Theoretical analysis of total-pressure loss and airflow distribution for tubular turbojet combustors with constant annulus and liner cross-sectional areas Page: 1 of 26
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REPORT 1373
THEORETICAL ANALYSIS OF TOTAL-PRESSURE LOSS AND AIRFLOW DISTRIBUTION FOR
TUBULAR TURBOJET COMBUSTORS WITH CONSTANT ANNULUS AND LINER
CROSS-SECTIONAL AREAS 1
By CHARLns C. GRAVES and JACK S. GROBMANSUMMARY
Compressible- and incompressible-flow calculations were
made of the combustor total-pressure-loss coefficient and liner
airflow distribution for tubular turbojet combustors having con-
stant annulus and liner cross-sectional areas along the com-
bustor axis. Information on static- and total-pressure dis-
tribution and liner air-jet entrance angles along the length of
the combustor was obtained as an intermediate step in the
calculations. The calculations include the effects of heat re-
lease, annulus wall friction, and variation in discharge co-
efficients of the liner wall openings along the combustor.
The combustor total-pressure-loss coeficient and liner air-
flow distribution are -presented graphically in terms of the fol-
lowing dimensionless parameters: (1) combustor reference
A'iach number, (2) ratio of combustor-exit to -inlet total tem-
perature, (3) fraction of total airflow passing through the liner
dome, (4) ratio of total open hole area in liner wall to total
combustor cross-sectional area, and (5) ratio of liner cross-
sectional area to total combustor cross-sectional area.
INTRODUCTION
In the design of combustors for turbojet and ramjet
engines, it is desirable to be able to predict the combustor
total-pressure loss and liner airflow distribution from the
combustor geometry and operating conditions. Low values
of combustor total-pressure loss are desired since such
losses reduce engine thrust and cycle efficiency (ref: 1). Air-
flow distribution and liner air-jet entrance angles are of
direct interest to the combustor designer since they in-
fluence combustion efficiency and stability and combustor-
outlet temperature profile (ref. 2). A combustion research
program being conducted at the Lewis laboratory is con-
cerned with these aerodynamic aspects of combustor design.
The loss in total pressure across a combustor may be
attributed primarily to losses resulting from (1) mixing of
high-velocity liner air jets with the liner gas stream, (2) heat
release in the liner, and (3) annulus wall friction. The
effects of these factors on combustor total-pressure loss are
considered in the calculations of the present report. The
liner airflow distribution and liner air-jet entrance angles
are obtained in the course of the combustor total-pressure-
loss calculations.Previous analytical investigations of combustor total-
pressure loss and liner airflow distribution have involved
stepwise calculations in which the combustor is divided into
an arbitary number of transverse sections. In a trial-and-
error method presented in reference 3, the liner airflow dis-
tribution and combustor total-pressure loss are calcu-
lated for an assigned liner open hole area distribution. In a
more rapid method presented in reference 4, the liner open
hole area distribution is calculated for an assigned liner air-
flow distribution and combustor total-pressure loss. Both
methods include the effects of heat release on the calculated
values and could account for variation along the combustor
of the discharge coefficient of the liner wall openings.
For particular combustor configurations, stepwise calcu-
lation methods such as presented in references 3 and 4 have
been used to calculate the combustor flow conditions. How-
ever, there is a need for generalized curves that can be used
to obtain preliminary estimates of combustor total-pressure
loss, liner airflow distribution, and liner airjet entrance
angles. Such curves are not intended as a substitute for
the stepwise calculation methods, but would serve as a
supplement. The curves would also be useful in indicating
the relative effects of combustor geometry and operating
conditions on combustor total-pressure loss and airflow dis-
tribution. The present report is concerned with the de-
velopment of such generalized curves for tubular combustors
having (1) constant annulus and liner cross-sectional areas
along the combustor axis and (2) flush circular holes in the
liner wall. The results should apply approximately to
cannular combustors and to annular combustors having
equal velocities in the inner and outer annuli at all stations
along the combustor.
From compressible- and incompressible-flow calculations,
the combustor total-pressure-loss coefficient and fractional
liner airflow distribution are obtained in terms of the fol-
lowing dimensionless parameters: (1) combustor reference
Mach number, (2) ratio of combustor-exit to -inlet total
temperature, (3) fraction of total airflow passing through the
liner dome, (4) ratio of total open hole area in liner wall to
total combustor cross-sectional area, and (5) ratio of liner
cross-sectional area to total combustor cross-sectional area.
The calculations include the effects of heat release, annulus
wall friction, and variation in the discharge coefficient of the
liner wall openings along the combustor.I Supersedes recently declassified NACA Research Memorandum E58IOI by Charles C. Graves and Jack S. Orobman, 1957.
899
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Graves, Charles C. & Grobman, Jack S. Theoretical analysis of total-pressure loss and airflow distribution for tubular turbojet combustors with constant annulus and liner cross-sectional areas, report, September 17, 1956; (https://digital.library.unt.edu/ark:/67531/metadc60792/m1/1/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.