MRF,Sliding Mesh and Dynamic Mesh|| Differences With Simulations for better understanding

Summary

This video explains the differences between various simulation techniques used in Computational Fluid Dynamics (CFD), such as Amana, Sliding Mesh, and Dynamic Mesh. It covers their application in rotational body simulations, particularly in tools like ANSYS Fluent. The video dives into concepts like moving reference frames (MRF), angular velocity, and mesh deformation, discussing their roles in accurately modeling rotating systems. Additionally, it addresses the importance of boundary conditions, mesh quality, and remeshing in dynamic simulations. The goal is to help users understand the nuances of each technique for more effective CFD analysis.

Takeaways

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• 😀 The Amara sliding machine, dynamic mesh, and MRF (Moving Reference Frame) are methods used for simulating rotational bodies in CFD tools like ANSYS Fluent.
• 😀 MRF involves creating a domain that encloses the rotating part and applying motion using the free motion option with speed in radians per second or RPM.
• 😀 The velocity in MRF is determined by the relationship between the radius of the rotating domain and the angular velocity (Omega).
• 😀 In MRF, the velocity at each point is calculated by the formula V = R * Omega, considering the direction of rotation.
• 😀 The governing equations (Navier-Stokes, energy, and continuity equations) are modified to account for the extra velocity imparted by the moving reference frame.
• 😀 The moving wall boundary condition in MRF ensures the wall rotates at the same angular velocity as the moving reference frame, even though it is considered stationary.
• 😀 The sliding mesh method differs from MRF as it accounts for continuous angular velocity variation, making it more accurate but computationally expensive.
• 😀 Dynamic mesh methods like smoothing, dynamic layering, and local refinement are used to adjust mesh quality in response to deformation, ensuring accurate simulations.
• 😀 Dynamic layering techniques adjust mesh thickness in response to geometry changes, triggering remeshing when certain thresholds (e.g., height ratio) are met to avoid mesh distortion.

Q & A

What is the main difference between the MRF (Moving Reference Frame) and Sliding Mesh methods in CFD?

The MRF method assumes that the rotating object or domain remains stationary and the angular velocity is applied across the domain. In contrast, the Sliding Mesh method allows the mesh to physically move and slide over stationary zones, making it more accurate but computationally expensive compared to MRF.

How is angular velocity used in the MRF method?

In MRF, the angular velocity is calculated by multiplying the radius (distance from the center of the domain to a point) by the angular velocity (Omega), resulting in the velocity at a point in the rotating domain.

What role does the moving reference frame play in the MRF method?

The moving reference frame in MRF represents a zone that is rotating with a defined angular velocity, and it assumes that everything within the zone rotates with this velocity. This is treated as a moving frame of reference for calculating the fluid's motion relative to the rotating body.

What are the advantages of using the Sliding Mesh method?

The Sliding Mesh method provides more accurate results because it allows the mesh to deform and move dynamically, modeling the actual physical movement of the object. It is particularly useful when the object rotates and interacts with other elements, but it is computationally more expensive than MRF.

Why is dynamic mesh useful in CFD simulations?

Dynamic mesh allows the mesh to deform in response to changes in the geometry, making it ideal for simulations where the domain changes over time, such as rotating blades or moving bodies. This method helps maintain mesh quality and ensures accurate results for transient simulations.

What are the different types of methods used in dynamic mesh?

In dynamic mesh, there are three main methods: smoothing, dynamic layering, and localization. These methods help manage mesh deformation and prevent issues like skewness or poor element quality during simulations.

How does the dynamic layering method work in CFD simulations?

Dynamic layering in CFD is used for hexagonal or prismatic mesh types. It adjusts the mesh layers based on the movement of boundaries and ensures that the mesh remains consistent and well-shaped, particularly when the domain changes in height or shape.

What is the significance of mesh quality in CFD simulations?

Mesh quality is crucial in CFD because poor mesh quality, such as skewed or distorted cells, can lead to inaccurate results. Ensuring a high-quality mesh helps maintain the stability of the simulation and produces more reliable outcomes.

How does the zero-speed wall condition work in MRF?

In MRF, when applying a wall condition, the velocity of the wall is set to zero relative to the rotating reference frame. This means the wall is treated as stationary in the rotating domain, even though it is effectively moving with the rotating frame.

What challenges are associated with the Sliding Mesh method?

The Sliding Mesh method is more computationally intensive than MRF because it requires continuous re-meshing and handling of transient conditions. It involves more time to simulate as the mesh is physically moving and needs to adapt to new configurations.