跨声速风扇叶片的反扭设计研究

发展适合于叶轮机械风扇叶片反扭设计的流固耦合计算方法,综合考虑气动力和离心力对叶片变形的影响;以设计叶型为目标,预测冷态加工叶型并进行叶片的变形分析,比较变形后叶型和设计叶片的偏差并修正冷态叶型直到迭代收敛.在叶片变形分析中考虑了气动力随叶型变化的非线性作用,在每一时间步同步求解流体运动方程和叶片变形的控制方程并交换边界信息;流体域求解了时间精确的非定常雷诺平均Navier-Stokes方程,以得到每一步由于叶片变形而引起的流场变化;叶片变形则由积分叶片表面受到的气动力并求解结构动动力学方程得到;流体域和固体域的信息交换采用了一种使用投影-形函数插值的新方法.采用该方法对NASA ROTOR67风扇叶片进行反扭设计,得到冷态制造叶型和叶片扭转角随叶高的变化规律.     

气固耦合空气静压导轨气膜非定常流动分析

引入有限体积法,将空气静压导轨受力特性方程与气体流动方程相结合构成耦合方程体系,对导轨润滑气膜等温条件下的非定常流动进行数值分析,研究了气膜建立初期的导轨振动及气膜动刚度特性.结果表明:导轨工作面非定常气动力作用使导轨产生阻尼自激振动;导轨工作面压力、承载力、气膜厚度及气膜刚度随时间变化曲线振动周期相等,承载力与气膜厚度成反比;空气静压导轨刚度研究中应考虑动刚度对导轨特性的影响.     

悬臂梁压电式能量收集器方向性效率的研究

为了研究振动激励方向变化对悬臂梁压电能量收集器(VEH)的电能输出的影响,建立了单悬臂梁能量收集器在任意方向振动激励下的动力学模型以及压电效应的输出模型。振动激励方向根据悬臂梁平面建立的球面坐标系的两个角度参数φ和θ定义,通过理论和仿真分析,发现振动激励方向改变时能量收集器的吸收效率随φ的增加呈余弦变化,随θ的增加呈正弦变化,但φ对收集效率的影响远大于θ的影响。实验表明,θ=0°时,φ从0°增加到90°,吸收效率从理论最高效率的93.52%降低到2.88%,而φ=90°时,θ从0°增加到90°,吸收效率则从2.88%变化到3.88%,得到了悬臂梁能量收集器的输出和激励方向之间的关系,对悬臂梁压电振动能量收集器的设计和研究具有一定的参考价值。     

带迟滞非线性环节二元机翼的气动弹性响应分析

基于Theodorsen非定常气动力理论,采用Roger拟合得到时域气动力表达式;针对二元机翼俯仰自由度带有迟滞非线性环节的情况,采用分段线性方式,建立了二元机翼气动弹性系统无量纲运动方程。通过数值仿真得到了系统极限环振动响应的时间历程和相轨迹,并与带中心间隙型非线性刚度环节二元机翼的气动弹性响应特性进行了比较;结果表明在一定的来流速度下,二元机翼俯仰自由度具有的迟滞特性会导致整个系统的极限环振动;最后用描述函数法给出了迟滞非线性环节的等效刚度及等效阻尼表达式,并进行了具有迟滞非线性环节二元机翼气动弹性系统颤振边界的等效线化分析,与直接数值仿真的计算结果吻合较好。     

船用离心风机内部流动诱发蜗壳振动的数值研究

针对船用离心风机内部非定常流动诱发蜗壳结构振动响应,发展了一种数值计算方法,该方法首先通过风机内部非定常流场计算获得振动激励源,其次采用流固弱耦合算法实现节点的插值和载荷加载,最后基于有限元的模态叠加法得到蜗壳结构动力响应。流场压力脉动和振动计算结果和实验测试结果分别做了对比,结果吻合较好,表明本文的方法能较准确地模拟叶轮机械内部流动诱发外部壳体的振动响应。从流场和振动响应两个方面阐述了流动诱发振动的机理:基频的非定常气动力是流固耦合振动的主要激励源,基频分量在振动的频率响应函数中占据主导地位,蜗壳的最大振动响应是基频下的非定常气动力和基频振动模态共同作用的结果。     

