Study On Numerical Simulation Of Wind Effects For Large-Scale Dish Solar Concentrator

The parabolic dish concentrating system is a focused thermoelectric conversion system supported by steel frame structure based on two-axis solar ray tracing.During the operation,the azimuth and elevation angles are adjusted in real time as the angle of the solar ray changes.The concentrator is the main equipment and the costly part of the system.This research on the anti-wind performance of dish concentrator is one of the most critical issues in its design.In the process of tracking the sun's rays,the incident solar rays are always accurately projected to the focal spot in the spatial position after being reflected by the mirror,which is enforced by a concentrator.The high dish concentrator focusing ratio,small relative rotation axis displacement or tiny deformation of reflecting surface can cause significant deviation of the focal spot of light,which has a direct impact on the thermal efficiency.Due to the particularity of the thermal engine of dish power generation technology,increasing the reflective area of a single concentrator and developing a large-scale concentrator can effectively reduce the average power cost.Furthermore,the increase of the concentrator area makes it more sensitive to the atmospheric boundary layer wind effect.In addition,solar thermal power generation systems are usually built in open and flat fields.Thereby,the turbulence flow near the ground has a great effect on the wind force generated by the concentrator and the distribution of wind pressure in the shape of the spatial paraboloid is also complicated due to the difference in pitch angle and azimuth angle.Meanwhile,how to solve the concentrated heating device to work properly at the permitted wind speed and keep the structure safety in strong wind environment is still a focus of the solar thermal power generation technology development of all countries.This paper aims at analyzing the aerodynamic load of the concentrator component of the dish solar thermal power generation system under the wind load effect,providing a reference for the structural design and dynamic performance analysis of the dish solar concentrator.The main research contents are as follows:(1)Based on computational fluid dynamics and atmospheric boundary layer turbulence theory,a large-scale parabolic dish concentrator aerodynamic numerical wind tunnel calculation model is established with Navier-Stokes equation and the SST k-? equation.An efficient calculation method for the bluff body flow of a large-scale parabolic dish concentrator is established with the finite volume method and polyhedron multi-grid optimization control technology.In the case of considering the change of the pitch angle and azimuth angle of the dish concentrator under working conditions,the simulation environment of the aerodynamics and atmospheric wind speed distribution of the dish concentrator is constructed.The calculation accuracy of parabolic surface with different Reynolds turbulence models is also compared.(2)The variation of the wind coefficient of the dish concentrator with the pitch angle and azimuth angle is obtained through the wind tunnel simulation based on CFD technology to determine the most unfavorable wind attitude and the best shelter position of the concentrator.Hence the average wind pressure distribution and pressure coefficient contour map on the surface of the dish concentrator under typical operating conditions are obtained and the variation law of wind pressure distribution with vertical elevation angle and horizontal azimuth angle is analyzed.(3)By analyzing the variation laws of the drag coefficient,lift coefficient,lateral force coefficient,overturning moment coefficient and total resultant force coefficient of the dish concentrator with the vertical elevation angle and horizontal azimuth angle at different design values of the size of the mirror gap from 0 to 60 mm to study the generation and optimization strategy of grid for thin wall body and dense small gap,the spatial position where the wind load of the concentrator is most sensitive to the influence of different gap sizes is obtained.The distribution of the average wind pressure coefficient on the reflective surface and the back surface of the concentrator is studied under the influence of the mirror gap.The characteristics of the gap size on the center of the mirror element and the distribution of the wind pressure gradient at the edge are summarized.In addition,the influence of different gap sizes on the effective reflection area of the concentrator and the overall wind reduction range are analyzed.The influence of the change of the mirror gap size on the cost and thermal economy of the dish concentrator is discussed.(4)According to the optimization algorithm,the optimal array spacing of the dish concentrator array is calculated and the numerical calculation model of the 3×3 array concentrator group is established to simulate the wind speed distribution,wind coefficient and interference factor around the dish concentrator of the dish concentrator array group in atmospheric boundary layer environment under different designed altitude and azimuth conditions.The variation law and flow disturbance mechanism of interference effect between undisturbed concentrator and disturbed concentrator under different altitude angle and azimuth angle are studied emphatically.The difference between the concentrator under wind load and the concentrator without interference is analyzed.(5)Based on the wind characteristics and the surface wind pressure distribution of the concentrator under the concentrator group interference effect,the finite element model for the strength calculation of the concentrator reflective structure is established.The fluid–structure interaction method is used to analyze the aerodynamic response of the concentrator,and the finite element software is used to analyze the static strength of the dish solar thermal power generation unit under different elevation and azimuth conditions.The dynamic characteristic parameters of the concentrator structure are obtained under different elevation angles including stress intensity and strain deformation of the key support structure of the concentrator.The fluid–structure interaction analysis results of the mirror deformation under the interference of concentrator array group under the wind effect are applied to Focusing accuracy analysis of concentrator and the relevant mathematical model was established to verify the effect of the mirror deformation on the focal spot deformation under wind load.