Duo to fluctuations in atmospheric turbulence and yaw control strategies,wind turbines are often in a yaw state.To predict the far wake velocity field of wind turbines quickly and accurately,a wake velocity model was ...Duo to fluctuations in atmospheric turbulence and yaw control strategies,wind turbines are often in a yaw state.To predict the far wake velocity field of wind turbines quickly and accurately,a wake velocity model was derived based on the method of momentum conservation considering the wake steering of the wind turbine under yaw conditions.To consider the shear effect of the vertical incoming wind direction,a two-dimensional Gaussian distribution function was introduced to model the velocity loss at different axial positions in the far wake region based on the assumption of nonlinear wake expansion.This work also developed a“prediction-correction”method to solve the wake velocity field,and the accuracy of the model results was verified in wake experiments on the Garrad Hassan wind turbine.Moreover,a 33-kW two-blade horizontal axis wind turbine was simulated using this method,and the results were compared with the classical wake model under the same parameters and the computational fluid dynamics(CFD)simulation results.The results show that the nonlinear wake model well reflected the influence of incoming flow shear and yaw wake steering in the wake velocity field.Finally,computation of the wake flow for the Horns Rev offshore wind farm with 80 wind turbines showed an error within 8%compared to the experimental values.The established wake model is less computationally intensive than other methods,has a faster calculation speed,and can be used for engineering calculations of the wake velocity in the far wakefield of wind turbines.展开更多
A modified wake model was proposed for the newly developed bubble-induced three-phase inverse fluidized bed(BIFB),by combining the generalized wake model and the gas-perturbed liquid model.On the basis of the modified...A modified wake model was proposed for the newly developed bubble-induced three-phase inverse fluidized bed(BIFB),by combining the generalized wake model and the gas-perturbed liquid model.On the basis of the modified wake model,the solids and liquid holdups and the complete fluidization gas velocity in BIFB system have been successfully predicted with two established correlations.The predictions achieved very good agreements with the experimental data.展开更多
It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations(VIV) of cylinders. In this paper, a novel in-line(IL) and cross-flow(CF) coupling VIV prediction model for circular c...It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations(VIV) of cylinders. In this paper, a novel in-line(IL) and cross-flow(CF) coupling VIV prediction model for circular cylinders has been proposed, in which the influence of the Reynolds number was comprehensively considered. The Strouhal number linked with the vortex shedding frequency was calculated through a function of the Reynolds number. The coefficient of the mean drag force was fitted as a new piecewise function of the Reynolds number, and its amplification resulted from the CF VIV was also taken into account. The oscillating drag and lift forces were modelled with classical van der Pol wake oscillators and their empirical parameters were determined based on the lock-in boundaries and the peak-amplitude formulas. A new peak-amplitude formula for the IL VIV was developed under the resonance condition with respect to the mass-damping ratio and the Reynolds number. When compared with the results from the experiments and some other prediction models, the present model could give good estimations on the vibration amplitudes and frequencies of the VIV both for elastically-mounted rigid and long flexible cylinders. The present model considering the influence of the Reynolds number could generally provide better results than that neglecting the effect of the Reynolds number.展开更多
Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the ...Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory, where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial (central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found, and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade, is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.展开更多
With the assumption of the Park model that the wake region is in linear expansion and the cross-wind is in multinomial and Gaussian distribution in wake region,one develops the Park-polynomial model and the ParkGaussi...With the assumption of the Park model that the wake region is in linear expansion and the cross-wind is in multinomial and Gaussian distribution in wake region,one develops the Park-polynomial model and the ParkGaussian model to numerically simulate the wake flow field for a single wind turbine.Compared with the measured data of wind farm and the wind tunnel test,it shows that the prediction precision of wake field has been improved obviously under the modified initial wake radius.Moreover,both of the newly modified two models could well simulate the wind velocity in wake region,because the predicted results is approximately consistent with the test result,and the cross-wind distribution conforms to that of the real flow field.The two models have still inherited many advantages of engineering models,such as simple form,easy-to-code,and high computational efficiency.Particularly,the Park-Gaussian model is the best in overall performance among them.展开更多
