Andrej Predin

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 Analysis of the Impact of Particles on Cavitation Flow Development

The purpose of this paper is to present an analysis of the impact of solid particles on the development of cavitation flow conditions around a hydrofoil. Experimental studies were conducted in a cavitation tunnel with different mixtures of particles and water. The effect of the particles on the development of cavitation flows was modeled by using an additional phase particle dispersion model (Euler-Euler). Numerical modeling was performed using the CFD software. The impact on the cavity model with the parametric analysis of the entry conditions of particles in the calculation domain was investigated, with a focus on the solid shear viscosity. Another purpose of this research was to present the possibility of modeling the development of the vapor phase in the commercial CFD software package, while taking into account the impact of particles. This paper presents the results of the experimental measurements and their comparison with numerical simulations.

Performances and Flow Analysis in the Centrifugal Vortex Pump

Improvements to the characteristics of a centrifugal pump through the addition of a vortex rotor were investigated both experimentally and with computational fluid dynamic (CFD) analysis. The idea behind that improvement is in creating so-called coherent structures of eddies and turbulence in the peripheral area of the vortex rotor mounted at the back side of centrifugal rotor. Research on the energy transformations in the centrifugal vortex pump in this work was carried out using numerical simulations of the flow in the centrifugal and the centrifugal vortex pump. Measurements of relevant parameters that describe the performance of pumps, at their physical models, were gained from experiments. The measurement results were used as experimental validation of numerical simulations. In contrast, flow visualization derived from the numerical simulation was used to interpret measurements. In deriving the experimental procedure, special care was taken with the flow measurements. The reason for this is in the fact that the flow measurements had the biggest influence on the overall measurement uncertainty. However, flow measurements were the most demanding with regards to the experiment design and in taking the measurement readings. This experimental-CFD research made it possible to undertake an assessment of vortex rotor contribution on the head of the centrifugal vortex pump. The influence of the vortex rotor on the efficiency of the centrifugal vortex pump was investigated by comparing it with the efficiency of the centrifugal pump with the same geometry. An analysis of the flow structure was conducted in order to better understand the energy transformations that are the result of the interaction between the flow from the channels of the centrifugal part of the centrifugal vortex rotor and vortices formed at the vortex part of the centrifugal vortex rotor as well as their interactions with the stator. It was shown that this additional energy significantly increases pump head while increasing pump stability. This synergetic work has demonstrated that while vortex rotor gives additional energy to the fluid particles, that did not enter stator due to the energy lack by changing their momentum ; at the same time, some of the kinetic energy contained in the vortex rotor induced vortices is also added to those fluid particles.

CFD flow analysis in the centrifugal vortex pump

Purpose – Aging of the oil wells leads to a decrease in reservoir pressure and also to an increase in the water, gas and abrasive particles content. Therefore, there is a need for the oil pumps exploitation characteristics improvements. This paper aims to generate a valuable numerical model which will provide a useful tool to study various cases. Design/methodology/approach – Computational fluid dynamics (CFD) analysis of the generation of so-called coherent structures of eddies and turbulence in the peripheral area of the vortex rotor mounted at the back side of centrifugal rotor was undertaken. After detailed analysis of the influence of the used turbulence models on the results, a hybrid turbulent model Detached Eddies Simulation (DES) was chosen as the most suitable. Findings – Numerical control volume method with unsteady solver and DES turbulence model was proven to be valuable tool for flow analysis in the centrifugal pumps. Having in mind that DES turbulence model consumes much less computational ...

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.

Torsional Vibrations at Guide-Vane Shaft of Pump–Turbine Model

This article focuses on the problem of guide-vane vibrations of reversible pump–turbines, especially, in the pump mode. These vibrations are transmitted to the guide-vane shaft torque. The guide-vane vibrations are caused by the impeller exit flow, which has a turbulent and partly nondeterministic property. Experimentally determined flow velocities at the impeller exit are given. The mathematical models for theoretical torsional vibration prediction formulated using linear and nonlinear differential equations are presented. The results of theoretical calculations are compared with measurement results. The possibility of transferring the parameters from the model to the prototype is discussed.

Emergency Gate Vibration of the Pipe-Turbine Model

The vibration behavior of an emergency gate situated on a horizontal-shaft Kaplan turbine is studied. The analysis and transfer of the dynamic movements of the gate are quite complex. In particular the behavior is examined of the emergency gate for the case when the power unit is disconnected from the system or there is a breakdown of the guide vane system at the moment when the maximal head and capacity are achieved. Experimental-numerical methods both in the time domain and in the frequency domain are employed. Natural vibrations characterize a first zone, corresponding to relatively small gate openings. As the gate opening increases, the vibration behavior of the gate becomes increasingly dependent on the swirl pulsations in the draft tube of the turbine. Finally, the data transfer from the model to the prototype by use of the dynamic similitude law is discussed.

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...