Numerical and Experimental Investigations of the Cavitation Structure in Inducer

在之前的项目中，可以证明，只要既定的设计程序规定了诱导轮的轴向设计，就不能设计诱导轮，以达到规定的压力升高。因此，出现的问题是，比既定设计程序规定的长度更短的诱导轮是否能够完全或充分地减少轴向的气穴现象，从而不会影响后面的叶轮的功能。这个问题还没有在公开文献中处理到现在。 基本上，问题是诱导轮的轴向尺寸必须有多长才能完全实现其功能（增加压力，减少气穴）。在本项目中，将制定标准，使设计具有足够轴向长度的诱导轮成为可能。公开的科学文献表明，诱导轮的后掠前缘可改善NPSH性能。这可以从上一个项目的结果中得到证实。为什么后掠前缘导致改进的NPSH性能，这是一个悬而未决的问题。这个问题涉及到发展最佳后掠前缘准则的要求。在本项目中，将对前缘区域的压力分布进行研究，以便找出后掠前缘具有更好的NPSH特性的原因。最后，公开的文献没有给出诱导轮与叶轮之间相互作用的答案。诱导轮产生了一个涡流，该涡流施加在沿主流方向跟随叶轮的流入侧。另一方面，叶轮影响诱导轮的涡流。在目前的项目中，这个问题将通过测量和CFD模拟研究诱导轮的涡流而不受叶轮的影响来处理。在此基础上，考虑了叶轮的影响。在最后一步中，生产出与诱导轮一起工作良好的改进的叶轮。

In the previous project it could be demonstrated that an inducer must not be designed in the axial direction as long as it is prescribed by the established design procedures in order to reach a prescribed pressure rise. Therefore the question arises whether an inducer, which is shorter designed than the established design procedures prescribe, is able to reduce the cavitation completely or sufficiently in axial direction, respectively, so that the following impeller is not affected in its function. This question has not been treated in the open literature until now. Basically, the question arises how long the axial dimension of an inducer must be to fulfil its function (increase of pressure, reduction of cavitation) completely. In the present project criterions are to be developed making it possible to design an inducer with sufficient axial length. In the open scientific literature it is shown that a swept leading edge of an inducer leads to an improvement of the NPSH-behaviour. This could be confirmed by the results of the previous project. It is an open question why a swept leading edge leads to an improved NPSH-behaviour. This question is related to the request to develop criterions of an optimal swept leading edge. In the present project the pressure distribution is to be investigated in the leading edge region in order to find out why a swept leading edges processes a better NPSH-behaviour. Finally, the open literature does not give an answer of the interaction between inducer and impeller. The inducer produced a swirl which is imposed on the inflow side of the in main stream direction following impeller. On the other hand the impeller influences the swirl of the inducer. In the present project this problem is to be treated by investigating the swirl of the inducer without influence of the impeller by measurements and CFD-simulation. After that the influence of the impeller is taken into account. In a last step a modified impeller is produced which works well together with the inducer.