Influence de la géométrie de l'environnement aval de la roue sur les caractéristiques des pompes à débit partiel

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This paper discusses the influence of geometrical parameters of vaned diffusors and volutes on partial-flow characteristics of centrifugal pumps. The analysed results originate from publications or some manufacturers' internal notes, members of the l-c working group of the "Société Hydrotechnique de France". Some test results involving only modifications of the casing downstream of the impeller are presented here in a non-dimensional form. Generally speaking, these modifications concern many geometrical parameters, and it is not easy to characterise the results : only trends emerge. These trends vary according to the type of pump (specific speed influence) and to the impeller geometry : general trend seems to be much more difficult to obtain for pumps operating at low specific speed. The first part shows the influence of some changes made in the volute on the partial-flow characteristics of single-volute pumps. The volute tongue appears to be most important, especially the relative radial gap and the tongue radius : head coefficients increase and power coefficients tend to decrease when these parameters increase. The second part covers the results correlated to modifications of vaned-diffusor inlet parts. The influence of the relative radial gap, the blade inlet radius, the blade inlet angle, the diffuser throat area, the diffusor's axial position in relation to the impeller and gaps between impeller and-easing can be revealed in the same way.