Extending the buffet envelope: step change in data quantity and quality of analysis

下一代飞机可能需要在技术上进行重大变革，以满足燃油消耗、二氧化碳、氮氧化物和噪音排放等方面的雄心勃勃的目标。集成的计算机辅助工程是降低破坏性变化和新设计概念带来的风险的关键推动因素。此外，数字化飞机设计和认证的长期愿景，以减少对风洞和飞行中测试的依赖，需要在最高保真的流动模拟方面实现飞跃。我们重新审视了飞机空气动力学的一个巨大挑战，使用最先进的工业和下一代仿真工具，使识别相干流结构的机制，导致跨音速机翼激波抖振和构成的不稳定性，尽管密集的研究工作仍然存在争议。激波抖振在高速飞行中表现为一种流动不稳定性，对飞机的性能、经济性和乘客安全都有不利影响。关于流动不稳定性的文献有很多，但对与航空航天工业有关的实际流动的分析却很有限，而且常常局限于简化的情况。两个关键技术演示为这项工作提供了背景。第一个是最近的全球稳定性分析的跨音速激波抖振流与三个不均匀的空间方向上的行业相关的测试用例，使用工业级的计算流体动力学（CFD）求解器套件和雷诺平均Navier-Stokes（RANS）的空气动力学模型。然而，由于没有通用模型来预测湍流分离流，因此，工业标准计算流体动力学解的高置信度仅在巡航点附近的工作飞行包线内的一个小区域内给出。因此，最近的第二个关键成就是超临界跨音速翼型流动的高雷诺数直接数值模拟（DNS），这也提供了进入全局模式的途径。工作计划的前提是，依靠高性能计算和先进的数值流动分析，重要的新要素已经到位，以开发适用于下一代跨音速机翼的下一代抖振预测方案。我们调查全球范围内的空气动力学模型（从RANS到DNS）应用于低阻力配置（后掠，层流，超临界）翼型和机翼，最终在一个现代远程，宽体飞机机翼几何形状的全局和预解模式分析。实际的目的是发展出可靠的、经济有效的方法来确定未来机翼的抖振边界。沿着这条路，我们将学到更多关于激波引起的非定常性的物理学知识，以及在跨音速机翼绕流中引起激波抖振的机理。

Next-generation aircraft are likely to require significant changes in technology to meet ambitious targets on fuel burn, CO2, NOX and noise emissions. Integrated computer-aided engineering is a key enabler to mitigate the risk coming with disruptive change and new design concepts. Moreover, the long-term vision of digital aircraft design and certification, to reduce reliance on wind tunnel and in-flight testing, requires leaps in highest-fidelity flow simulation. We revisit a grand challenge of aircraft aerodynamics using both state-of-the-art industrial and next-generation simulation tools enabled for the identification of coherent flow structures targeting the mechanisms leading to transonic wing shock buffet and constituting the instability, which despite intensive research efforts remains controversial. Shock buffet manifests itself as a flow instability in high-speed flight with detrimental effects on the aircraft performance, economic efficiency, and ultimately passenger safety. A vast amount of literature on flow instability exists, yet analysis of practical flows relevant to the aerospace industry is limited and often confined to simplified cases.Two key technology demonstrations provide the background to the work. The first is a recent global stability analysis of transonic shock buffet flow with three inhomogeneous spatial directions on an industry-relevant test case using an industry-grade computational fluid dynamics (CFD) solver suite and a Reynolds-averaged Navier-Stokes (RANS) aerodynamic model. However, high confidence in industry-standard CFD solutions is given only in a small region in the operating flight envelope near the cruise point due to the unavailability of general models to predict turbulent separated flow. Hence, the second recent key achievement is high Reynolds number direct numerical simulation (DNS) of supercritical transonic aerofoil flow, which also provides access to global modes.The premise of the work programme is that significant new elements, relying on high-performance computing and advanced numerical flow analysis, are in place to develop next-generation buffet prediction schemes suitable for next-generation transonic wings. We investigate global and resolvent mode analysis across the range of aerodynamic models (from RANS to DNS) applied to low-drag configuration (swept, laminar flow, supercritical) aerofoils and wings, culminating in a modern long-range, wide-body aircraft wing geometry. The practical aim is to develop robust, cost-effective methods to determine the buffet boundary of the wings of the future. Along the way, we will learn more about the physics of shock-induced unsteadiness and the mechanisms leading to shock buffet in the flow around transonic wings.