Description
In the current validation example, we investigate wind pressure coefficient (Cp) for both main structural design and secondary structural design, such as cladding or façade systems based on Canada wind load standard (NBC 2020) [1] and Japanese Wind Tunnel Data Base for low-rise building with 45-degree slope. The recommended setting for a three-dimensional low-rise building with 45-degree slope will be described in the next part.
The key factor of CFD simulation is finding the most compatible configurations with wind load standards regarding input data, such as turbulence models, wind velocity profiles, turbulence intensities, boundary layer conditions, order of discretization, and other factors. The important point is that the standards do not cover the required information for numerical simulation, such as CFD simulation. In the current VE, we presented the most compatible RWIND settings concerning the example of the NBC 2020 low-rise building with a 45-degree slope and experimental data from Japanese Wind Tunnel Data Base .
Analytical Solution and Results
The enclosed sharp eaves model is assumed according to Figure 1, which has eight zones (1,1E,2,2E,3,3E,4,4E). The external wind pressure coefficients of global and local areas for low-rise buildings with 45-degree slopes are presented in Figures 4.1.7.6.-A and Table 4.1.7.6. in NBC 2020. The important assumptions and input data for RWIND that is used for numerical CFD simulation are also shown in Table 1.
| Table 1: Dimensional Ratio and Input Data | |||
| Basic Wind Velocity | V | 22 | m/s |
| Terrain Category | 2 | - | - |
| Crosswind Dimension | b | 16 | m |
| Alongwind Dimension | d | 16 | m |
| Mean Roof Height | href | 12 | m |
| Roof Angle | θroof | 45 | Degree |
| Air Density - RWIND | ρ | 1.25 | kg/m3 |
| Wind Directions | θwind | 0, 22.5, 30, 45 | Degree |
| Turbulence Model - RWIND | Steady RANS k-ω SST | - | - |
| Kinematic Viscosity (Equation 7.15, EN 1991-1-4) - RWIND | ν | 1.5*10-5 | m2/s |
| Scheme Order - RWIND | Second | - | - |
| Residual Target Value - RWIND | 10-4 | - | - |
| Residual Type - RWIND | Pressure | - | - |
| Minimum Number of Iterations - RWIND | 800 | - | - |
| Boundary Layer - RWIND | NL | 10 | - |
| Type of Wall Function - RWIND | Enhanced / Blended | - | - |
| Turbulence Intensity (Best Fit) - RWIND | I | Terrain 2 | - |
The global and local wind pressure coefficients are calculated for all zones considering wind velocity and turbulence intensities based on the terrain two category. Also, four wind directions (θ = 0, 22.5, 30, 45 degrees) are considered to calculate the corresponding values of global Cp value regarding the NBC 2020 and Japanese Wind Tunnel Data Base . The wind velocity profile and global Cp contour for experimental and numerical study with RWIND are illustrated in Figure 2, Figure 4, and Figure 4, respectively, in which the value of global and local Cp for main and secondary structural members are compared between experimental data from the Japanisch wind tunnel test and RWIND 2. Furthermore, the diagram of Cp,ave, and Cp,local values of experimental simulation, NBC 2020, and RWIND are compared in Figure 5 and Figure 6 regarding eight zones for low-rise building with 45-degree slope.
The experimental values are obtained manually by observation of the Cp,ave, and RMS contour pictures in the Japanese Wind Tunnel Data Base . Also, the wind velocity and turbulence profile in RWIND is set with the terrain two category, which is variant in height and also better matched with references. It is important to note the results of steady state simulation by using RANS k-ω SST which is considred in the current validation example shows good agreement especially with the experimental study. The critical cases are considered different wind directions for variable turbulence intensity in height (based on terrain 2). The deviation from positive Cp value is higher for numerical and experimental simulation compared to NBC 2020, which can be interpreted as a very conservative approach for the positive regions.
Conclusion
In the cuurent validation example, we investigate wind pressure coefficient (Cp) obtained from RWIND for both main structural design and secondary structural design, such as cladding or façade systems based on Canada wind load standard (NBC 2020) [1] and Japanese Wind Tunnel Data Base for low-rise building with 45-degree slope. The results show that the recommended RWIND configuration has good agreement with most zones in Eurocode. The higher turbulence intensity close to the variant turbulence profile of Terrain 2 shows more accurate results. It is important to consider the critical wind direction scenario and transient simulation to obtain the extreme value of NBC 2020. The deviation values mostly came from safety factors and the statistical approach, which presents a more conservative approach, especially for positive Cp regions compared to another standard such as ASCE 7-22.
Also, the flat roof model with recommended settings is available to download here:
