Thesis-2005-Chua.pdf (45.07 MB)
Experimental characterisation of the coolant film generated by various gas turbine combustor liner geometrics
thesis
posted on 2013-07-08, 14:16 authored by Khim Heng ChuaIn modern, low emission, gas turbine combustion systems the amount of air
available for cooling of the flame tube liner is limited. This has led to the
development of more complex cooling systems such as cooling tiles i.e. a double
skin system, as opposed to the use of more conventional cooling slots i.e. a single
skin system. An isothennal experimental facility has been constructed which can
incorporate 10 times full size single and double skin (cooling tile) test specimens.
The specimens can be tested with or without effusion cooling and measurements
have been made to characterise the flow through each cooling system along with
the velocity field and cooling effectiveness distributions that subsequently develop
along the length of each test section. The velocity field of the coolant film has
been defined using pneumatic probes, hot-wire anemometry and PIV
instrumentation, whilst gas tracing technique is used to indicate (i) the adiabatic
film cooling effectiveness and (ii) mixing of the coolant film with the mainstream
flow. Tests have been undertaken both with a datum low turbulence mainstream
flow passing over the test section, along with various configurations in which
large magnitudes and scales of turbulence were present in the mainstream flow.
These high turbulence test cases simulate some of the flow conditions found
within a gas turbine combustor. Results are presented relating to a variety of
operating conditions for both types of cooling system.
The nominal operating condition for the double skin system was at a coolant to
mainstream blowing ratio of approximately 1.0. At this condition, mixing of the
mainstream and coolant film was relatively small with low mainstream
turbulence. However, at high mainstream turbulence levels there was rapid
penetration of the mainstream flow into the coolant film. This break up of the
coolant film leads to a significant reduction in the cooling effectiveness. In
addition to the time-averaged characteristics, the time dependent behaviour of the
.:coolantfilm was. also investigated. In particular, unsteadiness associated with
large scale structures in the mainstream flow was observed within the coolant film
and adjacent to the tile surface. Relative to a double skin system the single skin geometry requires a higher
coolant flow rate that, along with other geometrical changes, results in typically
higher coolant to mainstream velocity ratios. At low mainstream turbulence levels
this difference in velocity between the coolant and mainstream promotes the
generation of turbulence and mixing between the streams so leading to some
reduction in cooling effectiveness. However, this higher momentum coolant fluid
is more resistant to high mainstream turbulence levels and scales so that the
coolant film break up is not as significant under these conditions as that observed
for the double skin system.
For all the configurations tested the use of effusion cooling helped restore the
coolant film along the rear of the test section. For the same total coolant flow, the
minimum value of cooling effectiveness observed along the test section was
increased relative to the no effusion case. In addition the effectiveness of the
effusion patch depends on the amount of coolant injected and the axial location of
the patch.
The overall experimental data suggested the importance of the initial cooling film
conditions together with better understanding of the possible mechanisms that
results in the rapid cooling film break-up, such as high turbulence mainstream
flow and scales, and this will lead to a more effective cooling system design. This
experimental data is also thought to be ideal for the validation of numerical
predictions.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Aeronautical and Automotive Engineering
Publisher
© K H ChuaPublication date
2005Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.488529Language
- en