Analysis of Unsteady Flow in a Vaned Diffuser Radial Flow Pump

To understand the phenomena that occur at off-design conditions, it is necessary to take into account unsteady ef¬fects that are mainly the consequences of rotor-stator inter¬actions. These interactions can now be analysed with the help of computer codes, but the numerical procedures still require experimental data for their validation. A numerical analysis of the flow in a low-pressure stage of a two-stage pump with a seven-blade runner, is pre¬sented with experimental valida¬tion at various opera-tion conditions. In order to focus upon the role of the stator-rotor inter-action on the unsteady effects and the recirculation on¬set, the single impeller was first analysed. Experimental and numerical analyses was carried out on the pump equipped with a van¬eless diffuser designed as the original multistage configuration of the vaned dif¬fuser passages. Successively, the annular cascade of stationary vanes was inserted and the influence of the stator/rotor interactions on the onset of unsteady reverse flow zones was analysed. The velocity components were measured in the vane-less part of the diffuser, and pressure measurements were performed on diffuser vanes surfaces. Furthermore, a piezo¬electric transducer placed flush with the wall was used to measure the mean pres¬sure level inside the blade channels in order to find a link between the flow field at part load and acoustic radiation. The experimental data were then compared with re-sults that were obtained with help of CFX-TASC Flow com¬puter code (AEA Technology), focusing on the chang-ing flow field at part load. The paper summarizes the impeller flow structure, the development and decay of the blade, through-flow wake, and the main features of the diffuser flow with vane¬less and vaned combinations. These evolutions was analysed considering both the lo¬cal impeller outlet flow conditions in the blade to blade section, the interactions with the diffuser blades and the influence of the leakage flow near the shroud. The leakage flow rate was experimentally evaluated.