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# Advanced Tutorial: Pedestrian Wind Comfort Simulation

This article will provide you with a step-by-step tutorial of how to create a pedestrian wind comfort simulation and post-process the results within SimScale.

Note

This tutorial uses the Lattice Boltzmann method (LBM) by Pacefish®$$^1$$ to solve the simulation, which is only accessible through professional licenses.
If you want to perform external aerodynamics with a community license, you can check out the fluid dynamics section of the main tutorial page.

## Overview:

This tutorial will teach you how to:

• Set up and run a pedestrian wind comfort simulation.
• Define trees as porous media in your model.
• Export results.

We are following the common workflow in SimScale:

1. Preparing the CAD model for the simulation.
2. Setting up the simulation.
3. Running the simulation and analyzing the results.

## 1. CAD Mode and Analysis Selection

You can import the tutorial project into your SimScale Workbench by clicking the button below.

By importing the tutorial project, a new project will be created for you and the Workbench will open with the prepared tutorial geometry already loaded into the viewer.

If you want to scale your geometry, you can use the built-in Scaling operation in SimScale’s CAD mode interface. In order to enter the environment, click on this icon:

At the top of the interface, all the features are placed. Click on the ‘Scale’ operation to shrink the model:

Set the scaling factor to ‘0.5’. This means all dimensions will be reduced to half. Click apply to get started with the procedure:

After the scaling operation has finished, you can go back to the Workbench by selecting the ‘Finish’ option at the top right of the page:

A second geometry will appear under the Geometries tree, which is a copy created from the original version, after the CAD mode operations. You can go ahead and delete the initial version, as it is no longer necessary:

You can also rename the model you are going to work with:

• To create a new simulation, click on the ‘+’ button next to Simulations in the simulations tree or the ‘Create Simulation’ button on the geometry panel.
• Now, the SimScale analysis library will pop up:
• Select the ‘Pedestrian Wind Comfort’ analysis type and click ‘Create Simulation’.
• Now, a new simulation tree will pop up. The simulation tree shows all the components you will need to define to run a simulation.
• All the setup steps that are completed are highlighted with a green check. Steps that require some user input are shown with a red circle and steps that have a blue circle indicate optional settings.

## 2. Set up the Simulation

### 2.1 Geometry

The geometry is automatically assigned to this simulation.

### 2.2 Define Region

Firstly, you will need to define the region of the simulation and you can do this by clicking the ‘Region of Interest’ menu in the simulation tree.

Here is a brief explanation of the settings that are available:

• Disc Radius: The radius of the area that we want to cover.
• Center point: The center point of the area that we want to simulate.
• Ground height: The ground height for the wind tunnel for the simulation.
• North angle: The north angle that will be used in the simulation.

For this simulation, you can follow the defined parameters below.

### 2.3 Define Wind Rose

The wind conditions that will be used in the simulation can be set automatically by entering a location for the simulation. For example, we will be using the city of Rotterdam, Netherlands for this simulation:

After entering a location, it will show the chosen location and the details of the data that is used. The wind engineering standard that is used and the coordinates of the location are shown. We will be using the AS/NZS/ 1170.2 standard for this simulation.

After entering the location of your simulation you have two options for importing a wind rose:

1. You can get the data of the wind rose from Meteoblue by hitting ‘Import wind data’.
2. If you want to use your own wind data you can upload it using the ‘Browse files’ option.

Note that you have to enter the location for both cases to access the upload options.

After importing the data, we can see the wind rose:

• At this time, we can change the Number of wind directions that will be used in the simulation. For this simulation, we will use 8 wind directions.
• Wind exposures of the different directions can also be modified depending on the terrain and we will be using the City Center (4) as the terrain for all directions.

Number of Wind Directions!

If you are not sure about the wind directions required for the analysis, our knowledge base article can answer your question, “How many wind directions should I run for a pedestrian wind comfort analysis?”

### 2.4 Define Pedestrian Region

We will need to define a pedestrian region to define where the comfort criteria will be calculated. You can set your pedestrian zones when you click the ‘Pedestrian comfort map’ in the simulation tree. This leads to the following settings:

We will change the definition of the ground to Ground absolute instead of Ground relative.

• Height above ground: The height where the simulation will run.
• Ground: Defines the definition of the ground of the geometry. There are two options:
• Ground relative: This option uses assigned faces as reference.
• Absolute: This option uses the bottom of the region of interest as reference.

### 2.5 Simulation Control

In Simulation control, the default values will be enough for the simulation.

### 2.6 Advanced Modelling – Trees

We can define porous objects and surface roughness of selected volumes in the domain under advanced concepts. We will specifically discuss how to set up trees for this simulation.

A common use of applying porous media in a pedestrian wind comfort simulation is when there are trees in the geometry that act as a natural barrier against the wind and to study effective barriers for wind disturbance in a city. SimScale has built a feature to model porous media and you can do this with the following steps:

• First, click the “+” sign beside Porous objects.
• Select Tree as your porous media and a dialog box will pop up asking us how the trees will be defined.
• The type of tree will be a Plane tree. SimScale has built a list of general existing trees and the physical characteristics will change accordingly.
• The model of trees can be selected in the model by assigning the rows of trees located northwest and southwest of the dark blue colored building.

You can find more information regarding advanced modelling and porous media for a pedestrian wind comfort simulation below:

We can also define additional results that we want to have by the end of the simulation. The additional results that are available are:

• Forces and Moments: calculates the forces and moments on a selected face, or group of faces.
• Probe points: place probe points on the domain to monitor velocity and pressure.
• Transient output: transient results of the simulation.
• Statistical averaging: time-averaged result for each wind direction simulated and over a selected fraction of the time selected.

