Research Papers

Large Eddy Simulation for Turbines: Methodologies, Cost and Future Outlooks

[+] Author and Article Information
James Tyacke

Whittle Laboratory,
University of Cambridge,
Cambridge CB30DY, UK
e-mail: jct53@cam.ac.uk

Paul Tucker, Richard Jefferson-Loveday, Nagabushana Rao Vadlamani, Robert Watson, Iftekhar Naqavi, Xiaoyu Yang

Whittle Laboratory,
University of Cambridge,
Cambridge CB30DY, UK

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 11, 2013; final manuscript received July 16, 2013; published online November 19, 2013. Editor: Ronald Bunker.

J. Turbomach 136(6), 061009 (Nov 19, 2013) (13 pages) Paper No: TURBO-13-1148; doi: 10.1115/1.4025589 History: Received July 11, 2013; Revised July 16, 2013

Flows throughout different zones of turbines have been investigated using large eddy simulation (LES) and hybrid Reynolds-averaged Navier–Stokes-LES (RANS-LES) methods and contrasted with RANS modeling, which is more typically used in the design environment. The studied cases include low and high-pressure turbine cascades, real surface roughness effects, internal cooling ducts, trailing edge cut-backs, and labyrinth and rim seals. Evidence is presented that shows that LES and hybrid RANS-LES produces higher quality data than RANS/URANS for a wide range of flows. The higher level of physics that is resolved allows for greater flow physics insight, which is valuable for improving designs and refining lower order models. Turbine zones are categorized by flow type to assist in choosing the appropriate eddy resolving method and to estimate the computational cost.

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Fig. 1

Grid requirements for the turbine region (from Tucker [18]) with suggested modeling of different flows. Anticlockwise from top-left; LPT blade; CBTE; ribbed cooling ducts; rim seals; labyrinth seals; HPT blade.

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Fig. 2

RANS-NLES approach: (a) modified length scale l versus true wall distance d, and (b) modified length scale contours for a turbine blade

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Fig. 3

Vorticity magnitude isosurface colored by pressure for the high pressure turbine blade using RANS-NLES (code B)

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Fig. 4

Pressure coefficient profiles at different spanwise locations using: (a) URANS (code A), and (b) RANS-NLES (code B)

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Fig. 5

Computational domain and the boundary conditions considered (code B)

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Fig. 6

Comparison of axial Reynolds stress profiles of simulation B with DNS data (code B)

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Fig. 7

(a) Slot flow schematic and vorticity contours showing K–H development downstream of the slot exit (code F), and (b) growth of vortical structures from the shear layer (code F)

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Fig. 8

CBTE η for various RANS models (code D) and a RANS-NLES simulation (code A)

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Fig. 9

Comparison of the LES and measured mean velocity and turbulent stress profiles for the Kacker and Whitelaw case [43]. The LES and measurements are represented by the solid line with filled symbols and the dashed line with unfilled symbols is for the blowing ratios of 2.3 and 0.75, respectively (code F).

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Fig. 10

(a) Grid for the Martini et al. [11] case, (b) η plot for the RANS and RANS-NLES at the blowing ratio = 0.35–0.5 (code A), and (c) the pedestal influence on the Kelvin–Helmholtz type vortices (vorticity magnitude isosurfaces)

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Fig. 11

Internal cooling duct: (a) velocity profile location in the center of the duct, (b) geometry with vorticity isosurfaces (code A), and (c) the Nusselt number profile on the lower wall

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Fig. 12

(a) Velocity profiles for the RANS and LES methods, and (b) lower wall Nusselt number distribution (codes A and D are indicated by the line legend in brackets)

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Fig. 13

Section of the seal, with the convergent flow direction and velocity profile locations indicated

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Fig. 14

Convergent flow, tangential velocity profiles at location A: (a) RANS, and (b) LES. Note: the code used is displayed in the line legends in brackets.

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Fig. 15

Pitchwise-averaged total pressure loss coefficient for (a) the baseline no-cavity validation case (circular symbols: measurements [50]; solid line: RANS-NLES), (b) Hamilton–Jacobi (HJ) length scale and standard model versus high order RANS-NLES for the included cavity case (triangular symbols: RANS-NLES; solid line: HJ-RANS; dashed line: standard RANS), and (c) vorticity magnitude isosurfaces for the included cavity geometry. All using code B.

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Fig. 16

DNS mesh over highly irregular surface roughness elements

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Fig. 17

Mean velocity profiles showing agreement between smooth wall DNS and the law of the wall, sand grain roughness and real surface roughness (code B, DNS)

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Fig. 18

Difference in the near wall streaklike structure (isosurfaces of U) between: (a) smooth, and (b) rough wall DNS

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Fig. 19

Extent of κ−5/3 range (fraction of the fan κ−5/3 range of length scales)

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Fig. 20

(a) RANS grid (enlarged wake region inset), and (b) percentage of resolved energy contours and refinement strategy

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Fig. 21

(a) Refined LES grid (enlarged wake region in inset), and (b) percentage of resolved energy for the refined LES grid




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