# Spray CFD Simulation Using Injection in DPM

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The present problem simulates the process of spraying water into a cubic space applying DPM.

This ANSYS Fluent project includes CFD simulation files and a training movie.

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## Description

## Project Description

The present problem simulates the process of water spray into a cubic space. The aim of the present study is to investigate the behavior of water flow during the spraying process from a very small circular section to the inner space of an area with a larger volume, which examines the behavior of water flow by tracing every particle. Therefore, to simulate this model, the Lagrangian perspective should be used, which is possible in the form of a Discrete Phase Model (DPM).

In fact, the difference between Lagrangian and Eulerian view is that fluid behavior in Lagrangian is examined in terms of particle tracing in fluid flow, while fluid behavior in Eulerian is based on the assumption of a finite volume element in the fluid flow path. In addition, the drawing space in the form of a cube in the present model is a general space, which the walls of the cube have the boundary condition of atmospheric pressure. The present simulation is unsteady and the time step size is 0.00000999.

## Geometry & Mesh

We draw the present 3-ِ model using the ِِDesign Modeler software. The geometric structure of the model consists of a rectangular cube area with a square cross-section of 50 mm in length and 100 mm in height, with a circular cross-section of 5.6 mm in diameter as the input of the fluid flow on the upper wall of the domain. The figure below shows a view of geometry.

We carry out the meshing of the present model using ANSYS Meshing software. The mesh type is unstructured and the element number is 25464. The size of the grids in the input section of the fluid flow is smaller and has higher accuracy. The following figure shows the mesh.

## Injection CFD Simulation

To simulate the present model, several assumptions are considered, which are:

- The Pressure-Based solver has been performed.
- We ignore the heat transfer simulation.
- The present model is unsteady because the nature of the spraying process depends on the time.
- We do not consider the effect of gravity on the fluid.

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

Models (spray) | |||

k-epsilon | Viscous model | ||

RNG | k-epsilon model | ||

standard wall function | near-wall treatment | ||

on | Discrete phase | ||

Interaction with continuous phase, update DPM sources every flow iterations | interaction | ||

water | material in injection | ||

inert | particle type in injection | ||

surface | injection type | ||

Boundary conditions (spray) | |||

mass flow inlet | Inlet | ||

1 kg.s^{-1} | mass flow rate | ||

0 pascal | supersonic/initial gauge pressure | ||

escape | discrete phase BC type | ||

pressure outlet | side walls and bottom wall | ||

0 pascal | gauge pressure | ||

reflect | discrete phase BC type | ||

wall | top wall | ||

reflect | discrete phase BC type | ||

Solution Methods (spray) | |||

SIMPLE | | Pressure-velocity coupling | |

PRESTO | pressure | Spatial discretization | |

second order upwind | momentum | ||

first order upwind | turbulent kinetic energy | ||

first order upwind | turbulent dissipation rate | ||

Initialization (spray) | |||

Standard | Initialization method | ||

0 pascal | gauge pressure | ||

0 m.s^{-1} | velocity (x,y,z) |

### DPM (Injection)

A Discrete Phase Model (DPM) is used when the aim is to investigate the behavior of the particles from a Lagrangian and discrete perspective. In the present model, water is sprayed from the inlet section in a rectangular cube space filled with air. By selecting interaction with continuous phase, the behavior of water-dispersion particles is affected by the continuous flow of primary air in the rectangular cubic space. The injection process is also defined for the discrete phase. The material of the injected particles in the present model is water and it enters the space from the inlet boundary of the model (inlet).

The type of injection process is in the form of a surface and the type of water particles is inert. The inert mode is an element of the discrete phase (particle, droplet, or bubble) that follows the balance of forces. The point properties for each particle of water in the present model include velocity magnitude, a total flow rate of 0.01139 kg / s, and total particle size based on the maximum, minimum and average diameters (min, max, mean diameter) are 0.000006, 0.00035 and 0.00025 meters, respectively.

Also, to define the boundary conditions related to the discrete phase model, three types of discrete particle behavior are applied to the boundary regions, so that the escape mode is for when the discrete phase passes only the desired boundary. The trap mode is used when the discrete phase is trapped near the desired boundary and the reflection state for when the discrete phase is reflected after reaching and colliding with the desired boundary from the boundary. In the present model, escape mode is used in the inlet section and reflect is used in the existing walls.

### Spray Results

After the solution process is completed, the two-dimensional and three-dimensional contours related to the velocity and mass concentration of the water particles in the last second of the simulation process are obtained. We obtain the two-dimensional Y-Z contour at a location passing through the center of a rectangular cube. Also, particle track related to spraying particles in three-dimensional space is obtained based on the speed of spraying particles and the diameter of spraying particles.

All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.

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