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基于POD和DMD方法的跨声速抖振模态分析 总被引:2,自引:0,他引:2
跨声速抖振现象是由于非定常跨声速流动中激波的自激振荡而引起的结构强迫振荡,这种现象在跨声速飞行器中普遍存在,对飞机的结构强度和疲劳寿命有不利影响。基于模态分解的分析方法是进一步发展抖振控制手段的有效工具。本文通过两类典型模态分析方法(本征正交分解(POD)和动态模态分解(DMD))对OAT15A翼型的跨声速抖振现象进行分析,通过对模态频率、翼面压力分布、流场重构误差等方面的研究,将两种模态分解方法进行对比。发现基于频率特征的DMD方法能够准确捕捉抖振的临界稳定特征和抖振主频的典型模态,同时能够更准确反映流场变量在激波间断附近随时间的变化过程;而POD方法尽管在流场重构时具有较小的总体误差,但对激波附近压强随时间的变化历程拟合较差。 相似文献
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采用非定常雷诺平均Navier-Stokes(URANS)方法计算了18%双圆弧翼型的跨声速抖振特性,分析了翼面激波振荡及流场结构演化的特点,研究了在翼型表面开通气空腔抑制跨声速抖振的可行性,对空腔深度、开缝数目对激波振荡的抑制效果进行了对比分析。计算发现,18%双圆弧翼型的跨声速激波自激振荡只有向前的运动,没有向后的运动,开缝空腔能够抑制翼型跨声速抖振,但对抖振频率影响不大;空腔深度大,抑制效果好,但空腔深度变化对振荡频率影响不大;开2、3、4个槽缝抑制抖振的效果差别不大,开缝数量对抖振频率影响不大。 相似文献
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跨声速抖振引起的非定常脉动载荷会造成飞行器结构疲劳甚至引发飞行事故,所以跨声速抖振的控制研究逐渐成为航空领域的热点。采用基于Spalart-Allmaras(S-A)湍流模型的非定常雷诺平均方程开展了基于谐振舵面的跨声速抖振抑制研究。首先验证静止NACA0012翼型的抖振边界和频率特性,然后分别从舵偏平衡位置、舵偏幅值、频率以及相角等角度研究了谐振舵面的控制效果。舵偏平衡位置等效于减小了翼型的有效迎角;幅值和频率对抖振抑制效果影响较大,当舵面振荡频率与抖振频率接近时发生共振现象;相角对控制效果有一定影响,在270°相角附近,升力系数幅值减小了60%。在合适的舵偏幅值、频率以及相角组合下,谐振舵面有可能成为跨声速抖振的有效开环控制策略。 相似文献
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绕机翼的跨声速抖振流动是典型的复杂不稳定流动,对其非定常特性及失稳机制的研究具有重要的工程和学术价值。通过非定常雷诺平均Navier-Stokes(URANS)仿真方法和动模态分解(DMD)分析手段,研究了CRM(Common Research Model)等典型机翼的跨声速抖振流动特性及其主要失稳模态。数值仿真结果表明机翼的跨声速抖振表现为多失稳模式下的宽频特性。除了激波的弦向失稳,还会伴随发生激波的展向失稳,它们都表现为低频特性。翼梢处的高频响应可能是由激波诱导的低频失稳与翼尖涡相互耦合形成。DMD分析结果显示机翼展长和后掠因素诱导了激波展向失稳模态。本研究对抖振流动的物理建模、控制及理解相关的气动弹性现象具有指导意义。 相似文献
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由于受到流动环境中的不确定因素影响,针对流动系统设计的闭环控制律需要考虑这些不确定因素,自动适应随机扰动和突发扰动.基于流动模型所设计的闭环最优控制,虽然可以以较小的控制量获得满足目标函数的最优控制效果,但随着流动模型的引入,随之而来的建模精度、未建模动态等问题也会出现,固定的流动模型也会限制控制系统的自适应能力.针对翼型在跨声速流动中遇到的激波抖振问题,为了消除不同来流状态的激波抖振带来的脉动载荷,开展了基于数据驱动方法的无模型自适应控制.流场数值仿真采用URANS方法,作动机构采用尾缘舵面,以升力系数作为反馈信号.当流动状态变化时,无模型自适应控制利用输入输出数据在线将流动系统等价转化为动态线性化数据模型,最小化性能指标得到控制律,使系统自动地工作于最优或接近最优的状态.时域仿真结果显示,无模型自适应控制效果优于开环控制和比例控制,并且当来流状态随时间发生变化时,无模型自适应控制也能够完全消除抖振脉动载荷. 相似文献
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《Progress in Aerospace Sciences》2001,37(2):147-196
Self-sustained shock wave oscillations on airfoils at transonic flow conditions are associated with the phenomenon of buffeting. The physical mechanisms of the periodic shock motion are not yet fully understood even though experiments performed over fifty years ago have demonstrated the presence of oscillatory shock waves on the airfoil surfaces at high subsonic speeds. The unsteady pressure fluctuations generated by the low-frequency large-amplitude shock motions are highly undesirable from the structural integrity and aircraft maneuverability point of view. For modern supercritical wing design with thick profiles, the shock-induced fluctuations are particularly severe and methods to reduce the shock wave amplitudes to lower values or even to delay the oscillations to higher Mach numbers or incidence angles will result in expanding the buffet boundary of the airfoil. This review begins with a recapitulation of the classical work on shock-induced bubble separation and trailing edge separation of a turbulent boundary layer. The characteristics of the unsteady pressure fluctuations are used to classify the types of shock-boundary layer interaction. The various modes of shock wave motion for different flow conditions and airfoil configurations are described. The buffet boundaries obtained using the standard trailing edge pressure divergence technique and an alternative approach of measuring the divergence of normal fluctuating forces are compared to show the equivalence. The mechanisms of self-sustained shock oscillations are discussed for symmetrical circular-arc airfoils at zero incidence and for supercritical airfoils at high incidence angles with fully separated flows. The properties of disturbances in the wake are examined from linear stability analysis of two-dimensional compressible flows. The advances in high-speed computing make predictions of buffeting flows possible. Navier–Stokes solvers and approximate boundary layer-inviscid flow interaction methods are shown to give good correlation of frequencies and other unsteady flow characteristics with experiments. Finally, passive and active methods of shock oscillation control show promising results in delaying buffet onset to higher Mach numbers or incidence angles, thus enhancing the transonic performance of airfoils. 相似文献