巡飞导弹纵向弹性动态特性分析

为了设计巡飞导弹在弹性振动时的控制器,对其纵向动态特性进行了分析。采用NASTRAN软件计算了结构的固有模态,研究了弹性振动时的附加非定常气动力,采用线性化理论建立了刚体扰动运动方程组,将弹性振动引起的附加非定常气动力作为干扰输入项代入扰动运动方程组。从而得到了弹性振动下的动态响应。响应结果表明,在满足气动与结构稳定的前提下,弹性振动引起的纵向姿态变化量非常微小,对飞行稳定性不造成显著影响。     

倾转变形四旋翼飞行器的设计和实现

针对灾难搜救、军事侦察等应用中的狭窄空间飞行需求,提出一种俯仰姿态可以独立控制的四旋翼飞行器。该飞行器在普通四旋翼飞行器的基础上增加了一个倾转自由度,由一个驱动来独立控制飞行器的俯仰姿态,实现指定倾转角的悬停和飞行。建立了飞行器气动力仿真模型,仿真分析了倾转状态下旋翼间气流干扰对气动力特性的影响。搭建了气动力特性测试平台,通过实验验证了气动力仿真模型的有效性。最后,研制了飞行器原理样机,进行了倾转悬停和倾转飞行实验。研究结果表明,飞行器可以实现接近90°的倾转悬停,同时可以以倾转60°的俯仰姿态稳定飞行,验证了倾转变形四旋翼飞行器穿越狭窄空间的可行性。     

采用非定常涡气动力理论的非线性颤振主动抑制仿真研究

针对带后缘操纵面的二元机翼系统,采用非定常涡气动力理论建立了相应的气动弹性运动方程。对俯仰自由度存在迟滞型非线性刚度环节的情况,以后缘操纵面作为控制面,进行了非线性颤振主动抑制仿真。研究结果表明,对机翼颤振的抑制效果明显,所用非定常涡气动力理论适于进行非线性颤振的主动抑制仿真研究。     

气动升力下磁浮车辆非线性响应研究

磁浮列车在高速运行时受到的气动升力包含定常分量和非定常波动量,而非定常气动升力在某种程度上可以视为周期扰动.建立考虑非线性电磁力的磁浮系统二级悬挂的模型,推导了控制方程.利用增量谐波平衡法求解非线性方程,对考虑定常气动升力和周期性非定常气动升力条件下的磁浮系统非线性响应特性进行分析.开展了线性和非线性模型对比、控制增益参数和气动力系数影响规律分析.结果 表明,采用PD控制器时,周期扰动的气动力会使得车辆振动中心发生偏移,反馈控制参数对振动偏移具有较大影响.     

基于混合子结构法的输电导线风雨激振气动特性

为了探究输电导线风雨激振的诱发机理,基于混合子结构方法对输电导线风雨激振非定常气动力进行了针对性的研究。首先,分别构建结构子结构(输电导线和上雨线)和流体动力计算(computational fluid dynamics,简称CFD)数值流场子结构;其次,利用自制的风洞模拟实验台及相关测试系统,获取结构子结构的振动响应(频率,振幅);最后,将测得振动响应作为CFD数值模拟的边界条件,计算绕流场特性并获取气动力特性参数,将计算得到的气动力施加到输电导线上,得到输电导线的振动响应并与实验结果比较。分析结果表明,混合子结构方法能够准确获得输电导线发生风雨激振时的气动特性,该方法为不便于实验获取气动力特性振动问题研究提供了一种有效途径。     

Experimental study of effects of circular-cross-section riblets on the aerodynamic performance of Risø airfoil at transient flow regime

New drag reduction methods have received much attention due to the importance of drag reduction in airplanes and wind turbines. One of the ways for drag reduction is the use of riblets. We investigated the effects of riblets on the aerodynamic performance of the Risø airfoil quantitatively. By installing a load cell and using the one-sided force measurement method, the drag and lift coefficients of the Risø airfoil were measured in two modes: With and without riblets at three different arrangements. The shape of riblets is a circularcross- section and the ratio of riblets’ diameter to the airfoil chord is equal to 0.005. The tests were carried out in transient flow regime (Two Reynolds numbers of 2.02×10⁵ and 1.4×10⁵), and at attack angles from 0 to 20 degrees. The results indicate that the extent of the riblets effect on the aerodynamic performance of the airfoil depends on the angle of attack, Reynolds number, and arrangement of the riblets on the airfoil. The maximum drag reduction at the Reynolds numbers of 2.02×10⁵ and 1.4×10⁵ is about 29.7 % and 54 %, respectively, that occurs at an attack angle of 7 degrees for both two Reynolds numbers.     

