Nichtlineare Stadien der Transition in einer verzögerten Flügel-Grenzschichtströmung bei kontrolliertem, kontinuierlichen und bei natürlichen Störspektrum

本申请的主要目标是深化最近获得的关于飞行条件下自然层流-湍流转捩的第一非线性阶段的知识，并通过扩展的en方法将其转化为改进的转捩预测。实验，弱非线性理论和直接数值模拟采用的联合项目。一个程序将被开发到帐户的自我生成的低频模式和随后的放大过程中的弱非线性阶段。这种方法可以类似于可变（缩减）n因子方法，或者等效地，可以通过考虑低频模式的n提升来设计，以在较短的流向运行长度处实现过渡处的n标准值。EN方法是最广泛使用的过渡预测方法，尽管尝试采用基于幅度的工具与感受性，增长和击穿模块。然而，后者需要一个准确的迎面干扰频谱，这是非常难以预测的，而且，在安静的飞行情况下，往往是徒劳的。en方法的改进将对层流翼型的设计产生重大影响，满足对环境负责的航空的要求，并提高风力涡轮机可再生能源生产的效率。

The main goal of the present application is to deepen the recently gained knowledge about the first nonlinear stages of natural laminar-turbulent transition at flight conditions and to transfer it into an improved transition prediction by an extended en-method. Experiments, weakly nonlinear theory, and direct numerical simulations are employed within a joint project. A procedure will be developed to account for the self-generation of low frequency modes and subsequent amplification during the weakly non-linear stage. This approach can be similar to the variable (reduced-) n-factor method, or equivalently, can be designed to achieve standard values of n at transition at a shorter streamwise running length by accounting for an n-boost of low frequency modes. The en-method is the most widely used transition prediction method despite attempts to employ amplitude based tools with receptivity-, growth-, and breakdown modules. However the latter need an accurate oncoming disturbance spectrum that is very difficult to predict, and, moreover, often is futile in quiet flight situations. Improvements of the en-method will have a significant impact on the design of laminar wing profiles, meeting the requirements of environmentally responsible aviation and increased efficiency of renewable energy production by wind turbines.