A nonlinear wake model of a wind turbine considering the yaw wake steering

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.

Assessment of scale interactions associated with wake meandering using bispectral analysis methodologies

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.

Wake Effects on A Hybrid Semi-Submersible Floating Wind Farm with Multiple Hub Heights

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.

Three-dimensional dynamics of a single bubble rising near a vertical wall:Paths and wakes

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.

Linear logistic regression with weight thresholding for flow regime classification of a stratified wake

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.

Excitation and power spectrum analysis of electromagnetic radiation for the plasma wake of reentry vehicles

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.

On the structure of the turbulent/non-turbulent interface in a fully developed spatially evolving axisymmetric wake

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.

基于LSTM-POD的汽车湍流尾迹的高时间分辨速度场重构

本文针对方背Ahmed汽车标模的湍流尾迹,建立基于长短时记忆法(long short-term memory,LSTM)和本征正交分解(proper orthogonal decomposition, POD)相结合的深度学习模型LSTM-POD。通过建立非时间分辨平面速度场POD模态系数和若干离散点的时间分辨速度信号的映射关系,实现了方背Ahmed汽车标模湍流尾迹流场的高时间分辨率重构,并对比了不同时间步长配置,即单时间步长(LSTM-Sin)和多时间步长(LSTM-Mul)对重构效果的影响。研究表明:LSTM-POD模型在时间序列重构中具有较强的学习和泛化能力。另外,LSTM-Mul考虑到了时间上的连续性和相关性,相较于LSTM-Sin,其重构出的低阶模态系数和速度场与POD的重构结果更吻合。本研究提出的深度学习模型可以缓解通过实验及高精度数值模拟获取高时间分辨率流场数据资源消耗大、计算效率低等问题。

高速列车尾车垂向偏置对列车气动性能影响

在长期的高速列车运营过程中,极易形成前后车辆的不同形式偏置,造成列车气动性能改变,甚至可能引发行车平稳性问题,极大影响乘坐舒适性和安全性。以高速列车尾车作为研究对象,探究尾车上下偏置时,高速列车尾部流场变化以及气动特性。基于SST k-ω双方程湍流模型,采用数值仿真方法研究了350 km/h高速列车尾车无偏置、尾车下降20 mm、尾车下降40 mm、尾车下降60 mm、尾车上升20 mm、尾车上升40 mm以及尾车上升60 mm 7种工况下列车的气动性能,分析高速列车气动阻力的变化规律,揭示了不同垂向位移下高速列车尾部流场特性以及列车表面压力分布情况。研究结果表明:高速列车尾部垂向位移对列车整体气动阻力影响较小,但对高速列车气动阻力分布以及流场特性造成一定影响。当尾车偏置位移达到60 mm时,列车车体气动阻力相对于无偏置工况分别降低了-1.11%和2.64%,转向架气动阻力相对无偏置情况下分别降低了11.35%和-17.43%。此外,尾车偏置对列车近尾流区域流场结构有一定影响,尾车鼻锥下方排障器周围漩涡结构由双漩涡结构向单漩涡结构转变;鼻尖处漩涡结构随着尾车高度下降而增大,随着尾车高度上升而逐渐变小。本研究结果丰富了列车尾部偏置情况下的相关研究,对列车检修以及CR450高速列车设计等具有重要指导意义。

基于时间间隔标准的尾流安全评估分析方法

科学地优化飞机间尾流间隔是提升机场吞吐量的重要举措,确保安全是尾流间隔实施的首要前提。首先,基于大涡模拟试验数据,对经典的两阶段消散模型(Wake Two-Stage Decay Model,D2P)模型进行改进,创建顶风对尾涡环量衰减的影响模型。然后,针对基于时间间隔(Time-Based Separation,TBS)未考虑顶风会影响尾涡移动和尾涡环量衰减,通过转化为飞机地速和构建改进D2P模型深刻分析两因素对尾涡遭遇严重度的影响。最后,计算实施TBS时不同风速不同机型组合对应的最小尾流间隔,并综合分析对应间隔的尾涡遭遇严重度。结果表明:虽然TBS未考虑顶风对尾涡移动和环量衰减的影响,但可以确保前后机安全性;在顶风8 m/s应用TBS方案时,各机型组合的尾涡遭遇严重度约为静风时的30%。TBS安全地缩减了顶风时的尾流间隔。

