Off-design performance is of key importance now in the design of automotive turbocharger turbines. Due to automotive drive cycles, a turbine that can extract more energy at high pressure ratios and lower rotational speeds is desirable. Typically a radial turbine provides peak efficiency at U/C values of 0.7, but at high pressure ratios and low rotational speeds, the U/C value will be low and the rotor will experience high values of positive incidence at the inlet. The positive incidence causes high blade loading resulting in additional tip leakage flow in the rotor as well as flow separation on the suction surface of the blade. An experimental assessment has been performed on a scaled automotive VGS (variable geometry system). Three different stator vane positions have been analyzed: minimum, 25%, and maximum flow position. The first tests were to establish whether positioning the endwall clearance on the hub or shroud side of the stator vanes produced a different impact on turbine efficiency. Following this, a back swept rotor was tested to establish the potential gains to be achieved during off-design operation. A single passage CFD model of the test rig was developed and used to provide information on the flow features affecting performance in both the stator vanes and turbine. It was seen that off-design performance was improved by implementing clearance on the hub side of the stator vanes rather than on the shroud side. Through CFD analysis and tests, it was seen that two leakage vortices form, one at the leading edge and one after the spindle of the stator vane. The vortices affect the flow angle at the inlet to the rotor, in the hub region. The flow angle is shifted to more negative values of incidence, which is beneficial at the off-design conditions but detrimental at the design point. The back swept rotor was tested with the hub side stator vane clearance configuration. The efficiency and MFR were increased at the minimum and 25% stator vane position. At the design point, the efficiency and MFR were decreased. The CFD investigation showed that the incidence angle was improved at the off-design conditions for the back swept rotor. This reduction in the positive incidence angle, along with the improvement caused by the stator vane tip leakage flow, reduced flow separation on the suction surface of the rotor. At the design point, both the tip leakage flow of the stator vanes and the back swept blade angle caused flow separation on the pressure surface of the rotor. This resulted in additional blockage at the throat of the rotor reducing MFR and efficiency.

References

References
1.
Japikse
,
D.
, and
Baines
,
N. C.
,
1994
,
Introduction to Turbomachinery
,
Concepts NREC, Wilder
,
VT
.
2.
Baines
,
N. C.
,
2005
,
Fundamentals of Turbocharging
,
Concepts NREC, Wilder
,
VT
.
3.
Mulloy
,
J. M.
, and
Weber
,
H. G.
,
1982
, “
Radial Inflow Turbine Impeller for Improved Off-Design Performance
,”
Proceedings of the 27th ASME International Gas Turbine Conference and Exhibit
,
London, March 18–22
, Paper No. 82-GT-101.
4.
Fredmonski
,
A. J.
,
Huber
,
F. W.
,
Roelke
,
R. J.
, and
Simonyi
,
S.
,
1991
, “
Design and Experimental Evaluation of Compact Radial Inflow Turbines
,”
NASA Lewis Research Centre
, Report No. AIAA-91-2127.
5.
Spence
,
S. W. T.
, and
Artt
,
D. W.
,
1998
, “
Experimental Performance Evaluation of a 99.0 mm Radial Inflow Nozzled Turbine With Different Stator Throat Areas
,”
Proc. Inst. Mech. Eng., Part A
,
212
(
1
), pp.
27
42
.10.1243/0957650981536727
6.
Spence
,
S. W. T.
,
Doran
,
W. J.
, and
Artt
,
D. W.
,
1999
, “
Experimental Performance Evaluation of a 99.0 mm Radial Inflow Nozzled Turbine at Larger Stator-Rotor Throat Area Ratios
,”
Proc. Inst. Mech. Eng., Part A
,
213
(
3
), pp.
205
218
.10.1243/0957650991537554
7.
Spence
,
S. W. T.
, and
Artt
,
D. W.
,
1998
, “
An Experimental Assessment of Incidence Losses in a Radial Inflow Turbine Rotor
,”
Proc. Inst. Mech. Eng., Part A
,
212
(
1
), pp.
43
53
.10.1243/0957650981536727
8.
O’Neill
,
J. W.
,
Spence
,
S. W. T.
, and
Cunningham
,
G.
,
2005
, “
An Assessment of Stator Vane Leakage in a Variable Geometry Radial Turbine
,”
Proceedings of the ETC 6th European Conference on Turbomachinery
, Lille, France, March 7–11, Vol.
2
, Paper No. RT-065_04/65.
9.
Natkaniec
,
C. K.
,
Kammeyer
,
J.
, and
Seume
,
J. R.
,
2011
, “
Secondary Flow Structures and Losses in a Radial Turbine Nozzle
,”
Proceedings of the ASME Turbo Expo, Power for Land, Sea and Air
, Vancouver, Canada, June 6–10,
ASME
Paper No. GT2011-46753. 10.1115/GT2011-46753
10.
Palfreyman
,
D.
, and
Martinez-Botas
,
R.
,
2002
, “
Numerical Study of the Internal Flow Field Characteristics in Mixed Flow Turbines
,”
Proceedings of the ASME Turbo Expo
,
Amsterdam
, June 3–6,
ASME
Paper No. GT2002-30372. 10.1115/GT2002-30372
11.
Meitner
,
P. L.
, and
Glassman
,
A. J.
,
1983
, “
Computer Code for Off-Design Performance Analysis of Radial-Inflow Turbines With Rotor Blade Sweep
,”
NASA Technical Paper
, Report No. 2199.
12.
Barr
,
L.
,
Spence
,
S. W. T.
, and
Eynon
,
P.
,
2008
, “
Improved Performance of a Radial Turbine Through the Implementation of Back Swept Blading
,”
Proceedings of the ASME Turbo Expo
, Berlin, June 9–13,
ASME
Paper No. GT2008-50064. 10.1115/GT2008-50064
13.
Walkingshaw
,
J. R.
,
Spence
,
S. W. T.
,
Ehrhard
,
J.
, and
Thornhill
,
D.
,
2010
, “
A Numerical Study of the Flow Fields in a Highly Off-Design Variable Geometry Turbine
,”
Proceedings of the ASME Turbo Expo
, Glasgow, UK, June 14–18,
ASME
Paper No. GT2010-22669. 10.1115/GT2010-22669
14.
Walkingshaw
,
J. R.
,
Spence
,
S. W. T.
, and
Ehrhard
,
J.
,
2011
, “
A Numerical Study of Stator Vane Tip Leakage Effects on Flow Development in a Variable Geometry Turbocharger Turbine
,”
Proceedings of the ETC 9th European Conference on Turbomachinery
, Istanbul, Turkey, March 21–25, Paper No. B269.
15.
Walkingshaw
,
J.
,
Spence
,
S. W. T.
,
Ehrhard
,
J.
, and
Thornhill
,
D.
,
2011
, “
An Investigation Into Improving Off-Design Performance in a Turbocharger Turbine Utilizing Non-Radial Blading
,”
Proceedings of the ASME Turbo Expo
, Vancouver, Canada, June 6–10,
ASME
Paper No. GT2011-45717.10.1115/GT2011-45717
16.
Menter
,
F. R.
,
1994
, “
Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications
,”
AIAA J.
,
32
(
8
), pp.
1598
1605
.10.2514/3.12149
17.
Bardina
,
J. E.
,
Huang
,
P. G.
, and
Coakley
,
T. J.
,
1997
, “
Turbulence Modeling Validation, Testing, and Development
,”
Ames Research Center, NASA Technical Memorandum
, Report No. 110446.
You do not currently have access to this content.