11th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
The ongoing research on counter-rotating blade rows in single stage machines has shown promising results on improvement of efficiency and pressure ratios in high specific speed impellers, with conventional applications such as naval propulsion etc, axial pump and fan. The focus of the design presented below has been the development of a compact design with high power density and improved cavitation performance. The new design offers a downsizing opportunity with its two impellers: a mixed-flow front rotor (FR) and the radial rear rotor (RR), instead of a stationary bladed diffuser. With this set the off-design working range can be extended, reaching a high adaptability at different flow conditions. An improvement on cavitations performance can be obtained also moving the load from the FR to the RR. In this paper the first prototype is numerically and experimentally analyzed. Head drop and cavitation inception curves besides the characteristic curves are highlighted. Design improvements have finally permitted to develop two new versions of the FR, which have been numerically investigated. The first one is expected to provide improved cavitation performance, while the second one higher power density. Finally the sensitivity of the system to the speed ratio has been experimentally investigated. The CFD results show good agreement with the tests within the uncertainty of the experimental measurements.