交感神经兴奋性与醒后脑卒中发生发展的相关性研究

目的 分析交感神经兴奋性与醒后脑卒中发生发展的相关性。方法 选取2020年7月至2022年1月我院收治的100例急性脑卒中住院患者,依据是否发生醒后脑卒中将患者分为醒后脑卒中组和非醒后脑卒中组。采用Logistic回归分析交感神经兴奋与醒后脑卒中发生发展的关系。结果 多因素分析显示,血压变异性、心率变异性、血糖变异性、电解质紊乱、25-羟维生素D_(3)、尿香草苦杏仁酸、儿茶酚胺是醒后脑卒中发生发展的危险因素(均P<0.05)。结论 交感神经兴奋性与醒后脑卒中发生发展具有相关性,血压变异性、心率变异性、血糖变异性、电解质紊乱、25-羟维生素D3、尿香草苦杏仁酸、儿茶酚胺是醒后脑卒中发生发展的危险因素。

基于激光雷达探测的飞机尾流融合预测方法

为提高基于激光雷达的飞机尾流探测反演精度,根据扫描出的径向风速数据,建立了基于Kolmogorov结构函数的大气背景湍流耗散率(EDR)估计方法;然后基于两阶段消散预测模型,计入湍流对尾流消散过程的影响,实现基于历史探测数据的尾涡强度环量和涡核运动趋势的预测;通过环境探测数据与预测模型的结合,提高尾涡特性参数的反演精度。研究表明,相较于反演算法,采用本文模型预测的尾涡轨迹在径向距离和角度的精度上分别提高了59.5%、64.8%。

基于等效粗糙度模型的风电场尾流数值模拟方法

随着风电场规模的扩大和密度的增加,风电场整场的尾流效应也日益显著且备受关注。准确评估风电场尾流效应对于风电场的建设和开发具有重要的意义,但目前仍缺乏同时兼顾计算精度和效率的尾流计算方法。本文基于OpenFOAM平台中的雷诺时均方法,实现了风电场等效粗糙度模型和雷诺平均方法的嵌套。结果表明,该方法相较于工程中常用的Jensen尾流模型和尾流叠加模型,计算精度得到了大幅的提高,且因为其对于风电场建模简单,所需计算资源较少,是用在大型风电场的一种工程应用价值较高的下游尾流计算方法。

变弯度导叶铰接位置对风扇振动特性的影响

针对变弯度导叶尾迹激励引起的转子叶片共振,基于谐响应模态叠加法对风扇转子进行强迫振动分析,研究了不同铰接位置的变弯度导叶对风扇气动性能及其振动特性的影响。结果表明,随着铰接位置向尾缘移动,风扇转子流量、压比和效率增加,稳定裕度降低,主要影响下游转子叶根部位的进气角度。在气动激励方面,随着铰接位置后移,转子叶片表面的压力幅值增大,相位变化剧烈,通过将非定常气动力转换到模态空间中,可以看到叶片所受模态气动力在铰接位置为35%C (C为轴向弦长)的情况下达到最大值,后呈现先减小后增加的规律,这与振动响应的变化规律一致。铰接位置对所关注的高阶局部模态的气动阻尼影响较小,最大差异为0.046%。在振动响应方面,转子叶片的振动应力随铰接位置剧烈改变,且为非单调变化。在设计位置处叶片的振动应力最小,在35%C处振动应力达到设计位置的15倍。对于本文所研究的模型及工况,最优铰接位置为45%C,与仅考虑气动性能的25%C不同。因此在变弯度导叶设计时,需要考虑其对叶片振动特性的影响。

基于雷达探测数据的尾涡危险区评估

针对尾涡危险区域的研究可以有效避免后机尾涡危险遭遇事件的发生,提出了一种基于激光雷达探测数据的尾涡危险区计算方法。根据雷达实测数据反演飞机尾涡的演化轨迹和速度环量;基于后机遭遇前机尾涡的空气动力学响应构建滚转力矩系数模型;考虑尾涡在实际场景下的演化情况,结合反演得到的尾涡特征参数,计算飞机遭遇尾涡时的滚转力矩并计算尾涡危险区。结果表明:基于激光雷达探测数据反演尾涡特征参数,左涡和右涡的位置、环量并不一致,据此结合滚转力矩系数模型计算得到的整体危险区域也具有不对称性,当单涡更稳定时,对应的危险区域也更大。以B738为后机,选取某一尾涡探测片段验证,对于涡心坐标位置为左涡(390 m,8.61°),右涡(435 m,8.85°)的尾涡,左涡、右涡的环量分别为256.83 m^(2)/s和223.35 m^(2)/s,左涡相对右涡实际划设的危险区覆盖范围更大,因此后机与前机左右尾涡的安全阈值区域不同,可据此对横向间隔做出不同调整,因此所提方法有利于为分析后机遭遇安全性、缩短尾流间隔提出重要参考。

