Virtual Disk Mesh Refinement Reference

When you select the Virtual Disk model together with the Adaptive Mesh model, you can add the Virtual Disk Mesh Refinement as model-specific criterion.

Virtual Disk Mesh Refinement Properties

Max Refinement Level: Specifies an upper limit of cell refinement requested by the adaption criterion. See also Max Refinement Level. The default value is 4.

Enabled: Activates the adaptive mesh criterion for all the virtual disks within the virtual disk model.
In case of multiple virtual disks, deactivating this property disables AMR for all the virtual disks. The AMR Parameters node also disappears from all the virtual disks.

AMR Parameters Properties

Depending on the VDM method you select for the virtual disk, the AMR Parameters node can have different properties:

Enabled

Enables the AMR for this specific virtual disk.

Volumetric Refinement

Specifies a uniform refinement based on the volume of the marked finite volume mesh in the background. This refinement activates different expert parameters according to the virtual disk model you select:

Virtual Disk Method	Expert Property
1D Momentum Method Body Force Propeller Method	Disk Volume Tolerance Specifies a refinement criterion based on the percentage, which is defined as: $\| \frac{{V_{T} - V}_{D}}{V_{T}} \|$ in % where $V_{D}$ is the marked discrete volume and $V_{T}$ and analytic disk volume . When the percentage volume difference is greater than the specified tolerance, Simcenter STAR-CCM+ refines the marked cells. For example, the default value of 5.0 sets a tolerence of 5%. If the volume difference is above 5%, Simcenter STAR-CCM+ proceeds with finite volume mesh refinement.
Blade Element Method User Defined Method Both methods require underlying interpolation grid.	Blade Element Cell Density Specifies a refinement criterion based on the ratio of all the marked cells to the number of interpolation grid elements (buckets). For Time Averaged BEM, the ratio is: $\frac{n_{D i s k}}{n_{T h e t a} \times n_{R}}$ where $n_{D i s k}$ is the number of cells with their centroids lying inside the disk geometry. $n_{T h e t a}$ is the Azimuthal Resolution and $n_{R}$ is the Radial Resolution of the disk. The number of elements is then equal to $n_{T h e t a} \times n_{R}$ . See also: Resolution of Interpolation Grid. For the user defined method, 3D interpolation grid is applied. The ratio is then $\frac{n_{D i s k}}{n_{T h e t a} \times n_{R} \times n_{Z}}$ . where $n_{Z}$ is the Normal Resolution. The inflow plane of the user defined method is refined based on the specified resolution. The ratio is then calculated using the cell count inside the inflow plane plus $n_{R} \times n_{T h e t a}$ . For the Time Accurate BEM, the ratio is: $\frac{n_{B l a d e s}}{n_{R} \times n u m b e r o f b l a d e s}$ where $n_{B l a d e s}$ is the number of cells with their centroids lying inside the blades. $n_{R}$ is the Radial Resolution of the blade. The default value is 20.0. It indicates if the ratio drops below 20.0, Simcenter STAR-CCM+ proceeds with finite volume mesh refinement.

Virtual Disk Method

Expert Property

1D Momentum Method

Body Force Propeller Method

Disk Volume Tolerance

Specifies a refinement criterion based on the percentage, which is defined as:

$| \frac{{V_{T} - V}_{D}}{V_{T}} |$ in %

where $V_{D}$ is the marked discrete volume and $V_{T}$ and analytic disk volume .

When the percentage volume difference is greater than the specified tolerance, Simcenter STAR-CCM+ refines the marked cells.

For example, the default value of 5.0 sets a tolerence of 5%. If the volume difference is above 5%, Simcenter STAR-CCM+ proceeds with finite volume mesh refinement.

Blade Element Method

User Defined Method

Both methods require underlying interpolation grid.

Blade Element Cell Density

Specifies a refinement criterion based on the ratio of all the marked cells to the number of interpolation grid elements (buckets).

For Time Averaged BEM, the ratio is:

$\frac{n_{D i s k}}{n_{T h e t a} \times n_{R}}$

where $n_{D i s k}$ is the number of cells with their centroids lying inside the disk geometry. $n_{T h e t a}$ is the Azimuthal Resolution and $n_{R}$ is the Radial Resolution of the disk. The number of elements is then equal to $n_{T h e t a} \times n_{R}$ . See also: Resolution of Interpolation Grid.

For the user defined method, 3D interpolation grid is applied. The ratio is then $\frac{n_{D i s k}}{n_{T h e t a} \times n_{R} \times n_{Z}}$ .

where $n_{Z}$ is the Normal Resolution.

The inflow plane of the user defined method is refined based on the specified resolution. The ratio is then calculated using the cell count inside the inflow plane plus $n_{R} \times n_{T h e t a}$ .

For the Time Accurate BEM, the ratio is:

$\frac{n_{B l a d e s}}{n_{R} \times n u m b e r o f b l a d e s}$

where $n_{B l a d e s}$ is the number of cells with their centroids lying inside the blades. $n_{R}$ is the Radial Resolution of the blade.

The default value is 20.0. It indicates if the ratio drops below 20.0, Simcenter STAR-CCM+ proceeds with finite volume mesh refinement.

Rotor Plane Refinement

Specifies a non-uniform refinement for the central plane (one or two cell layers) of the virtual disk. An example of central planes for virtual disks with various cell layers is shown below:

It activates the Number of Layers, which specifies the maximum number of layers across the disk thickness. You can use it as a cut-off value to stop the refinement process.

The resulting mesh may exceed this limit in cases where the current number of layers is one less than the specified value and after the AMR refines the mesh the resulting mesh has one more layer than the specified value. This behavior is expected.

Note	If you activate Enabled property of the AMR Parameters node, while leaving all other properties deactivated, the AMR model only refines the mesh in case there are no underlying volume cells found for this virtual disk.

Note	The AMR model executes the refinements defined within the AMR Parameters when the Max Refinement Level of the Virtual Disk Mesh Refinement criterion allows.