Wind around Buildings - CFD Simulation SimFlow Tutorial

In this tutorial we will present the simulation of wind flow around the buildings. Aerodynamic of the building is a growing challenge in today’s construction industry. Here we will present one of the possible way of analysing the wind flow through the urbanized areas.

An important aspect of this problem is the proper modeling of the boundary conditions. We will use specially dedicated boundary condition for the inlet - Atmospheric Inlet. It defines the flow profiles of mean wind speed and turbulence quantities that are applied in the inlet plane. These profiles model fully developed and representative of the terrain characteristics of the upstream part that is not include in the computational domain.

Finally, we will read the wind velocity which may affect pedestrians between the building. We will display the pressures on buildings that may affect their construction.

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 buildings

Firstly, we need to Download GeometryBuildings
The geometry will be imported in the same units as it was exported to the STEP format.

In some cases, the imported external geometry may contain multiple parts. SimFlow will ask you whether you want to join all geometries into a single component. If not, each part will be put into separate items.

For the purposes of this tutorial, we will combine all parts into a single geometry.

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

To be able to better resolve flow around the buildings, we will create an area with a higher mesh resolution. To do this, we will add box geometry.

After geometry is ready, we can proceed to define meshing properties. To better resolve the flow around the buildings, we want to refine mesh near the buildings geometries by specifying minimum and maximum refinement levels.

The refinement geometry should be used only for marking refinement zones. Set the proper parameters for the refinement regions.

Base Mesh is a domain mesh of our simulation from which the final mesh will be created by carving out the geometry of the buildings.

We need to assign individual names to each side of the base mesh in order to be later able to define different conditions on each side. To achieve simplified slip condition on side and top boundaries we will use symmetry as a boundary type.

Material Point tells the meshing algorithm on which side of the geometry the mesh is to be retained. We are simulating flow around the buildings so our material point needs to be located inside the base mesh but outside the buildings.

Everything is now set up for meshing.

The new mesh will be displayed in the graphics window. To show the mesh of the buildings we can use the Graphics Object List to hide some boundaries.

You can hide domain boundaries to inspect the mesh on the buildings.

We want to analyze incompressible turbulent flow around the buildings. For this purpose, we will use the SIMPLE (simpleFoam) solver.

We are going to use the \(RNG \; k{-}\epsilon\) model to handle turbulence.

On the inlet boundary, we are going to apply Atmospheric Inlet boundary condition. It is dedicated condition for atmospheric airflow. The Atmospheric Inlet provides log-law type ground-normal inlet boundary conditions for wind velocity and turbulence quantities. It is applied for homogeneous, two-dimensional, dry-air equilibrium and neutral atmospheric boundary layer modelling. More about Atmospheric Inlet boundary condition you can find here.

During the calculation, we can observe intermediate results on a section plane. To add sampling data on a plane we need to define plane properties and also select fields that will be sampled. We will monitor the pressure and velocity at a height of 2 metres from the ground. Note that runtime post-processing can only be defined before starting calculations and can not be changed later on.

Now, create a vertical slice.

Now, specify which results should be sampled on the section planes.

Finally, we can start our computation.

To speed up the calculation process increase the number of CPUs basing on your PC capability. 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: 4 minutes

When the calculation is finished we should see a similar residual plot.

Slices tab appears next to the Residuals tab. Under this tab, we can preview results on the defined section plane.

After computations are finished, we can do complex visualization of our results with ParaView.

Load the results into the program.

To limit the investigation area we will Clip the domain by the box.

Now we will create velocity magnitude parameter. It will be helpful in scaling and coloring the velocity vector field.

To visualize the flow around the building we will create vector field.

To display results with the original geometry, we can import the case once again and select only suitable boundaries. Now, we will import the buildings and the ground boundaries.

Now we can see the velocity vector field around the buildings.

To display pressure on the buildings we need to hide vector field and change the coloring to the pressure.

Pressure field is displayed on the selected boundaries.