Dual Scale Control Of Greenhouse Environment Based On CFD

In this paper,a dual scale greenhouse environmental control scheme based on Computational Fluid Dynamics(CFD)is proposed for a solar greenhouse in Jinzhong City,Shanxi Province.Greenhouse environment is a very complex system,the growth of various crops in the greenhouse and the change of temperature are mutually affected,the growth rate of crops changes slowly,and the heat change in the greenhouse is relatively rapid,there is an obvious difference in time and size between the systems.Aiming at this characteristic,a hierarchical control system of greenhouse temperature based on different time scales is proposed in this paper to track the optimal growth temperature of crops and adjust the indoor temperature according to this value.In addition,the environmental sensing control system based on sensors is fed back in the form of "points",which cannot achieve uniform regulation of greenhouse temperature,resulting in regional differences in crop growth.In this study,by using CFD technology to simulate the greenhouse environment,the data of the greenhouse environmental field was obtained,and then the uniformity control of the greenhouse environment was improved.The experimental results show that the dual-scale greenhouse environmental control scheme based on CFD can control the greenhouse environment well,and its control accuracy is 98.2%.The proposal and implementation of this scheme provide a new idea for greenhouse production control.The main research contents and results of this paper are as follows:(1)Determine the mathematical model and method of CFD simulation through in-depth study of the fluid motion characteristics and heat transfer characteristics of greenhouse indoor air,and on this basis,determine the solution method of the model.To realize the simulation of the environmental temperature field in the greenhouse.(2)For the test of single span glass greenhouse,using Gambit software established in accordance with the proportion of 1:1 greenhouse equal three-dimensional model with the experiment,the determination of boundary conditions and initial conditions to select agricultural cloud monitoring platform measuring data,based on the choice of physical and mathematical model of greenhouse,the lettuce grown in greenhouse temperature field using CFD technology was studied by means of numerical simulation and comparison test and verify.Results show that the simulated values and measured values are certain error,the maximum relative error is 1.5%,this could be due to spontaneous heat sensor,but the simulated data and the measured data of the same change trend,which shows that CFD model established in this paper to a certain extent,can reflect the change condition of the temperature field inside the greenhouse lettuce,for the further research of greenhouse environment provide theoretical and technical support online tracking control.(3)The relationship function between crop dry weight and greenhouse environment is obtained by using lettuce growth model and greenhouse environmental value.To find the greenhouse environmental plan when the dry weight of crops reaches the maximum,which can be used as the reference index for the next greenhouse environmental control.(4)Based on the distribution of greenhouse temperature field simulated by CFD technology and the output environmental control index of crop layer,the optimization controller of environment layer is designed,so as to realize the uniformity control of greenhouse environment.The control scheme proposed in this paper will provide theoretical basis and guiding significance in practical production and application.