Experimental and numerical investigation of three, constant and variable pitch, inducers.

Authors

Djaafer Fedala  - Global Technology, Sulzer pumps
Sofien Bouajila - Global Technology, Sulzer pumps
Stefan Berten - Global Technology, Sulzer pumps
Tobias Roeseler - Global Technology, Sulzer pumps
Laurent Chatagny - Global Technology, Sulzer pumps

Abstract

Inducer are coupled to pump impellers to improve their suction performance without increasing the size of the pumps. Different cavitation modes could appear inside inducers depending on the operating conditions. Such three-dimensional and unsteady phenomena influence their performances and their stability. Design parameters have been identified to have a direct impact on cavitation regime developments. In this context, an experimental and numerical investigation has been carried out on three inducer prototypes: a basic constant pitch 11° beta angle inducer, a variable pitch inducer with same main dimensions and a swept version of the variable pitch inducer. The test configuration has been built to quantify inducer performance alone, without the interaction of the suction pump impeller. A campaign of tests has been conducted on this test bench allowing cavitation observations, performances and vibration levels measurements on the three inducers. Meanwhile, CFD simulations of the flow inside the inducers have been conducted using ANSYS-CFX software and different models: one interblade channel/full rotor, steady/unsteady, single phase/homogeneous cavitation model. Obtained results allowed to assess CFD accuracy on performance prediction depending on the cost of the different CFD modeling. Unsteady simulations show direct correlation between suction pressure fluctuations and measured vibration levels. On the three configurations, it has been shown to be a good approach to evaluate the instability flow region. While the prediction of the head drop curves remains a challenge, the development of cavitation pockets on the blade correlates well with the breakdown of the inducers. The constant pitch proved to have the best suction performances for low flow coefficients, while the variable pitch inducer reduces instability flow rate. Positive effect of the sweep has been observed on suction performances and limitations of instability magnitudes.