Tuesday, September 06, 2005

Materials, Mimicry and MEMS by Dr. Julia King

It’s all about fans! Prof. Julia King, from rolls royce today delivered really a fascinating talk on aero-engine in our prestigious faculty hall. When I first saw those real huge jet engines, I wondered how much science and technology must have been gone into it. She today talked about the physics, engineering and design of the fans and the engine as a whole!
Her talk started with the general concern on global warming and the contribution of aerospace industries to it. She showed a B-52 bombers emitting considerable amount of un-burnt hydrocarbon. According to her noise pollution due to high engine noise levels is also a cause of concern primarily in cities. So she addressed all the problems in sequence. Her presentation began with an animations on how an engine works. It was evident that materials design is the key for the turbines blades inside the engine! The material they use for the fans are Ni bases super alloys and there is a problem with the randomly oriented polycrystals. The grain boundaries parallel to the air flow is a bad news: they are the site where the fatigue crack initiates under cyclic loading so the blades were processed with oriented grains with boundaries perpendicular to the air flow. Final step towards this grain boundary engineering was to remove the grain boundaries, i.e. use of single crystals! No boundaries so no flaws. It is important to reduce the weight of the blades which is a new field of research and shape memory alloys and metallic foam appeared to be potential material for that. There was a job also for the combustion engineers but from the material scientist point of view it was necessary to talk about the chamber material. Composite materials were shown to have better run for that. When the discussion boiled down to noise she mentioned how the noise is generated from the engine, the solution for that was to have a turbulent mix of two kinds of air coming out of the jet, for that it was observed serrated outer wall of the jet instead of smooth wall is quite effective. The criteria was it should remain close while it is flying at low altitudes (high temp. region) and at high altitude they should open up . In a nice experiment she showed actually how shape memory alloys acts as an actuater under changing temperature; it was really a nice piece of experiment. There was an ineresting info: eagles can fly at a speed of 200 Mph and consume an energy equivalent to only 10% of its own weight. At the end of her talk she showed some video clippings of some testing on the fans. They were amazing! First one was under tremendous water flow, 2nd one was fans performance under cold condition (T= 233 K), 3rd one was what if a single blade breaks? And final one was what happens when birds hit the jet, I am not going to tell you what happens then, you have to listen to Dr. King. I could not put any of her slides which I would loved to post, may be some other day......

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