Large industrial gas turbines for combined heat and power generation normally have axial diffusers leading to the heat recovery steam generator. The diffusers operate with high inlet axial Mach number (0.6) and with a nonuniform inlet total pressure profile from the turbine. Tests have been carried out on a generic highly loaded axial diffuser in a scaled axial diffuser test rig, with different inlet total pressure profiles including those that might be met in practice. The results show that the inlet total pressure profile has a strong effect on the position of flow separation, whereby a hub-strong profile tends to separate at the casing and the tip-strong profile on the hub. Steady computational fluid dynamics (CFD) simulations using the shear stress transport (SST) turbulence model have been carried out based on extensive studies of the best way to model the inlet boundary conditions. These simulations provide good agreement with the prediction of separation in the diffuser but the separated regions often persist too long so that, in this highly loaded case with flow separation, the calculated diffuser pressure recovery can be in error by up to 30%.

1.
Japikse
,
D.
, and
Baines
,
N. C.
, 1998,
Diffuser Design Technology
,
Concepts ETI
,
Norwich, VT
.
2.
Sovran
,
G.
, and
Klomp
,
E. D.
, 1967, “
Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross-Section
,”
Fluid Mechanics of Internal Flow
,
G.
Sovran
, ed.,
Elsevier
,
Amsterdam
.
3.
Vassiliev
,
V.
,
Irmisch
,
S.
,
Claridge
,
M.
, and
Richardson
,
D. P.
, 2003, “
Experimental and Numerical Investigation of the Impact of Swirl on the Performance of Industrial Gas Turbines Exhaust Diffusers
,”
Proceedings of ASME, Turbo Expo Power for Land, Sea and Air
, Atlanta, GA.
4.
Fleige
,
H. U.
, 2002,
Experimentelle und numerische Untersuchungen am Modell eines Turbinenaustrittsdiffusors
,
VDI Verlag
,
Dusseldorf, Germany
.
5.
Sieker
,
O.
, and
Seume
,
J. R.
, 2007, “
Influence of Rotating Wakes on Separation in Turbine Exhaust Diffusers
,”
Proceedings of the Eighth International Symposium on Experimental and Computational Aerothermodynamics of Internal Flows
, Lyon.
6.
Ubertini
,
S.
, and
Desideri
,
U.
, 2000, “
Experimental Performance Analysis of an Annular Diffuser With and Without Struts
,”
Exp. Therm. Fluid Sci.
0894-1777,
22
, pp.
183
195
.
7.
DIN Deutsches Institut für Normung e.V.
, 1999, Leitfaden zur Angabe der Unsicherheit beim Messen, DIN V ENV 13005, Beuth Verlag.
8.
Becker
,
S.
,
Gretschel
,
E. -Ch.
, and
Casey
,
M. V.
, 2005, “
Influence of a Tip Clearance Jet on a Swirling Flow in an Axial-Radial Diffuser
,”
Proceedings of the Sixth European Turbomachinery Conference
, Lille.
9.
Cumpsty
,
N. A.
, and
Horlock
,
J. H.
, 2006, “
Averaging Nonuniform Flow for a Purpose
,”
ASME J. Turbomach.
0889-504X,
128
, pp.
120
129
.
10.
ANSYS Europe, Ltd.
, 2005, ANSYS CFX-Solver, Release 10.0, Modelling.
11.
Casey
,
M. V.
, and
Wintergerste
,
T.
, 2000,
ERCOFTAC Best Practice Guidelines for Industrial CFD
,
ERCOFTAC
,
Brussels, Belgium
.
12.
Menter
,
F. R.
, 1994, “
Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications
,”
AIAA J.
0001-1452,
32
, pp.
1598
1605
.
13.
Kluss
,
D.
,
Stoff
,
H.
, and
Wiedermann
,
A.
, 2009, “
Effect of Wakes and Secondary Flow on Re-Attachment of Turbine Exit Annular Diffuser Flow
,”
ASME J. Turbomach.
0889-504X,
131
, p.
041012
.
You do not currently have access to this content.