Numerical and Experimental Investigation of Secondary Flow and Loss Generation in Inducers

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Until now there are no quantitative investigations about secondary flow in inducer impellers, if the pictures of B. Lakshminarayana (1996) are not taken into account. B. Pictures of Lakshminarayana only provide a qualitative picture and contains no information about the extent of single regions (3D-boundary layer, 3D-separation lines, singular points, kernel flow etc.). Secondary flow pictures on blades, hub and casing are not included. This knowledge gap is to be closed by the intended project. CFD flow simulations are to be performed for several inducers and the secondary flow is to be depicted. By measurements (performance- and field measurements) and oil pictures the CFD results are to be validated. Furthermore it is to be found out whether the actual design rules are appropriate to determine the axial length of an inducer. For the determination of the axial length the singularity method of Li provides a suitable method, although the loss model is insufficient from the applicant point of view. The aims are: 1) By CFD-simulations the flow topology of the three-dimensional boundary layer is to be determined for 80%, 100% and 120% (Best Point of Efficiency). The applicant is aware that by CFD this aim can be reached only partly. But the applicant succeeded in bringing together experimental and numerical oil pictures of compressor cascades in a successfully closed DFG-Project, so that he is of the opinion that it will work although he knows very well the shortcomings of this method. 2) The flow topology is to be determined by experimental oil pictures. Therefore oil paint (Company: Leinos Typ: Natural-White, Nr. 820, Density: 1,19 g/cm³) is to be mixed with petroleum (density approximately 0.85g/cm³) so that the mixture possesses nearly the density of water. At the chair SAM investigations were performed in order to test the feasibility of this method which shows satisfactory results. This method was also applied for an axial impeller pump at Pfleiderer Institute of TU Braunschweig (today IFAS). 3) The influence of sweep of the leading edge on the flow topology of the hub region is to be determined. The applicant supposes that the swept leading edge has an identifiable influence on the flow topology of the hub boundary layer, but that the influence on the flow losses is small.