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Research Papers: Gas Turbines: Turbomachinery

# The Experimental Studies of Improving the Aerodynamic Performance of a Turbine Exhaust System

[+] Author and Article Information
Stephen Guillot

Techsburg, Inc.,
Christiansburg, VA 24073
e-mail: sguillot@techsburg.com

Wing F. Ng

Techsburg, Inc.,
Christiansburg, VA 24073
e-mail: wng@techsburg.com

Hans D. Hamm

Solar Turbines, Inc.,
San Diego, CA 92186
e-mail: Hamm_Hans_D@solarturbines.com

Ulrich E. Stang

Solar Turbines, Inc.,
San Diego, CA 92186
e-mail: Stang_Ulrich_E@solarturbines.com

Kevin T. Lowe

Virginia Tech,
Blacksburg, VA 24061
e-mail: kelowe@exchange.vt.edu

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 9, 2014; final manuscript received July 10, 2014; published online August 5, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(1), 012601 (Aug 05, 2014) (13 pages) Paper No: GTP-14-1343; doi: 10.1115/1.4028020 History: Received July 09, 2014; Revised July 10, 2014

## Abstract

Analysis and testing were conducted to optimize an axial diffuser–collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this program. A 1/12th scale test rig enabled rapid and efficient evaluation of multiple geometries. This test facility was designed to run continuously at an inlet Mach number of 0.41 and an inlet hydraulic diameter-based Reynolds number of 3.4 × 105. A 1/4th geometric scale test rig was designed and built to validate the data in the 1/12th scale rig. This blow-down rig facilitated testing at a nominally equivalent inlet Mach number, while the Reynolds number was matched to realistic engine conditions via back pressure. Multihole pneumatic pressure probes, particle image velocimetry (PIV), and surface oil flow visualization were deployed in conjunction with computational tools to explore physics-based alterations to the exhaust geometry. The design modifications resulted in a substantial increase in the overall pressure recovery coefficient of +0.07 (experimental result) above the baseline geometry. The optimized performance, first measured at 1/12th scale and obtained using computational fluid dynamics (CFD) was validated at the full scale Reynolds number.

## Figures

Fig. 1

Cut-away view of the fundamental components of an axial flow gas turbine system with an EC installed (Titan™ 250—Solar Turbines Inc.)

Fig. 2

Section view of the flow conditioning components upstream of the baseline diffuser–collector (1/12th scale facility)

Fig. 3

Subsonic wind tunnel facility for the testing of 1/4th scale diffuser collector. A mannequin standing 1.75 m is shown next to the facility for scale.

Fig. 4

(a) View looking upstream of the circumferential radial traverse locations and (b) pressure tap locations on the hub

Fig. 5

Isometric view of the exit traverse plane (collector back wall and hub removed)

Fig. 6

Sectional view of the 1/12th scale baseline diffuser– collector

Fig. 7

(a) Specification of geometry parameters and (b) sectional view of the radial diffuser–collectors with baseline diffuser as a comparison

Fig. 8

Increment of area ratio ΔA2/A1 and ideal ΔCp_ideal from baseline of the diffuser geometries considered (diffuser only, without collector)

Fig. 9

Overview of the computational domain

Fig. 10

Circumferential inlet distributions of pressure coefficient deviations and Mach number

Fig. 17

Separation point on the hub at the 180 deg location (bottom)

Fig. 16

Close up of the baseline hub between 0 deg (top) to 90 deg

Fig. 15

Surface oil flow visualization in the baseline diffuser–collector configuration (view looking upstream)

Fig. 14

Secondary flow velocity vectors with a color gradient to represent the normal-to-plane velocity component magnitude at the exit of baseline diffuser–collector

Fig. 13

Contour plot of the velocity out of the page (Uy) at the exit section of the baseline diffuser–collector geometry (1/12th scale experimental data)

Fig. 12

Inlet circumferential pressure coefficient

Fig. 11

Hub static pressure (normalized by Cp_ideal at collector exit) profile in the diffuser of the baseline configuration

Fig. 24

Inlet static pressure coefficient distribution for radial diffuser

Fig. 23

Diffuser performance versus r/hCp based on the baseline experimental data)

Fig. 22

Normalized velocity vectors in the baseline collector

Fig. 21

Normalized exit velocity contour planes in the baseline collector

Fig. 20

PIV traversed laser sheet within the quarter scale EC

Fig. 19

LaVision PIV system used with the 1/4th scale facility

Fig. 18

Radially averaged circumferential distribution of inlet static pressure coefficient deviation and Mach number of 1/12th and 1/4th scale baseline geometry

Fig. 25

Back flow on the inner surface of r/h = 1.0 radial diffuser case near 180 deg position

Fig. 26

(a)–(e) Contour plots of exit velocity for evaluated designs (flow exiting the collector is out of the page)

Fig. 27

CFD prediction of static pressure profile for studied cases (baseline diffuser 1/4th scale)

Fig. 28

Comparison of diffuser–collector overall performance between CFD prediction and experimental results

Fig. 29

Vector plot of flow field at 0 deg circumferential location of different configuration

Fig. 31

Potential flow pressure gradient imposed due to a flat plate stagnation

Fig. 30

Vector plot of flow field at 180 deg circumferential location of different configuration

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