I've worked on simulating 3D VIV (a cylinder forced by Karman vortex street) and been stuck with settings. Considering the transition to turbulence due to the oscillation of cylinder (Re≤200, laminar upstream), "SST k-ω coupling with intermittency transition" is my scheme now.
However, I'm not sure whether I should enable "intermittency transition" since I don't fully understand the statement given in the user's guide, which says "The Transition SST model is not Galilean invariant and should therefore not be applied to surfaces that move relative to the coordinate system for which the velocity field is computed; for such cases the Intermittency Transition model should be used instead."
I don't understand the bold sentence in the statement especially. Does it mean the moving surface of cylinder (in my case)? Hope anyone can provide any guideline. Thank you so much.
In your case, it is appropriate to use the intermittency transition model, which is an extension of the SST k-ω turbulence model. This model is more suitable for cases involving moving surfaces or unsteady flow situations, like the oscillating cylinder you're simulating.
The statement you mentioned from the user's guide addresses the issue of Galilean invariance. A model is Galilean invariant if its predictions remain consistent when the frame of reference is changed. In other words, the model should provide the same results regardless of whether you analyze the flow from a stationary or moving reference frame.
The Transition SST model is not Galilean invariant, meaning that its predictions may change when the frame of reference is altered. Therefore, it is not suitable for cases where surfaces move relative to the coordinate system in which the velocity field is computed. The Intermittency Transition model, on the other hand, has been developed to handle such cases.
In your 3D VIV simulation of a cylinder forced by a Karman vortex street, the cylinder oscillates due to the flow-induced forces. This oscillation can cause the transition to turbulence in the boundary layer. Since the cylinder surface is moving relative to the flow coordinate system, the intermittency transition model should be used instead of the Transition SST model.
So, for your simulation of an oscillating cylinder with Re ≤ 200 and laminar upstream flow, it is recommended to use the "SST k-ω coupling with intermittency transition" model.
Alessandro Rizzo Thanks for your clear and detailed response! And I’m also curious whether I should spend some time to pick up “Galilean invariant” since I didn’t find this term in Fluid Dynamics textbook. (I’m still undergraduate and a beginner in this field.)
Hope you can provide any suggestion. Thank you so much.
Milne Ciou, understanding the concept of Galilean invariance can indeed be beneficial in the field of fluid dynamics, especially if you plan to pursue a career in computational fluid dynamics (CFD) or similar areas. While the term may not appear explicitly in some introductory fluid dynamics textbooks, it is a fundamental concept in physics and is particularly relevant in CFD.
Galilean invariance, also known as Galilean relativity, states that the laws of physics should be the same in all inertial frames of reference. In the context of fluid dynamics and CFD, this means that the predictions of a model should remain consistent when the frame of reference is changed. In other words, the model should provide the same results regardless of whether you analyze the flow from a stationary or moving reference frame.
As you progress in your studies and delve deeper into fluid dynamics and CFD, you may encounter various turbulence models with different levels of Galilean invariance. Understanding this concept will help you make informed decisions when choosing the appropriate turbulence model for a particular simulation.
So, if you plan to work with CFD or fluid dynamics in the future, it would be worthwhile to spend some time learning about Galilean invariance. You can start by exploring classical mechanics or introductory physics textbooks, as well as online resources, to build a strong foundation in this concept.
Good luck with your studies, and feel free to reach out if you have any further questions! Regards,
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