A CFD transient model of leaf wetness duration on greenhouse cucumber leaves

The estimation of leaf wetness duration (LWD) is important for crop disease monitoring and early warning, because LWD provides the necessary conditions for pathogen infection. Crop canopy condensation caused by high humidity in greenhouses is one of the main causes of LWD formation, and measuring LWD in greenhouses is difficult. A simulation model based on agricultural meteorological parameters is typically used to replace field measurements. This study was conducted in a Chinese solar greenhouse. A 2D transient model based on computational fluid dynamics (CFD) was used to estimate the distribution of cucumber leaf condensation in a solar greenhouse during early summer nights in Beijing. The LWD was estimated by considering the duration of the simulated leaf condensation at each point and simulating the dehumidification effect under ventilation conditions. The visual observations of leaf condensation were compared with the simulation results from May 31 to June 1 and from June 3 to June 4, 2021 (cloudy and clear days, respectively). The horizontal leaf condensation was observed first near the south roof, whereas the vertical canopy had a longer LWD at 1 m from the ground (average value of 8 h). LWD was estimated using relative humidity thresholds (RMSE of 1.944 h on cloudy days and RMSE of 0.5 h on clear days), and the good agreement between measurements and estimation indicated that the 2D CFD model combined with the relative humidity threshold method could be used to estimate the temporal and spatial distribution of canopy LWD.