Rotating Instabilities in a Radial Vaneless Diffuser

The paper reports on experimental and numerical investigations of large-scale instabilities in a vaneless diffuser of a radial flow pump. The flow field structures were analysed at off-design operating conditions by a stereoscopic time resolved PIV technique and pressure transducers, placed flush with the diffuser walls. Spectral analyses were carried out both on the velocity and pressure signals to identify the characteristics of the instabilities. The experimental data were compared with the numerical results obtained by ANSYS CFX computer code to study the evolution of the flow field instabilities at part load. The numerical computation was performed on the entire pump with the transient sliding faces and the turbulence DES model. The leakage effects were taken into account. The time step for the calculations was chosen according to a runner rotation of about 1 degree