Ignacijo Biluš

Numerical and experimental approach to cavitation surge obstruction in water pump

Purpose – This study aims to present the analysis of methods for cavitaion surge obstruction in water pump systems with particular focus on the two different inlet geometry configurations.Design/methodology/approach – A cavitating flow field was simulated by RANS based computational fluid dynamics (CFD) program for different pump configurations operating in the unstable cavitation regime, inducing surging process. Numerical simulation results were compared to visualization and measurements results.Findings – Presented results show that a hydro dynamically induced surging regime could be limited and further advantages regarding operating characteristics of radial pumps could be achieved with presented geometry modifications.Originality/value – This study provides insight into complicated transient cavitation flow patterns in conventional centrifugal pumps and introduces effective geometry optimization ideas useful to researchers and engineers in the area of fluid dynamics and hydromachinery.

The extended homogenous cavitation transport model

Cavitating flows are complex three dimensional flows with phase change in the low pressure regions. These are very sensitive to bubbles formation process and to velocity/pressure pulsations caused by turbulence. The presented cavitation model derived from a reduced Rayleigh–Plesset equation accounts for some of these effects. This model is based on the additional generic transport equation for vapour phase. The cavitation influence over the mixture density and viscosity is included in the model, which is implemented in commercial, general purpose Computational Fluid Dynamics code and validated on practical flow examples

Influence of additional inlet flow on the prerotation and performance of centrifugal impellers

In this paper we present the results of our experimental analysis regarding the influence of additional flow when added at the radial impeller entrance eye. This analysis was done on both operating and prerotation flow characteristics. The experimental system tested was arranged to operate using air. The additional flow adding system (AFAS) was placed at the entrance eye of the impeller through the guide system, which consists of the spiral volute at the entrance, ring guide pipe (where the guide vanes are placed), and a ring - like hollow at the end of the AFAS. The ring - like hollow was placed near the shroud at the entrance edge of the impeller blades. The guide vanes in the AFAS were placed in the axial direction, so that the added flow had no swirl component. The operating regime was tested, whereby the AFAS was filled by the flow under atmospheric pressure (non-forced loading). A good influence was evident on the operating characteristic. The stable operating range was enlarged and the operating noise decreased. The achieved impeller head and the overall efficiency increased.

Non-contact method for analysis of cavitating flows

&NA; This paper presents a novel non‐contact method for simultaneous analysis of pressure and velocity conditions in cavitating flows. The method (implemented in our software ADMflow) is based on high‐speed camera flow visualization and was evaluated in an experiment with ultrasonically induced acoustic cavitation of different intensities. Attached cavitation with clearly visible cavitation structures occurred on the tip of an ultrasonic probe immersed in distilled water. Using the high‐speed imaging data, pressure fluctuations were calculated by a computer‐aided algorithm based on the Brennens theory of cavitation cloud kinematics and a modified version of the Rayleigh‐Plesset equation. Reference measurements of pressure pulsations were conducted by a hydrophone installed at the bottom of the liquid container. The analysis of cavitation structure dynamics was complemented by calculation of velocity fields from the imaging data, the algorithm for which is based on the advection‐diffusion equation. Calculated pressure fluctuations were analyzed in the spatial, temporal and spectral domain. Presented results indicate a strong correlation between the fields of velocity and pressure fluctuations during the growth and collapse of cavitation structures. A comparison of time series and power spectra demonstrates that our cavitation analysis method is in a reasonably good agreement with results of the reference measurement methods and can therefore be used for non‐contact analysis of pressure and velocity conditions in cavitating flows. HighlightsA method for simultaneous flow pressure and velocity measurement is presented.Method evaluation on high‐speed images of ultrasonic cavitation on a sonotrode.Deviations of optically and hydrophone measured pressures are reasonably low.Optically and hydrophone measured pressure power spectra are in good agreement.Subharmonic pressure oscillations are detected by both measurement methods.

Extended homogenous mathematical transport model for thermo dynamical surge analysis

Purpose – The purpose of the paper is numerical simulation and experimental analysis of a cavitation operating regime in a centrifugal water pump. The main goal is to extend the mathematical model to be able to predict the phenomena where thermodynamic process is controlled by an hydrodynamic flow pattern.Design/methodology/approach – The mathematical model is being extended and used for numerical simulation of an unstable operating regime in a water pump. Numerical simulation results were compared to thermal imaging system visualisation and flow variables measurements results.Findings – The presented approach increases the system stability. The model can be used for simulation of system instabilities that involve not just the pump characteristics but those of the complete piping system. Modified turbulence model including compressibility effects lead to reliable simulation results of pump unsteady cavitation behaviour.Research limitations/implications – The research was limited to an homogenous cavitatio...