TY - JOUR
T1 - Towards a physics-based understanding of fruit frost protection using wind machines
AU - Heusinkveld, Vincent W.J.
AU - Antoon van Hooft, J.
AU - Schilperoort, Bart
AU - Baas, Peter
AU - Veldhuis, Marie claire ten
AU - van de Wiel, Bas J.H.
PY - 2020
Y1 - 2020
N2 - Wind machines are used in the agricultural sector to prevent or mitigate the adverse effects of night frost in spring. In this study we aim to quantify the impact of wind machine operation on the local temperature field in an orchard. To this end, a field experiment is conducted and experimental analysis is combined with numerical simulation studies in order to assess the functional relations between wind machine performance and the dominating physical processes occurring during radiative frost events. Experimental observations showed that the temperature response strongly depends on the radial distance to the fan and the height above the surface. In agreement with previous studies, the wind machine was able to achieve rotation-averaged temperature increases of up to 50% of the inversion strength ( ≈ 3 K) in an area of 3–5 ha at 1 m height. Furthermore, it was observed that even weak ambient winds (<1 m/s) already may cause strong upwind-downwind asymmetries in the protected area, the downwind area being larger. The numerical model, inspired by the field experiment, showed similar spatial temperature responses as compared to observations. Interestingly, it was found that slower rotation times of the wind machine (3 to 6 min) lead to a significant increase of affected area, while the temperature enhancement itself stayed relatively constant. Variation of the horizontal tilt angle showed that, in our model, temperature enhancement was maximized between 8∘ and 16∘. This nearly horizontal flow already facilitates efficient vertical mixing of momentum and heat, presumably due to generation of shear instabilities at the lower edge of the jet. Finally, like in the observations also the numerical result showed strong upwind-downwind asymmetry in the affected area due to background wind.
AB - Wind machines are used in the agricultural sector to prevent or mitigate the adverse effects of night frost in spring. In this study we aim to quantify the impact of wind machine operation on the local temperature field in an orchard. To this end, a field experiment is conducted and experimental analysis is combined with numerical simulation studies in order to assess the functional relations between wind machine performance and the dominating physical processes occurring during radiative frost events. Experimental observations showed that the temperature response strongly depends on the radial distance to the fan and the height above the surface. In agreement with previous studies, the wind machine was able to achieve rotation-averaged temperature increases of up to 50% of the inversion strength ( ≈ 3 K) in an area of 3–5 ha at 1 m height. Furthermore, it was observed that even weak ambient winds (<1 m/s) already may cause strong upwind-downwind asymmetries in the protected area, the downwind area being larger. The numerical model, inspired by the field experiment, showed similar spatial temperature responses as compared to observations. Interestingly, it was found that slower rotation times of the wind machine (3 to 6 min) lead to a significant increase of affected area, while the temperature enhancement itself stayed relatively constant. Variation of the horizontal tilt angle showed that, in our model, temperature enhancement was maximized between 8∘ and 16∘. This nearly horizontal flow already facilitates efficient vertical mixing of momentum and heat, presumably due to generation of shear instabilities at the lower edge of the jet. Finally, like in the observations also the numerical result showed strong upwind-downwind asymmetry in the affected area due to background wind.
UR - http://www.scopus.com/inward/record.url?scp=85076699615&partnerID=8YFLogxK
U2 - 10.1016/j.agrformet.2019.107868
DO - 10.1016/j.agrformet.2019.107868
M3 - Article
SN - 0168-1923
VL - 282-283
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
M1 - 107868
ER -