Control allows significant diffuser length and weight reduction, reduces combustor exhaust emissions during engine idle, and improves combustor altitude relight capability

Holdeman, J. D.

Juhasz, A. J.

English

NASA Technical Reports Server

.inuet veuocuty rroiile 
May 1972	 B72-10178 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code XI, Washington, D.C. 20546. 
Airflow Distribution Control for

Improved Turbine Engine Performance 
The problem: 
To provide a practical method by which the distri-
bution of airflow entering aircraft gas turbine engine 
combustors can be varied to improve engine performance 
at idle, take off, cruise, and altitude relight. The advan-
tages of a gas turbine engine equipped with combustor 
airflow distribution control would be threefold: (1) a 
significant reduction in diffuser length, and hence 
weight, since the short diffuser flow separation problem 
could be controlled; (2) annoying combustor exhaust 
emissions during engine idle could be drastically re-
duced by reducing airflow to the primary combustion 
zone; (3) combustor altitude relight capability could be 
greatly improved by creating a low velocity recirculation 
zone around the fuel nozzles and ignitors. 
The solution: 
Velocity profile control experiments conducted with 
a short annular diffuser equipped with wall bleed (suc-
tion) capability indicate that the diffuser bleed tech-
nique could be effectively used in controlling gas turbine 
combustor airflow distribution. Preliminary data obtain-
ed from a full scale gas turbine combustor using a bleed-
type diffuser also demonstrate this combustor airflow 
control capability, even though the combustor had not 
been designed to operate with a bleed-type diffuser.
Fuel Nozzle	 I gnitor 
Bleed Ports 
Inlet Velocity 
Profile
	 \\
Primary
Zone 
Air Flow
DiffuserE
__.^_Cpormbustor 
A. IDLE OR ALTITUDE RELIGHT OPERATION 
Outer 
BIeE 
Outer WaII..__ 
mmo-
Inner WalI	
MMIZI 
B. CRUISE OR TAKEOFF OPERATION 
How it's done: 
A short annular combustor designed to operate with 
the diffuser bleed concept, referred to as a "controlled 
separation combustor," is shown schematically in the 
figures. The diffuser geometry is asymmetric with a 
rapidly diverging outer wall and a gradually diverging 
inner wall. Bleed ports (or slots) permit a small fraction 
of the diffuser inlet airflow to be ducted through the 
diffuser walls at certain operating conditions. 
The use of bleed flow would depend on the desired 
combustor inlet velocity distribution at a given operating
condition. When no wall bleed is used, the asymmetric 
diffuser geometry causes the flow to adhere to the inner 
wall but to separate from the outer wall. The resulting 
combustor inlet velocity distribution would allow most 
of the flow to bypass the primary zone of the combustor 
as required for engine idle and altitude relight condi-
tions. Hence, the desired velocity distribution could be 
obtained at these conditions without applying diffuser 
bleed as indicated in Figure A. 
Figure B shows the proposed bleed combustor during 
(continued overleaf) 
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takeoff or cruise operation. Since now there is sufficient 
static pressure differential between the diffuser and tur-
bine inlet stations, a certain percentage of the airflow 
may be bled off through the bleed ports in the outer 
wall of the diffuser and used for turbine cooling. The 
effect of bleed on diffuser flow would be to cause 
attachment to the outer wall, thereby flattening the 
velocity profile. A small amount of bleed on the inner 
wall could also be applied to trim the profile if neces-
sary. The uniform airflow distribution would provide 
sufficient cooling air for inner and outer combustor 
liners and also improve the pattern factor at the turbine 
inlet. Also, the high diffuser effectiveness obtainable 
with a uniform outlet profile would improve engine 
cycle efficiency by reducing combustor pressure loss. 
Notes: 
1. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA TN-D-6435 (N71-30817), Preliminary 
Investigation of Diffuser Wall Bleed to Con-
trol Combustor Inlet Airflow Distribution
2. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10178 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Stop 500-311 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: A.J. Juhasz and J.D. Holdeman
Lewis Research Center 
(LEW-1 1593) 
B72-10178	 Category 07


Airflow distribution control for improved turbine engine performance

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