Fluid-structure coupling effects on periodically transient flow of a single-blade sewage centrifugal pump

A partitioned fluid-structure interaction (FSI) solving strategy that depends on problem characteristics is applied to quantitatively obtain the coupling effects of a fluid-structure system in a single-blade centrifugal pump on the unsteady flow. A two-way coupling method is employed to realize strong FSI effects in the calculation procedure. The successful impeller oscillation measurement using two proximity sensors validated the FSI simulation accuracy in a complicated and practical fluid-structure system having a rotating component. The results show that the hydrodynamic force deviation can be observed in the results for the coupled versus uncoupled cases. Additionally, the coupled unsteady pressure is larger than the uncoupled value for every monitoring point at every impeller rotation position. Comparison results for different monitoring points under an overload condition and partial-load condition display the same regularities. To some extent, this interaction mechanism would affect the accuracy and reliability of the unsteady flow and rotor deflection analysis.     

An investigation on the effects of irregular airfoils on the aerodynamic performance of small axial flow fans

In this paper, the effects of airfoils on the aerodynamic performance of small axial flow fans were investigated to reduce airflow turbulence on the blade surface and to improve the aerodynamic performance of small axial flow fans. Irregular airfoils where several convex grooves are bound in the blade pressure surface of the fans have two kinds. The wave-shaped edge is bound to the blade trailing edge of the fans and is designed from the smooth airfoil of the fans. The filtered N-S equations with the finite volume method and the standard k-? turbulence model were adopted to carry out the steady simulation calculation. The large eddy simulation and the FH-W noise models were adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation are in good agreement with the tests, which proves that the numerical calculation method is feasible. The spectrum characteristics of aerodynamic noise of the smooth airfoil and the two kinds of irregular airfoils were analyzed. Although the fans of the three airfoils are regarded as noise sources, the vortex distribution features in the unsteady flow field are also described. Noise reduction mechanisms of the irregular designs of the airfoils were also discussed. The results of this research may provide proof of the parameter optimization and the structural design of small axial flow fans with low noise.     

On the aerodynamic forces of a plunging airfoil

The generation of aerodynamic forces by a plunging NACA0012 airfoil at a Reynolds number of 20,000 was studied for a range of non-dimensional plunge frequenciesk and amplitudesh using a 2D unsteady compressible Navier-Stokes solver, an unsteady panel method (UPM) and Garrick’s analysis. Calculations using these two methods indicate that the forces collapse reasonably well withkh (or equivalents the Strouhal number), but are only weak functions ofk. In contrast results from the NS code indicate that the forces are dependent on bothk andkh independently, with large variations at low frequencies. The frequency dependence was found to be a result of vortex shedding from the leading edge of the airfoil, and appears to result from two factors. Firstly at high plunge frequenciesk, the leading edge vortex does not have sufficient time to grow, whereas at lowk the vortex can become a sizeable fraction of the airfoil chord before separating. Secondly once the vortex separates, it is convected downstream over the surface of the airfoil. Due to the low pressure in the vortex core, thrust is maintained while the vortex is upstream of the airfoil maximum thickness point (where the airfoil surface is tilted upstream and the vortex low pressure creates an upstream suction force). Once past this point, the airfoil surface is tilted downstream and the vortex contributes to drag rather than thrust. At high plunge frequencies the vortex cannot be convected far downstream before the motion cycle creates another leading edge vortex on the opposite side of the airfoil, so the impact is lessened. At lowk however the vortex travels far downstream over the airfoil surface, causing drag for a larger portion of the flapping cycle, and therefore lower propulsive efficiency. These results have strong implications on how the thrust and the propulsive efficiency can be maximised by controlling the relative amplitudes and phases of combined pitching and plunging motions of an airfoil.     

