4D Particle Tracking Velocimetry system (4D-PTV)

目前世界范围内水利工程面临的主要挑战之一是检查和修复现有的水坝，这些水坝往往超过了它们的预期寿命。正在建造新的结构，主要是为了开发水电潜力和防洪。现有的和新的结构都必须考虑到各种不同的条件，特别是气候变化造成的条件。水力结构需要在水力效率方面进行优化，并提供足够的安全水平-即使在未来可能出现的极端条件下以及考虑到老化和磨损。在这方面，下游能量耗散是特别感兴趣的。大多数现有的设计方法都是在实验室测试中使用相对简单的仪器开发的，这可能会简化经常发现三维流动过程的现实。除了经典的1D/2D测量设备外，最近还开发了光学3D方法，这为流动分析提供了越来越多的细节。现代粒子跟踪测速（PTV）方法允许在实验室实验中使用一组多个高速相机以高时空分辨率（4D）重建单个水粒子的运动。除了速度场之外，还可以评估相关参数，例如3D压力场。在此，提出了一种非侵入式4D PTV系统。新算法即使在高颗粒密度下也能识别单个颗粒，因此与以前的方法相比，可用信息可以显着增加。该系统允许以近似全高清分辨率和高达1 kHz的采样率记录颗粒场景，用于可变尺寸和长达数分米的边缘长度的测试体积。由于非侵入式设计，避免了对流场的影响。高性能LED被用作光源。荧光示踪剂和照相机滤光器的使用使得能够分离水相和空气相，并且因此能够在适度充气的流中使用该系统。所提出的4D-PTV系统允许第一次在时间和空间上解决的大体积的水流与流体-结构相互作用的调查。因此，它可以为获得水利工程领域的知识做出重大贡献，特别是在高度湍流的能量耗散过程中。

One of the major current challenges in hydraulic engineering worldwide is the inspection and rehabilitation of existing dams, which have often exceeded their presumed life time. New structures are being built primarily to develop hydropower potential and to provide flood protection. Varying conditions, particularly due to climate change, must be taken into account for both, existing and new structures. Hydraulic structures need to be optimized in terms of hydraulic efficiency and provide adequate safety level – even under extreme conditions that may arise in future as well as in view of aging and wearing. In this regard, downstream energy dissipation is of particular interest. The majority of existing design approaches were developed in laboratory tests using relatively simple instrumentation, which may simplify reality where often three-dimensional flow processes are found. In addition to classic 1D/2D measuring devices, optical 3D methods have been developed in the recent past, which offer an increasing level of detail in flow analysis. Modern Particle Tracking Velocimetry (PTV) methods allow the reconstruction of individual water particle movement in laboratory experiments with high spatio-temporal resolution (4D) using a set of multiple high-speed cameras. In addition to the velocity fields, depending parameters, e.g. 3D pressure fields, can be evaluated. Herein, a non-intrusive 4D PTV system is proposed. New algorithms enable the identification of individual particles even at high particle densities, so that available information can be significantly increased compared to previous methods. The system allows recording of particle scenes with approximately Full HD resolution and a sampling rate of up to 1 kHz for test volumes of variable dimensions and edge lengths of up to several decimeters. Due to the non-intrusive design, influences on the flow field are avoided. High-performance LEDs are used as a light source. The use of fluorescent tracers and camera filters enables the separation of water and air phases and thus the use of the system in moderately aerated flows. The proposed 4D-PTV system allows for the first time the temporally and spatially resolved investigation of large volumes in water flows with fluid-structure interactions. It can thus make significant contribution to gaining knowledge in the field of hydraulic engineering, in particular in relation to energy dissipation processes in highly turbulent flows.