MRF CFD Simulation

What are Multiple Reference Frames (MRF) and Single Reference Frames (SRF)?

SRF and MRF are used in CFD simulations of rotating devices such as turbomachines. In SRF (Single Reference Frame), it is assumed that the rotating components are fixed, and the rotational speed of the turbine is applied to the fluid flow. In other words, the flow is analyzed from the perspective of an observer within the rotating parts. In systems such as mixers, where both fixed and rotating components exist, MRF (Multiple Reference Frames) is used. In MRF, the rotating components are considered in a separate zone from the rest of the system, and the rotational speed is applied only to the fluid flow within that zone.

For example, suppose you want to simulate the fluid flow around a wind turbine. By considering one blade of the turbine and applying the periodic boundary condition, there is no need to simulate the other two blades. Using SRF, you can simulate the desired phenomenon efficiently and accurately.

MRF VS. Sliding Mesh

Both methods are used to simulate rotating components. For more information about sliding mesh, refer to “Sliding Mesh CFD Simulation”. The difference between these methods is:

• In sliding mesh, the entire domain rotates around the rotating components along with them. Due to convergence issues, the time step needs to be much smaller compared to the MRF solution. In sliding mesh, meshing is much more complicated than in MRF.
• The mesh at the interface between the rotating and fixed domains is nonconformal, meaning the boundaries of the mesh do not coincide, which makes this solution very complicated.
• To check for stability in a solution, it is not possible to set the initial conditions for a steady solution in sliding mesh; the problem must be solved transiently. In contrast, with MRF, the problem can be set up from the beginning for steady conditions.
• In situations where the fluid velocity is very high, the use of sliding mesh is recommended.
• In the transient state, if the problem involves MRF rather than SRF, the use of sliding mesh is recommended. This is because the relative stability of the rotating components compared to the entire system in the transient state can cause errors.
• Overall, sliding mesh requires significantly more computational power compared to MRF due to the complexity of the meshing and the need for smaller time steps to ensure convergence.

MRF and SRF Applications

Here are some key applications of MRF and SRF:

Turbomachinery

In all turbomachines, the rotating part, which consists of several blades, moves and causes fluid movement or is influenced by fluid movement. CFD simulation methods, SRF and MRF are designed for these rotating parts. Many simulations have been conducted to design and optimize turbomachines using SRF and MRF methods.

Aerospace

In aerospace engineering, many rotating components are used. For example, helicopter blades have very complex designs and controls that can be simulated with SRF and MRF methods. In a jet engine, there are both a compressor and a turbine and MRF simulation is a very suitable option for simulating the jet engine.

Marine Engineering

All ships and submarines use rotating propellers for movement. Due to the liquid phase of the studied fluid (water), simulations in this field often consider special cases such as cavitation. MRF and SRF are suitable methods for simulation in this context. Additionally, there are rotating components in torpedoes, making MRF or SRF suitable options for their simulation.

In the picture, a torpedo can be seen from behind. Torpedoes, like ships, move using rotating components and blades. Therefore, the simulation of torpedo movement is a suitable application for the MRF method.

Centrifuge device

In this device, different phases are separated by creating centrifugal force. CFD simulation of this device with MRF and SRF methods is a suitable option.

Mixer

Different models of mixers are used in many industries, such as the food industry. The simulation of mixers is usually multiphase, and they are a suitable option for MRF and SRF simulations.

Mixers are a good choice for MRF and SRF simulations due to their rotating components.

MRF and SRF Simulation by ANSYS Fluent

ANSYS Fluent CFD simulation software is a very suitable option for simulating rotating components, either by sliding mesh, MRF, or SRF methods. The user can perform MRF and SRF simulations with the updated and advanced algorithms of this software and adjust the details of each method.

In the simulation of rotating components, multiphase flow is often needed, or the flow is turbulent and needs to be simulated using various turbulent flow methods, or the deformation of rotating components needs to be considered (FSI simulations). ANSYS Fluent is a very powerful tool for all these challenges. This software has been used in various industries and by large companies, demonstrating its capabilities, making it the choice of many engineers for simulating rotating components.

Force distribution wastewater sewage mixer, simulated by ANSYS Fluent. Adopted from “Wastewater Sewage Mixer with MRF CFD Simulation”

CFDLAND expertise in MRF and SRF Simulations Using ANSYS Fluent Software

Our experts at CFDLAND have completed many projects in the field of CFD simulation using the MRF method in ANSYS Fluent. You can see some of these projects at the top of this page. To see all our ready-made projects, visit CFDSHOP; perhaps one of them will suit your needs.

Trust our capabilities and order your CFD simulation projects at ORDERPROJECT. You will be impressed by the quality of our work.