Week 8- Moving zones approach in Fluent

AIM:

1. What are the approaches by which you would model moving zones?
2. Which approach would you use to model unsteady phenomena?
3. Simulate rotary motion for the geometry given
   • Plot the velocity profile of the fluid motion

THEORY:

1. In fluid flow, there are two forms of motion: rectilinear and rotating motion.

Modeling rotational motion may be done in two ways:

• Moving reference frame
• Moving mesh approach.

Moving reference frame:

A Moving Reference Frame (MRF) is a steady-state Computational Fluid Dynamics modeling approach for simulating rotating equipment that is very simple, robust, and efficient. MRFs may be used to model the rotors of a quadcopter, for example.

The main purpose of using a moving reference frame is to make a problem that is unstable in the stationary (inertial) frame stable in the moving frame. It is feasible to transfer the equations of fluid motion to the rotating frame in order to get steady-state solutions for a steadily rotating frame (i.e., the rotational speed is constant). Fluent allows the activation of a moving reference frame with a constant rotational speed by default. The modified equations will have extra terms that are not included in the fluent formulation if the rotational speed is not constant. Moving reference frames with constant rotational speed can be used to study unstable simulations. For several zones, there are two techniques. It's a steady-state approximation in which variable rotational and translational speeds can be attributed to distinct cell zones. The moving reference frame equations are used to solve the flow in each moving cell zone. The equations simplify to their stationary versions when the zone is stationary (w = 0). A local reference frame transformation is conducted at the interfaces between cell zones to allow flow variables from one zone to be utilized to compute fluxes at the border of the neighboring zone. In Section 2, we'll go through the MRF interface formulation in greater depth.

It's worth noting that the MRF method ignores the relative motion of a moving zone in relation to surrounding zones (which might be moving or stationary); the mesh stays constant during the computation. This is similar to stopping the motion of a moving element in a given position and measuring the instantaneous flow field while the rotor is in that position. As a result, the MRF is also known as the "frozen rotor strategy." While the MRF method is clearly an approximation, it can produce a suitable flow model in many situations. The MRF model, for example, can be employed in turbomachinery applications when the rotor-stator interaction is mild and the flow at the interface between the moving and stationary zones is reasonably simple. Large-scale transient effects are not present in mixing tanks, for example, since the impeller-baffle interactions are rather mild. Therefore, the MRF model may be utilized. The MRF model may also be used to calculate a flow field that can be utilized as an initial condition for a transient sliding mesh computation. The multiple reference frame model should not be utilized since it avoids the requirement for a starting computation; nevertheless, if it is important to mimic the transients that may occur in powerful rotor-stator interactions, the sliding mesh model alone should be employed.

There are two types of moving reference frame approaches:

• Single moving reference frame.
• Multiple moving reference frame that uses a mixing plane approach.

Contact region or the interface :

• This is the region existing in contact with the stationary plane or the moving plane.
• Section or region of intersection of the two frames.

Circular type of interface :

• The Navier stokes equation is the stationary frame and the moving frame is solved separately.
• Data is transferred from one frame to another through the interface

There are three methods of data transfer namely:

• Area Averaging Method
• Mixed approach

In this approach, the partial differential equations are solved. the momentum equation, energy equation, and continuity equation are solved simultaneously.

2. Moving mesh approach :

This approach gives the best result.

• Unsteady flows are modeled using the moving mesh method. Generally, vortex-induced flows are employed, and moving mesh approaches are used for flows including vortex contact with bodies. Physical PDEs and a mesh equation generated from the equidistribution of an error metric (referred to as the monitor function) are solved concurrently in moving mesh techniques, and meshes are dynamically concentrated on steep sections.

3. SETUP:

 Import the mesh file of the model into the setup 

Viscous Model : 

Material : 

 Cell Zone Conditions :

 Boundary Condition : 

            For aerofoil, Select a wall motion as Moving Wall and we check the motion is selected as Relative to Adjacent cell zone and Rotational. 

Solution :

 The solution scheme is set to Coupled and the spatial discretization is set to second-order upwind.

Initialization:

Run the simulation for 1000 iterations:

The solution is converged at 114 iterations.

RESULTS:

Residual Plot:

Velocity Contour:

Velocity Vector Plot:

• From the pressure contour, we observed that the pressure is negative at the inner side of the rotating domain where the suction of air takes place near the centre of impeller. and the pressure is maximum at the outer side of the rotating domain. and at the leading edge of the airfoil.
• The velocity is maximum (26.2m/sec) at the rotating domain outer and minimum (10m/sec) at the rotating domain inner .
• The velocity separation is observed at the Top edge of the airfoil,and velocity at Trailing edge of the aerfoil is also minimum

CONCLUSION:

• The approaches by which we would model moving zones is defined
• The approach we use to model unsteady phenomena is defined
• Simulation of rotary motion for the given geometry and also plotted the velocity profile of the fluid motion