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
Large atmospheric boundary layer fluctuations and smaller turbine-scale vorticity dynamics are separately hypothesized to initiate the wind turbine wake meandering phenomenon,a coherent,dynamic,turbine-scale oscillati...Large atmospheric boundary layer fluctuations and smaller turbine-scale vorticity dynamics are separately hypothesized to initiate the wind turbine wake meandering phenomenon,a coherent,dynamic,turbine-scale oscillation of the far wake.Triadic interactions,the mechanism of energy transfers between scales,manifest as triples of wavenumbers or frequencies and can be characterized through bispectral analyses.The bispectrum,which correlates the two frequencies to their sum,is calculated by two recently developed multi-dimensional modal decomposition methods:scale-specific energy transfer method and bispectral mode decomposition.Large-eddy simulation of a utility-scale wind turbine in an atmospheric boundary layer with a broad range of large length-scales is used to acquire instantaneous velocity snapshots.The bispectrum from both methods identifies prominent upwind and wake meandering interactions that create a broad range of energy scales including the wake meandering scale.The coherent kinetic energy associated with the interactions shows strong correlation between upwind scales and wake meandering.展开更多
In order to clarify the migration mechanism and wake behavior of a single bubble rising near a vertical wall,three-dimensional direct numerical simulations are implemented based on the open-source soft-ware Basilisk a...In order to clarify the migration mechanism and wake behavior of a single bubble rising near a vertical wall,three-dimensional direct numerical simulations are implemented based on the open-source soft-ware Basilisk and various types of migration paths like linear,zigzag and spiral are investigated.The volume of fluid(VOF)method is used to capture the bubble interface at a small scale,while the gas-liquid interface and high-velocity-gradient regions in the flow field are encrypted with the adaptive mesh refinement technology.The results show that the vertical wall has an obstructive effect on the diffusion of the vortex boundary layer on the surface of the bubble migrating in a straight line,and the resulting reaction force tends to push the bubbles away from the wall surface.For the zigzag or spiral movement of a bubble in the x-y plane,the perpendicular wall is an unstable factor,but on the contrary,the motion in the z-y plane is stabilized.展开更多
A stratified wake has multiple flow regimes,and exhibits different behaviors in these regimes due to the competing physical effects of momentum and buoyancy.This work aims at automated classification of the weakly and...A stratified wake has multiple flow regimes,and exhibits different behaviors in these regimes due to the competing physical effects of momentum and buoyancy.This work aims at automated classification of the weakly and the strongly stratified turbulence regimes based on information available in a full Reynolds stress model.First,we generate a direct numerical simulation database with Reynolds numbers from 10,000 to 50,000 and Froude numbers from 2 to 50.Order(100)independent realizations of temporally evolving wakes are computed to get converged statistics.Second,we train a linear logistic regression classifier with weight thresholding for automated flow regime classification.The classifier is designed to identify the physics critical to classification.Trained against data at one flow condition,the classifier is found to generalize well to other Reynolds and Froude numbers.The results show that the physics governing wake evolution is universal,and that the classifier captures that physics.展开更多
The plasma wake of reentry vehicles has the advantages of extensive space range and long traceability,which provides new possibilities for the detection and monitoring of reentry vehicles.Based on the Zakharov model,t...The plasma wake of reentry vehicles has the advantages of extensive space range and long traceability,which provides new possibilities for the detection and monitoring of reentry vehicles.Based on the Zakharov model,this work investigates the excitation and power spectrum characteristics of electromagnetic radiation for the plasma wake of a typical reentry vehicle.With the aid of parametric decay instability,the excitation condition of electromagnetic radiation for a typical plasma wake is evaluated first.The power spectrum characteristics of electromagnetic radiation,including the effects of both the flight parameters and incident wave parameters are analyzed in detail.The results show that when the phenomenon of excited electromagnetic radiation occurs,plasma wakes closer to the bottom of the vehicle and with faster speeds require higher incident frequencies and thresholds of the electric field.As the frequency of the incident wave increases,peaks appear in the power spectra of plasma wakes,and their magnitudes increase gradually.The frequency shifts of the secondary peaks are equal,whereas,the peaks of the downshifted spectral lines are generally larger than those of the upshifted spectral lines.The work in this paper provides a new idea and method for the tracking of reentry vehicles,which has potential application value in the field of reentry vehicle detection.展开更多
