A wind profile describes the incoming wind at the inlet of the wind tunnel. It represents one of the properties of a load case of the "Wind Simulation" analysis type (see the image "Analysis Type" of Load Case ).
Click the
button in the "Wind Profile" area (2). The New Wind Profile dialog box appears.
The wind profiles are managed in the Load Wizards category of the navigator. You can also use the shortcut menu to define a new wind profile.
Wind Profile Type
Select the Wind Profile Type from the list. It can be either "User-Defined" where you can manually define the wind properties or "According to Standard" where the code selected in the "Base Data" is applied.
User-Defined Profile
When the user-defined type of profile is selected, you can define the wind profile parameters manually. Enter the "Height" z and assign the "Wind Velocity" v in the "Input Values" table. Under the table, the air density is defined. Next, the turbulence of the incoming wind must be defined. It is considered when "Consider turbulence" is set on the Main tab of the "Wind Simulation Analysis Settings" dialog box.
By default, a constant "Turbulence Intensity" 1% is preset in the "I" check box below the table. Turbulence intensity is a ratio of the root mean square of turbulent velocity fluctuations to the mean wind velocity. An idealized flow of air with absolutely no fluctuations in wind speed or direction would have a turbulence intensity value of 0%. For high-turbulence cases, the turbulence intensity is typically between 5% and 20% (see CFD Online). The turbulence intensity is set to 1% by default to cover most medium- and low-turbulence cases.
However, a non-uniform turbulence intensity or other turbulent quantities could be defined. It can be selected in the "Inlet turbulence definition type" combo-box.
The default option is "I and TuL". By default, the turbulence intensity is uniform; however, by unchecking the "I" check box, a profile along the height can be defined. The turbulence length scale TuL is calculated automatically from the dimensions of the model; however, it can be defined manually under the "Input Values" table.
An alternative approach is to use the turbulent kinetic energy k and turbulent dissipation rate ε ("k and ε") or the turbulent kinetic energy k and turbulent specific dissipation rate ω ("k and ω"). These quantities could be obtained by calculating the wind profiles using, e.g., the atmospheric boundary layer approach based on the aerodynamic surface roughness length (terrain category).
Profile According to Standard
The wind load is determined over the height of the building, depending on standard-specific parameters. The standards EN 1991‑1‑4 [1], ASCE/SEI 7‑16 [2], and NBC&cnbsp;2015 [3] are available for selection. The Wind Profile image above illustrates the parameters associated with EN 1991‑1‑4 [1]. When a different standard is set, the content of this section is adjusted to the regulations of the code.
When you activate the text box next to the "Terrain category" in the "Parameters" branch, different categories are available for selection. They depend on the standard and National Annex that you have set in the "Base Data" of the model.
For some National Annexes, the wind velocity is also dependent on the altitude of the terrain.
As the result of all parameters, the "Fundamental wind velocity" vb,0 is displayed. The wind profile is calculated from this value, taking into account the overall height of the model. According to EN 1991‑1‑4 [1], 4.2, this value is the characteristic 10-minute mean wind velocity, irrespective of wind direction and time of year, at 10 m above ground level in open country terrain with low vegetation, such as grass and isolated obstacles with separations of at least 20 obstacle heights. You can review the wind velocities of each height in a table (second tab, marked "Table Values"), or in the graphic on the right. Instead of the fundamental wind velocity, you can "Consider the mean velocity". According to EN 1991‑1‑4 [1], 4.3, the mean wind velocity vm(z) at a height z above the terrain depends on the terrain roughness and orography. It is determined according to EN& 1991‑1‑4 [1], Expression& (4.3). This accounts for the fact that effects of peak velocity pressure appearing on the model are considered by a specific wind tunnel simulation, which allows for the application of lower mean velocities. When this option is activated, the table and chart are updated.
The profiles of the mean velocities vm are specified in the National Annex for Germany, Table& NA.B.2 for the four terrain categories, for example.
The "Density" of the air is dependent on the altitude, temperature, atmospheric pressure, and humidity. It has an effect on the dynamic behavior of the fluid.