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《中国航空学报》2020,33(5):1405-1420
In transonic flow, buffet is a phenomenon of flow instability caused by shock wave/boundary layer interaction and flow separation. The phenomenon is common in transonic flow, and it has serious impact on the structural strength and fatigue life of aircraft. In this paper, three typical airfoils: the supercritical OAT15A, the high-speed symmetrical NACA64A010, and the thin, transonic/supersonic NACA64A204 are selected as the research objects. The flow fields of these airfoils under pre-buffet and buffet onset conditions are simulated by Unsteady Reynolds Averaged Navier-Stokes (URANS) method, and the mode analysis of numerical results is carried out by Dynamic Mode Decomposition (DMD). Qualitative and quantitative analysis of the shock wave motion, shock wave intensity, shock foot bubble and trailing edge separation, and pressure coefficient fluctuation were performed to attain deep insight of transonic buffet flow features of different airfoils near buffet onset conditions. The results of DMD analysis show that the energy proportion of the steady mode of these airfoils decreases dramatically when approaching the buffet onset angle of attack, while the growth rate of the primary mode increases inversely. It was found that at the onset of buffet, there exist different degrees of merging behavior between shock foot bubble and trailing edge separation during one buffet cycle, and the instability of shock wave and separation induced shear layer are closely related to the merging behavior. 相似文献
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Current research shows that the traditional shock control bump (SCB) can weaken the intensity of shock and better the transonic buffet performance.The author finds that when SCB is placed downstream of the shock,it can decrease the adverse pressure gradient.This may prevent the shock foot separation bubble to merge with the trailing edge separation and finally improve the buffet performance.Based on RAE2822 airfoil,two types of SCB are designed according to the two different mechanisms.By using Reynolds-averaged Navier-Stokes (RANS) and unsteady Reynolds-averaged Navier-Stokes (URANS) methods to analyze the properties of RAE2822 airfoil with and without SCB,the results show that the downstream SCB can better the buffet performance under a wide range of freestream Mach number and the steady aerodynamics characteristic is similar to that of RAE2822 airfoil.The traditional SCB can only weaken the intensity of the shock under the design condition.Under the off-design conditions,the SCB does not do much to or even worsen the buffet performance.Indeed,the use of backward bump can flatten the leeward side of the airfoil,and this is similar to the mechanism that supercritical airfoil can weaken the recompression of shock wave. 相似文献
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大迎角(AoA)机动飞行能力是先进战斗机的标志性指标之一,中国先进战斗机采用V型垂尾布局的气动设计方案,可充分实现其良好的大迎角机动可控飞行。飞机在大迎角机动飞行时,前机身分离流所产生的高强度脱体涡破裂后产生的非定常扰流将不可避免地打在V型垂尾翼面上,导致V尾结构发生严重的抖振,这不仅会影响飞机的飞行品质等性能,还会导致V尾结构的疲劳损伤,大幅增加飞机的使用维护成本。本文详细阐述了其研发设计过程中攻克的以下关键技术:全动V尾抖振风洞试验"刚/弹"组合模型的设计技术与风洞试验方法,抖振风洞试验的动态测试结果向飞机尺度进行相似转换的原理;基于RANS/LES混合算法进行V尾结构抖振响应的CFD/CSD耦合计算方法;基于正加速度反馈(PAF)的V尾抖振响应压电控制技术;V尾抖振动态疲劳载荷谱的编谱方法与试验实施方案。本文为解决中国先进战斗机、无人机V尾结构抗抖振动强度设计与验证建立了一套较完备理论分析技术、设计准则和试验方法。 相似文献