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Aerodynamic Instability Modeling of a High Speed Centrifugal Compressor

Saboori, Rozhin | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44140 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Ghorbanian, Kaveh
  7. Abstract:
  8. The present thesis investigates the surge phenomenon of high speed centrifugal compressors. Surge is a highly undesired condition and may cause severe damage to the machine and thus the plant. Traditionally, surge is avoided via a surge avoidance scheme wih recycle valve in discharge at the most common approach. A one dimensional technique is developed where the Greitzer lumped parameter model along with the Gravdahl one dimensional model is considered as the basis. Shaft dynamics, volume dynamics, losses, energy transfer and time lag are imbedded in the present model to improve the prediction of the compressor characteristics beyond the stability region. On the other hand, in order to capture all the phenomena related to high speed, the mean streamline analysis is being used to produce the compressor map in high speed operations. To increase the accuracy of the model, the state equation is changed from ideal gas to real gas and sonic speed is calculated as a function of the temperature. Thus in high speed compressor the high Mach number will affect the temperature, enthalpy, entropy and associated effects are entered through the dynamic model by γRT. On the Other hand, to make the surge prediction model more precise, the bulk model of the compressor in the lumped parameter model is modified to a stage-by-stage model. Since the assumptions of lumped parameter model decrease the accuracy, stage-by-stage analysis makes the solution more reliable and precise. Further, conventional passive controller is linked with the basic models. For the conventional passive controller the recycling system is investigated
  9. Keywords:
  10. Surge (Fluid) ; Stage by Stage Model ; Centrifugal Compressor ; Instability Analysis ; Instability in Compressors ; Lumped Parameter Method

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