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According to the experimental data, the swirling films have higher
cooling efficiency compared to the nonswirling ones, with comparatively
low relative flow rates of cooling gas to the film (
˙
m
f
= 0
.
236
) which is of
pragmatic interest with regard to the cost efficiency.
It could be related to the fact that the centrifugal force pushes the film
flow to the wall and prevents its premature washout by the main flow
combustion products.
In order to study the coolant type influence on the cooling efficiency,
gaseous oxygen and nitrogen were used as film gas in [7]. With the
nonswirling films, the cooling efficiency does not depend on the type of film
gas, whereas swirling films have higher efficiency with a nitrogen injection
than with an oxygen one. The author attributes this fact to a fraction of the
injected oxygen being involved into the combustion process. However, as
it was mentioned earlier, the centrifugal force emerging with the swirling
flow should also be taken into account, this force prevents the film from
mixing with the main flow in different ways. That is why, when using gases
with various physical properties, such as density, viscousity, heat capacity,
and thermal conductivity, the difference in their efficiency as films can be
attributed to the difference in both heat-mass transfer and mass transfer
conditions, with all other conditions being equal.
Another subject in [7] was the influence of coolant relative mass flow-
rate on the gas film efficiency: the greater the flow-rate is, the higher the
efficiency becomes.
The experiments in [8] were aimed at establishing how the film slot
positioning affected the cooling efficiency. The testing facility was a
rocket engine working on CH
4
(g) + O
2
(l) propellant combination. Gaseous
methane was used as a coolant.
Similar to [6] the research was done for two film slot positioning
configurations: in the first configuration the slot was located directly behind
the external coaxial spray injector, in the second configuration the slots were
located between the injectors.
The experimental data confirmed that the film slot positioning influenced
the film cooling efficiency considerably. Thus, the slot positioned between
the periphery injectors is the most favorable one in terms of cooling the
combustion chamber walls. The authors attribute it to the superposition
of the adjacent flows, which create a layer of a cold film fuel component
preventing the wall from being heated by the exhaust products coming
from the injector located between these slots.
The influence of the mass flow-rate on the film cooling efficiency
was also considered in [9]. The object of the research was RE working
on kerosene + O
2
(g) propellant combination. Gaseous nitrogen N
2
and
kerosene were used as a coolant. The study was conducted at the chamber
84 ISSN 0236-3941. HERALD of the BMSTU. Series “Mechanical Engineering”. 2014. No. 1