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Effects of multiblocking and axial gap distance on performance of partial admission turbines: A numerical analysis
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2011 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, no 3, p. 031028-Article in journal (Refereed) Published
Abstract [en]

In this paper, the effects of axial gap distance between the first stage stator and rotor blades and multiblocking on aerodynamics and performance of partial admission turbines are analyzed numerically. The selected test case is a two stage axial steam turbine with low reaction blades operating with compressed air. The multiblocking effect is studied by blocking the inlet annulus of the turbine in a single arc and in two opposing blocked arcs, each having the same admission degree. The effect of axial gap distance between the first stage stator and rotor blades is studied while varying the axial gap by 20% compared with the design gap distance. Finally, full admission turbine is modeled numerically for comparison. Performance of various computational cases showed that the first stage efficiency of the two stage partial admission turbine with double blockage was better than that of the single blockage turbine; however, the extra mixing losses of the double blockage turbine caused the efficiency to deteriorate in the downstream stage. It was shown that the two stage partial admission turbine with smaller axial gap than the design value had better efficiency of the first stage due to lower main flow and leakage flow interactions; however, the efficiency at the second stage decreased faster compared with the other cases. Numerical computations showed that the parameters, which increased the axial force of the first stage rotor wheel for the partial admission turbine, were longer blocked arc, single blocked arc, and reduced axial gap distance between the first stage stator and rotor blades.

Place, publisher, year, edition, pages
2011. Vol. 133, no 3, p. 031028-
Keywords [en]
Aerodynamics, Cold storage, Compressed air, Leakage (fluid), Marine engines, Numerical analysis, Rotors, Stators, Steam turbines
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-13590DOI: 10.1115/1.4002415ISI: 000287810000003Scopus ID: 2-s2.0-79952036294OAI: oai:DiVA.org:kth-13590DiVA, id: diva2:326150
Note

QC 20100622

Available from: 2010-06-22 Created: 2010-06-21 Last updated: 2024-03-18Bibliographically approved
In thesis
1. Numerical Analysis of Partial Admission in Axial Turbines
Open this publication in new window or tab >>Numerical Analysis of Partial Admission in Axial Turbines
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

HTML clipboard Numerical analysis of partial admission in axial turbines is performed in this work. Geometrical details of an existing two stage turbine facility with low reaction blades is used for this purpose. For validation of the numerical results, experimental measurements of one partial admission configuration at design point was used. The partial admission turbine with single blockage had unsymmetrical shape; therefore the full annulus of the turbine had to be modeled numerically.

The numerical grid included the full annulus geometry together with the disc gaps and rotor shrouds. Importance of various parameters in accurate modeling of the unsteady flow field of partial admission turbines was assessed. Two simpler models were selected to study the effect of accurate modeling of radial distribution of flow parameters. In the first numerical model, the computational grid was two dimensional and the radial distribution of flow parameters was neglected. The second case was three-dimensional and full blades’ span height was modeled but the leakage flows at disc cavity and rotor shroud were neglected. Detailed validation of the results from various computational models with the experimental data showed that modeling of the leakage flow at disc cavities and rotor shroud of partial admission turbines has substantial importance in accuracy of numerical computations. Comparison of the results from two computational models with varying inlet extension showed that modeling of the inlet cone has considerable importance in accuracy of results but with increased computational cost.

Partial admission turbine with admission degree of  ε = 0.524 in one blocked arc and two opposing blocked arcs were tested. Results showed that blocking the inlet annulus in one single arc produce better overall efficiency compared to the two blocked arc model. Effect of varying axial gap distance between the first stage stator and rotor rows was also tested numerically for the partial admission turbine with admission degree of  ε = 0.726. Results showed higher efficiency for the reduced axial gap model.

Computations showed that the main flow leave the blade path down to the disc cavity and re-enter into the flow channel downstream the blockage, this flow would pass the rotor with very low efficiency. First stage rotor blades are subject to large unsteady forces due to the non-uniform inlet flow. Plotting the unsteady forces of first stage rotor blades for partial admission turbine with single blockage showed that the blades experience large changes in magnitude and direction while traveling along the circumference. Unsteady forces of first stage rotor blades were plotted in frequency domain using Fourier transform. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction.

Results obtained from the numerical computations showed that the discs have nonuniform pressure distribution especially in the first stage of partial admission turbines. The axial force of the first rotor wheel was considerably higher when the axial gap distance was reduced between the first stage stator and rotor rows. The commercial codes used in this work are ANSYS ICEM-CFD 11.0 as mesh generator and FLUENT 6.3 as flow solver.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. p. 114
Series
Trita-KRV, ISSN 1100-7990 ; 2010:02
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-12856 (URN)978-91-7415-390-3 (ISBN)
Public defence
2010-05-21, Sal M2, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100622Available from: 2010-05-17 Created: 2010-05-17 Last updated: 2022-06-25Bibliographically approved

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Baagherzadeh Hushmandi, NarminFransson, Torsten

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