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.

References

References
1.
Adamczyk
,
J. J.
,
1999
, “
Aerodynamic Analysis of Multistage Turbomachinery Flows in Support of Aerodynamic Design
,”
ASME
Paper No. 99-GT-080
.
2.
Denton
,
J. D.
,
2010
, “
Some Limitations of Turbomachinery CFD
,”
ASME
Paper No. GT2010-22540
.
3.
Wennerstrom
,
A. J.
,
1991
, “
A Review of Predictive Efforts for Transport Phenomena in Axial Flow Compressors
,”
ASME J. Turbomach.
,
113
(
2
), pp.
175
179
.
4.
Adkins
,
G. G.
, and
Smith
,
L. H.
,
1982
, “
Spanwise Mixing in Axial-Flow Turbomachines
,”
J. Eng. Power
,
104
(
1
), pp.
97
104
.
5.
Gallimore
,
S. J.
, and
Cumpsty
,
N. A.
,
1986
, “
Spanwise Mixing in Multistage Axial Flow Compressors—Part I: Experimental Investigation
,”
ASME J. Turbomach.
,
108
(
1
), pp.
2
9
.
6.
Gallimore
,
S. J.
,
1986
, “
Spanwise Mixing in Multistage Axial Flow Compressors—Part II: Throughflow Calculations Including Mixing
,”
ASME J. Turbomach.
,
108
(
1
), pp.
10
16
.
7.
Wisler
,
D. C.
,
Bauer
,
R. C.
, and
Okiishi
,
T. H.
,
1987
, “
Secondary Flow, Turbulent Diffusion, and Mixing in Axial-Flow Compressors
,”
ASME J. Turbomach.
,
109
(
4
), pp.
455
482
.
8.
Leylek
,
J. H.
, and
Wisler
,
D. C.
,
1991
, “
Mixing in Axial-Flow Compressors: Conclusions Drawn From 3-D Navier–Stokes Analyses and Experiments
,”
ASME J. Turbomach.
,
113
(
2
), pp.
139
155
.
9.
Cozzi
,
L.
,
Rubechini
,
F.
,
Marconcini
,
M.
,
Arnone
,
A.
,
Astrua
,
P.
,
Schneider
,
A.
, and
Silingardi
,
A.
,
2017
, “
Facing the Challenges in CFD Modelling of Multistage Axial Compressors
,”
ASME
Paper No. GT2017-63240.
10.
Arnone
,
A.
,
1994
, “
Viscous Analysis of Three-Dimensional Rotor Flow Using a Multigrid Method
,”
ASME J. Turbomach.
,
116
(
3
), pp.
435
445
.
11.
Arnone
,
A.
,
Liou
,
M. S.
, and
Povinelli
,
L. A.
,
1995
, “
Integration of Navier–Stokes Equations Using Dual Time Stepping and a Multigrid Method
,”
AIAA J.
,
33
(
6
), pp.
985
990
.
12.
Jameson
,
A.
,
Schmidt
,
W.
, and
Turkel
,
E.
,
1981
, “
Numerical Solutions of the Euler Equations by Finite Volume Methods Using Runge-Kutta Time-Stepping Schemes
,”
AIAA
Paper No. 81-1259
.
13.
Swanson
,
R. C.
, and
Turkel
,
E.
,
1992
, “
On Central-Difference and Upwind Schemes
,”
J. Comput. Phys.
,
101
(
2
), pp.
292
306
.
14.
Baldwin
,
B. S.
, and
Lomax
,
H.
,
1978
, “
Thin Layer Approximation and Algebraic Model for Separated Turbulent Flows
,”
AIAA
Paper No. 78-257
.
15.
Spalart
,
P. R.
, and
Allmaras
,
S. R.
,
1994
, “
A One–Equation Turbulence Model for Aerodynamic Flows
,”
Rech. Aérosp.
,
1
, pp.
5
21
.
16.
Wilcox
,
D. C.
,
1998
,
Turbulence Modeling for CFD
,
2nd ed.
,
DCW Industries
,
La Cañada, CA
.
17.
Boncinelli
,
P.
,
Rubechini
,
F.
,
Arnone
,
A.
,
Cecconi
,
M.
, and
Cortese
,
C.
,
2004
, “
Real Gas Effects in Turbomachinery Flows: A CFD Model for Fast Computations
,”
ASME J. Turbomach.
,
126
(
2
), pp.
268
276
.
18.
Giles
,
M. B.
,
1988
, “
Non–Reflecting Boundary Conditions for the Euler Equations
,” MIT Department of Aeronautics and Astronautics, Cambridge, MA, CFDL Report No. 88-1.
19.
Giles
,
M. B.
,
1988
, “
UNSFLO: A Numerical Method for Unsteady Inviscid Flow in Turbomachinery
,” MIT Department of Aeronautics and Astronautics, Cambridge, MA, Report No. GTL 195.
20.
Saxer
,
A. P.
, and
Giles
,
M. B.
,
1993
, “
Quasi-Three-Dimensional Nonreflecting Boundary Conditions for Euler Equations Calculations
,”
J. Propul. Power
,
9
(
2
), pp.
263
271
.
21.
Giovannini
,
M.
,
Marconcini
,
M.
,
Arnone
,
A.
, and
Bertini
,
F.
,
2014
, “
Evaluation of Unsteady Computational Fluid Dynamics Models Applied to the Analysis of a Transonic High-Pressure Turbine Stage
,”
Proc. Inst. Mech. Eng. Part A
,
228
(
7
), pp.
813
824
.
22.
Rubechini
,
F.
,
Marconcini
,
M.
,
Giovannini
,
M.
,
Bellucci
,
J.
, and
Arnone
,
A.
,
2015
, “
Accounting for Unsteady Interaction in Transonic Stages
,”
ASME J. Eng. Gas Turbines Power
,
137
(
5
), p.
052602
.
23.
Greitzer
,
E. M.
,
Tan
,
C. S.
, and
Graf
,
M. B.
,
2004
,
Internal Flow: Concepts and Applications
,
Cambridge University Press
,
Cambridge, UK
.
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