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Documentation

Pedestrian Wind Comfort Analysis

Overview

The Pedestrian Wind Comfort (PWC) analysis type is used to assess the effects of building external aerodynamics on pedestrians, this typically returns a comfort map in a built up environment of what activities can be done and where. This is usually done to demonstrate that a new development does not interfere with pedestrian comfort, or if it can be used to experiment with mitigation features (trees, screens, and canopies for example) to ensure that pedestrians remain comfortable. 

Mean wind velocities at pedestrian level in a typical urban environment

The PWC analysis type is extremely streamlined to allow the user to set up and run a simulation from geometry upload in minutes with 3 simple steps. The setup is automated using best practices and validation exercises to ensure that fast results are complemented with accuracy. Although this highly automated workflow is in place, much of the parameters can be manually adjusted if required.

A pedestrian wind comfort analysis setup in three simple steps

The underlying technology used to solve the fluid flow around the buildings is the Lattice Boltzmann Method (LBM). There are several key things that make this stand out in comparison to its competition. LBM is able to solve almost regardless of the geometry quality given to it, and therefore, geometry preparation and cleaning are almost removed providing some guidelines are followed, in some real cases, this has reduced weeks of CAD preparation work to a matter of hours. This method also uses a different technology to solve on, where the standard openFOAM solvers use CPU’s to solve, LBM uses GPU’s (Graphics processors) this enables many more parallel processes to occur and therefore solve times are rarely longer than a few hours for a complex case. This puts the PWC solver in a good place where users can expect an entire turnaround in a day once they are familiar with the processes.

Multiple common wind comfort criteria are automatically evaluated and can be interrogated fully in 3D within the integrated post-processing environment

Geometry for Pedestrian Wind Comfort

Our PWC analysis type takes all the standard geometry formats that we advertise in the geometry upload section of the documentation. Typically, however, geometry comes from one of the common tools used by architect firms and wind engineers, which are mainly Revit and Rhino (others exist and if they can export STL then they are also fine). Therefore the main format types relevant here are Rhino (.3dm) and STL (.stl). 

More details regarding geometry requirements and how to prepare the CAD for best results with Pedestrian Wind Comfort can be found here.

Region of Interest

The region of interest is a very important stage of simulation setup as it is used to automate the simulation setup making the setup very simple. The core functionality of the region of interest is to define the area around the main building on which the pedestrian comfort should be evaluated. additionally, it is used as a reference to automatically size and orient the virtual wind tunnel.

The parameters that are able to be changed are the Disk Radius, the Centre Point, the Ground Height and the North Angle. Additionally, under Advanced settings, there is the option to make the Wind Tunnel Size larger than default, or to make a completely custom sized Wind Tunnel by defining the extension in each direction. 

Region of interest definition on a city model with north direction indicated

More details on how to correctly define the region of interest parameters can be found here.

Wind Conditions

The wind conditions is a very important setting of the Pedestrian Wind Comfort analysis. Here not only the local wind statistics for the target area are defined, but also the wind engineering standard, according to which the analysis will be run and the results will be evaluated.

Currently four different Wind Engineering Standards are available on SimScale – Eurocode  EN 1991-1-4 the standard in Europe including the UK, AS/NZS 1170.2 the standard in Australia and New Zealand or NEN8100 the standard for the Netherlands and most recently also the London City Wind Microclimate Guidelines (coming soon), which were specifically designed for the City of London region.

Wind Conditions settings with wind engineering standard definition and wind statistics import

Depending on the wind standard chosen, different options for uploading or importing the local wind statistics are available. For both EN 1991-1-4 and AS/NZS 1170.2 the wind data can be imported with a single click directly via our Meteoblue historic wind data import, or uploaded via a stat file. For the NEN8100 standard the official data out of the NPR 6097:2006 program can be used, while for the London City Wind Microclimate Guidelines no data upload is needed as the standard already includes the wind data to be used.

Additionally, the user needs to select the terrain categories for each of the incoming wind directions, which will define the atmospheric boundary layer (ABL) profile and are also used for correcting the wind statistics data to the local terrain.

More details about the correct setup of the wind conditions can be found here.

Pedestrian Wind Comfort Map

Wind comfort study should be assessed at the mean pedestrian level, since the comfort level is correlated to pedestrian-level winds. Height above ground input should be defined by taking pedestrian height into account.  Ground reference can be set as an absolute reference height or as a relative reference height.

The reference height used will be the height at which the comfort criteria will calculated. Currently, SimScale has implemented a number of comfort criteria, for example: Lawson criterion, Davenport criterion, NEN8100 Comfort criterion and others.

More details regarding the setup of the pedestrian height can be found here.

Simulation Control

Simulation control contains all the necessary parameters to control the run-time of the simulation. The maximum run time and the number of fluid passes is defined in this part.

The maximum runtime defines the maximum runtime for the simulation in physical time and the number of fluid passes defines how long a transient simulation runs in terms of time (counted in seconds).

More details on how to define the runtime and the number of fluid passes can be found here.

Advanced Modelling

Additional physical parameters can be defined in advanced modelling. The additional parameters which can be defined are surface roughness and porous objects.

If the effect of friction on the flow wants to be observed then it is necessary to define the surface roughness. The value defined for the surface roughness is the equivalent sand-grain roughness and can be set manually by the user.

Porous media is used to model permeable obstructions such as trees, hedges, wind screens, and other wind mitigation measures. When air flows through a porous body, a pressure gradient along the direction of the flow is generated. Using porous media simplification reduces CAD and mesh complexity, and saves computational time and expenses. 

More details on defining surface roughness and porous media can be found here.

Mesh Settings

The mesh generated for a pedestrian wind comfort simulation is based on the Lattice-Boltzmann method. Here a Cartesian background mesh is generated, that is composed of cube elements that are not necessarily aligned with the geometry of the buildings or the terrain.

The necessary fineness of the mesh can be defined in the global mesh settings and refinements can be added to the mesh in the refinements settings.

More details regarding the setup of the mesh can be found here.

Starting a Run and Run Information

When all of the settings and physical conditions are applied, a simulation run can begin. The simulation runs a simulation in each direction in parallel and will be compiled into the statistical results based on the comfort criteria once it is finished.

More details regarding how to start a run and the information of the run can be seen here.

Simulation result assessment

Once all individual wind directions have been computed and also the statistical analysis on the wind comfort had been carried out, the simulation run changes to “finished” state and the user is informed via email that the results of the run are now ready for visualization.

Results structure of a finished Pedestrian Wind Comfort analysis. Highlighted access to the wind comfort criteria (green frame) and results for the individual wind directions (blue)

Clicking either the Post-process results button, or the green highlighted item Statistical surface solution will open the wind comfort results in the online post-processor.

Post-processor interface for the Pedestrian Wind Comfort results evaluation

Above highlighted are the 5 main interaction items for the post processor:

  1. This is the main result field and appearance selection panel. In the Pedestrian Wind Comfort item, the individual comfort criteria can be selected for visualization. The Parts Color item enables setting the color and opacity for the buildings.
  2. The post-processor toolbar allows the switch between multiple views and renders modes, toggling the legend visibility, picking specific locations for result inspection, and taking a screenshot of the whole viewer scene.
  3. In the result topology tree, the individual visibility of the result parts as well es the pedestrian zones can be toggled on or off.
  4. The result legend shows the relation of the wind comfort criteria to the viewer colors. For each criterion the specific threshold velocity, as well as the threshold frequency, are given.
  5. The orientation cube helps with resetting the view and selecting standardized views for result comparison.

More details regarding how to use the post-processor for wind comfort coming soon!

Last updated: September 2nd, 2020

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