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# Airflow on the Dimpled Rotating Cylinder CFD Simulation, ANSYS Fluent Training

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The project aim is to investigate the pressure distribution, rotational phenomena, and flow behavior around a rotating dimpled cylindrical wall.

This product includes Geometry & Mesh file and a comprehensive Training Movie.

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## Project Description

The problem is going to simulate airflow in a rectangular channel by ANSYS Fluent software. A cylindrical object is placed in the channel. The airflow enters the rectangular channel at a horizontal velocity of 0.45 m / s, and it collides with the cylindrical body. The cylindrical body rotates at an angular velocity of 20 radians per second (rad/s) around the central axis; thus, the moving wall must be defined. Therefore, the fluid simulation area is divided into two parts, which include the rotating area (having a cylinder with a constant angular velocity) and the area of the fluid (the inner space of the rectangular channel other than the cylinder).

Hence, by creating a cylindrical wall in the form of an interface (a common surface between two areas that allows fluid to flow through its boundary), a special flow area in the form of a hollow cylinder around the wall creates a rotating cylinder; thus, the Frame Motion method is used to simulate the internal cylinder area created at the same speed as the angle of rotation of the main cylinder. The cylinder wall has dimples whose protruding position is on the inside of the cylinder and whose recess is on the outside of the cylinder. The aim is to investigate the pressure distribution and rotational phenomena around a rotating cylindrical wall. Therefore, the presence of dimples on the cylinder surface affects fluid behavior.

## Geometry & Mesh

The geometry of the present model is three-dimensional and is designed using SOLIDWORKS software. The geometry of the model consists of a rectangular channel with a cylindrical object inside the interior as a rotating object, and a cylindrical space around the rotating cylinder inside the channel is distinguished. Also, dimples or protrusions have been created on the surface of the cylinder, which has a roughness ratio of 0.5 called the ratio of the depth of the dimple cavity to the diameter of the dimple. Also, since the model is symmetrical with respect to the plane perpendicular to the central axis of the cylinder, the geometry of the model is halved to reduce computational cost. The figure below shows a view of the geometry. (Airflow on the Dimpled Rotating Cylinder) The meshing of the present model has been done using ANSYS Meshing software. The mesh type is structured and the element number is equal to 1064903. The figure below shows an overview of the meshing.

(Airflow on the Dimpled Rotating Cylinder) ## Airflow on the Dimpled Rotating Cylinder CFD Simulation

To simulate the present model, we consider several assumptions, which are:

• The solver is Pressure-Based.
• We ignore the gravity effect.

The following is a summary of the steps for defining a problem and defining its solution:

 Models (Airflow on the Dimpled Rotating Cylinder) k-omega Viscous model standard k-omega model SST k-omega options Boundary conditions (Airflow on the Dimpled Rotating Cylinder) velocity-inlet (Airflow on the Dimpled Rotating Cylinder) Inlet 0.45 m.s-1 velocity magnitude Pressure outlet Outlet 0 Pascal gauge pressure wall Wall-cylinder moving wall (0 rad.s-1) wall motion Other walls stationary wall (0 rad.s-1) wall motion Solution Methods (Airflow on the Dimpled Rotating Cylinder) SIMPLE (Airflow on the Dimpled Rotating Cylinder) Pressure-velocity coupling second-order pressure Spatial discretization second-order upwind momentum first-order upwind turbulent kinetic energy first-order upwind specific dissipation rate Initialization (Airflow on the Dimpled Rotating Cylinder) Standard Initialization method -0.45 m.s-1 x-velocity 0 pascal gauge pressure (Airflow on the Dimpled Rotating Cylinder) 0 m.s-1 y-velocity, z-velocity

### K-Omega SST Turbulence Model (Airflow on the Dimpled Rotating Cylinder)

Since the present simulation is about the free flow of fluid around a given object, we use the k-omega model. The k-omega SST (shear stress transport) model acts as a hybrid function, gradually transferring the flow from the k-omega model in areas close to the wall to the k-epsilon model in areas farther from the boundary layer. We use this model for flows with reverse pressure gradient and in simulations of separation models such as fluid flow around spherical or cylindrical objects. Since the k-omega model does not define the wall function, we should use smaller grids in areas close to the walls of the object. However, in this turbulence model, due to the transfer from one model to another, the probability of divergence or weak convergence increases.

### Frame Motion (Airflow on the Dimpled Rotating Cylinder)

The aim of the present simulation is the interaction of the horizontal fluid flow and the rotational motion of the cylindrical object, and predicting the pressure distribution around the object and the calculation of drag and lift forces on the surface of the object. In this case, the cylindrical body rotates at a rotational speed of 20 rad.s-1 around its central axis and the air rotates in the area around the cylinder. Now, using this method, we can assume the cylinder to be constant and the wind flow around the cylinder to be rotating at the same rotational speed of 20 rad.s-1 around the central axis of the cylinder. Also, since the simulation is steady, we disable the Mesh Motion option because we use this option when the problem is transient (unsteady).

You can obtain Geometry & Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.

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