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Research Papers

Capturing Radial Mixing in Axial Compressors With Computational Fluid Dynamics

[+] Author and Article Information
Lorenzo Cozzi

Dipartimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Lorenzo.Cozzi@unifi.it

Filippo Rubechini

Dipartimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Filippo.Rubechini@unifi.it

Matteo Giovannini

Dipartimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Matteo.Giovannini@unifi.it

Michele Marconcini

Dipartimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Michele.Marconcini@unifi.it

Andrea Arnone

Dipartimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Andrea.Arnone@unifi.it

Andrea Schneider

Ansaldo Energia,
Via Lorenzi 8,
Genova 16152, Italy
e-mail: Andrea.Schneider@ansaldoenergia.com

Pio Astrua

Ansaldo Energia,
Via Lorenzi 8,
Genova 16152, Italy
e-mail: Pio.Astrua@ansaldoenergia.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 3, 2018; final manuscript received October 12, 2018; published online January 21, 2019. Editor: Kenneth Hall.

J. Turbomach 141(3), 031012 (Jan 21, 2019) (9 pages) Paper No: TURBO-18-1184; doi: 10.1115/1.4041738 History: Received August 03, 2018; Revised October 12, 2018

The current industrial standard for numerical simulations of axial compressors is the steady Reynolds-averaged Navier–Stokes (RANS) approach. Besides the well-known limitations of mixing planes, namely their inherent inability to capture the potential interaction and the wakes from the upstream blades, there is another flow feature which is lost, and which is a major accountable for the radial mixing: the transport of streamwise vorticity. Streamwise vorticity is generated for various reasons, mainly associated with secondary and tip-clearance flows. A strong link exists between the strain field associated with the vortices and the mixing augmentation: the strain field increases both the area available for mixing and the local gradients in fluid properties, which provide the driving potential for the mixing. In the rear compressor stages, due to high clearances and low aspect ratios, only accounting for the development of secondary and clearance flow structures, it is possible to properly predict the spanwise mixing. In this work, the results of steady and unsteady simulations on a heavy-duty axial compressor are compared with experimental data. Adopting an unsteady framework, the enhanced mixing in the rear stages is properly captured, in remarkable agreement with experimental distributions. On the contrary, steady analyses strongly underestimate the radial transport. It is inferred that the streamwise vorticity associated with clearance flows is a major driver of radial mixing, and restraining it by pitch-averaging the flow at mixing planes is the reason why the steady approach cannot predict the radial transport in the rear part of the compressor.

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Figures

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Fig. 3

O-type structured clearance mesh

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Fig. 2

Meridional view of the high-pressure section of the compressor adopted as case study

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Fig. 1

Total temperature distribution at compressor outlet

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Fig. 4

Spanwise total temperature distribution at computational domain outlet section for the three models investigated

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Fig. 5

Spanwise total pressure distribution at computational domain outlet section for the three models investigated

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Fig. 6

Instantaneous entropy field visualization at compressor midspan section

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Fig. 7

Average pressure distributions at 80% blade span for the last rotor row of the high-pressure compressor

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Fig. 10

Axial vorticity field upstream and downstream of an inter-row interface for a steady-state analysis (only one fourth of grid lines are shown for the sake of clarity)

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Fig. 11

Axial vorticity field upstream and downstream of an inter-row interface for an unsteady analysis (only one-fourth of grid lines are shown for sake of clarity)

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Fig. 8

Development of the integral value of term 2 magnitude along the meridional flow path

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Fig. 9

Spanwise distribution of term 2 magnitude upstream of a rotor/stator interface for an unsteady computation

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Fig. 12

Average radial distributions of total temperature upstream of the last high-pressure compressor vane

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Fig. 13

Average radial distributions of total pressure upstream of the last high-pressure compressor vane

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Fig. 14

Clearance flow and axial vorticity contours visualization in a blade passage (only one fourth of grid lines are shown for sake of clarity)

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