By David Flin
There are over 1200 LM2500 gas turbines in operation with navies in various parts of the world, and the GE fleet of propulsion gas turbines has proved to be a reliable power provider in these conditions. GTW talks to George Awiszus, Director of Military Marketing for GE Marine, about what is needed for gas turbine propulsion units in naval applications.
HMAS Canberra RAN is one of more than 1200 LM2500 gas turbine units operating in 35 navies around the world.
Warships face a unique set of operating conditions and therefore developing gas turbines for them presents several challenges. For instance, surface combatants are subjected to the harsh salt environment and have varying operational load demands. Engines also can be subjected to major shock events while the warship is in harm’s way. It is therefore of vital importance to have the gas turbine always available and operating under these very challenging conditions.
There are more than 1200 LM2500 gas turbine units operating in 35 navies around the world, including with the US, Canadian, Spanish, Australian, Canadian, German, and South Korea navies, among others.
The LM2500 gas turbine is derived from the CF6 aero engine. However, George Awiszus, Director of Military Marketing for GE Marine, explained that there is a key difference between aero engines and industrial and maritime gas turbines.
Aero engines are designed to generate thrust, and as a result, involve a different set of loadings to industrial and maritime turbines. When developing aero engines for use in maritime applications, GE first adapts the engine for use in industrial applications, and when the unit is proven here, it is then developed for use in maritime settings.
Industrial usage gives experience in the modifications, although the changes are often small.
Reliability is the critical issue for gas turbines used in naval ships. A third party track of reliability and availability data has been made through the Operational Reliability Analysis Program (ORAP). This demonstrated that the LM2500 achieved greater than 99 per cent reliability and greater than 98 per cent availability.
The biggest difference between the industrial and the maritime versions is in the package. In a naval environment, space and weight are at a premium. Power density of a gas turbine is a major requirement. Reducing size is important in space-constrained frigates, which need to balance propulsion, weapons and crew accommodations. Awiszus said www.gasturbineworld.com GAS TURBINE WORLD May - June 2018 11 that the LM2500 has the best in class in power density, traditionally 20 per cent better than the nearest equivalent sized turbine and increasing to 30 per cent.
The reason for the 10 per cent power density improvement has been through using composite materials. These were developed as a collaboration between the US Navy, General Dynamics Bath Iron Works and GE. They developed a new one-piece composite carbon fibre enclosure for the LM2500. It was designed and performance verified in accordance to a complete set of US Navy military and shock specifications.
Replacing steel with this composite in the enclosure has enabled a weight reduction of 2500 kg. Using composite rather than steel walls give better sound attenuation, and the outside of the wall is not as hot, with a surface temperature heat reduction of 15-35°C, making it safer to touch. This is an important consideration when working in the confined space of a ship’s engine room, particularly when manoeuvrability of the ship is likely to cause significant changes in speed and direction, and hence stability of the platform for operators.
Doors into the package made with composites are both larger and lighter, making access significantly easier. In addition, composites do not corrode in salt water, while steel does.
Another important factor required for gas turbines in a naval ship is the ability to withstand shock loading. To test that their gas turbines meet US Navy requirements, GE carries out shock testing in accordance with MIL-S-901. This involves mounting the gas turbine on a barge, which is then floated in a test pond. Then depth charges are detonated at set distances in the water, and the effect on the turbine measured. The turbine continued to operate after the test. This test has been carried out on GE gas turbine equipment four times, and it provides a clear demonstration of the robustness of the turbine under such conditions.
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