A tight formation of unmanned aerial vehicles(UAVs) has many advantages, such as fuel saving and deceiving enemy radar during battlefield entry. As a result, research on UAVs in close formation has received much atten...A tight formation of unmanned aerial vehicles(UAVs) has many advantages, such as fuel saving and deceiving enemy radar during battlefield entry. As a result, research on UAVs in close formation has received much attention, and the controller design for formation holding has become a popular research topic in the control field. However, there are many unknown disturbances in tight formation, and the tail aircraft is disturbed by the wake. This paper establishes a mathematical model of wake vortices for tail aircraft that considers uncertainty and strong interference. Two UAVs are simulated by Computational Fluid Dynamics software, followed by the design of a semiphysical simulation model predictive control(MPC) scheme that suppresses uncertainty and interference sufficiently to enable the tail aircraft to accurately track the lead aircraft and maintain a stable, tight formation. The tight formation controller is verified by numerical simulation and semiphysical simulation. The results show that the designed controller has an excellent control effect in the case of disturbance caused by the wake vortex.展开更多
Wind tunnel measurements using particle image velocimetry have been performed around two perforated discs, with varying streamwise distance, in order to simulate the wake interaction between wind turbines. The static ...Wind tunnel measurements using particle image velocimetry have been performed around two perforated discs, with varying streamwise distance, in order to simulate the wake interaction between wind turbines. The static pressure footprint (p-f) on ground level associated with the wake behind the disc and wake velocity data for both the streamwise and wall-normal velocity components with the corresponding turbulence intensities are reported. The p-f method shows that the size of the wake regions, behind the wind turbine models, initially drop when a second disc is placed just downstream of the first one. From a mutual distance (Δ χ) of about five disc diameters (5D), both wake footprints increase as the mutual distance is increased, and for very large mutual distances, approximately Δ χ/ D > 15, the footprint of the downstream disc has recovered and is about the same as for a single disc. At last we conclude that despite very different inlet conditions to the discs, with about 50% of reduced velocity on the centre line upstream of the second disc and an increase of the maximum streamwise fluctuations by 90%, the mean velocities in the wake are proven to scale with the hub height velocity.展开更多
规模效果导致在模型规模和实际轮船的 wake 地之间的大差异,并且在在预言实际轮船的表演的成穴性能和令人激动的力量测试引起差别。因此,从轮船模型的测试数据是什么时候,直接使用了预言实际轮船的表演,测试结果必须受到实验修正。...规模效果导致在模型规模和实际轮船的 wake 地之间的大差异,并且在在预言实际轮船的表演的成穴性能和令人激动的力量测试引起差别。因此,从轮船模型的测试数据是什么时候,直接使用了预言实际轮船的表演,测试结果必须受到实验修正。这研究为壳模型的反向的设计建议一个方法。比作一个几何上类似的壳模型,修改模型产生的 wake 地接近一艘实际轮船的。一非 -- 轮船和海洋工程(KRISO ) s 容器轮船(KCS ) 的一个朝鲜研究院的几何上类似的模型被设计。数字模拟用这个模型被执行,并且它的结果与照原尺寸的计算结果相比。由非几何上类似的模型得到照原尺寸的轮船的 wake 领域的变丑方法成功地被用于 KCS。展开更多
降低风电场出力波动性有利于促进电网友好运行,而尾流优化控制是降低整场出力波动的重要措施。现有尾流优化控制大都基于稳态模型,却忽略尾流动态迟延特性。但尾流迟延在风速不确定性基础上会进一步增加风电场出力的波动性。为此,该文...降低风电场出力波动性有利于促进电网友好运行,而尾流优化控制是降低整场出力波动的重要措施。现有尾流优化控制大都基于稳态模型,却忽略尾流动态迟延特性。但尾流迟延在风速不确定性基础上会进一步增加风电场出力的波动性。为此,该文基于稳态尾流模型辅以迟延计算,构建风电场准稳态尾流模型以同时兼顾尾流干涉作用与动态迟延特性。在此基础上,提出一种考虑迟延的模型预测平稳控制方法(predictive control considering delay,MPC-D),以指令跟踪与功率波动最小为目标协调各机组出力。最后,在WFSim上构建含33台机组的风电场仿真模型,并基于此分析尾流迟延对风电机组以及整场运行性能影响。结果表明,所建准稳态尾流模型能同时模拟尾流速度损失、机组功率迟延和整场功率阶梯变化等特性。并且由MPC-D所得整场出力较基于稳态模型的控制方法平均相对误差、均方根误差以及滑动均方根误差均得到改善,同时能防止机组桨距角频繁动作。展开更多
基金Supported by the Key R&D Program of Shandong Province,China(No.2023ZLYS01)the National Key R&D Program of China(No.2022YFC3104200)+2 种基金the National Natural Science Foundation of China(No.12302301)the China Postdoctoral Science Foundation(No.2023M742229)the Zhejiang Provincial Natural Science Foundation(ZJNSF)(No.LQ22F030002)。
