风力机二维翼型Gurney襟翼增升的数值模拟

采用了以湍流模型为基础的SST(Sherr Stress Transport)模型进行数值计算,分析了翼型添加Gurney襟翼时的气动特性.选用了在风力机中应用较多的NACA63-215翼型,通过数值计算表明:在风力机翼型上添加Gurney襟翼,能够提高翼型的有效升力系数,襟翼高度越大,升力系数越大,阻力系数也相应越大.     

低雷诺数条件下马格努斯翼型气动性能数值分析与优化研究

以马格努斯翼型为研究对象,采用数值分析方法,研究低雷诺数条件下马格努斯效应关键参数(周速比、间隙、半径及位置)对翼型边界层流动及升阻性能的影响规律;基于拉丁超立方和Kriging模型,建立周速比、半径、间隙和位置多因素与翼型升阻特性的隐型非线性耦合响应关系模型,量化马格努斯效应影响;采用遗传算法全局寻优获得优化马格努斯...     

低雷诺数下翼型绕流的格子Boltzmann方法数值模拟

文章采用混合格子Boltzmann方法模拟NACA0012翼型流场分离,该方法是将标准格子Boltzmann方法与非结构化有限体积方程相结合的一种方法。首先,分析不同网格分辨率下的计算精度;然后,分析了在雷诺数等于103的情况下不同攻角下翼型的气动特性;最后,计算了不同雷诺数下攻角为0°时的翼型流场。结果证明,混合格子Boltzmann方法在固体壁面有较高的计算精度,可以准确地评估翼型绕流流场。     

低雷诺数翼型的气动外形优化设计

在雷诺数Re=3×10^5条件下,利用遗传算法对翼型S826进行了气动外形优化设计。优化过程中,为了防止尾缘厚度太小,缩小了影响尾缘厚度参数的变化范围,降低了局部的优化幅度。结果显示,优化后的翼型,最佳升阻比提升了约9.9%,气动性有了明显的改善,且优化翼型尾缘厚度基本没有变薄,保证了工程的实用性,说明了利用遗传算法进行低雷诺数翼型气动外形优化的可行性。     

具有低湍流度的VAWT系列翼型正向设计方法

文章选取了NACA0012,NACA2412及NACA23012等传统航空通用翼型,分析比较了在不同叶尖速比下各翼型的湍动能、湍流耗散速率、湍流粘度等湍流特性指标。当翼型弦线与流线重合时,沿流线的弦线能有效地抑制湍流的形成,使翼型对周围气流的扰动最小。并以此为思路,通过正向设计的方法,结合儒可夫斯基转换和特雷夫茨图解法正向设计了一种适用于VAWT的低湍流度系列新翼型。在数值仿真方面,选用k-ω标准湍流模型,采用稳态分析和面积分计算的方法,计算了各翼型在弧形计算域内的湍流特性,发现新翼型在湍流特性方面具有明显的优势,同时也验证了设计原理及方法的合理性。     

低雷诺数下NACA64-418翼型的流动分离研究

通过粒子图像测速（PIV）技术,在低速风洞中研究了0°~15°攻角和雷诺数分别为1.54×105、2.57×105和3.59×105下NACA64-418翼型的压力性能,并基于γ-Reθ转捩模型分析了翼型表面的流动分离及涡脱落情况。 研究表明:NACA64-418翼型具有较大的失速攻角,PIV结果的时均流场和瞬时流场表明,NACA64-418翼型具有较大的失速攻角,随着雷诺数的增加,失速攻角变小;从翼型壁面回流区可以看出γ－Reθ转捩模型可以准确评估翼型表面从层流到湍流流动的变化;数值结果与实验结果进行比较,验证了γ－Reθ转捩模型的预测是准确的。     

翼型失速及雷诺数变化对风力机气动性能影响的数值研究

利用数值模拟的方法,研究了翼犁失速及风速变化引起的雷诺数改变对风力机气动性能的影响.数值计算将k-ω的SST湍流模型与单方程的SA模型结合使用,以模拟大攻角范围的翼型绕流.结果显示:随攻角增大,上翼面分离会依次经历尾缘分离涡与前后缘交替脱落分离涡两个阶段,后者依据分离涡对下翼面压力分布有无影响又呈现两种不同情况,使得不同攻角范围失速时的流场形态及对气动性能的影响存在很大差异;雷诺数变化主要影响上翼面前后缘出现交替脱落分离涡时的攻角区域,且雷诺数越大,其变化引起的升阻系数变化越小.     

低雷诺数下凹坑结构对翼型层流分离影响的数值研究

在低雷诺数Re工况下,翼型表面容易发生流动分离,形成的层流分离泡会导致翼型气动性能恶化,且分离泡在尾缘周期性脱落,会诱发振动,影响叶片的结构安全.文章以NACA4415翼型为例,采用大涡模拟(LES)方法,在低Re下,对光滑翼型及布置凹坑结构翼型的层流分离进行了研究.研究结果表明:凹坑结构对翼型在低Re下出现的层流分离...     

