浓缩风能装置扩散管流场模拟验证及其凸缘结构优化设计

Flow field simulation verification and flanged structure optimized design of concentrated wind energy device diffuser

浓缩风能装置的扩散管结构直接影响浓缩风能型风电机组的输出功率。为提高浓缩风能装置的浓缩效率,以浓缩风能装置为研究对象,采用数值模拟方法,研究扩散管凸缘的几何参数对浓缩风能装置内部流场特性的影响规律;并通过试验验证数值模拟的可靠性。结果表明:扩散管凸缘结构能够明显提高浓缩风能装置对自然风的加速作用和风能利用率;且装置内部流场的流速和风轮扫掠面积上的可利用风能随着凸缘高度L的增加而增大。综合分析可得,带有L为450 mm、凸缘角度α为+9°的扩散管凸缘的浓缩风能装置模型流场流速和可利用风能较高;与原始模型相比,其内部流场最大流速提高了30.738%,可利用风能提高了84.26%,是所研究模型中流场性能较佳的浓缩风能装置结构。

Concentrated wind energy device is the core component of concentrated wind energy turbine, and the flanged diffuser can enhance the swabbing effect of the concentrated wind energy device, which can increase the flow velocity of internal flow field and improve the wind power quality consequently. To enhance the efficiency of the concentrated wind energy device, internal flow field characteristics of flanged diffuser models with different diameters（flange height ranging from 90 to 450 mm and angel from-15° to ＋15°） were simulated and analyzed. In the process of the numerical simulation, the fluid medium was the air with the temperature of 296.75 K and the density of 1.153 kg/m^3. Besides, the velocity-inlet and pressure-outlet were adopted as the boundary condition of computational field. Other boundaries were set as stationary wall and no slip. The physical model was simplified to the steady incompressible fluid problem without heat transfer, and basic governing equations were continuity equations and Navier-Stokes equations. The turbulence model was SST（shear-stress transport） k-ω model. Simulation results show that the flanged diffuser could strength the acceleration and concentration efficiency of concentrated wind energy device. And the flow velocity and usable wind energy of the rotor swept area were increased with the increasing of flange height. In all the models, when the flow velocity and usable wind energy were considered together, the model with flanged diffuser of height of 450 mm and angel of ＋9° was the optimal structure of concentrated wind energy device. Compared with the original model, the maximum flow velocity of the optimal model was increased by 30.738%, and the usable wind energy was increased by 84.26%. The feasibility of the model and simulation method were verified by wind tunnel experiment with the nominal wind speed of 10 m/s. Flow field calibration was proceeded in the wind tunnel firstly to choose a suitable flow field for the experiment. Then the concentrated wind energy device model, having the same scale with the numerical calculation model, was fixed at the selected location inside the wind tunnel and the center line was in the middle section of the tunnel. The total pressure and static pressure of different test points on radial direction inside the model were measured by the Pitot tube and multi-channel pressure gauge. The temperature recorded during the test fluctuated from-1 to-0.5 ℃ and the atmospheric pressure was from 899 to 900 h Pa. Numerical calculation results were reasonably verified by wind tunnel experiments. Although numerical results were greater than the experimental data obtained with the model of the same size, the general trends were almost the same. The main reason of the difference between the results was that the numerical simulation model was too idealized to embody the complex flow conditions inside the model. All the conclusions obtained from the research can provide a basis for the structure optimization of concentrated wind energy device.