High-speed and high-resolution 4 D optical flow-diagnostics system

卡尔斯鲁厄理工学院流体力学研究所(ISTM)在研究近壁湍流及其通过特定几何图案、壁面粗糙度或通过主动和被动流动控制方法进行控制或修正方面享有国际参考的声誉。目前的提议旨在实现在ISTM最近升级的两个设施中进行高保真光学测量：低雷诺数(Re)通道流动隧道和大型高再开放喷流风洞。对于这两种流动构型，设想进行互补的实验和数值研究。这使得以下关于壁面湍流机制和控制的整体研究方法成为可能：对于正则槽道流动，高保真的直接数值模拟(DNS)推动了对基本物理的理解。这些对统计二维和空间充分发展的流动状态的经典模拟得到了时空分辨实验的补充。这些实验允许评估流动发展和三维效应，最重要的是，提供了对由致动器或表面粗糙度触发的流动现象的访问，即使在dns中，这些现象也是基于模型假设而包括的，因此需要验证数据。这些研究所需要的最先进的设备被称为(时间和体积分辨的)高速4D光学流动诊断系统。除了对渠道流动形态的基础研究外，流动控制和修正策略被转移到更复杂的形态；具体地说，转移到更高雷诺数的复杂几何形状的外部流动中。对于这种流动类型，高保真模拟是极其苛刻的，甚至是不可能的。因此，部署了基于湍流模型的求解器。为了改进模型，允许包含由于非光滑表面或执行器的存在而修改的边界条件，必须提供用于输入和验证的可靠的实验数据。这就需要对大流区进行高分辨率的体积测量。为此，需要第二套流动诊断系统，称为高分辨率四维光学流动诊断系统。该系统可与ISTM已有的激光光源结合使用，以提供四个时间相关的体积测量序列。采集的数据集将使用基于拉格朗日粒子跟踪(LPT)方法的最先进算法进行处理，包括最先进的体积拉格朗日测速软件，该软件可以检索高质量的测量数据，并进行高效的数据评估。因此，所要求的设备允许充分利用ISTM新翻新的风洞基础设施，以便能够进行独特的整体流动诊断和控制研究。

The institute of fluid mechanics (ISTM) at Karlsruhe Institute of Technology (KIT) has developed a reputation as international reference for the studies on near wall turbulence and its control or modification through specific geometric patterns, wall roughness or by means of both active and passive flow control approaches. The present proposal aims at enabling high fidelity optical measurements in the two recently upgraded facilities at ISTM: a low Reynolds number (Re) channel-flow tunnel and a large high-Re open jet wind tunnel. Complementary experimental and numerical investigations are envisioned for both flow configurations. This enables the following holistic research approach on wall-turbulence mechanisms and control: For the canonical channel flow, high-fidelity direct numerical simulations (DNS) drive the fundamental understanding of the underlying physics. These classical simulations of a statistically 2 D and spatially fully developed flow state are complemented by spatio-temporally resolved experiments. These experiments allow to assess flow development and three-dimensionality effects absent in DNS and, most importantly, provide access to flow phenomena triggered by actuators or surface roughness, which even in DNS are included based on model assumptions and thus require validation data. The state-of-the-art equipment requested for these studies is referred to as (temporally and volumetrically resolved) high-speed 4 D optical flow-diagnostics system. In addition to their fundamental investigation in the channel flow configuration, the flow control and modification strategies are transferred to more complex configurations; specifically, to external flows along complex geometries at higher Re. For this flow type high-fidelity simulations are extremely demanding or impossible. Therefore, turbulence-model based solvers are deployed. In order to advance models that allow the incorporation of modified boundary conditions due to non-smooth surfaces or the presence of actuators, reliable experimental data for input and validation are mandatory. This requires high resolution volumetric measurements of large flow domains. For this sake, a second flow diagnostics system is requested, which is referred to as high-resolution 4 D optical flow-diagnostics system. This system can be used in combination with an already available laser source at ISTM, to deliver four temporally-correlated sequences of volumetric measurements. The acquired datasets will be processed with the most advanced algorithms based on the Lagrangian particle tracking (LPT) approach, including state-of-the-art volumetric Lagrangian velocimetry software retrieving high-quality measurements with computationally-efficient data evaluation. The requested equipment thus allows to fully exploit the newly refurbished wind tunnel infrastructure at ISTM in order to enable a unique holistic flow diagnostics and control research.