Multiphase flows occurring in various scientific and engineering fields and application areas like biotechnology, bio-defense, micro-fluidics, chemical processing and environmental research etc., can be modeled using the Macroparticle module in CFD-ACE+. Macroparticles are considered to be large particles that block a significant portion of the flow path and thus affect the surrounding flow field.  In such cases, the Spray module method is not suitable and the Macroparticle technique should be used.

Below is a list of features for the Macroparticle module:

• Allows usage of multiple particles
• Accounts for particle-particle interactions
• Coupled with the Flow, Turbulence, User Scalar, and Biochemistry options
• Particle motion includes translation and rotation in X, Y and Z directions
• Accounts for pressure forces and viscous forces on the particles
• User subroutine access for defining particle shape, external forces, etc.

For more information on Macroparticles, please refer to the Macroparticle chapter in the Modules section of CFD-ACE+ WebHelp.

In the example for this user tip, a user subroutine is used to add a body force to the particle immersed in an infinite medium filled with a quiescent fluid.

Example Case

In this example, a periodic body force is added to the macroparticle using the UPBLOCK_BFORCE user subroutine available in CFD-ACE+.  

A 50m x 50m x 50m cube with no-slip wall boundary condition was taken. In order to achieve neutral buoyant condition the gravity force was set to zero. The spherical macroparticle was taken to be small compared to the size of the cube and placed at the centre. The initial velocity for the particle was set to zero, but it was subjected to an external periodic force (along X-direction) through a user subroutine called “Upblock_bforce” subroutine, thus taking the external periodic force on the macro particle as a body force.

Figure 1.  Initial position of the particle in the domain 

The body force applied to the particle is a function of time.  The current time in the simulation is obtained using the get_time() subroutine which returns the current time and time step number for the simulation.  Using the set_macp_valuer() routine, the body force in the X direction ( variable name in CFD-ACE-SOLVER is "GBFX") is set on the particle.

If you would like the source code for the user subroutine and the DTF file used in this case, please click here.

Regards,
Shivakumar, GT
ESI CFD Support Team