Modeling the warming effectiveness of wind machines operation in fruit orchards

Spring frost events can cause significant economic losses in the agricultural sector. Wind machines have become increasingly popular for mitigating frost damage. During radiative frost nights, wind machines generate strong jets to erode the near-surface thermal inversion through air mixing. This process accelerates both vertical air-air and local plant-air heat exchange, which causes the plants to warm up. However, previous studies have been limited in scope, either focusing on the warming effectiveness of inversion erosion (air-air) or local plant-air heat exchange at specific measurement points. The dynamic interaction between the warm air jet and canopy layer, as well as the heterogeneous plant-air heat exchange over the orchard, are not yet fully understood.

 

To this end, we introduce a multilayer canopy model (Patton et al., 2016) and a wind machine model (Heusinkveld et al., 2020) in a large-eddy simulation (LES). The wind machine model incorporates a momentum source with an idealized actuator disk. The coupled canopy model parametrizes canopy-induced drag, turbulence dissipation, and plant-air heat exchange (Boekee et al., 2023). This coupled model allows evaluation of the wind machine effectiveness in enhancing plant tissue temperature. We evaluate model performance with two observational cases in different seasons (leafless and full leave periods). Temperature data were obtained using a grid of fiber optic cables with a resolution of 25 cm along the cable over 6.75 ha. The preliminary results indicate that the coupled model is capable to simulate both plant-air heat exchange and in-canopy temperature dynamics. Finally, as to guide optimal frost mitigation, we conducted a sensitivity analysis for various machine operation scenarios in different seasons. This will guide wind machine operation and reduce fruit frost damage.