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Introduction and Summary
Perhaps the most important and, at the same time, most difficult
Problem in the design and development of gas turbine combustion chambers,
is that of achieving a satisfactory and consistent distribution of
temperature in the efflux gases discharging into the turbine. In the
past, experience has played a major role in the determination of dilution-zone
geometry, and trial and error methods have of necessity been employed
in developing the temperature-traverse quality of individual combustor
designs to a satisfactory standard. Experimental investigations into
dilution-zone performance carried out on actual chambers have led to
useful empirical-design data, but very often it has proved difficult or
impossible to distinguish the separate influences of all the variables
involved. Thus although it is now generally accepted that a satisfactory
temperature profile is dependent upon adequate penetration of the dilution
jets, coupled with the correct number of jets to form sufficient localized
mixing regions, the manner in which the total dilution-hole area is
Utilized in terms of number and size of holes is still largely a matter
of experience. Unfortunately, more basic studies of jet mixing do not
usually yield results that can readily be expressed in the parameters
which are most familiar to those concerned with combustion-chamber design.
However, some of these investigations can provide a useful guide to the
relationships involved.
One such investigation resulted in the accumulation of a large amount
of data on the mixing of cold jets when injected into hot streams under
conditions where the temperature and velocity of the hot and cold streams,
the injection-hole diameter, the angle of injection, and the mixing length
could be accurately controlled and varied over a wide range. These data
are used here, firstly to demonstrate a logical method of dilution zone
design and, secondly, to provide quantitative data on the rate of exchange
between temperature traverse quality and the relevant design parameters
such as dilution zone length, dilution hole diameter and pressure loss
factor. The effects of chamber inlet velocity and inlet velocity profile
are also examined.
Finally, it is proposed that the aerodynamic performance and stability
of a combustion chamber may, for most practical purposes, be adequately
described in terms of a parameter p which is the ratio of the flametube
pressure loss to the overall pressure loss. Evidence is presented in |
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