Optimizing aerodynamic shape in an agricultural greenhouse under flow field distribution

Aerodynamic profile is one of the most important influencing factors on the wind resistance in the agricultural greenhouse structures. In this research, a systematic investigation was conducted to optimize aerodynamic shape in a greenhouse under flow field distribution. Three cross-sectional types were selected: the arched, M-shaped, and gable-roof greenhouses. A robust and multi-scale approach was also employed. Initially, Particle image velocity (PIV) experiments were performed to acquire detailed data on the external flow fields around scale models. The spatial distribution and key differences were determined among the three shapes. Subsequently, Large eddy simulation (LES) was utilized to conduct on the instantaneous distributions of fluctuation vorticity and surface wind pressure coefficients in the external flow fields. Empirical datasets were integrated from the PIV with the high-fidelity numerical data after LES. A comparative analysis was performed on the surface wind pressure coefficients, overall wind loads, and fundamental flow mechanisms in each cross-section. Finally, the specific flow separation was identified for the gable-roof type. A parametric method was applied to optimize its aerodynamic shape. The results revealed that a vorticity peak was consistently observed near the roof region, the magnitude of which was slightly lower in the gable-roof greenhouse than that in the arched and M-shaped types. In the wake region, both the M-shaped and gable-roof greenhouses exhibited a smaller zone of negative (reverse) flow velocity, compared with the arched design. Their sharp geometric edges induced more abrupt flow separation, leading to the stronger components of the vertical velocity. In the near-surface flow topology, the extensive attached vortex systems were present on the windward sides of the arched and M-shaped roofs, while the gable-roof profile demonstrated markedly cleaner flow attachment with minimal attached vortices. The different flow interaction directly resulted in substantial variances in aerodynamic forces. The lift force on the gable-roof greenhouse was calculated to be approximately 49% and 28% lower than that on the arched and M-shaped greenhouses, respectively. The superior resistance to the wind uplift, a critical performance metric, was then realized under strong wind conditions. The parametric shape optimization involved a downstream shift of the ridge line for the gable-roof type. The surface vortices were attenuated under a 0° wind direction after modification. The wind pressure on the windward surface was also transitioned from positive to negative with a decreasing magnitude. There was a more dispersed contour distribution. Concurrently, the leeward suction pressure also decreased with the more gradual spatial gradient. Consequently, the overall wind load on the structure was reduced significantly. Specifically, the total lift and drag forces on the greenhouse surface decreased by 29% and 45%, respectively, in the optimal configuration (the case with a ridge-to-span ratio of 17:3), compared with the baseline in the most forward ridge ( the case with a ridge-to-span ratio of 3:17). The wind resistance of the optimal structure was enhanced under the optimal configuration. In conclusion, the experimental and numerical simulations were integrated to determine the influence of cross-sectional geometry on the complex flow-structure interaction and the wind loads on agricultural greenhouses. The performance of the optimal gable-roof can provide valuable guidance for the wind resistance of such structures. The findings can also greatly contribute to their safety and durability in wind-prone environments.