8 / 10
Fig. 6. Coolant injection methods layout:
а
— slot height and slot wall thickness,
b
— coolant outflow angle;
c
– radial and
tangential coolant feed
The influence of the coolant turbulence in the slot and the main flow was
analyzed in [15, 16]. Changing the coolant turbulence intensity in the slot
from 5.5% to 9.5% slightly affects the film cooling efficiency [15], while
reducing the main flow turbulence intensity from 3.2% to 22% decreases
film cooling efficiency considerably [16]. The results of this research can
be limitedly applied to LTRE, since nitrogen at approximately 810 K was
used as the main flow; its temperature was significantly lower than the ones
in the LTRE combustion chambers.
It should be noted that the specialized thermoanemometric equipment
is required for conducting an accurate experiment, which is intended to
determine the film turbulence influence on its efficiency. However, there
are certain constraints which do not allow using it for studying the LTRE
combustion chamber processes [17]. These constraints include: a very high
temperature in the RE combustion chamber, a rapidly changing flow under
testing, sophisticated equipment installation in the combustion chamber,
discontinuity of the natural flow due to the probe, and a high cost of the
equipment.
As a result, the efficiency of the film cooling is influenced by a whole
set of factors. The main factors include:
1) cooling system design and the coolant injection method: the slot
height
s
(Fig. 6,
a
); wall thickness above the slot
h
(Fig. 6,
a
); a cooling
gas output angle (Fig. 6,
b
); the radial or tangential injection of the cooling
component (Fig. 6,
c
), film slots positioning relative to the injectors;
2) film characteristics: coolant mass flow-rate or relative mass flow-
rate; coolant chemical composition; coolant temperature; cooling gas flow
turbulence level;
ISSN 0236-3941. HERALD of the BMSTU. Series “Mechanical Engineering”. 2014. No. 1 87