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Evaluation of mixing plane techniques for 3D analysis of multistage compressors
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The behavior of the complex flow field in a turbomachine fan or compressor, is largely governed by the unsteady rotor-stator interaction, Well proven CFD techniques have been developed for describing these types of flow phenomena. For engineering problems all flow details is not always necessary to be predicted, therefore approximate models have been designed. We will here use a model called ”steady three-dimensional multistage method” [3]. This model aims at taking into account a significant part of the blade row interaction phenomena between stators and rotors in a compressor or fan, by passing the averaged flow states between blade row domains, at the interface. In order to transfer information between rotary and stationary blade rows, the method uses the mixing-plane approach, which calculates a ”mixed-out” flow state, that can be used as a boundary condition for the interface. First a steady (time averaged) flow state is computed in the blade passage, in the blade rows own reference frame. At the mixing planes, which separate the blade row passages, a change of reference frame and an exchange of tangentially averaged flow quantities takes place. In this thesis we carry out an evaluation of different averaging techniques, and numerical implementation of the mixing-plane interface, on a one and a half stage fan. In order to ensure conservation, flux correction is required on both sides of the interface. Several types of weighting coefficients are tested on the tangential distribution of the correction term. The results indicate that variation in averaging techniques, yield little or no differences in the computed flow field, the fact that an average is required has more importance by itself, than the details of the averaging procedure. The different averaging techniques proved to have some influence on the total efficiency ç of the fan. Previous investigation for a 2-D case, comparing steady and unsteady solutions, with regards to isentropic efficiency, recommended energy averaging for obtaining the best correlation concerning the predicted efficiency. The computation time for area and energy averaging can be considered equal, while the flux method requires 20% more computation time per iteration. Comparing the results for the different weighting factors for the flux correction, there are negligible influences on the flow field and on the fan’s total efficiency. In the future one would like to expand the mixing-plane method, so it can be used for off design problems, for example to predict rotating stall. This means that unsteady effects must be included in the mixing-plane approach, either via extra source terms (so called deterministic stress), or via unsteady boundary conditions.

Place, publisher, year, edition, pages
2001.
Keyword [en]
Technology, Fluid mechanics, Navier-Stokes, Turbomachinery, Fan, Compressors, Mixing-plane, Rotor Stator blad, Averageing, Fluxes
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-52150ISRN: LTU-EX--01/014--SELocal ID: 94aab4a5-3f8a-42da-88a9-3af505dd9b80OAI: oai:DiVA.org:ltu-52150DiVA: diva2:1025517
Subject / course
Student thesis, at least 30 credits
Educational program
Computer Science and Engineering, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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