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Research Papers

Blade Tip Carving Effects on the Aerothermal Performance of a Transonic Turbine

[+] Author and Article Information
C. De Maesschalck

Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse,
Brussels BE-1640, Belgium
e-mail: demaess@vki.ac.be

S. Lavagnoli

Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse,
Brussels BE-1640, Belgium
e-mail: lavagnoli@vki.ac.be

G. Paniagua

Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse,
Brussels BE-1640, Belgium
e-mail: paniagua@vki.ac.be

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received January 23, 2014; final manuscript received July 28, 2014; published online September 16, 2014. Assoc. Editor: Cengiz Camci.

J. Turbomach 137(2), 021005 (Sep 16, 2014) (10 pages) Paper No: TURBO-14-1010; doi: 10.1115/1.4028326 History: Received January 23, 2014; Revised July 28, 2014

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping. The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern rotor blade (Reynolds number of 5.5 × 105 and a relative exit Mach number of 0.9) by means of three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) calculations. Two novel contoured tip geometries were designed based on a two-dimensional (2D) tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.

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Figures

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Fig. 1

Tip carving design methodology

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Fig. 2

Detailed view of the computational domain

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Fig. 3

Geometrical cut sections for the evaluated tip shapes

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Fig. 4

Difference in heat transfer (ΔQ) onto the tip, SS (upper 25%) and the shroud between the medium and fine mesh solution

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Fig. 5

(a) Flat-tip rotor geometry and computational grid and (b) detail of the unstructured overtip mesh for different tip designs

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Fig. 6

Comparison of experimental [38] and numerical isentropic Mach number and Nusselt number distributions

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Fig. 7

Midgap flow angle for the four investigated tip geometries: (a) variation along the midgap camberline and (b) contours of midgap flow angle for the flat and squealer (twice the range) blade tip designs

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Fig. 8

Relative Mach number distribution in the midgap section with overtip flow streamlines

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Fig. 9

Tip (a), shroud (b), and upper 25% SS (c) heat transfer along the machine axis (fraction of flat tip average heat load (W/m2))

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Fig. 10

Heat transfer distribution onto the blade tip, shroud and upper 25% of the rotor SS

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Fig. 11

Relative Mach number contours in four planes normal to the blade SS and rotor heat transfer

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Fig. 12

Total pressure and vorticity magnitude contours for the four tip geometries, 0.5Cax downstream of the rotor trailing edge

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Fig. 13

Pitchwise-averaged radial distributions of relative total pressure and vorticity magnitude (normalized by the flat tip average), 0.5Cax downstream of the rotor trailing edge

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Fig. 14

Overall performance comparison against a flat tip configuration

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