PIV VERIFICATION OF GREENHOUSE VENTILATION AIR FLOWS TO EVALUATE CFD ACCURACY

Abstract

A computational fluid dynamics (CFD) model was developed to investigate the natural ventilation of greenhouses. Before investigating its accuracy, a wind tunnel and particle image velocimetry (PIV) test was initially conducted to find the best experimental conditions and improve the PIV accuracy. After many trials of the PIV tests, good results were obtained in the PIV accuracy test, and the errors were shown to be mostly in the .2.1% range, with a maximum of 5.4%. A single-span, wide-span greenhouse, one of the most popular types of multi-span greenhouses in Korea, was used to get qualitative and quantitative airflow distribution in the greenhouse using PIV and CFD. To improve the CFD accuracy, the PIV- and CFD-computed airflows in the greenhouse were compared, particularly on the distribution, local air velocity, and turbulent intensity in the greenhouse. The quality of the mesh density and the design of the boundary condition, especially that of the wind velocity and turbulence profiles, were found to be very important for getting accurate results. Assuming the PIV results were accurate, the most accurate CFD results were obtained when using renormalization-group (RNG) k-. and Reynolds stress turbulence numerical models. The errors of the CFD-computed air velocity when using the RNG k-. and Reynolds stress models were -7.9% and -7.6%, respectively. However, the average errors of turbulent intensity when the RNG k-. and Reynolds stress turbulence numerical models were used were -37.5% and -43.2%, respectively.