The performance of a jet engine can significantly deteriorate with the deposition of molten particles on the interior surface. A group of scientists from Japan has simulated the solidification process of a molten droplet as it touches a cooler flat surface.
This technique employs a mesh-less method to precisely predict the spread and the solidification of the droplet and is capable of elevating the efficiency of turbines in the future.
The gas turbine engines in the plane deliver the needed thrust by sucking in the air and heating it to a very high temperature in the combustion chamber and ultimately exhausts it at high velocities. During this process, there are chances of small inorganic ash, like volcanic ash, being sucked in. These particles are melted in the high-temperature zones and tend to solidify onto the cooler zones in the engines like the turbine blades.
As the droplets solidify and accumulate over time, they potentially deform the blades and block the cooling holes, leading to a decline in the engine performance and life.
These deposition cases are unavoidable, but it is possible to predict and modify the engine design. A key feature of the deposition process is quantifying the way in which molten droplets solidify in contact with a cooler surface, and it is a primary requirement to develop a precise simulation of this process.
The study was published in the International Journal of Heat and Mass Transfer.
A research team from Japan developed a model capable of performing a faster and precise simulation of the solidification of a single molten droplet on a flat surface. The model demands no prior data to set up and can predict deposition in jet engines.
The research team included Dr. Koji Fukudome and Prof. Makoto Yamamoto from the Tokyo University of Science, Dr. Ken Yamamoto from Osaka University, and Dr. Hiroya Mamori from The University of Electro-Communications.
While the earlier model considered the surface to be at a constant temperature, the new approach simulates the process, analyzing the droplet behavior and the heat transfer between the hotter droplet and the cooler surface.
We have been simulating droplet impact, but we could not ignore the difference from the experiment. In this study, we thought that taking into account the temperature change of the colliding wall surface would be consistent with the experiment.
Dr. Koji Fukudome, Tokyo University of Science
With an objective to develop a less computationally intensive model, the scientists chose a mesh-less moving particle semi-implicit (MPS) approach that requires no multiple computations on every grid.
The MPS approach is built on basic equations of fluid flow, similar to incompressible Navier-Stokes equations and mass balance conservation equations. The method is widely employed to simulate complicated flow.
The temperature variation occurring inside the substrate was calculated using the grid-based method, enabling the coupling technique of both particle-based and grid-based methods.
The researchers employed this method to simulate the solidification of a molten tin droplet on a stainless steel substrate. The model delivered a relatively good performance and was capable of replicating the solidification process observed in experiments.
The simulation also offered a keen view into the solidification process, remarking the extending behavior and the temperature distribution of the droplet as it interacts with the surface.
The simulation revealed that the solidification is reliant on the thickness of the liquid film that was formed after the interaction of molten droplets with the surface. The solidification begins after the film expands on the surface and was initially identified at the edge of the liquid film near the surface. With the continued spread of the liquid film and reduction in thickness, the solidification advances until the whole film turns into solid particles.
The study can contribute to the enhancement of existing solidification models and the team is expecting to apply the current approach to construct more complex deposition models.
There is no universal model for predicting depositions. Therefore, when considering the deposition of a certain droplet, a model is created by conducting experiments in advance, and numerical predictions are made. This study is expected to be a pioneer in the development of a universal deposition model.
Dr. Koji Fukudome, Tokyo University of Science
The study can help scientists and engineers to learn more about the complex deposition phenomena and jet engine designs, enabling a safer and long-lasting redesign.
Fukudome, K., et al. (2021) Numerical simulation of the solidification phenomena of single molten droplets impinging on non-isothermal flat plate using explicit moving particle simulation method. International Journal of Heat and Mass Transfer. doi.org/10.1016/j.ijheatmasstransfer.2021.121810.