The effect of turbulence on natural ventilation of a proposed octagonal greenhouse in a transient flow
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ORIGINAL PAPER
The effect of turbulence on natural ventilation of a proposed octagonal greenhouse in a transient flow J. Javadi Moghaddam1 Received: 25 April 2020 / Revised: 22 August 2020 / Accepted: 23 September 2020 © Islamic Azad University (IAU) 2020
Abstract This study presents the effect of openings on the ventilation rate of an experimental proposed octagonal greenhouse in a transient flow. Furthermore, it makes a comparison between the free ventilation of the proposed greenhouse with an Arc greenhouse with two-dimensional computational fluid dynamic simulation. To simulate airflow in the Arc greenhouse, we selected a one-side roof vent openings, butterfly-type side vent openings and one-side-face to face-roof vent openings as opening designs. Moreover, two octagonal greenhouse portions were selected due to changes in cross-sectional area. The results showed that the average wind speed in the greenhouse equipped with butterfly-type side vent opening was higher than other greenhouses, but the temperature of air inlet was distributed less slowly. To illustrate the accuracy, the computational fluid dynamic results, which include wind speed and temperature, were compared with the measured values from the proposed octagonal greenhouse. Moreover, this study investigates the effect of greenhouse shape and openings on turbulence formation and the effect of turbulence on greenhouse climate. After 10 min of simulation, the average total temperature in the greenhouses with butterfly-type side vent openings and one-side-face to face-roof vent openings models had still not reached the outside air temperature. Based on observations, like the average total temperature, the average total airflow velocity was also close in both sides of the octagonal greenhouse. The simulation results show that the speed of free ventilation and temperature distribution in the proposed octagonal greenhouse were higher than the Arc greenhouse with other openings design. Keywords Greenhouse · Octagonal · Turbulence · Natural · Ventilation List of symbols u Wind Velocity, m s−1 a Absorption coefficient P Fluid pressure, Pa hs Sensible enthalpy, J/kg 𝜌 Density, kg/m3 T Temperature, K C𝜀1 , C𝜀2 Adjustable constant t Time, s 𝜎𝜀 , 𝜎k Prandtl numbers 𝜀 Turbulent dissipation rate, J/(kg s) 𝜇 Dynamic viscosity, Pa s 𝜇T Turbulence dynamic viscosity, Pa s Editorial responsibility: Parveen Fatemeh Rupani. * J. Javadi Moghaddam [email protected] 1
Agricultural Engineering Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
𝛿w+ Distance from the wall, m C𝜇 Proportional number IT Initial turbulence intensity, % Uref Reference velocity scale, m s−1 𝛿w+ Dimensionless wall offset Cp Specific heat capacity, J/(kg K) kef Effective conductivity, W/m K κ Von Karman constant JD Diffusion flux of species 𝛷 Phase function MAPE Mean absolute error EF Model efficiency RMSE Root-mean-square error u𝜏 Friction velocity, m s−1 u+ Tangential velocity in viscous units, dimensio
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