Aeroelastic control of gas turbine blades

叶片振动和噪声的产生都是轴流式涡轮内部非定常流动过程的不良后果，因此也是设计者所关注的重要问题。在这两者中，振动问题受到了更多的关注，因为它们可能导致发动机的结构故障，并可能造成包括生命损失在内的广泛损害。空气动力引起的叶片振动通常分为两大类：自持问题和受迫问题。在前者中，维持叶片运动的气动力被认为仅仅依赖于该运动（例如在颤振中），而在后者中，激发叶片运动的气动力与该运动无关（例如在抖振和叶片失谐中）。本文的研究重点将放在后一类问题上。新型综合转子叶片设计（BLISKS）的发展引起了人们对振动相关问题的新关注，因为传统叶片附件所带来的自然结构阻尼现在已经消失了。因此，使用“智能”结构致动器和传感器（如压电）来检查涡轮机器结构完整性和/或减少振动的控制系统是研究工作的重点。绰号为Smart Spring的致动器装置最适合用于利用摩擦主动改变结构的边界条件，因此，它们可以合并到BLISKS中，以提供人工阻尼增强。在目前的应用中，将采用这种方法来减弱涡轮机械的涡轮和压气机级最常见的强迫振动问题。这一目标将需要使用复杂的计算流体动力学模型，这些模型必须与数值模拟的结构控制理想化相联系。为此，为了提高计算效率，将首先采用降阶气动弹性模型建立包括非定常气动效应、叶片相间角和失谐在内的叶栅流动降阶气动弹性模型。

Blade vibration and noise generation are both undesirable consequences of the unsteady flow processes that occur within an axial-flow turbomachines and are, therefore, important concerns of the designer. Of the two, vibration problems have received more attention because they can lead to a structural failure of the engine and, possibly, to extensive damages including life losses. Aerodynamically-induced blade vibrations are usually classified into two general categories: self-sustained and forced problems. In the former, the aerodynamic forces that sustain the blade motion are regarded as being dependent solely on that motion (e.g. in flutter), whereas in the latter, the aerodynamic forces that excite the blade motion are independent of that motion (e.g. in buffeting and blade mistuning). This research will be more focused in the latter class of problems. The development of new integrated rotor-blade designs (BLISKS) led to renewed concerns about vibration-related problems because the natural structural damping due to the traditional blade attachments is now absent. Therefore, control systems for the interrogation of the structural integrity of turbomachines and/or reduction of vibration using "smart" structures actuators and sensors such as piezoelectrics are a matter of research effort. The actuator device nicknamed Smart Spring is best suited to be used to actively alter the boundary conditions of structures using friction and, as such, they may be incorporated to BLISKS to provide theur artificial damping augmentation. In the current application this approach will be taken to attenuate the forced-vibration problems most commonly encountered in turbine and compressor stages of turbomachineries. This objective will require the use of complex Computational Fluid Dynamic models that must be linked to structural control idealizations for the numerical simulations. For this, reduced-order aeroelastic models of cascade flows including unsteady aerodynamic effects, blade inter-phase angles and mistuning will be firstly developed using reduced-order aeroelastic models for the sake of computation efficiency.