Augmented backside cooling is when the backside convection of the combustor liner is enhanced using certain heat transfer surfaces to fully utilise the cooling air by maximising the heat transfer to pumping ratio characteristic.

Although film cooling has and still is widely used in the gas turbine industry, augmented backside cooling has been in development for decades now. The reason for this is to reduce the amount of air used for liner cooling and also reduce the emissions caused by using film cooling in the primary zones.

For the same reasons, this type of cooling is being developed for micro gas turbines, where the conservation of the cooling air is of even greater importance due to the limited amount of air used in the overall system to start with and the constant demand of higher overall efficiencies from them. Currently, some very simple designs are being used in the form of straight plain fins or trip strips but the creation of high-efficiency surfaces in such small sizes becomes very difficult with traditional subtractive manufacturing methods. Due to this difficulty, additive manufacturing is ideal for constructing high-efficiency heat transfer surfaces in small sizes.

This paper covers the comparison of experimental results of two different AM liner cooling surfaces against a blank liner. The one surface is a rotating plain fin and the other is an offset strip cooling surface. The liners were tested in an AM built reverse flow radial swirl stabilised combustion chamber at certain operating conditions. During the experiment, the surfaces were compared using a thermal camera to record the outer liner temperature which was view through a quartz outer casing.

The experimental results showed that the cooling surfaces were effective at reducing the liner temperature to the desired value in order to maximise its lifetime. The temperatures, pressures, and heat transfer capability results were then compared against the CFD and analytical methods used to design the surfaces initially.

From this comparison, it was noticed that some errors were present, which are thought to be due to not being able to accurately predict the flame temperature and due to inaccuracies in the emissivity values used in the analytical design methods.


Experimental and Computational Analysis of Additive Manufactured Augmented Backside Liner Cooling Surfaces for Use in Micro Gas Turbines

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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