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N89 - 12893 


COMBUSTOR DIFFUSER INTERACTION PROGRAM 

Ram Srinivasan and Daniel Thorp 
Garrett Turbine Engine Co., Phoenix 


INTRODUCTION 


Advances in gas turbine engine performance are achieved by using compressor 
systems with high stage loading and low part count, which result In high exit Mach 
numbers. The diffuser and combustor systems in such engines should be optimized to 
reduce system pressure loss and to maximize the engine thrust-to-welght ratio and 
minimize length. The state-of-the-art combustor-diffuser systems do not meet these 
requirements. Detailed understanding of the combustor-diffuser flow field inter- 
action Is required for designing advanced gas turbine engines. 

An experimental study of the combustor-diffuser interaction (CDI) is being con- 
ducted to obtain data for the evaluation and Improvement of analytical models 
applicable to a wide variety of diffuser designs. The CDI program consists of four 
technical phases: 


Phase I 
Phase II - 
Phase III - 
Phase IV - 


Literature Search 
Baseline Configuration 
Parametric Configurations 
Performance Configurations 


Phase II of the program is in progress. 


OBJECTIVES 


Objectives of the Phase II efforts are to: 

o Identify the mechanisms and the magnitude of aerodynamic losses in the 
prediffuser, dome, and shroud regions of an annular combustor-diffuser 
system 

o Determine the effects of geometric changes in the prediffuser, dome, and 
shroud wall on aerodynamic losses and loss mechanisms 

o Obtain a data base that can be used to assess advanced numerical aerody- 
namic computer models for predicting flowfleld conditions In an annular 
combustor-diffuser system 

o Assess the ability of current analytical models to predict flowfield char- 
acteristics in annular combustor-diffuser systems. Including pressure dis- 
tributions 

o Upgrade the analytical models based on the experimental data for flowfield 


*Work done under USAF Contract F33615-84-C-2427 . 




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S’ANK NOT FU*D 


133 



DESCRIPTION OF TEST CONDITIONS AND RIG 


The test rig is a 60-degree sector of a full annular combustor-diffuser system 
whose cross-sectional details are shown in Figure 1. Air flow through the rig is 
established by connecting discharge ducts to vacuum lines. The airflow rate in each 
of the three lines is controlled to produce the desired flow split and a rig inlet 
Mach number of 0.35. The test rig performance evaluation is being made for 15 dif- 
ferent flow conditions as shown in Table 1. 

RESULTS 

Water flow visualization tests were performed for all 15 flow conditions. The 
streamline patterns were photographed and compared with predicted results, which 
showed good agreement. A typical comparison is shown In Figure 2 for one of the 
test conditions. Subsequent to the flow visualization tests, detailed pressure and 
wall shear stress distribution measurements were made for these flow conditions. 

The instrumentation for pressure measurements are shown In Figure 3. 

Shear stress distributions were measured only along the prediffuser walls 
(Figure 4). These data are being processed. The three-component LDV system 
(Figure 5) has been set up, and LDV measurements in the CDI test rig will be 
initiated to obtain detailed velocity field and turbulence quantities. Analytical 
model assessment and upgrade efforts will be performed in conjunction with the LDV 
measurements. Design efforts of the test rig for Phase III (Parametric Configura- 
tions) are underway. Figure 6 shows the configurations which will be test evaluated 
during this phase. 


134 



TABLE 1. FLOW CONDITIONS USED DURING PHASE II TESTING 


Percent Flow Split 

Test 

No. 

Outer 

Annulus 

Dome 

Inner 

Annulus 

1 

32.9 

20.0 

47.1 

2 

40.0 

20.0 

40.0 

3 

48.0 

20.0 

32.0 

4 

55.0 

20.0 

25.0 

5 

60.0 

20.0 

20.0 

6 

26.8 

35.0 

38.2 

7 

32.5 

35.0 

32.5 

8 

39.0 

35.0 

20.3 

9 

44.7 

35.0 

20.3 

10 

48.8 

35.0 

16.2 

n 

20.6 

i 

50.0 

| 

29.4 

12 

25.0 

50.0 

25.0 

13 

30.0 

50.0 

20.0 

14 

34.4 

50.0 

15.6 

15 

| 

37.5 

: 

50.0 

12.5 


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original page is 

OF POOR QUALITt 


DESCRIPTION OF THE BASELINE TEST RIG, 



INNER TO OUTER DIAMETER RATIO AT 


PREDIFFUSER INLET 0.92:1 

PREOIFFUSER AREA RATIO 1.86:1 

PREDIFFUSER LENGTH TO INLET 

HEIGHT RATIO 3.778:1 

WALL DIVERGENCE ANGLE 6.5 OEGREES 

RATIO OF DUMP GAP TO PREDIFFUSER 

EXIT HEIGHT 0.52 

RATIO OF COMBUSTOR CHANNEL HEIGHT 
TO INLET DUCT HEIGHT 310 

RATIO OF OUTER TO INNER 

ANNULUS AREA 1.5 


FIGURE 1. 


FLOW VISUALIZATION TEST RESULTS AND PREDICTED STREAMLINES. 



TEST CONDITION NO. 6 


FIGURE 2 



WALL STATIC, TOTAL PRESSURE RAKE, AND PRESSURE SURVEY LOCATIONS 


ASTATIC PRESSURE PROBE (3 PROBES AT EACH LOCATION CIRCUMFERENTIALLY UNLESS NOTED) 132 
■ TOTAL PRESSURE RAKE-5 PROBES 4 

• THERMOCOUPLE 4 

x LOCATION OF PRESSURE SURVEY 
- INLET. 10 LOCATIONS 



FIGURE 3 



LOCATIONS OF FLUSH-MOUNTED HOT FILM SENSORS USED TO DIRECTLY MEASURE 
HALL SHEAR-STRESSES IN THE PREDIFFUSER. 


4.882 — ~ 



SMOOTH WITHIN 0.001 IN. 


WALL-SHEAR MEASUREMENT SENSOR 


FIGURE 4. 


138 


SCHEMATIC OF THE THREE-COLOR, THREE-COMPONENT LDV SYSTEM 



SYSTEM DESCRIPTION 

• CHANNEL SEPARATION BY 3-COLOR 

• 3.75x BEAM EXPANSION 

• 450mm FOCAL LEN6TH. 152mm OBJECTIVE LENSES 

• OFF-AXIS BACKSCATTER COLLECTION 

• DISPERSION PRISM COLOR SEPARATION 

• 150 M Hz BAND WITH SIGNAL CONDITIONING 

• 3-AXIS COMPUTER CONTROLLED TRAVERSIGN SYSTEM 

• PROBE VOLUME SIZE 

- DIAMETER = 0.6mm 

- LENGTH = 0.22mm 

• ESTIMATED ACCURACY ON VELOCITY COMPONENTS 
ABOUT 1 PERCENT WITH 30° SEPARATION ANGLE 

• VELOCITY RESOLUTION 

0.25% AT 40 M Hz OR 0.037 M/S AT 150 M/S 


FIGURE 5. 


SCHEMATICS OF PARAMETRIC CONFIGURATIONS FOR PHASE III TEST EVALUATION. 

00 PEAKED PROFILE ID PEAKED PROFILE DUMP GAP (2) 



CURVED WALL DIFFUSER TRUMPET DIFFUSER ELLIPTICAL DOME SHROUD 



FIGURE 6. 


139