Trouble Using Grid Independent Mesh for Other Velocity

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  • Last Post 19 May 2020
regitasyali posted this 29 April 2020

Hello,

I'm analyzing the increase of friction coefficient due to the growth of marine fouling on ship hull. Currently, I've been doing simulations using ANSYS Fluent on a flat plate with five different velocities (3 m/s, 6 m/s, 9 m/s, 12 m/s, and 15 m/s) and four different types of roughness for each velocity. I still need to do simulations for the ship model, but right now I'm still stuck on this problem with grid-independent mesh.

The simulation used a single-phase fluid, the air, as its purpose is to validate my former colleague's experiment of a similar analysis that was done by using a wind tunnel. I've done the grid-independence study for the smallest velocity with the smooth condition of the plate and found that the suitable grid consists of around 1.1 million cells, with a 3.84% error from the experiment result. I've used the k-w SST turbulent model with y+ = 1 for the near-wall treatment. I've used the tetrahedral patch conforming method for the mesh.

The problem is that when I tried to do a simulation for 6 m/s using the same meshing configuration as the previous grid-independent mesh for V = 3 m/s, the result turned out to be 9% different from the wind tunnel experiment result. I only changed the first layer thickness value. Up to this day, I'm still clueless about what has gone wrong. I also tried using cut cell and multizone methods to no avail. I also have asked for help from my seniors and supervisor, but I am still stuck here. If you can help me find out what's wrong with my simulation, it'd be very appreciated.

Thank you so much, I hope you all stay healthy and safe in the middle of this pandemic situation.

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Kremella posted this 30 April 2020

Hello,

For different velocities, does the flow field change? Also, when you are changing the y+ mesh, does it change the overall mesh? What happens to the 9% case when you refine the mesh further? Do you get a better result?

Also, what variable are you really comparing with experiments? 

Thanks.

Best,

karthik

regitasyali posted this 08 May 2020

Hello, thank you for answering.

I haven't checked the flow field. I'm gonna check it soon and let you know. No, I used the same y+ value, which equals to 1, for every velocity. So, I only changed the first layer thickness value for every velocity, and I didn't change the rest of the mesh configuration. I did try to refine the mesh further until it reached 2 million cells, but it didn't work. 

I am comparing the total drag results between my CFD simulations and my colleague's wind tunnel experiment. Both are done for a flat plate.

Thank you, Karthik.

regitasyali posted this 19 May 2020

I am using full viscous simulations and I am not sure how to model the flow field as one would model the flow field for free surface simulation

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