DPM-Drag Macro, UDF, Drag between Particles and Fluid CFD Simulation

Description

In this project, we performed a numerical simulation using ANSYS Fluent software’s User-Defined Function (UDF). For this CFD product, we used DPM-Drag-Macro to write UDF programming. We considered a simple chamber that is a place for spraying discrete particles. So, we defined an inlet for spraying discrete particles. When discrete particles are sprayed in a continuous fluid, a drag force is created between the discrete particles and the continuous fluid.‌Hence, we need to define a relation to define the drag force between discrete particles and continuous fluid.

First, we modeled the geometry in 3D with Design Modeler software. Then, we meshed the model with ANSYS Meshing software. Meshing is unstructured, and 127,100 cells are created. Finally, we numerically simulated the current model based on the CFD method by ANSYS Fluent software.

Methodology (UDF)

In this project, we defined a Discrete Phase Model (DPM) so that discrete particle spraying occurs. To define the discrete phase, we need to define an Injection to model the spray process. When the injection is defined, the drag force is applied between the particles and the fluid. So, we need to define a particular relation for drag force. A Drag Law is then used to calculate the drag force. Different drag laws include Spherical, Stokes-Cunningham, Non-Spherical, and High-Mach-Number.

In addition, we can define a method to calculate the drag force by defining the User-Defined function (UDF). We need to use the DPM-DRAG Macro (DEFINE_DPM_DRAG macro) for this UDF. The drag force relations we use are defined as follows. According to these relations, the drag force depends on the Reynolds number.

Conclusion (UDF)

After completing the calculation, we will review the results. First, we performed simulations with different drag laws to compare the results with each other. We performed the same simulation for spherical, non-spherical, and stokes-cunningham models. Then, we performed the same simulation using the UDF.

Finally, we compared the results of different methods in a plot. We evaluated the Penetration Length parameter to determine the effectiveness of each drag force calculation model.

Penetration length shows how far the discrete particles spread in the fluid. So, the drag force can be effective in decreasing or increasing the penetration of particles.

In the next step, we only consider the simulation using UDF. We obtained Particle Tracking since we used the discrete phase model in this simulation. Particle tracking is used to check the trajectory of particles.

We performed the modeling in an unsteady (Transient) state for 4 seconds. So, we obtained the particle tracking at different times to obtain the movement path of the particles in the fluid.