文摘Duo to fluctuations in atmospheric turbulence and yaw control strategies,wind turbines are often in a yaw state.To predict the far wake velocity field of wind turbines quickly and accurately,a wake velocity model was derived based on the method of momentum conservation considering the wake steering of the wind turbine under yaw conditions.To consider the shear effect of the vertical incoming wind direction,a two-dimensional Gaussian distribution function was introduced to model the velocity loss at different axial positions in the far wake region based on the assumption of nonlinear wake expansion.This work also developed a“prediction-correction”method to solve the wake velocity field,and the accuracy of the model results was verified in wake experiments on the Garrad Hassan wind turbine.Moreover,a 33-kW two-blade horizontal axis wind turbine was simulated using this method,and the results were compared with the classical wake model under the same parameters and the computational fluid dynamics(CFD)simulation results.The results show that the nonlinear wake model well reflected the influence of incoming flow shear and yaw wake steering in the wake velocity field.Finally,computation of the wake flow for the Horns Rev offshore wind farm with 80 wind turbines showed an error within 8%compared to the experimental values.The established wake model is less computationally intensive than other methods,has a faster calculation speed,and can be used for engineering calculations of the wake velocity in the far wakefield of wind turbines.
文摘A modified wake model was proposed for the newly developed bubble-induced three-phase inverse fluidized bed(BIFB),by combining the generalized wake model and the gas-perturbed liquid model.On the basis of the modified wake model,the solids and liquid holdups and the complete fluidization gas velocity in BIFB system have been successfully predicted with two established correlations.The predictions achieved very good agreements with the experimental data.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51379144,51479135 and51679167)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621092)
文摘It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations(VIV) of cylinders. In this paper, a novel in-line(IL) and cross-flow(CF) coupling VIV prediction model for circular cylinders has been proposed, in which the influence of the Reynolds number was comprehensively considered. The Strouhal number linked with the vortex shedding frequency was calculated through a function of the Reynolds number. The coefficient of the mean drag force was fitted as a new piecewise function of the Reynolds number, and its amplification resulted from the CF VIV was also taken into account. The oscillating drag and lift forces were modelled with classical van der Pol wake oscillators and their empirical parameters were determined based on the lock-in boundaries and the peak-amplitude formulas. A new peak-amplitude formula for the IL VIV was developed under the resonance condition with respect to the mass-damping ratio and the Reynolds number. When compared with the results from the experiments and some other prediction models, the present model could give good estimations on the vibration amplitudes and frequencies of the VIV both for elastically-mounted rigid and long flexible cylinders. The present model considering the influence of the Reynolds number could generally provide better results than that neglecting the effect of the Reynolds number.
基金State Key Development Program for Basic Research of China (No.2006CB200305), the National Natural Sci-ence Foundation of China (No.50376004), and Ph.D. Program Foundation of Ministry of Education of China (No.20030007028).
基金Project supported by the National Basic Research Program of China(No.2014CB046201)the National Natural Science Foundation of China(Nos.51766009,51566011,and 51479114)
文摘Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory, where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial (central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found, and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade, is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.
基金funded jointly by the National Basic Research Program of China(″973″Program)(No2014CB046200)the Natural Science Foundation of Jiangsu Province(BK2014059)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘With the assumption of the Park model that the wake region is in linear expansion and the cross-wind is in multinomial and Gaussian distribution in wake region,one develops the Park-polynomial model and the ParkGaussian model to numerically simulate the wake flow field for a single wind turbine.Compared with the measured data of wind farm and the wind tunnel test,it shows that the prediction precision of wake field has been improved obviously under the modified initial wake radius.Moreover,both of the newly modified two models could well simulate the wind velocity in wake region,because the predicted results is approximately consistent with the test result,and the cross-wind distribution conforms to that of the real flow field.The two models have still inherited many advantages of engineering models,such as simple form,easy-to-code,and high computational efficiency.Particularly,the Park-Gaussian model is the best in overall performance among them.
