Research Papers: Internal Combustion Engines

Aerodynamic Optimization of the High Pressure Turbine and Interstage Duct in a Two-Stage Air System for a Heavy-Duty Diesel Engine

[+] Author and Article Information
Uswah B. Khairuddin

Department of Mechanical Engineering,
Imperial College London,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: u.khairuddin13@imperial.ac.uk

Aaron W. Costall

Department of Mechanical Engineering,
Imperial College London,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: a.costall@imperial.ac.uk

1Corresponding author.

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 30, 2017; final manuscript received August 5, 2017; published online November 28, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(5), 052801 (Nov 28, 2017) (10 pages) Paper No: GTP-17-1239; doi: 10.1115/1.4038024 History: Received June 30, 2017; Revised August 05, 2017

Turbochargers reduce fuel consumption and CO2 emissions from heavy-duty internal combustion engines by enabling downsizing and downspeeding through greater power density. This requires greater pressure ratios and thus air systems with multiple stages and interconnecting ducting, all subject to tight packaging constraints. This paper considers the aerodynamic optimization of the exhaust side of a two-stage air system for a Caterpillar 4.4 l heavy-duty diesel engine, focusing on the high pressure turbine (HPT) wheel and interstage duct (ISD). Using current production designs as a baseline, a genetic algorithm (GA)-based aerodynamic optimization process was carried out separately for the wheel and duct components to evaluate seven key operating points. While efficiency was a clear choice of cost function for turbine wheel optimization, different objectives were explored for ISD optimization to assess their impact. Optimized designs are influenced by the engine operating point, so each design was evaluated at every other engine operating point, to determine which should be carried forward. Prototypes of the best compromise high pressure turbine wheel and ISD designs were manufactured and tested against the baseline to validate computational fluid dynamics (CFD) predictions. The best performing high pressure turbine design was predicted to show an efficiency improvement of 2.15% points, for on-design operation. Meanwhile, the optimized ISD contributed a 0.2% and 0.5% point efficiency increase for the HPT and low pressure turbine (LPT), respectively.

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Fig. 1

Side view of the CAT C4.4 ACERT™ Industrial Engine [8], indicating the air system components of interest

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Fig. 2

Full 3D CFD domain components

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Fig. 3

Stations for the two-stage turbines

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Fig. 4

Baseline ISD design showing interface with bellows

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Fig. 5

Control splines and boundary for ISD shape change

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Fig. 6

Rotating inlet boundary applied at domain inlet

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Fig. 7

Velocity streamlines and vectors for full-stage and rotating inlet boundaries (identical scales)

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Fig. 8

HPT wheel geometry constraints and parametrization

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Fig. 9

Single passage CFD domain

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Fig. 10

Comparison of baseline ISD and optimized design DA2

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Fig. 11

Seven optimized ISD designs: (a) baseline, (b) DA2, (c) DB, (d) DC, (e) DD, (f) DE, (g) DF, and (h) DG

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Fig. 12

Optimized wheel A: meridional and camberline views

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Fig. 13

Velocity streamlines for baseline and optimized wheel A

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Fig. 14

Comparison of baseline and optimized wheel A CFD results: (a) flow capacity and (b) efficiency, at ∼123,000 rpm

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Fig. 15

Experimentally measured HPT efficiency for baseline, optimized DA1, and straight ISDs, at (a) 30,000, (b) 42,000 and (c) 48,000 rpm

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Fig. 16

Baseline and optimized wheel A test pieces

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Fig. 17

Experimentally measured flow capacity and efficiency for baseline HPT and optimized wheel A, at 30,000, 42,000, and 48,000 rpm

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Fig. 18

CFD versus experiment: (a) flow capacity and (b) efficiency

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Fig. 19

Off-design baseline and wheel A velocity streamlines




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