I am going to simulate a spherical blunt body moving in water along Z axis in a limited range of oscillation. I know I have to use transient condition with dynamic mesh but I need more details about the set up condition?
In the case of one-dimensional motion through the flow, it's a routine procedure in every commercial solver to use the relative motion concept between flow and the rigid body. because of limited solving tools you should limit your solving domain by make it smaller. hence, users can access to this subject by trying limited region of solving.
for example, if you are trying to simulate this sphere it's better to make it fixed through the water and then give the velocity to the fluid around of it. in this approach you can lower your mesh number and you'll have a good control on the flow around the object.
in the case of rigid body solution , CFX and fluent have poor quality in Dynamic mech.for example, lots of negative element volume error. i suggest you to use StarCCM CFD software with power full overset mech method for like this rigid bodies.
rigid body solutions also need huge computing power and with by using this software you can send your Run in university's HPCC(high performance computing center).
i prepare a movie with aim of how to use StarCCM in HPC ,that you can find it on HPPCC site and enjoy.
Thanks for your answer Ahmad
But the problem I am having now is that I do not have access to the HPCC right now and I have to use a personal system with limited function such as CFX & Fluent. By this way, I need some piece of guide to help me how to set the simulation in this respect.
Hello, Dear Hamed.
1. What are the flow characteristics?
2. Is the sphere rigid?
3. and does it contain any fluid?
Dear Hamed,
To rigid body motion simulation in CFX you should introduce the motion's equation as expression in set up section and it is not simple. either you should be really expert in these software or you have to select other CFD simulation software like StarCCM or COMSOL multyphysics. COMSOL has numerous examples regarding your requested problem.
Best Regards,
Alireza Heidarian
M.Sc student
Dear Reza,
It supposed to be a rigid sphere which is moving in the water. There is nothing special with the flow character in advance, but we can assume it as compressible fluid.
Regards,
Dear Alireza,
I know that it could be a hard task to perform but there has been a good results particularly by fluent in this issue. Anyhow CFX is not a common software in Iran. Furthermore, one thing I really wish to know is whether it could be difference in considering the sphere as a stationary rigid body and moving the fluid or vice versa?
regards,
Dear Hamed,
Certainly, when you consider the sphere as a rigid body and your simulation is rigid body motion you will receive many precise results but the results of mesh motion simulation are not too bad and it depends on you and your problem. I do believe that you should first find a paper about it and then start to simulate your problem first mesh motion and compare your results with paper, If your results were acceptable and the error was neglectable it is very good if it was not you have to start to learn rigid body motion. I have some files I hope I could find them and will send it to you.
Best Regards,
Alireza Heidarian
M.Sc student
In the case of one-dimensional motion through the flow, it's a routine procedure in every commercial solver to use the relative motion concept between flow and the rigid body. because of limited solving tools you should limit your solving domain by make it smaller. hence, users can access to this subject by trying limited region of solving.
for example, if you are trying to simulate this sphere it's better to make it fixed through the water and then give the velocity to the fluid around of it. in this approach you can lower your mesh number and you'll have a good control on the flow around the object.
Recommended physical conditions are:
Three Dimensional
Implicit Unsteady(Transient)
Liquid
Coupled Flow
Constant Density
Turbulent >>> K-Omega Turbulence + SST
Gravity
Dear Reza & Alireza,
I have Found two methods for this case in CFX tutorial lecture:
Immersed Solid Method
Mesh resolved method
Immersed Solid Method is using overlapping mesh for body & fluid but the obtained results are somehow constrained.
Mesh resolved method is using no mesh for solid part and deformable mesh fluid while solid is moving and it reports good results.
By this way there is one problem in this issue: I could find the complete explanation of first method on tutorial but there is not any explanation for 2nd method which is the better method on tutorial.
Regarding above you can find the file as attach.
Regards
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