An Investigation of Effects of Flame-Holder Gutter Shape on Afterburner Performance Page: 3 of 51
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NACA RM E53J14
INTRODUCTION
In many cases of current turbojet power plants for aircraft, the
need for thrust augmentation during certain periods of flight operation
dictates the use of afterburners. More extensive needs have arisen in
aircraft designed for transonic and supersonic flight. Some of the per-
formance characteristics desirable in afterburners for such aircraft are
high combustion efficiency at low pressures, stable combustion over a
wide range of fuel-air ratio, and low internal drag to keep tail-pipe
pressure loss and, hence, thrust loss to a minimum, particularly during
nonburning operation, such as in cruise flight.
As has been shown in numerous afterburner investigations, refer-
ences 1 to 3, for example, increasing burner inlet velocity and de-
creasing burner pressure have deleterious effects on both combustion
efficiency and stability limits. Efforts to minimize the harmful effects
on afterburner performance at increasing velocity and decreasing pressure
or to improve 'performance at given conditions of operation have been
centered primarily about design of the fuel injection system, the inlet
diffuser, and the flame-holder blockage or gutter width. The afterburners
of references 1 to 3 and other afterburners have generally used flame
holders made up of gutter elements having a V, an H, or a semicircular
cross section. Investigations of the effects of systematic changes in
gutter shape on afterburner performance have been limited in scope,
however.
Published literature on basic studies of flame stabilization and
propagation such as references 4 and 5 reported stability limits to be a
function of approach stream velocity and gutter width. Tn reference 5
it was postulated that hot burned gases in the recirculation zones
immediately behind the flame holders raised the temperature of the
approaching mixture and provided continuous ignition. Although the
studies of both references 4 and 5 indicate that blow-out velocity was
independent-of the particular stabilizer shapes tested over the range
of conditions covered by the investigations, it appeared that radical
changes in gutter shape which would strongly affect the character of
recirculation behind the gutter might correspondingly affect the limits
of flame stabilization. It was possible also that the degeneration of
combustion performance at the low pressure and high velocity flow con-
ditions encountered in afterburner operation might be partially depen-
dent upon the shape of the flame-holder gutter elements.
An investigation of the isothermal wake flow characteristics behind
various gutter shapes was accordingly conducted and is reported in ref-
erence 6. The gutter shape altered the frequency and strength of vor-
tices shed from the body in the absence of combustion. An attempt was
made to relate the flow characteristics with parameters which might be
indicative of the amount of recirculatory mass flow behind the gutter,
and which might in turn have some bearing upon the combustion process
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Nakanishi, S.; Velie, W. W. & Bryant, L. An Investigation of Effects of Flame-Holder Gutter Shape on Afterburner Performance, report, February 10, 1954; (https://digital.library.unt.edu/ark:/67531/metadc59948/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.