Ph.D. Thesis Proposal by
(Advisor: Dr. J.V.R. Prasad)
“Modelling of Multistage Axial-Centrifugal Compressor Configuration using Stream Tube Approach”
Wednesday, November 15, 2017 @ 3 p.m.
Montgomery Knight 325
Quasi-1D flow models based upon mean-line analysis are quite popular for design and performance evaluation of multistage axial and centrifugal compressors. However, they are not so readily used for analyzing the dynamic behavior of the compressor. In this work, an unsteady 1D axial-centrifugal compressor model has been proposed, where the stage elements i.e. rotors and stators are modelled as diffusing stream tube components. The analysis being independent of any stage aerodynamic force and work terms, accurately predicts the performance of a four-stage axial industrial compressor by the incorporation of various loss mechanisms compounding to total stagnation pressure losses within stage elements. The flow communicates dynamically between two connected stream tubes through a boundary element called Compact Interface Element (CIE) which has been implemented by making use of the characteristic-based approach. CIE achieves reference frame transformation between the successive elements and also incorporates losses due to sudden flow turning occurring in a compact zone. These inlet turning and mixing loss models constitute an important feature of this work and have been implemented by the inclusion of a single model parameter. This parameter called mixing loss factor, is then tuned for nominal shaft speed and is subsequently used to predict the compressor performance for different speeds ranging from 50% to 105%. The surge line has also been accurately predicted by the suitable choice of critical incidence angle for stage elements.
Another aspect of compressor operation is the observance of aerodynamic instabilities as the compressor is throttled to stall. Several simulations performed through the numerical solution of unsteady flow equations indicate the existence of modal perturbations prior to the stall. However, at very high compressor speeds such modal perturbations are generally not present and the compressor plunges into surge through the mechanism of spike or abrupt stall. For large plenum attached at the compressor end, the stability criterion at high speed coincides with the peak of characteristic curve.
Dr. J.V.R. Prasad (Advisor)
Dr. Yedidia Neumeier
Dr. Lakshmi Sankar (AE)
Dr. Jechiel Jagoda (AE)
Dr. Rakesh Srivastava (Honeywell)