Abstract
A photographic technique is used here to give quantitative measurements of the three-dimensional flow pattern in pump impellers operating at conditions of practical interest. This technique is used to study the flow through a series of impellers of outlet angle varying between 20° and 35° and inlet angles constant at 20°, operating over a range of throughflows. Attention is here focused on the flow patterns at, and below, the best efficiency point.
Experimental results show that standing vortices can appear at both the leading surface near the impeller eye and at the trailing surface near the impeller tip, with the latter becoming more important as the throughflow is reduced. A qualitative explanation for the appearance of these vortices is given in terms of boundary-layer theory and the effect of the trailing surface vortex on the pump performance is discussed. Estimates are made of the internal slip coefficient and a study of the losses in the volute close to the impeller tip is made. The data are again analysed in terms of the Busemann potential flow theory. It is concluded that impeller design, by influencing the impeller flow pattern and introducing separation regions, can have an important effect on pump performance, particularly with reference to stability.
Get full access to this article
View all access options for this article.