In this work,we numerically study the structure of the turbulent/nonturbulent(T/NT)interface in a fully developed spatially evolving axisymmetric wake by means of direct numerical simulations.There is a continuous and...In this work,we numerically study the structure of the turbulent/nonturbulent(T/NT)interface in a fully developed spatially evolving axisymmetric wake by means of direct numerical simulations.There is a continuous and contorted pure shear layer(PSL)adjacent to the outer edge of the T/NT interface.The local thickness of the PSLδ_(PSL)exhibits a wide range of scales(from the Kolmogorov scale to the Taylor microscale)and the conditional mean thickness<δ_(PSL)>I/η_(c)≈6 withη_(c)being the centerline Kolmogorov scale is the same as the viscous superlayer.In the viscous superlayer,the pure shear motions without rotation are overwhelmingly dominant.It is also demonstrated that the physics of the turbulent sublayer is closely related to the PSL with a large thickness.Another significant finding is that the time averaged area of the rotational regionA R,and the pure shear region<A_(S)>at different streamwise locations scale with the square of the wake-width b_(U)^(2).This study opens an avenue for a better understanding of the structures of the T/NT interface.展开更多
Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind...Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind turbines(FWT).Some researchers find that wind farms with multiple hub heights could increase the annual energy production(AEP),while previous studies also indicate that wake meandering could increase fatigue loading. This study investigates the wake interaction within a hybrid floating wind farm with multiple hub heights. In this study, FAST.Farm is employed to simulate a hybrid wind farm which consists of four semi-submersible FWTs(5MW and 15MW) with two different hub heights. Three typical wind speeds(below-rated, rated, and over-rated) are considered in this paper to investigate the wake meandering effects on the dynamics of two FWTs. Damage equivalent loads(DEL) of the turbine critical components are computed and analyzed for several arrangements determined by the different spacing of the four turbines. The result shows that the dynamic wake meandering significantly affects downstream turbines’ global loadings and load effects. Differences in DEL show that blade-root flapwise bending moments and mooring fairlead tensions are sensitive to the spacing of the turbines.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.
基金supported by the National Science Foundation(Grant No.21-36371)supported by the National Science Foundation(Grant Nos.21-38259,21-38286,21-38307,21-37603,and 21-38296)。
文摘Large atmospheric boundary layer fluctuations and smaller turbine-scale vorticity dynamics are separately hypothesized to initiate the wind turbine wake meandering phenomenon,a coherent,dynamic,turbine-scale oscillation of the far wake.Triadic interactions,the mechanism of energy transfers between scales,manifest as triples of wavenumbers or frequencies and can be characterized through bispectral analyses.The bispectrum,which correlates the two frequencies to their sum,is calculated by two recently developed multi-dimensional modal decomposition methods:scale-specific energy transfer method and bispectral mode decomposition.Large-eddy simulation of a utility-scale wind turbine in an atmospheric boundary layer with a broad range of large length-scales is used to acquire instantaneous velocity snapshots.The bispectrum from both methods identifies prominent upwind and wake meandering interactions that create a broad range of energy scales including the wake meandering scale.The coherent kinetic energy associated with the interactions shows strong correlation between upwind scales and wake meandering.
基金supported by the National Natural Science Foundation of China(Grant No.51906262)the Hunan Provincial Natural Science Foundation of China(Grant No.2020JJ5735).
文摘In order to clarify the migration mechanism and wake behavior of a single bubble rising near a vertical wall,three-dimensional direct numerical simulations are implemented based on the open-source soft-ware Basilisk and various types of migration paths like linear,zigzag and spiral are investigated.The volume of fluid(VOF)method is used to capture the bubble interface at a small scale,while the gas-liquid interface and high-velocity-gradient regions in the flow field are encrypted with the adaptive mesh refinement technology.The results show that the vertical wall has an obstructive effect on the diffusion of the vortex boundary layer on the surface of the bubble migrating in a straight line,and the resulting reaction force tends to push the bubbles away from the wall surface.For the zigzag or spiral movement of a bubble in the x-y plane,the perpendicular wall is an unstable factor,but on the contrary,the motion in the z-y plane is stabilized.
基金This work is supported by ONR,contract N000142012315.
