position due to the change in the value of the external loads on the bearings. Also, their behavior depends on the bearing oil pressure.