Modelling and Simulation of Intermittent Flows

近年来，基于reynolds - avered Navier-Stokes （RANS）的CFD在工业领域的应用，导致了工程各个方面的设计和开发方法的巨大变化，实现了更高效的设计，降低了开发成本，并比以前更快、更经济地将产品推向市场。由于计算机运行时间的限制，在可预见的未来，RANS方法仍将是表示工程应用中湍流影响的主要方法。然而，这些方法中包含的湍流模型仍然依赖于被检查的流动配置，需要在其规范中使用实验数据，并逐个调整以准确预测特定类型的流动。具有自由边界的湍流剪切流具有间歇性，速度波动从旋转到无旋转变化很快，反之亦然。在许多实际流动中，间歇性是很重要的，例如边界层过渡，这仍然是一个主要的挑战，因为它与现代压气机、涡轮和翼型的设计有关。间歇性对于许多燃烧装置的安全和有效运行也很重要，这些装置依赖于具有显著间歇性的流动中发生的点火，以及对化学和加工工厂中可燃排放物潜在点火的危害和风险评估。在所有这些应用中，这些设备性能的增强和安全性的提高都依赖于对湍流和点火过程的详细了解，因此间歇性。目前使用的大多数工程湍流模型都是为充分发展的流动推导的，因此不能期望准确地预测自由剪切流动，其中外部区域被无旋流污染。因此，发展适应间歇性效应的湍流模型也具有根本的重要性。此外，包括这些效应有助于推广现有的湍流模型，并为上述应用中感兴趣的速度场和标量场提供更准确的预测。eoftac过渡模型问题特别兴趣小组和艾萨克·牛顿数学科学研究所湍流问题方案也确认了开展此类工作的必要性，特别是涉及到湍流工程模型需要更大的通用性，以及改进间歇性影响的建模，特别是对标量场的影响。该提案涉及使用分层方法开发更精确的间歇性湍流工程模型，通过直接数值模拟和大涡模拟的协调应用，为第二矩湍流闭包的制定和验证提供信息，该闭包更基本地基于现有方法。所提出的工作也将提高我们对这种流动的整体理解，湍流工程模型的通用性，并将验证开发的模型应用于广泛的实际流动。

In recent years, the use of Reynolds-Averged Navier-Stokes (RANS) based CFD within industry has led to a sea change in the design and development approaches used across all aspects of engineering, allowing more efficient design, reducing development costs, and bringing products to market more rapidly and economically than was previously possible. Because of computer run time constraints, RANS approaches will remain the principal method for representing the effects of turbulence for engineering application for the foreseeable future. However, the turbulence models embodied within such approaches are still dependent on the flow configuration being examined, requiring the use of experimental data in their specification, and case-by-case adjustment to accurately predict particular types of flow. Turbulent shear flows with free boundaries display an intermittent character, such that the fluctuations of velocity rapidly change from rotational to irrotational, and vice versa. Intermittency is important in many practical flows, for example, in boundary layer transition which remains a major challenge because of its relevance to the design of modern compressors and turbines, and airfoils. Intermittency is also important in the safe and efficient operation of many combustion devices, which are dependent on ignition occurring in flows with significant intermittency, as well as in hazard and risk assessments concerning the potential ignition of flammable releases on chemical and process plant. In all these applications, the enhanced performance of these devices, and improved safety, relies on a detailed understanding of turbulent flow and ignition processes, and hence intermittency. The majority of engineering turbulence models in use today were derived for fully developed flows, and hence cannot be expected to accurately predict free shear flows where the outer regions are contaminated with irrotational flow. The development of turbulence models that accommodate intermittency effects is therefore also of fundamental importance. Additionally, the inclusion of such effects helps to generalize existing turbulence models, and provide more accurate predictions of the velocity and scalar fields of interest to the applications noted above. The necessity for such work has also been identified by both the EROFTAC Special Interest Group on Transition Modelling, and the Isaac Newton Institute for Mathematical Sciences Programme on Turbulence, particularly in relation to the need for greater universality in engineering models of turbulence, and the improved modelling of the influence of intermittency, particularly on scalar fields. This proposal concerns the use of an hierarchical approach to the development of more accurate engineering models of intermittent turbulent flows through the co-ordinated application of direct numerical simulation and large eddy simulation to inform the formulation and validation of second-moment turbulence closures that are more fundamentally based that existing approaches. The work proposed will also improve our overall understanding of such flows, the universality of engineering models of turbulence, and will validate the models developed for application to a wide range of practical flows.