A computationally quick approach to predict molten droplet
solidification on a solid surface
Understanding the solidification process of molten droplets can help
develop a universal model to predict their deposition in jet engines

Date:
October 12, 2021
Source:
Tokyo University of Science
Summary:
The deposition of molten particles on the interior surface of jet
engines can cause significant damage and degrade the performance
of the engine.

Now, scientists successfully simulated the solidification process
of a molten droplet as it impinges on a cooler flat surface. This
approach uses a mesh-less method to accurately predict the spread
and the solidification of the droplet and could potentially boost
the efficiency of turbines in the future.



FULL STORY ==========================================================================
Gas turbine engines in planes provide the required thrust by sucking
in air, heating it to very high temperatures in a combustion chamber,
and finally exhausting it at high velocities. As they operate, small
inorganic particles such as volcanic ash get sucked in along with the
air. These particles melt in the high-temperature zones in the combustion chamber and solidify onto 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 cooling
holes, which deteriorates the performance and the life of the engine.


========================================================================== While the deposition phenomenon is unavoidable, 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 the International Journal of Heat and Mass
Transfer, a group of scientists from Japan developed a model that can
quickly and accurately simulate the solidification of a single molten
droplet on a flat surface. Their model does not require any prior
information to setup and can be used to develop models that can predict
the deposition process in jet engines.

The research term consisted of 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.

Unlike previous models that assumed the surface to be at a constant temperature, the new approach simulates the solidification process
by considering 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," explains Dr. Fukudome.

To have a less computationally intensive model, the researchers opted
for a mesh-less moving particle semi-implicit (MPS) method which did
not require multiple calculations on each grid. The MPS method is based
on fundamental equations of fluid flow (such as the incompressible Navier-Stokes equations and mass balance conservation equations) and has
been widely used to simulate complex flows. Meanwhile, the temperature
change inside the substrate was computed using the grid-based method,
so that we used the coupling method of both particle-based and grid-based methods.

Using this approach, the researchers simulated the solidification of
molten tin droplet on a stainless steel substrate. The model performed relatively well and was able to replicate the solidification process
observed in experiments. The simulations also provided an in-depth view
into the solidification process, highlighting the spreading behavior and
the temperature distribution of the droplet as it comes in contact with
the solid surface.

Their simulations showed that the solidification is dependent on the
thickness of the liquid film that was formed after the molten droplet
had come in contact with the surface. Solidification initiates as 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 spread and become thinner, solidification progresses until the entire film is turned into solid particles.

These findings are an improvement on current solidification models and
the team is hopeful that their current approach can be used to build 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. Fukudome remarks.

Thanks to this study, engineers and scientists can get a better
understanding of the complex deposition phenomena and jet engine designs
can be redesigned to be safer and long-lasting.

========================================================================== Story Source: Materials provided by Tokyo_University_of_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Koji Fukudome, Yusuke Muto, Ken Yamamoto, Hiroya Mamori, Makoto
Yamamoto.

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, 2021; 180: 121810 DOI:
10.1016/j.ijheatmasstransfer.2021.121810 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012154736.htm

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