Note

Keep in mind that the Transient output and Statistical averaging outputs are automatically applied to your region of interest. However, we will add a different region to each output to show how you can assign these to other regions.

a. Forces and Moments

For this tutorial, we will add Forces and Moments into our simulation, specifically for the face of the highest building that is facing the southwest direction. Forces and Moments can be added by following these steps:

• First, we will need to click the “+” sign beside Forces and Moments under Additional result export.
• Define the face where the forces and moments will be calculated. We will be selecting the face of the highest building that is facing the southwest direction.

b. Transient Output

It is important to remember for Transient output that the larger the region the longer it takes for the simulation to run. Therefore, we will apply a smaller size box. You can follow the steps below to determine the location of your transient output.

• First, click ‘Transient output’.
• Click the ‘+’ sign beside Geometry Primitives.
• Select ‘Local cartesian box’.
• Create your geometry primitives based on the dimensions below:
• Click the button to save.

c. Statistical Averaging

For statistical averaging, we will use the same settings as the ones we used for Transient Output. However, all you need to do now is to slide the toggle for the cartesian box created before.

### 2.8 Mesh

Under mesh settings, the fineness of the mesh can be selected. The selection is ranged from very coarse to very fine, but a coarse mesh will be sufficient for this simulation.

Meanwhile, if there are regions that are much smaller in size or of high importance, you can refine your mesh in those regions. You can find more regarding mesh refinement below:

## 3. Start Simulation

Now the simulation setup is complete, and you’re ready to start your simulation. In order to begin the simulation, a simulation Run needs to be created. A simulation Run creates a snapshot of the current setup and tries to compute the results based on the snapshot settings.

• To create a new Run, click ‘+’ next to Simulation Runs.
• Name your simulation and click on ‘Start’.

## 4. Results

After the simulation has finished, you will be informed via email once your simulation run has completed, and the results are ready to be analyzed. For this simulation you will have two results, which are:

• The statistical surface solution contains all the comfort and safety plots. These are taken from the frequencies provided by the weather data in the wind rose, as well as the average velocity results in each of the directions.
• Results from individual wind directions: the results from each wind direction will depend on what additional results you have defined before. For this simulation, you will have two results which are:
• Average result: averaged results from each wind direction over the final 20% of timesteps.
• Transient result: compilation of individual results of the last 20% of timestamps, and can be animated.

You can access the results of the simulation in two ways:

• When the simulation is finished, a dialog box will show that your simulation has finished. You can click on the Post-process results button to post-process your results, and it will take you to the averaged statistical results of the simulation.
• Click your simulation run in the simulation tree, and the results will be shown below the run.

### 4.1 Statistical Surface Solution

For the Statistical Surface Solution, you can change the pedestrian wind comfort criteria according to your needs. For example, the figure below is a visualization of the NEN8100 criteria.

Did you know that the following comfort criteria are available?

• Lawson
• Davenport
• London LDDC
• Lawson 2001
• Lawson LDDC Comfort
• NEN8100 Comfort
• NEN8100 Danger

### 4.2 Forces and Moments

If you click on each wind direction, you will be given a temporal graph of the calculated Forces and Moments for the face that we have defined. You can choose which data you want to display by clicking the legends, and this will then toggle the visibility of the data.

You can download the data either as an image or as a CSV file by clicking the three lines button in the top right. Below is an image of the calculated forces.

### 4.3 Average Result

As explained previously, you can also access averaged results from each individual wind direction. By selecting one of the wind directions, the results from each wind direction will appear underneath it. After selecting Average results, you will be directed to the post-processor.

In the post-processor, you can select which results you want to visualize. For example, one of the results of interest is the wind speed coming from the predominant wind direction. The predominant wind direction of this simulation is the southwesterly wind. Below is an example of a visualization of averaged velocity coming from the southwest direction.

### 4.4 Transient Results

You can access the transient results under Transient results, located below the Average result. In order to visualize what this could look like, below is an animation of the southwesterly wind velocity.

### 4.5 3D Data Export

You are also able to export 3D data from the region that you have defined before and apply additional post-processing features, such as: cutting planes and streamlines for this data. Below are some examples of the additional features that are accessible. You can access this data under ‘Additional Results’ of each individual wind direction that you have defined.

### 4.6 Cutting Planes

You can enable cutting planes by selecting Cutting Planes in the post-processor menu and configure the position of your cutting plane by sliding the toggle or selecting a point and control the orientation of the cutting plane according to the axises.

You can change which values to visualize by clicking the Scalar and Vector dropbox. You can control the opacity of the cutting plane and choose whether to cut the model intersecting the model or not. For instance, below is an example of a cutting plane showing wind pressure at the tallest building.

### 4.7 Particle Traces

You can enable Particle traces to visualize streamlines. In order to do this, you will need to select Particle traces in the post-processor, select your point of origin by going to Seeds and clicking Pick to pick the point of origin. In this tutorial, we will visualize the velocity streamlines going over the highest building in our model.

The origin of your streamline should be the face that is directly facing the building. You can see the orientation view below. You can also adjust the number of streamlines that you want to generate. In our example, we will adjust the number of streamlines to 6 in both the horizontal and vertical directions.

To control which values you want to visualize, use the Compute vector and Map Scalar dropbox and the shape of your streamline. Additionally, you can change the size of your streamlines by sliding the Radius toggle or by defining the desired radius.

Moreover, you can configure the width and height of your streamline points by going to Seeds and providing the desired number points horizontally and vertically. It is important to remember that Num u means the number of points horizontally, and Num v means the number of points vertically. In addition, you can adjust the spacing between your streamline points by adjusting the Spacing toggle or define a number.

Congratulations! You finished the pedestrian wind comfort simulation tutorial!

Note

If you have questions or suggestions, please reach out either via the forum or contact us directly.

References

Last updated: November 22nd, 2021

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