In this paper numerical results of wake and secondary flow interaction in diffuser flow fields are discussed. The wake and secondary flow are generated by a rotating wheel equipped with 30 cylindrical spokes with a diameter of 10 mm as a first approach to the turbine exit flow environment. The apex angle of the diffuser is chosen such that the flow is strongly separated according to the well-known performance charts of Sovran and Klomp (1967, “Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross-Section,” in Fluid Mechanics of Internal Flow, Elsevier, New York, pp. 272–319). This configuration has been tested in an experimental test rig at the Leibniz University Hannover (Sieker and Seume 2007, “Influence of Rotating Wakes on Separation in Turbine Exhaust Diffusers,” Paper No. ISAIF8-54). According to these experiments, the flow in the diffuser separates as free jet for low rotational speeds of the spoke-wheel, as expected by theory. However, if the 30 spokes of the upstream wheel rotate beyond the value of 500 rpm the measurements indicate that the flow remains attached to the outer diffuser wall. It will be shown by the present numerical analysis with the commercial solver ANSYS CFX-10.0 that only an unsteady approach using the elaborate scale adaptive simulation with the shear stress transport turbulence model is capable of predicting the stabilizing effect of the rotating wheel to the diffuser flow at larger rotational speeds. The favorable comparison with the experimental data suggests that the mixing effect of wakes and secondary flow pattern is responsible for the reattachment. As a result of our studies, it can be stated that the considerably higher numerical costs associated with unsteady calculations must be accepted in order to increase the understanding of the physical flow phenomena in turbine exit flow and its interaction with the downstream diffuser.
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October 2009
Research Papers
Effect of Wakes and Secondary Flow on Re-attachment of Turbine Exit Annular Diffuser Flow
David Kluß,
David Kluß
Department for Fluid Energy Machines,
e-mail: david.kluss@rub.de
Ruhr-Universität Bochum
, 44801 Bochum, Germany
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Horst Stoff,
Horst Stoff
Department for Fluid Energy Machines,
Ruhr-Universität Bochum
, 44801 Bochum, Germany
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Alexander Wiedermann
Alexander Wiedermann
Mem. ASME
MAN Turbo AG
, 46145 Oberhausen, Germany
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David Kluß
Department for Fluid Energy Machines,
Ruhr-Universität Bochum
, 44801 Bochum, Germanye-mail: david.kluss@rub.de
Horst Stoff
Department for Fluid Energy Machines,
Ruhr-Universität Bochum
, 44801 Bochum, Germany
Alexander Wiedermann
Mem. ASME
MAN Turbo AG
, 46145 Oberhausen, GermanyJ. Turbomach. Oct 2009, 131(4): 041012 (12 pages)
Published Online: July 6, 2009
Article history
Received:
August 22, 2008
Revised:
October 16, 2008
Published:
July 6, 2009
Citation
Kluß, D., Stoff, H., and Wiedermann, A. (July 6, 2009). "Effect of Wakes and Secondary Flow on Re-attachment of Turbine Exit Annular Diffuser Flow." ASME. J. Turbomach. October 2009; 131(4): 041012. https://doi.org/10.1115/1.3070577
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