Static pressure recovery analysis in the vane island diffuser of a centrifugal pump

The overall performance of a vane-island type diffuser of a centrifugal pump model was obtained by means of directional probe traverses. These measurements were performed in an air model of a real hydraulic pump for five volume flow rates. Directional probe traverses are performed with a classical three-hole probe to cover most of the complete inlet section of the diffuser from hub to shroud and from pressure to suction side. Existing Particle image velocimetry (PIV) measurement results are also used to compare probe measurement results between the inlet and outlet throats of vane island diffuser at mid-span. Some assistance from already existing unsteady calculation, including leakage effects, is used to evaluate the numerical approach capability and to correctly define the mean initial conditions at impeller’s outlet section. Pressure recovery and the measured total pressure loss levels inside this particular vane diffuser geometry are then calculated. Detailed analysis of the flow structure at the inlet section of the vane island diffuser is presented to focus on pressure evolution inside the entire diffuser section for different flow rates. The combined effects of incidence angle and blockage distributions along hub to shroud direction are found to play an important role on loss distribution in such a diffuser

"Low Cost" Approaches for the Prediction of Rotating Instabilities in the Vaneless Diffuser of a Radial Flow Pump

The instabilities, occurring in pumps operating at partial flow rates, may directly cause several negative effects, such as vibration, noise, mechanical damage. The present study is focused on the investigation of the instabilities developing in the vaneless diffuser of a radial flow pump. The prediction of this kind of complex phenomena by numerical simulation usually involves complex (3D unsteady) and expensive calculations. The main goal of this paper is to propose and evaluate some “low cost” numerical or analytical approaches to predict the arising and the characteristics of rotating stall instabilities. For that purpose, two-dimensional numerical unsteady calculations were used. The boundary condition for the diffuser inlet was based on the flow field at the impeller outlet and static pressure was set at the diffuser outlet. The simulations have been managed for several flow rates conditions. The results of the numerical simulation are discussed and compared to i/ an already existing database (including PIV and pressure measurements), ii/ results of a 2D linear stability analysis

Data reduction problems using a 3 holes directional pressure probe to investigate mean flow characteristics in the vaneless gap between impeller and diffuser radial pump

Among several different measurement techniques that have been already performed and presented in a radial impeller pump model including PIV, a directional pressure probe has been used to obtain mean velocity field and stagnation pressure between impeller outlet and the inlet vaned diffuser sections. These measurements are supposed to get more information not only about global pump head coefficient including vaned diffuser ones but also about impeller performances itself. Pressure probe information is affected by rotor-stator interactions and impeller rotation, and this paper presents a way to explain and correct pressure probe indications in order to achieve a better evaluation of overall impeller mean performances. The use of unsteady RANS calculation results is found to be a useful way to perform better data reduction analysis for this purpos

Optical PIV and LDV Comparisons of Internal Flow Investigations in SHF Impeller

The paper presents a comparison between two sets of experimental results in a centrifugal flow pump. The tested impeller is the so-called SHF impeller for which many experimental data have been continuously produced to built databases for CFD code validations with various levels of approximation. Measurements have been performed using optical techniques: 2D particle image velocimetry (PIV) technique on an air test model and 2D laser doppler velocimetry (LDV) technique on a water model, both for different flow rates. For the present study, results obtained by these optical techniques are compared together in terms of phase averaged velocity and velocity fluctuations inside the impeller flow passage for design flow rate