The trend of modern turbomachines towards lighter and slimmer blades exposed to higher loadings has made forced response problems emerge as a major concern in the design process of these machines. Forced response accounts for unsteady forces on the blade due to non-uniformities in the flow field. The clocking method, which consists in this case in changing the relative circumferential position between two consecutive stator blade rows, represents a possibility to reduce the excitation level of the blade’s natural modes. The goal of this investigation was to analyze the influence of the clocking method on a transonic compressor in order to find an optimum regarding aerodynamic forcing. The investigation was carried out in three parts. The first consisted in a computational fluid dynamics analysis which aimed at calculating the unsteady forces acting on the blades. The second consisted in a finite element analysis with the purpose of obtaining the mode shapes of the dangerous natural modes of the blades. In third part, the two analyses were coupled in order to evaluate the excitation level of the blades for seven equally-spaced clocking cases that covered a complete circumferential pitch. The results revealed that changing the circumferential position of the inlet guide vane with respect to the first stator blade row can reduce the excitation level of the rotor blade row in between by more than 50 percent and of the stator blade row by about 30 percent. Variations of the force distribution affecting sensible zones of the blade were detected, which explains the changes for the different clocking positions. An optimal clocking position was proposed regarding minimum excitation levels of the critical modes. Keywords: turbomachine, forced response, unsteady forces, clocking
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-39076 |
| Date | January 2011 |
| Creators | Villanueva, Daniel |
| Publisher | KTH, Kraft- och värmeteknologi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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