Experimental investigation and further development of the cavitation erosion scale effects and the cavitation erosion model

水力空化和由此产生的空蚀仍然是严重的、难以预测的问题。根据经验推导出的设计准则用于水电站设施中避免汽蚀。但是，这些准则取决于设计流量。因此，气候变化和随之而来的洪水流量增加对设施安全构成了严重威胁。因此，本研究项目致力于阐明水力空化侵蚀的基本机理，并使损害具有可预测性。以前的研究活动已经经验地阐明了空蚀尺度效应，特别是关于土木工程材料。然而，由于缺乏对实际损害机制的了解，其适用性仍然不清楚。单气泡实验中发现的微观损伤过程在流体动力空化过程中还不能转移到气泡团簇中。一种新的、有希望的空化侵蚀模型假定了空化云行为与侵蚀之间的关系。空化云的相干坍塌在气泡附近的边界上诱导出微喷流。本项目通过时间分辨光学观测研究空化云的动力学和尺度效应，以澄清与侵蚀的相关性。用时间分辨的微观方法观察水力空化的实际损伤过程。分析了微射流的幅值、频率及其在时间和空间上的相关云层行为和破坏模式。这项研究将产生关于实际破坏机制的基本知识，以及规模效应的基本原理和可转移性。验证了现有的空蚀模型。

Hydrodynamic cavitation and the resulting cavitation erosion remain serious and hardly predictable problems. The empirically deduced design guidelines are used to avoid cavitation in hydro power facilities. However these guidelines depend on the design discharge. Thus the climate change and the resulting increase in flood discharges pose severe threats to the facility safety. Therefore the present research project seeks to clarify the basic mechanism of hydrodynamic cavitation erosion and to make damage predictable. Former research campaigns already have empirically elucidated the cavitation erosion scale effects, especially concerning civil engineering materials. However the applicability remains unclear due to a lack of knowledge of the actual damage mechanism. The microscopic damage process which was found in single bubble experiments could not yet be transferred to bubble ensembles in hydrodynamic cavitation. A new, promising cavitation erosion model postulates a relation between the cavitation cloud behaviour and the erosion. The coherent collapse of a cavitation cloud induces a micro jet in a boundary near bubble. The present project investigates the dynamics and scale effects of the cavitation cloud by time resolved optical observation to clarify correlations to the erosion. The actual damage process of hydrodynamic cavitation will be observed with a time resolved, microscopic method. Amplitude, frequency of micro jets and its temporal and special correlation cloud behaviour and damage patterns are analysed. The research will yield basic knowledge about the actual damage mechanism and the fundamentals and transferability of scale effects. It will verify the current cavitation erosion model.