Abstract

Radial or mixed flow turbines are very common in industrial application, spanning turbochargers, small turbines for power generation, and energy recovery systems. Secondary flows have received a limited attention in the literature, and this papers aims to fill this gap of knowledge. The secondary flow structures in mixed flow turbines are particularly complex due to its geometry, high curvature, and the appearance of Coriolis and centrifugal forces. The focus of the present work is to investigate the evolution of secondary flows and their losses in a mixed flow turbine by using an experimentally validated three-dimensional computational fluid dynamics (CFD). The flow topology is analyzed to explain the formation and evolution of flow separations at the pressure, suction, and hub surfaces. The suction surface separation is caused by centrifugal forces, and it induces the formation of a hub separation. As the inlet velocity decreases, the hub separation increases in strength. A major feature found is the pressure surface separation, located at the leading edge tip, formed due to flow incidence; as the incidence decreases, this separation extends to the hub. Losses caused by those separations as well as the tip leakage vortex are studied by calculating locally entropy generation. Results show that the tip-leakage vortex accounts for the majority of losses (60%) and renders the losses caused by suction surface and induced hub separations to be small. The presence of the more severe hub separation was also found to have a significant detrimental effect on the turbine efficiency, which increases losses on the hub and the suction surface from 40% to 65%. Pressure surface separation, however, does not vary the total amount of losses significantly but rather redistributes the losses in the blade passage.

References

1.
Martinez-botas
,
R. F.
,
Pesiridis
,
A.
, and
Yang
,
M. Y.
,
2016
, “
Overview of Boosting Options for Future Downsized Engines
,”
Science China
,
54
(
2
), pp.
318
331
.
2.
Denton
,
J. D.
,
1993
, “
Loss Mechanisms in Turbomachines
,”
International Gas Turbine and Aeroengine Congress and Exposition
,
Cincinnati, OH
,
May 24–27
, p.
93–GT–435
.
3.
Gregory-Smith
,
D. G.
,
1982
, “
Secondary Flows and Losses in Axial Flow Turbines
,”
J. Eng. Power
,
104
(
4
), pp.
819
822
. 10.1115/1.3227350
4.
Sieverding
,
C. H.
,
1985
, “
Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages
,”
ASME J. Eng. Gas Turbines Power
,
107
(
2
), pp.
248
257
. 10.1115/1.3239704
5.
Huntsman
,
I.
,
1993
, “
An Investigation of Radial Turbine Aerodynamics
,” Ph.D. thesis,
University of Cambridge
,
Cambridge, UK
.
6.
Woolley
,
N. H.
, and
Hatton
,
A. P.
,
1973
, “
Viscous Flow in Radial Turbomachine Blade Passages
,”
Conference on Heat and Fluid Flow in Steam and Gas Turbine Plant
,
Coventry, UK
,
Apr. 3–5
, pp.
175
181
.
7.
Karamanis
,
N.
,
Martinez-Botas
,
R. F.
, and
Su
,
C. C.
,
2001
, “
Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions
,”
ASME J. Turbomach.
,
123
(
2
), pp.
359
371
. 10.1115/1.1354141
8.
Su
,
C. C.
,
1999
, “
Flow Characteristics and Performance of Mixed Flow Turbine
,” Ph.D. thesis,
Imperial College London
,
London, UK
.
9.
Zangeneh-Kazemi
,
M.
,
Dawes
,
W. N.
, and
Hawthorne
,
W. R.
,
1988
, “
Three Dimensional Flow in Radial-Inflow Turbines
,”
International Gas Turbine and Aeroengine Congress and Exposition
,
Amsterdam, The Netherlands
,
June 6–9
, p.
V001T01A046
.
10.
Dambach
,
R.
, and
Hodson
,
H. P.
,
2001
, “
Tip Leakage Flow in a Radial In Ow Turbine Introduction
,”
J. Propul. Power
,
17
(
3
), pp.
644
650
. 10.2514/2.5791
11.
Kim
,
C. M.
, and
Civinskas
,
K. C.
,
1994
, “
An Aerodynamic Analysis of a Mixed Flow Turbine
,”
NASA Technical Memorandum 106674, Technical Report
.
12.
Kitson
,
S. T.
,
1992
, “
Aerodynamic Investigation of Radial Turbines Using Computational Methods
,”
VKI Lecture Series
,
5
, pp.
1
44
.
13.
Kirtley
,
K. R.
,
Beach
,
T. A.
, and
Rogo
,
C.
,
2016
, “
Aeroloads and Secondary Flows in a Transonic Mixed-Flow Turbine
,”
ASME J. Turbomach.
,
115
(
3
), pp.
590
600
. 10.1115/1.2929294
14.
Baines
,
N. C.
,
1996
, “
Flow Development in Radial Turbine Rotors
,”
International Gas Turbine and Aeroengine Congress and Exhibition
,
Birmingham, UK
,
June 10–13
, p.
96–GT–65
.
15.
Palfreyman
,
D.
,
2004
, “
Aerodynamics of a Mixed Flow Turbocharger Turbine Under Steady and Pulse Flow Conditions: A Numerical Study
,” Ph.D. thesis,
Imperial College London
,
London, UK
.
16.
Palfreyman
,
D.
, and
Martinez-Botas
,
R. F.
,
2002
, “
Numerical Study of the Internal Flow Field Characteristics in Mixed Flow Turbines
,”
ASME Turbo Expo 2002
,
Amsterdam, The Netherlands
,
June 3–6
, p.
GT–2002–30372
.
17.
Abidat
,
M.
,
1991
, “
Design and Testing of a Highly Loaded Mixed Flow Turbine
,” Ph.D. thesis,
Imperial College London
,
London, England
.
18.
Newton
,
P.
,
Palenschat
,
T.
,
Martinez-Botas
,
R. F.
, and
Seiler
,
M.
,
2015
, “
Entropy Generation Rate in a Mixed Flow Turbine Passage
,”
International Gas Turbine Congress
,
Toranomon Hills, Tokyo
,
Nov. 15–20
, pp.
911
920
.
19.
Tobak
,
M.
, and
Peake
,
D. J.
,
1982
, “
Topology of Three Dimensional Separated Flows
,”
Annu. Rev. Fluid Mech.
,
14
, pp.
61
85
. 10.1146/annurev.fl.14.010182.000425
20.
Delery
,
J.
,
2013
,
Three-Dimensional Separated Flow Topology
,
John Wiley & Sons
,
New York
.
21.
Herwig
,
H.
, and
Kock
,
F.
,
2007
, “
Direct and Indirect Methods of Calculating Entropy Generation Rates in Turbulent Convective Heat Transfer Problems
,”
Heat Mass Transfer
,
43
(
3
), pp.
207
215
. 10.1007/s00231-006-0086-x
You do not currently have access to this content.