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Flows in Complex Systems

Investigating the Cause of Computational Fluid Dynamics Deficiencies in Accurately Predicting the Efficiency and Performance of High Pressure Turbines: A Combined Experimental and Numerical Study

[+] Author and Article Information
Meinhard T. Schobeiri1

 Turbomachinery Performance and Flow Research Laboratory, Texas A&M University, College Station, TX 77843-3123tschobeiri@mengr.tamu.edu

S. Abdelfattah, H. Chibli

 Turbomachinery Performance and Flow Research Laboratory, Texas A&M University, College Station, TX 77843-3123

1

Corresponding author.

J. Fluids Eng 134(10), 101104 (Oct 05, 2012) (12 pages) doi:10.1115/1.4007679 History: Received May 04, 2011; Revised June 26, 2012; Published October 05, 2012; Online October 05, 2012

Despite the tremendous progress over the past three decades in the area of turbomachinery computational fluid dynamics, there are still substantial differences between the experimental and the numerical results pertaining to the individual flow quantities. These differences are integrally noticeable in terms of major discrepancies in aerodynamic losses, efficiency, and performance of the turbomachines. As a consequence, engine manufacturers are compelled to frequently calibrate their simulation package by performing a series of experiments before issuing efficiency and performance guaranty. This paper aims at identifying the quantities, whose simulation inaccuracies are preeminently responsible for the aforementioned differences. This task requires (a) a meticulous experimental investigation of all individual thermofluid quantities and their interactions, resulting in an integral behavior of the turbomachine in terms of efficiency and performance; (b) a detailed numerical investigation using appropriate grid densities based on simulation sensitivity; and (c) steady and transient simulations to ensure their impact on the final numerical results. To perform the above experimental and numerical tasks, a two-stage, high-pressure axial turbine rotor has been designed and inserted into the TPFL turbine research facility for generating benchmark data to compare with the numerical results. Detailed interstage radial and circumferential traversing presents a complete flow picture of the second stage. Performance measurements were carried out for design and off-design rotational speed. For comparison with numerical simulations, the turbine was numerically modeled using a commercial code. An extensive mesh sensitivity study was performed to achieve a grid-independent accuracy for both steady and transient analysis.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The TPFL research turbine facility with its components; the circumferential traversing system [9] is driven by another traversing system sitting on a frame and is perpendicular to this plane

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Figure 2

Detailed picture of the TPFL research turbine component with subcomponents: the radial and circumferential traversing system, clocking system, the integrated heater-inlet, torque meter, flexible couplings and the dynamometer

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Figure 6

Rotor blade profiles stacked from hub to tip with a strong flow deflection at the hub

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Figure 7

Positions of the three five-hole probes for radial and circumferential traverse of the flow field downstream of the first rotor, second stator, and second rotor. The probes are positioned in such a way that their wakes do not interfere with each other (see Fig. 4).

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Figure 8

Definition of the exit flow angles relative to the probe position

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Figure 9

Numerical analysis mesh (Mesh 4 shown)

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Figure 10

Grid sensitivity test; turbine efficiency variation as a function of number of elements

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Figure 11

(a) Change of residual values as a function of iteration number for RANS simulation. (b) Change of residual values as a function of normalized time step for URANS simulation.

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Figure 12

Comparison of the measured total pressures (top) and static pressure (bottom) at stations 3, 4, and 5 with the RANS and URANS computational results (solid, dashed curves, red, black, blue)

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Figure 13

Comparison of the measured absolute (top) and relative velocities (bottom) with the RANS and URANS computational results (solid, dashed curves, red, black, blue)

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Figure 14

Comparison of the measured absolute flow angle (top), relative flow angle (middle), and the meridional angle with the RANS and URANS computational results (solid, dashed curves, red, black, blue)

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Figure 15

Comparison of the measured stator and rotor loss coefficients (top) and their enlargement (middle) with RANS and URANS computational results. Bottom: RANS calculations of stator 1 and 2 and rotor 1 and 2 loss coefficients.

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Figure 16

Performance behavior of the two-stage turbine in terms of total-to-static efficiency versus u/co

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Figure 3

Stator blade with the a leaned only stacking from hub to tip

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Figure 5

Stator blade with the same profile, but circumferentially leaned from hub to tip

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Figure 4

Rotor blade with a strong flow deflection at the hub

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