文摘A stratified wake has multiple flow regimes,and exhibits different behaviors in these regimes due to the competing physical effects of momentum and buoyancy.This work aims at automated classification of the weakly and the strongly stratified turbulence regimes based on information available in a full Reynolds stress model.First,we generate a direct numerical simulation database with Reynolds numbers from 10,000 to 50,000 and Froude numbers from 2 to 50.Order(100)independent realizations of temporally evolving wakes are computed to get converged statistics.Second,we train a linear logistic regression classifier with weight thresholding for automated flow regime classification.The classifier is designed to identify the physics critical to classification.Trained against data at one flow condition,the classifier is found to generalize well to other Reynolds and Froude numbers.The results show that the physics governing wake evolution is universal,and that the classifier captures that physics.
基金supported by National Natural Science Foundation of China(Nos.62171355,61875156)the 111Project(No.B17035)+1 种基金the Natural Science Basic Research Program of Shaanxi Province(No.2021JM-135)the Stable Support Project of Basic Scientific Research Institutes(Nos.A131901W14,A132001W12)。
文摘The plasma wake of reentry vehicles has the advantages of extensive space range and long traceability,which provides new possibilities for the detection and monitoring of reentry vehicles.Based on the Zakharov model,this work investigates the excitation and power spectrum characteristics of electromagnetic radiation for the plasma wake of a typical reentry vehicle.With the aid of parametric decay instability,the excitation condition of electromagnetic radiation for a typical plasma wake is evaluated first.The power spectrum characteristics of electromagnetic radiation,including the effects of both the flight parameters and incident wave parameters are analyzed in detail.The results show that when the phenomenon of excited electromagnetic radiation occurs,plasma wakes closer to the bottom of the vehicle and with faster speeds require higher incident frequencies and thresholds of the electric field.As the frequency of the incident wave increases,peaks appear in the power spectra of plasma wakes,and their magnitudes increase gradually.The frequency shifts of the secondary peaks are equal,whereas,the peaks of the downshifted spectral lines are generally larger than those of the upshifted spectral lines.The work in this paper provides a new idea and method for the tracking of reentry vehicles,which has potential application value in the field of reentry vehicle detection.
基金This work was supported by the National Natural Sci-ence Foundation of China(No.91952105)the Six Tal-ent Peaks Project in Jiangsu Province(No.2019-SZCY-005)the Fundamental Research Funds for Central University(No.30921011212).
文摘In this work,we numerically study the structure of the turbulent/nonturbulent(T/NT)interface in a fully developed spatially evolving axisymmetric wake by means of direct numerical simulations.There is a continuous and contorted pure shear layer(PSL)adjacent to the outer edge of the T/NT interface.The local thickness of the PSLδ_(PSL)exhibits a wide range of scales(from the Kolmogorov scale to the Taylor microscale)and the conditional mean thickness<δ_(PSL)>I/η_(c)≈6 withη_(c)being the centerline Kolmogorov scale is the same as the viscous superlayer.In the viscous superlayer,the pure shear motions without rotation are overwhelmingly dominant.It is also demonstrated that the physics of the turbulent sublayer is closely related to the PSL with a large thickness.Another significant finding is that the time averaged area of the rotational regionA R,and the pure shear region<A_(S)>at different streamwise locations scale with the square of the wake-width b_(U)^(2).This study opens an avenue for a better understanding of the structures of the T/NT interface.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.51909109 and 52101314)the Natural Science Foundation of Jiangsu Province (Grant No.BK20190967)。
文摘Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind turbines(FWT).Some researchers find that wind farms with multiple hub heights could increase the annual energy production(AEP),while previous studies also indicate that wake meandering could increase fatigue loading. This study investigates the wake interaction within a hybrid floating wind farm with multiple hub heights. In this study, FAST.Farm is employed to simulate a hybrid wind farm which consists of four semi-submersible FWTs(5MW and 15MW) with two different hub heights. Three typical wind speeds(below-rated, rated, and over-rated) are considered in this paper to investigate the wake meandering effects on the dynamics of two FWTs. Damage equivalent loads(DEL) of the turbine critical components are computed and analyzed for several arrangements determined by the different spacing of the four turbines. The result shows that the dynamic wake meandering significantly affects downstream turbines’ global loadings and load effects. Differences in DEL show that blade-root flapwise bending moments and mooring fairlead tensions are sensitive to the spacing of the turbines.