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，以实现燃油消耗、二氧化碳、氮氧化物和噪音排放方面的宏伟目标。集成计算机辅助工程是减轻破坏性变化和新设计概念带来的风险的关键因素。此外，为了减少对风洞和飞行测试的依赖，数字化飞机设计和认证的长期愿景需要在最高保真度的流动模拟方面取得飞跃。我们使用最先进的工业和下一代模拟工具来重新审视飞机空气动力学的重大挑战，这些工具能够识别导致跨声速机翼冲击冲击和构成不稳定性的连贯流动结构，尽管进行了大量的研究，但仍然存在争议。冲击冲击在高速飞行中表现为一种流动不稳定性，对飞机性能、经济效率乃至乘客安全都有不利影响。关于流动不稳定性的文献大量存在，但对与航空航天工业有关的实际流动的分析有限，而且往往局限于简化的情况。两个关键技术演示为这项工作提供了背景。第一个是最近在一个行业相关的测试用例上，使用工业级计算流体动力学（CFD）求解器套件和reynolds -average Navier-Stokes （RANS）空气动力学模型，对具有三个非均匀空间方向的跨音速冲击冲击流进行了全局稳定性分析。然而，由于一般模型无法预测湍流分离流，工业标准CFD解决方案的高可信度仅在巡航点附近的运行飞行包线的小区域内给出。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），它也提供了对全局模式的访问。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，重要的新元素已经到位，以开发适用于下一代跨音速机翼的下一代自助餐预测方案。我们研究了适用于低阻力配置（掠流、层流、超临界）的气动模型（从RANS到DNS）的全局和解析模式分析，最终得出了现代远程宽体飞机机翼几何形状。实际目标是开发稳健、经济的方法来确定未来机翼的自助餐边界。在此过程中，我们将更多地了解激波引起的非定常的物理特性以及导致跨声速机翼周围流动中激波冲击的机制。

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.