CFD simulations of velocity fields and ventilation rates in a crop protection structure for the tropics.

摘要

The use of crop protection structures is essential in tropical areas to obtain quality production of important horticultural crops. These structures protect the crops from the extreme climate conditions, which characterize these areas (high solar radiation, high temperature, heavy rain, strong wind and high humidity). The structures must provide plant protection from insects and diseases. A simple single span greenhouse was developed for Malaysia that consisted of two vertical walls that supported a tunnel-shaped structure with a roof ventilator on the top. Under the climate conditions mentioned above, natural ventilation becomes the most practical and cheap method to modify the climate inside the greenhouse. Recent works have studied different ventilator configurations for this greenhouse to identify those designs that provided better air exchanges for thermally driven ventilation as well as wind driven ventilation for four different vent configurations of the same greenhouse using scale models and visualization techniques. The computational fluid dynamics (CFD) technique has been applied to simulate and analyse wind-driven ventilation for the same greenhouse. Qualitative vector fields obtained with CFD simulations have been compared with those obtained in previous works. Excellent agreement has been found for the four vent configurations studied. Ventilation rates were directly calculated from the average velocity vectors on the vents and good agreement was found for three of the four studied configurations in relation to the results presented in previous works. CFD simulations also proved that under windy conditions, a double-sided hinged roof ventilator could significantly improve (>20%) original roof ventilator design..