影响风力发电机翼型气动性能的因素研究

翼型气动性能的优劣影响着风力发电机的发电效率,研究影响叶片翼型气动性能的因素具有重要意义。本文采用数值方法计算了文献中NACA0012翼型在Re=10^6时的气动性能参数并与试验值比较,验证了数值方法的正确性。通过对相对厚度、相对弯度、雷诺数等影响翼型气动特性的参数进行研究,结果表明:相对厚度小的翼型在小攻角范围可以获得更好的气动性能;当攻角大于失速角12°后,相对厚度大的翼型的气动性能更佳。在0°~20°攻角范围内,相对弯度和雷诺数越大,翼型的气动性能越好。     

离心压缩机扩压器叶片不稳定脉动力及气动噪声预测

参照轴流压气机动叶尾迹衰减规律,利用流动损失系数代替叶栅阻力系数,给出了离心叶轮出口粘性尾迹速度亏缺值及其宽度的计算方法。基于薄机翼理论,每个叶片用一组连续分布涡来代替,把环形叶栅片模化成在圆周上连续分布涡组的等分排列,建立了在离心叶轮粘性尾迹作用下扩压器叶片上不稳定力计算式。在此基础上对离心压缩机气动噪声进行了理论计算。并与实测值进行了比较,二者吻合较好。     

合成射流对钝尾缘翼型气动特性的影响

研究吸力面存在合成射流的情况下,钝尾缘翼型TR-4000-2000流场结构的变化及其升阻力系数等气动特性参数的变化趋势。在相同射流入口速度条件下,采用计算流体力学软件Fluent对相同来流速度不同攻角情况下翼型流场进行非定常数值模拟计算,分析射流前后翼型升阻力系数变化及翼型表面压力的波动状况;在此基础上,对不同射流频率和不同射流速度情况下翼型流场进行模拟计算,寻求最佳射流参数。结果表明,由于射流及尾缘涡的相互作用导致翼型的升阻力特性不断变化,钝尾缘翼型吸力面合成射流有明显的增升减阻效果,在15°攻角时尤为明显,升力系数提高约40%,阻力系数减小约25%。在量纲一射流速度和量纲一射流频率均为1时,射流对翼型的增升减阻效果最佳。     

钝尾缘翼型对5MW风力机性能影响的研究

目前国内外对钝尾缘翼型的研究主要集中于翼型的改进方式与二维气动性能的模拟,对钝尾缘翼型应用于风力机时对其性能影响的研究较少,然而钝尾缘翼型应用于风力机时由于旋转效应的存在叶素翼型之间会发生相互影响。为了更好的研究钝尾缘翼型,了解钝尾缘翼型对风力机性能的影响,对NREL 5MW风力机叶片内侧翼型进行对称钝尾缘修型,分析二维翼型气动性能,发现一定范围内,翼型的升力系数、升阻比均随尾缘厚度的增加而增大。对原风力机进翼型替换,模拟并对比两类风力机的性能,研究表明改型后风力机的输出扭矩高于原机,而且随风速增大改型风力机的优势变得越来越突出;然而在相同工况下,改型后风力机的轴向力也大于原机。     

Computational study on wind turbine airfoils based on active control for deformable flaps

This study numerically investigates the aerodynamic performance of Deformable trailing edge flaps (DTEFs) to reduce the fatigue and ultimate loads of wind turbine blades. A parametric design is adopted to ensure the flexible deformation of the DTEFs. Based on experimental data, a simulation of a baseline airfoil is performed with two methods: A fully coupled viscous/inviscid method employed by the XFOIL program and a Reynolds-averaged Navier–Stokes solver with a Transition SST (T-SST) turbulence model. The static and dynamic performances of DTEFs are then investigated under different flow conditions by using T-SST and maximizing its numerous advantages. Results indicate that under steady conditions, the effects of flap deflection on the integral forces and flow field structures of airfoils vary from attached flow conditions to separated conditions. The gaps between unsteady aerodynamic responses and static values are greater in attached flow and light stall conditions than in deep stall conditions. The ability of DTEFs to control the fatigue loads on wind turbine blades is verified. Specifically, DTEFs effectively alleviate the force fluctuations on blades under gust-induced swinging when wind speed measurements are considered.