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

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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.