Gas turbine engines in airplanes provide the necessary thrust by sucking in air, heating it to very high temperatures in a combustion chamber and finally expelling it at high speeds. During operation, small inorganic particles such as volcanic ash are sucked in with the air. These particles melt in the high-temperature zones of the combustion chamber and solidify in the cooler zones in the engine such as the turbine blades. Over time, these droplets solidify and accumulate on the surface of the gas turbine, deforming the blades and blocking the cooling holes, which degrades the performance and life of the engine.
Although the deposit phenomenon is inevitable, predicting the process can help engineers develop and modify engine designs. One of the main aspects of the deposition process is determining how molten droplets solidify in contact with a cooler surface, and an accurate simulation of this process is fundamental to understanding the process.
In a study published in International magazine for heat and mass transfer, a group of scientists from Japan has developed a model that can quickly and accurately simulate the solidification of a single molten droplet on a flat surface. Your model does not require any prior construction information and can be used to develop models that can predict the deposition process in jet engines.
The research semester consisted of Dr. Koji Fukudome and Prof. Makoto Yamamoto from Tokyo University of Science, Dr. Ken Yamamoto from Osaka University and Dr. Hiroya Mamori from the University of Electro-Communications.
In contrast to earlier models, which assumed a constant surface temperature, the new approach simulates the solidification process taking into account the behavior of the droplets and the heat transfer between the hotter droplet and the cooler surface. âWe simulated the impact of droplets, but we couldn’t ignore the difference to the experiment. In this study we thought that taking into account the temperature change of the colliding wall surface would be compatible with the experiment, âexplains Dr. Fukudome.
In order to have a less computationally intensive model, the researchers opted for a semi-implicit (MPS) method with moving particles without a mesh, which did not require multiple calculations for each lattice. The MPS method is based on fundamental flow equations (such as the incompressible Navier-Stokes equations and the mass balance conservation equations) and is often used to simulate complex flows. Meanwhile, the temperature change inside the substrate was calculated using the grid-based method, so we used the coupling method of both the particle-based and the grid-based method.
Using this approach, the researchers simulated the solidification of a molten tin droplet on a stainless steel substrate. The model performed relatively well and was able to reproduce the solidification process observed in experiments. The simulations also provided a deep insight into the solidification process, highlighting the spreading behavior and temperature distribution of the droplet upon contact with the solid surface.
Their simulations showed that the solidification depends on the thickness of the liquid film that has formed after the molten drop came into contact with the surface. Solidification begins when the liquid film expands on the surface and was first observed at the edge of the liquid film near the surface. As the liquid film continues to expand and thin, solidification continues until the entire film is converted into solid particles.
These results represent an improvement on the current solidification models, and the team hopes that their current approach can be used to create more complex deposit models. âThere is no one-size-fits-all model for predicting deposits. Therefore, when considering the deposition of a particular droplet, a model is built through previous experiments and numerical predictions are made. This study aims to pioneer the development of a. its universal deposition model, “says Dr. Fukudome.
Thanks to this study, engineers and scientists can better understand the complex deposition phenomena and make jet engine designs safer and more durable.
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