Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 163

A fundamental issue in designing gas turbine combustors is the late stage of the
development process at which combustion dynamics phenomena become apparent.
Many, if not most of the critical performance parameters of a combustor can be
determined analytically or through a combination of analysis and component
testing. Although some indications of the susceptibility of a combustion system to
high levels of dynamics can sometimes be inferred from component tests, the
behavior of the full system cannot be predicted on the basis of either analysis or
component testing. The severity and character of the problem is not determined
until an engine test is conducted, at which point signi

“

cant changes to component
design are very expensive and are likely to have major schedule and development
cost impacts. Various acoustic control strategies, both passive and active, are then
applied to deal with the unacceptable dynamics levels. However, the application of
these strategies is a very empirical process with little assurance of success.

Some
additional insight is provided in Mongia et al. ( 2005 ). Nothing substantial has
changed during the last 10 years. The basic methodology

”

first successfully dem-

onstrated during the 1994 1996 time frame for solving dynamics on the industrial

engines LM2500 and LM6000 DLE, Fig. 53 , as shown schematically in Fig. 54
continues to evolve to meet signi

-

cantly more demanding requirements of aviation
engines combustion products including the CFM DAC and GEnx; and in coming
years for the LEAP-X and GE9X. Computationally expensive models have shown
some success in identifying potential resonant frequencies that can be used as
design guide. Fundamental experiments coupled with computational efforts (Gejji
et al. 2014 ), show enormous complexity of the phenomenon (viz. Figs. 55 and 56 ),
not exactly a morale booster for the technologists and designers. In the meantime,
the author along with his colleague Prof. Galen King and three PhD students are
working on a research project called proactive state selection in order to bypass the
annoying dynamics for the N + 3 technology elements (Mongia 2013e ).

Fig. 53 Schematic
comparison between the dry
low emissions (DLE)(top)
and rich-dome (bottom)
aeroderivative industrial
engines; adopted from Joshi
et al. ( 1998 )

30 PREMIXERS
COMPRISING 75
STAGED INJECTORS

4 PASSAGE
COMPRESSOR
DIFFUSER

30
30
15

SINGLE COMPRESSOR
DIFFUSER PASSAGE

SINGLE ROW OF 30
FUEL NOZZLES