Spray Combustion - CFD Simulation SimFlow Tutorial

In this tutorial, we demonstrate SimFlow’s capability in terms of modeling the combustion process. We will model particles of Heptane injected into the cylinder where the combustion process occurs. To consider heat transfer between the spray droplets and the surrounding gas, we utilize the Ranz-Marshall heat transfer model. Additionally, we incorporate the Evaporation&Boiling model to account for mass transfer from the droplets to the gas resulting from evaporation and boiling. Please note that this simulation demands increased CPU performance.

SimFlow is a general purpose CFD Software

To follow this tutorial, you will need SimFlow free version, you may download it via the following link:
Download SimFlow

Open SimFlow and create a new case named spray_combustion

Firstly we need to Download GeometryCylinder

The STL format does not contain the unit information which are defined during the geometry export. If we do not know the exported unit, we can estimate it based on the total size of the model. It is displayed next to Geometry size label. In our case, the default unit meter is correct.

After importing geometry, it will appear in the 3D window.

In order to create the mesh, we need to enable meshing for the newly imported geometry.

Now we will define the base mesh. The box geometry determines the background mesh domain. The model is symmetrical on the XZ and YZ planes so we do not need to mesh the whole geometry. Using the box dimensions we will choose only a quarter of a model.

We need to assign individual names to each side of the base mesh. This will allow us to apply different conditions to each side.

Material Point tells the meshing algorithm on which side of the geometry the mesh is to be retained. Since we are considering flow inside the cylinder we need to place the material point inside the geometry.

You can specify the point location from the 3D view. Hold the CTRL key and drag the arrows to the destination.

After the meshing process is complete, the mesh should appear in the graphics window. To zoom in or zoom out use the scroll wheel , or move the mouse up or down with pressed RMB (right mouse button).

We want to analyze the transient simulation of spray combustion. For this purpose, we will use the sprayFoam (sprayFoam) solver.

We will load the chemical kinetic mechanism as well as the thermodynamic properties database. We will consider only the one chemical reaction describing the process which is a simplification in order to decrease the computational cost and calculation time.

To complete this step we need to Download Fileschem.inptherm.dat
After that, import them to the SimFlow.

We will select the partially stirred reactor model which is used to simulate combustion.

We will select the pure heptane as a phase injected into the chamber.

We are going to create a cone injector and define its parameters.

We need to define the position of the injector and spray outflow direction.

We will select the Rosin-Rammler distribution model and define the necessary parameters. Models need to define the minimum and maximum spray droplet diameter and size which is the largest probability.

We need to define which models will be used in this simulation. We select the Sphere Drag model to account for the drag force acting on the droplets. We choose the Ranz-Marshall heat transfer model to take into account heat transfer between the spray droplets and surrounding gas. For accounting mass transfer from the droplets to the gas as a result of the evaporation and boiling we use the Evaporation & Boiling model.

For the purpose of this tutorial, we will simulate the turbulence phenomenon using the Realizable \(k {-} \varepsilon\) model.

To increase the stability of the simulation we will increase the number of iterations per time step.

Initially, the entire domain is filled with air. We will set the initial pressure and temperature in the chamber.

In order to measure maximum and minimum temperature, we will use the volume monitor.

Before running computations, adjust the time controls in order to capture the physical and chemical phenomena that occur during the process.

We can control how often results should be saved on the hard drive. We will write the results at the interval of \(5e-05\) second. Note, that only saved data will be available during postprocessing.

This simulation will require high CPU usage and might take several hours to finish the calculation depending on the machine used. To speed up the calculation process increase the number of CPUs basing on your PC capability. We recommend using at least 4 cores for this tutorial. The free version allows you to use only 2 processors in parallel mode. To get the full version, you can use the contact form to Request 30-day Trial

Estimated computation time for 2 processors: 2 hours

Keep track of the domain’s maximum and minimum temperature. A sudden increase in temperature is a result of the combustion process.

After the computation is finished we can do a comprehensive visualization of our results with ParaView.

Load the results into the program.

ParaView skips the initial time step by default, therefore we need to add the zero time to simulation.

We will slice the domain in the direction of spray combustion.

Now we will check the temperature distribution during the process.

Finally, we will look at the spray particle movement.

This concludes the tutorial, covering all the aspects we intended to showcase. For a finely tuned presentation of the results, you may take advantage of the more advanced features.

In ParaView, you can display streamlines, contour plots, vector fields, line or time plots, calculating volume or surface integrals and create animations.

To familiarize yourself with the ParaView capabilities, it’s worth checking out our video tutorial, Paraview CFD Tutorial - Advanced Postprocessing in ParaView, in which we demonstrate some of the most commonly used post-processing techniques.

Paraview CFD Tutorial - Advanced Postprocessing in ParaView