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

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- The problem numerically simulates the particle spraying in continuous fluid
**ANSYS Fluent**software. - We design the 3-D model with the
**Design Modeler**Â software. - We mesh the model with
**ANSYS Meshing**software, and the element number equals**127,100**. - We performed the simulation in
**Transient**(unsteady-state). - We use the
**Discrete Phase Model (DPM)**to define particle spraying. - We use the
**User-Defined Function (UDF)**to define a drag between particles and fluid. - We use the
**DPM-DRAG Macro**for UDF. - We compare different
**Drga Laws**, including Spherical, Stokes Cunningham, Non-spherical, and High-Mach.

## Description

**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.â€ŒHence, 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.

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