基金funded by the National Natural Science Foundation of China (Grant Nos. 62173277 and 61573286)the Natural Science Foundation of Shaanxi Province (Grant No. 2022JM-011)+1 种基金the Aeronautical Science Foundation of China (Grant No. 201905053004)the Shaanxi Province Key Laboratory of Flight Control and Simulation Technology。
文摘A tight formation of unmanned aerial vehicles(UAVs) has many advantages, such as fuel saving and deceiving enemy radar during battlefield entry. As a result, research on UAVs in close formation has received much attention, and the controller design for formation holding has become a popular research topic in the control field. However, there are many unknown disturbances in tight formation, and the tail aircraft is disturbed by the wake. This paper establishes a mathematical model of wake vortices for tail aircraft that considers uncertainty and strong interference. Two UAVs are simulated by Computational Fluid Dynamics software, followed by the design of a semiphysical simulation model predictive control(MPC) scheme that suppresses uncertainty and interference sufficiently to enable the tail aircraft to accurately track the lead aircraft and maintain a stable, tight formation. The tight formation controller is verified by numerical simulation and semiphysical simulation. The results show that the designed controller has an excellent control effect in the case of disturbance caused by the wake vortex.
文摘Wind tunnel measurements using particle image velocimetry have been performed around two perforated discs, with varying streamwise distance, in order to simulate the wake interaction between wind turbines. The static pressure footprint (p-f) on ground level associated with the wake behind the disc and wake velocity data for both the streamwise and wall-normal velocity components with the corresponding turbulence intensities are reported. The p-f method shows that the size of the wake regions, behind the wind turbine models, initially drop when a second disc is placed just downstream of the first one. From a mutual distance (Δ χ) of about five disc diameters (5D), both wake footprints increase as the mutual distance is increased, and for very large mutual distances, approximately Δ χ/ D > 15, the footprint of the downstream disc has recovered and is about the same as for a single disc. At last we conclude that despite very different inlet conditions to the discs, with about 50% of reduced velocity on the centre line upstream of the second disc and an increase of the maximum streamwise fluctuations by 90%, the mean velocities in the wake are proven to scale with the hub height velocity.
基金the National Natural Science Foundation of China,the Fundamental Research Funds for the Central Universities,the Specialized Research Fund for the Doctoral Program of Higher Education
文摘规模效果导致在模型规模和实际轮船的 wake 地之间的大差异,并且在在预言实际轮船的表演的成穴性能和令人激动的力量测试引起差别。因此,从轮船模型的测试数据是什么时候,直接使用了预言实际轮船的表演,测试结果必须受到实验修正。这研究为壳模型的反向的设计建议一个方法。比作一个几何上类似的壳模型,修改模型产生的 wake 地接近一艘实际轮船的。一非 -- 轮船和海洋工程(KRISO ) s 容器轮船(KCS ) 的一个朝鲜研究院的几何上类似的模型被设计。数字模拟用这个模型被执行,并且它的结果与照原尺寸的计算结果相比。由非几何上类似的模型得到照原尺寸的轮船的 wake 领域的变丑方法成功地被用于 KCS。
文摘降低风电场出力波动性有利于促进电网友好运行,而尾流优化控制是降低整场出力波动的重要措施。现有尾流优化控制大都基于稳态模型,却忽略尾流动态迟延特性。但尾流迟延在风速不确定性基础上会进一步增加风电场出力的波动性。为此,该文基于稳态尾流模型辅以迟延计算,构建风电场准稳态尾流模型以同时兼顾尾流干涉作用与动态迟延特性。在此基础上,提出一种考虑迟延的模型预测平稳控制方法(predictive control considering delay,MPC-D),以指令跟踪与功率波动最小为目标协调各机组出力。最后,在WFSim上构建含33台机组的风电场仿真模型,并基于此分析尾流迟延对风电机组以及整场运行性能影响。结果表明,所建准稳态尾流模型能同时模拟尾流速度损失、机组功率迟延和整场功率阶梯变化等特性。并且由MPC-D所得整场出力较基于稳态模型的控制方法平均相对误差、均方根误差以及滑动均方根误差均得到改善,同时能防止机组桨距角频繁动作。