2.4.2. Details of the Wind Environment Experiment and Simulations
- (1)
Measured Points Selection
To effectively analyze the typical horizontal flow fields within traditional village courtyard spaces and pinpoint the optimal locations for winter wind environment measurements, Computational Fluid Dynamics (CFD) was employed to simulate the wind environment for a specific courtyard case (Courtyard No. 109). This simulation aids in understanding the behavior of natural winter winds as they interact with the courtyard. Measurement points were strategically selected based on their positions within different flow field regions shaped by these interactions. The points are designated as follows: A (due north), B (northwest), C (due west), D (southwest), E (due south), F (southeast), G (due east), H (northeast), and I (center). These points correspond to specific areas of airflow dynamics, including the windward area, corner flow area, through flow area, vortex area, and wind shadow area, as depicted in
Figure 5a.
- (2)
Field Experiment Method
To ensure the validity of the coupling between measured and simulated wind speed values, this study capitalized on the pronounced variability of wind forces in the coastal villages of Quanzhou Bay, characterized by elevated wind speeds during strong wind events. The chosen date for the field measurements was 10 January 2024, from 9:00 a.m. to 5:00 p.m., selected for its clear and mostly cloudless conditions. Measurements were taken using the Kestrel 5500 handheld weather meter. Employing a fixed-point observation method with multiple observers, measurements were conducted at nine designated points (A, B, C, D, E, F, G, H, I) within Courtyard No. 109 in the Xunpu community. The setup for wind environment simulation scenarios subsequently mirrored these measurement points.
Each measurement station involved a wind speed meter mounted on a tripod, with the anemometer inlet positioned 1.5 m above the ground. Data were recorded hourly, with each data point representing the average wind speed over a 1 min interval. Minimum, average, and maximum wind speeds were recorded every 10 s. This protocol yielded 9 sets comprising 486 effective wind speed data points from 9:00 a.m. to 5:00 p.m. The average wind speed data for each hour was statistically analyzed and compared to assess the actual wind conditions at different points in the courtyard. The accuracy of the wind speed measurements using the NK500LNK weather meter is ±3%.
- (3)
Three-Dimensional Model Construction
The values of the most frequently occurring indices for the three key layout factors of traditional village courtyard spaces—area, orientation, and aspect ratio—were statistically derived from
Table 1. These indices helped to summarize the typical original model for the wind comfort simulation experiments of traditional village courtyard spaces, ensuring general applicability.
In terms of courtyard area, the index most frequently falls within the 20 to 80 square meter range, accounting for 50.73% of observations. Regarding orientation, the southeast direction is the most common, making up 31.7% of the data. For the aspect ratio, the range of 0.5 to 0.7 is the most frequent, representing 35.61% of the cases. Based on these findings, a typical original model of a traditional village courtyard space was established (
Figure 6). The model parameters were set with a courtyard area of 50 m
2, an orientation facing southeast, and an aspect ratio of 0.6. These configurations aim to facilitate comparative analysis of wind comfort differences influenced by variations in these three indices. The courtyard spaces in 204 traditional villages were analyzed based on their area, aspect ratio, and orientation. They were classified into five area index types: 20, 50, 110, 170, and 230 square meters (
Figure 7a–e). The aspect ratio classifications included indices of 0.32, 0.60, 0.80, 1.00, and 1.20 (
Figure 7f–j). The orientation index classifications comprised southeast, southwest, west, northeast, south, east, northwest, and north (
Figure 7k–r). Eighteen index models were developed from typical original models, corresponding to the specified areas, aspect ratios, and orientation indices. The simplified integer values of the 18 index models are detailed in
Table 3.
- 4)
CFD Simulation Settings
For Computational Fluid Dynamics (CFD) simulations, a variety of software options are available, such as PHOENICS, ANSYS FLUENT, ENVI-met, Airpak, and Butterfly. Among these, PHOENICS stands out as the world’s first commercial software developed specifically for CFD and heat transfer applications. It is widely used in the simulation of wind environments in residential areas, school districts, and landscape gardens. The use of PHOENICS in previous studies has demonstrated its effectiveness in various contexts: different height distribution patterns have been shown to influence changes in wind speed and pressure [
22], modifications in building layouts can significantly reduce community energy consumption and carbon emissions [
23], and the arrangement of courtyard plants can greatly affect outdoor microclimates and enhance residents’ comfort regarding wind and thermal conditions [
24]. Additionally, alterations in building spatial layout and aspect ratios have been effective in creating ecological buffer zones [
25]. Therefore, PHOENICS is deemed suitable for simulating the wind environment in the courtyard spaces of this study.
The specific CFD simulation settings and model setup in PHOENICS are as follows:
Model Selection: The RNG k-ε turbulence model is chosen for its robustness in handling high strain rates and complex flows, as specified in PHOENICS. This model is implemented as shown in Equations (4) and (5).
Discretization Scheme: The PRESTO! scheme is used for discretizing the pressure field, ensuring enhanced accuracy in scenarios with sharp gradients and complex geometries.
Velocity–Pressure Coupling: The built-in PARSOL (Partial Cell) function facilitates the execution of velocity–pressure coupling simulations, particularly beneficial in environments with complex boundaries and obstructions, using a fine-scale mesh to enhance calculation accuracy.
Convergence Detection: PHOENICS’s automatic convergence detection system ensures that simulation results achieve reasonable convergence, with a targeted convergence accuracy of 10⁻
5 [
26]. This system helps verify that the simulation outcomes are stable and reliable across different simulation scenarios.
These settings are meticulously designed to simulate the nuanced wind dynamics within traditional village courtyards, aiming to produce data that can effectively inform design decisions and environmental adjustments to enhance comfort and sustainability in coastal village settings.
In the equations, turbulent kinetic energy is denoted by k, and the turbulent dissipation rate is denoted by ε.
Mesh Settings: The computational domain for the CFD simulations is set to dimensions significantly larger than those of the actual scene model to ensure that boundary effects do not influence the results. Specifically, the length and width of the computational domain are established at five times the length and width of the scene model, respectively, and the height is set to three times that of the scene model. The mesh within this domain is categorized into two regions: central and edge. In the central region, where higher resolution is critical for capturing detailed flow patterns, the planar mesh density is set to 4 m × 4 m, with a vertical mesh density of 0.5 m. Conversely, the edge region, which typically experiences less variation in airflow, features a coarser planar mesh density of 8 m × 8 m and a vertical mesh density of 1 m. This strategic mesh configuration optimizes the balance between simulation accuracy and computational efficiency, reducing the number of mesh segments and thereby enhancing the time efficiency of the simulations (
Figure 5b).
Wind Condition Settings: For wind conditions, this study adheres to the “Code for Design of Heating, Ventilation, and Air Conditioning in Civil Buildings” [
27]. Additionally, wind data from sources such as the “China Weather Network”, “China Meteorological Network”, and “China Meteorological Data Network” indicate that the average winter wind speed in the Quanzhou area is 6.13 m/s, predominantly from the northeast. These specifics are incorporated into the inflow boundary condition of the simulations. The simulations are iterated 2000 times to ensure the stability and accuracy of the results. The ground roughness coefficient, denoted as
α, is set to 0.2, reflecting the typical ground surface roughness of the region, which affects wind flow behavior near the ground. This setting is crucial for accurately simulating wind interactions with the complex geometries of traditional village courtyards and their surroundings.