火箭弹尾流冲击效应研究

以火箭弹尾流场及发射平台为研究对象,基于计算流体动力学方法,采用有限体积法进行数值离散,建立火箭弹尾焰燃气流场数学物理模型进行计算。分析火箭弹尾焰射流与发射平台的相互作用,探究燃气流场速度、温度和压力等参数分布特性,并研究发射过程中尾焰燃气流对发射平台的冲击效应,得到发射平台关注区域表面压力、温度变化规律。之后对不同材料表面进行数值模拟及实验模拟对比,研究结果表明由钢材料替换铝材料后,钢材料表面温度低于熔点,可减小温度对平台的影响,为火箭弹发射平台防护及优化提供了理论依据。

不同前倾角度倾转旋翼噪声数值计算分析

基于自由尾迹结合FW-H(Ffowcs Williams-Hawkings)方程的方法建立了倾转旋翼气动噪声计算模型,并采用倾转旋翼模型噪声试验数据验证了计算分析方法的有效性。选取典型过渡路径,进行考虑配平的倾转双旋翼气动噪声特性计算,获得了旋翼桨叶剖面非定常气动载荷以及不同测点气动噪声等计算结果,分析了倾转旋翼在不同前倾角下噪声指向性和噪声声压级的变化。结果表明:由于双旋翼噪声在传播中的叠加和抵消,倾转双旋翼和孤立单旋翼的噪声指向特性存在较大的不同;倾转旋翼噪声随前倾角增加总体上呈现先增加后减小的变化趋势,在前倾角30°附近噪声最强;不同前倾角下噪声声压级和指向性的变化与旋翼桨尖马赫数、气动载荷和桨盘角度等多种因素相关。

垂直错列布局风力机群尾流特征研究

风力机尾流对风电场的输出功率有着重要影响,为深入研究增设小风力机对风电场整体出力的影响,采用OpenFOAM模拟2个大风力机和2个大风力机之间横向布置的3个小风力机的组合,并以小风力机与下游大风力机之间距离不同的4种工况和其中1种工况下小风力机高度不同为研究对象。该布局在2个大风力机之间增加3个小风力机,每排小风力机与下游大风力机的距离不同。结果表明:经距离不同和高度不同的计算对比,当小风力机高度设置为37 m时,随着与上游大风力机距离的增大,下游大风力机功率逐渐增加;当小风力机距离下游大风力机位置固定,增加小风力机轮毂高度则使得下游大风力机功率降低。

纳布啡对行切痂植皮术烧伤患者氧化应激及全麻苏醒期躁动的影响

目的:探究纳布啡对烧伤患者行切痂植皮术后全麻苏醒期躁动及氧化应激反应的影响。方法:选取2021年3月-2022年3月我院收治并行切痂植皮术的烧伤患者72例,采用随机数字法分为纳布啡组(n=36)和对照组(n=36)。纳布啡组患者在全身麻醉诱导前10 min静脉注射0.20 mg/kg纳布啡,对照组给予等量生理盐水,比较两组躁动发生率,拔管前(T1)、拔管即刻(T2)、拔管后10 min(T3)、拔管后30 min(T4)的Richmond躁动-镇静评分(RASS)、Ramsay镇静评分,以及术前术后的氧化应激反应和苏醒时间,比较两组恶心呕吐、呼吸抑制、嗜睡、眩晕等不良反应发生情况。结果:与对照组比较,纳布啡组躁动发生率更低,T3、T4时RASS评分均降低,T1、T4时Ramsay镇静评分升高(P <0.05);两组患者术前术后丙二醛(MDA)、脂质过氧化物(LPO)明显下降,超氧化物歧化酶(SOD)明显升高。术后苏醒期,纳布啡组SOD均高于对照组,MDA、LPO低于对照组(P <0.05);两组苏醒时间、恶心呕吐、呼吸抑制、嗜睡、眩晕的不良反应发生率,无统计学差异(P>0.05)。结论:采用纳布啡对行切痂植皮术的烧伤患者有较理想的镇静效果,降低患者全麻苏醒期的躁动,减轻氧化应激反应,且不影响麻醉苏醒时间及不良反应发生率。

基于中低分辨率卫星影像中舰船目标识别方法

目前,中低分辨率成像侦察卫星已经成为远距离情报保障的重要手段之一。然而,中低分辨率成像侦察卫星对海上机动舰船的侦察存在目标检测、识别难等问题,大大影响了情报使用效益。针对上述问题,提出基于霍夫变换的舰船开尔文尾迹提取方法,用于匹配并识别舰船型号。通过仿真得出不同型号舰船的开尔文尾迹尖头波平均距离,可以有效的识别出真实遥感影像中舰船属性,与实际影像数据对比分析,证明上述算法具有一定可行性。因此,基于霍夫变换的舰船开尔文尾迹提取方法可以在一定条件下基本实现目标舰船型号的识别,提升中低分辨率成像侦察卫星对海上机动舰船目标的识别准确率。