有弯度翼型垂直轴风力机的数值模拟研究

应用计算流体动力学有限体积法SIMPLE算法,配合SST k-ω湍流模型和滑动网格技术模拟分析了有弯度翼型4叶片垂直轴风力机的气动特性,以其作为有弯度翼型垂直轴风力机设计的参考依据。研究结果发现,在入口流速为10 m/s,尖速比为1.6时,该种风力机单个叶片的瞬时力矩系数为-0.03～0.18,并且在一个转动周期内正的瞬时力矩系数历时较长;整个风轮的的力矩系数在尖速比为1.6左右时达到最大值,功率系数在尖速比为1.7左右时达到最大值。     

尾缘加厚翼型的三维旋转特性研究

采用计算流体动力学(CFD)方法对MEXICO试验风力机叶片不同部位翼型在旋转状态下的升阻力系数进行计算,并与试验数据进行比较分析,验证了CFD方法能够准确预测翼型在旋转状态下的升阻力系数。通过采用尾缘对称加厚到5%翼型弦长的DU 97-W-300-05翼型和对应的尾缘未加厚的DU 97-W-300翼型设计,得到沿叶片径向具有相同弦长的风力机叶片,并采用CFD方法对该叶片在旋转状态下的气动特性进行计算。结果表明:在旋转状态下,当攻角小于15°时,尾缘加厚翼型的升力系数比相对应的尾缘未加厚翼型大10%左右;尾缘加厚翼型在旋转状态下的粗糙度敏感性好于相对应的尾缘未加厚翼型;随半径增大,尾缘加厚翼型和对应的尾缘未加厚翼型的升力系数都增大,但失速提前,尾缘加厚翼型升力系数增大得更明显。     

Numerical/experimental investigations on reducing drag penalty of passive vortex generators on a NACA 4415 airfoil

A study emphasizing the effects of passive vortex generators (VGs) on aerodynamic characteristics of a NACA 4415 airfoil is presented. Both experimental and numerical works have been carried out on an array of VGs attached to a NACA 4415 airfoil. Lift and drag measurements are made at various angles of attack by using three‐axis component balance system. On the numerical side, Reynolds‐averaged Navier‐Stokes (RANS) equations have been solved with ANSYS FLUENT 14.5 commercial code with fully structured mesh and three turbulence models (realizable k‐ε, k‐ω shear stress transport [SST] and the Spalart‐Allmaras model) at Reynolds number Re = 2 × 10⁵. Parametric studies have been conducted to find out optimal configurations with respect to span‐wise separation distance between VGs, along with their location along the chord. A very good agreement has been obtained between experimental and computational results indicating that this optimized configuration is robust for the considered parameters. It turns out that increasing the span‐wise separation length increases the aerodynamic performances (lift‐to‐drag ratio) at low attack angles for which low parasitic drag is achieved but conversely degrades it at higher ones. For the stream‐wise location along the chord, upstream position of VGs degrades the lift‐to‐drag ratio at low attack angles and conversely improves it at higher ones.     

Vibrational nonequilibrium stagnation shock layers at hypersonic speed and low reynolds number

The flow field near the stagnation streamline of a plane or axisymmetric blunt body is studied in the merged layer regime using the continuum approach. At the body surface the velocity slip and the jump of the translational and rotational temperature as well as that of the vibrational temperature are taken into account. The influence of the vibrational relaxation is discussed. Especially the wall temperature of an insulated body can be lowered considerably. Results are obtained not only for free flight conditions but also for wind tunnel tests. The latter agree with experimental results of other authors.     

低雷诺数振荡翼型非定常气动性能研究

应用包括非定常Hess-Smitll线元奇点法和二维非定常逆边界层法等边界层迭代法,结合Cebeci-Smith代数涡粘性公式,在低霄诺数条件下计算了水平轴风力机叶片翼型在俯仰,平移,斜坡式3种不同振荡形式下的非定常气动性能;计算和分析了在各自振荡形式下不同参数对翼型气动性能的影响.研究结果表明:翼型俯仰振荡时,翼型上的升力系数和阻力系数与振荡的幅值和频率有很大的关系;翼型平移振荡和斜坡式振荡时,气动力系数和振荡频率有关;俯仰和平移振荡时,都出现了负阻力,揭示了扑动翼产生推力的原因.     

The effect of non-equilibrium condensation on the drag coefficient in a transonic airfoil flow

In this study,a transonic flow past NACA0012 profile at angle of attack α=00 whose aspect ratio AR is 1.0 with non-equilibrium condensation is analyzed by numerical analysis using a TVD scheme and is investigated using an intermittent indraft type supersonic wind tunnel.Transonic flows of 0.78-0.90 in free stream Mach number with the variations of the stagnation relative humidity(Φ0)are tested.For the same free stream Mach number,the increase in Φ0 causes decrease in the drag coefficient of profile which is composed of the drag components of form,viscous and wave.In the case of the same M∞ and T0,for more than Φ0=30%,despite the irreversibility of process in non-equilibrium condensation,the drag by shock wave decreases considerably with the increase of Φ0.On the other hand,it shows that the effect of condensation on the drag coefficients of form and viscous is negligible.As an example,the decreasing rate in the drag coefficient of profile caused by the influence of non-equilibrium condensation for the case of M∞=0.9 and Φ0=50% amounts to 34%.Also,it were turned out that the size of supersonic bubble(that is,the maximum height of supersonic zone)and the deviation of pressure coefficient from the value for M=1 decrease with the increase of Φ0 for the same M∞.     

Turbulence intensity and time-mean velocity distributions in low reynolds number turbulent pipe flows

Measurements of the cross-sectional distributions of axial turbulence intensity and time-mean velocity in hydrodynamically developed pipe flows were made by means of a hot-film anemometer. The investigation was concerned with the low Reynolds number turbulent regime, and experiments were performed for five Reynolds numbers between 3200 and 24 000. Air was the working fluid. The present measurements, taken together with those of Laufer for high Reynolds number pipe flows (up to 500 000). establish that in the near-wall region characterized by y⁺ up to 25, the ratio of turbulence intensity to friction velocity is independent of Reynolds number. This same relative turbulence intensity is also independent of the Reynolds number in the neighborhood of the pipe centerline. The measured time-mean velocity distributions deviate more and more from the universal u⁺, y⁺ profile with decreasing Reynolds number below 10000. which corroborates the findings of previous investigations.