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Research Papers

Numerical and Experimental Investigation of Return Channel Vane Aerodynamics With Two-Dimensional and Three-Dimensional Vanes

[+] Author and Article Information
A. Hildebrandt

MAN Diesel & Turbo SE,
Steinbrinkstraße 1,
Oberhausen 46145, Germany
e-mail: andre.hildebrandt@man.eu

F. Schilling

MAN Diesel & Turbo SE,
Steinbrinkstraße 1,
Oberhausen 46145, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 20, 2016; final manuscript received July 26, 2016; published online September 20, 2016. Editor: Kenneth Hall.

J. Turbomach 139(1), 011010 (Sep 20, 2016) (11 pages) Paper No: TURBO-16-1118; doi: 10.1115/1.4034341 History: Received June 20, 2016; Revised July 26, 2016

The present paper deals with the numerical and experimental investigation of the effect of return channel (RCH) dimensions of a centrifugal compressor stage on the aerodynamic performance. Three different return channel stages were investigated, two stages comprising three-dimensional (3D) return channel blades and one stage comprising two-dimensional (2D) RCH vanes. The analysis was performed regarding both the investigation of overall performance (stage efficiency, RCH total pressure loss coefficient) and detailed flow-field performance. For detailed experimental flow-field investigation at the stage exit, six circumferentially traversed three-hole probes were positioned downstream the return channel exit in order to get two-dimensional flow-field information. Additionally, static pressure wall measurements were taken at the hub and shroud pressure and suction side (SS) of the 2D and 3D return channel blades. The return channel system overall performance was calculated by measurements of the circumferentially averaged 1D flow field downstream the diffuser exit and downstream the stage exit. Dependent on the type of return channel blade, the numerical and experimental results show a significant effect on the flow field overall and detail performance. In general, satisfactory agreement between computational fluid dynamics (CFD)-prediction and test-rig measurements was achieved regarding overall and flow-field performance. In comparison with the measurements, the CFD-calculated stage performance (efficiency and pressure rise coefficient) of all the 3D-RCH stages was slightly overpredicted. Very good agreement between CFD and measurement results was found for the static pressure distribution on the RCH wall surfaces while small CFD-deviations occur in the measured flow angle at the stage exit, dependent on the turbulence model selected.

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Figures

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Fig. 1

Geometry of the 2D-RCH and 3D-RCH, left 3D-sketch, right: meridional sketch

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Fig. 2

Experimental test rig setup at MDT-Oberhausen

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Fig. 3

Top: Overall sketch of MDT centrifugal stage test rig, bottom: Used total pressure probes: (a) and (b) five hole probe, (c) Kiel probe

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Fig. 4

Measured overall performance of 2D-RCH- and 3D-RCH-stage: left, work input ψi; middle, isentropic stage efficiency; right: RCH-total pressure loss coefficient

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Fig. 5

Computational domain for calculation of the 2D and 3D-RCH vane system stage

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Fig. 6

Comparison of CFD and measured 2D-RCH and 3D-RCH stage at Mau2  = 0.96: left, isentropic efficiency and right, work input ψi

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Fig. 7

Left: 2D-RCH and 3D-RCH total pressure loss coefficient and right: effect fillet radii modeling on 3D-RCH-stage and diffuser efficiency

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Fig. 8

3D-RCH flow cut and base flow stage: left, isentropic stage efficiency and right, work input ψi, SP-model

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Fig. 9

Left: Absolute flow angle at impeller exit and right: total pressure loss coefficient, SP-model

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Fig. 10

Top: 3D-RCH-ring and bottom: single 3D-RCH-vane comprising pressure measurement 1 mm wall holes

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Fig. 11

2D-RCH static pressure distribution in off-design φnorm = 0.93, φnorm = 1.0, and φnorm = 1.07; top: normalized pressure and bottom: pressure coefficient cp

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Fig. 12

2D-RCH static pressure distribution in off-design φnorm = 0.93, φnorm = 1.0, and φnorm = 1.07

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Fig. 13

Mach number distribution at 10% span (near hub) in design point (φnorm = 1.0), ke-Yang Shih model

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Fig. 14

Entropy distribution at 10% span, (near hub) in design point (φnorm = 1.0); k-epsilon Yang Shih model used

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Fig. 15

Mach number distribution at 90% span (near shroud) in design point (φnorm = 1.0); k-epsilon Yang Shih model used

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Fig. 16

Entropy distribution at 90% span (near shroud) in design point (φnorm = 1.0); k-epsilon Yang Shih model used

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Fig. 17

CFD calculated absolute flow angles and entropy of the 3D-RCH-flow cut stage at the return channel vane inlet, calculated with the SP model

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Fig. 18

Left: CFD RCH-incidence losses and right: RCH relative friction, incidence and secondary losses of 2D and 3D-RCH system, calculated with the SP model

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Fig. 19

Three-hole probe measuring positions at stage exit; left: circumferential traversal positions and right: three-hole probe channel height positions

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Fig. 20

Absolute flow angle at stage exit with 3D-RCH vane at u2 = 330 ms, φnorm = 1.0 (design point)

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Fig. 21

Absolute Mach number at stage exit with 3D-RCH vane at Mau2  = 0.96, φnorm = 1.0 (design point)

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Fig. 22

Measured stage exit flow angles at design speed in design point and off-design flow inlet conditions

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Fig. 23

Stage exit Mach number in design point and off-design flow inlet conditions

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