Sami Elaoud

Automated Framework for Water Looped Network Equilibrium

In this paper, a novel algorithm is proposed for balancing water looped network in steady state through a fully automated general framework of hydraulic networks regardless of their topological complexity. The model is developed by combining the following two steps, firstly a set of independent loops are identified based on a graph theoretical analysis in a looped network. Further the second step is devoted to the equilibrium process by determining the flow rate distribution within the network ducts and the pressure in the delivery nodes. The above such equilibrium process gives rise to a system of non linear algebraic equations which are solved numerically using both Hardy Cross (HC) and Newton Raphson (NR) methods. In HC method, the flow correction term is modified and a generalized expression is given to consider various possibilities of independent loops selection. Some real networks topologies that were commonly used as benchmarks, for testing various independent loops selection algorithms, are taken as case studies to apply the general automatic framework for hydraulic network analysis. Such network analysis enhances proving the applicability as well as the effectiveness of the proposed approach. Also, during the equilibrium procedure, it is proved that NR method is capable of producing accurate results and it converges more rapidly comparing to the widely used HC method. Moreover, it is demonstrated that NR’s iterative process, contrary to HC’s one, converges to reliable results even with a choice of random initial flow rates which makes a NR algorithm quite simple to implement without affecting the accuracy of the results.

Effect of the Volute Diffuser Shape on Pressure Pulsations and Radial Force in Centrifugal Pumps

Centrifugal pump is a major cause of pressure perturbations in hydraulic installations. The internal geometry of this turbomachine and its running conditions affect excessively the magnitude of these excitations. In the present study, a numerical investigation is conducted to analyze the influence of the volute diffuser type on flow characteristics in centrifugal pumps with the same impeller under wide range of flow rate. An unsteady numerical analysis was carried out in order to study the strong interaction between blade and tongue with two different geometries of the volute. The main objective is to analyze the characteristics of pressure and force fluctuations inside the pump. For tangential diffuser shape, the pressure fluctuation amplitudes are greater than that in the case of a radial diffuser. Based on the fast Fourier transform (FFT), the spectral analysis was performed on the pressure fluctuation signals in frequency domain under running condition for two volute at different monitoring points in the pump. The time frequency characteristics of these pressure fluctuations were affected greatly by both volute type and measurement locations in each diffuser. However, simulation results were compared with the available experimental data, and an acceptable agreement was obtained. The results obtained in this work can provide a useful reference for designing the type of volute diffuser in pump.

Independent Loops Selection in a Hydraulic Looped Network

As a preliminary important phase for a hydraulic network analysis procedure, loops identification process is studied in this paper by presenting an automated algorithm to select a set of independent loops for the network equilibrium. Through the presented study, the hydraulic network is modeled as an undirected graph edges-vertices. Also, to take into consideration the mechanical characteristics of the network, weights are assigned to pipes based on their hydraulic resistances. The assigned weights are taken as a selection criterion for loops identification. A numerical code under Matlab environment is generated and the established framework is tested on a set of real case networks. The obtained results are compared to those issued from previous researchers. Thus, the framework has proved its efficiency in identifying a set of independent loops even for complex network topologies. The mutual independence of the obtained loops is verified which allows to use the presented algorithm to build a general automated framework for water distribution network analysis.

Three-Dimensional Numerical Flow Simulation in a Centrifugal Pump

This paper shows numerical simulations of the three-dimensional fluid flow through centrifugal pump. The standard turbulence model k − − e is adopted to describe the turbulent flow process. These simulations have been made with a steady calculation using the multiple reference frames (MRF) technique to take into account the impeller volute interaction. The computational domain composed by a single stator and rotor blade passages is discretized by a structured multi-block meshes .The transport equations associated with the appropriate boundaries conditions are solved by the ANSYS CFX finite-volume code. In addition, the steady state simulation are made to construct the performance for centrifugal impeller. This work is aimed to analyze the pressure and velocity distribution inside the pump impeller using the ANSYS-CFX computational fluid dynamics simulation tool.

New Correlation for Hydrogen-Natural Gas Mixture Compressibility Factor

In this paper, new correlation of hydrogen-natural gas mixture compressibility factor will be built. Based on Soave Redlich-Kwong (SRK) real gases equation of state (EOS) and under an isothermal condition, the evolution of gas compressibility factor will be followed up and compared to experimental data. The established correlation will be used to solve equation of motions in steady state and to evaluate the pressure drop through hydrogen natural-gas mixture pipeline.

Iterative Methods for Steady State Looped Network Analysis

The aim of this paper is to numerically study the steady state of water flows in looped networks. This study will be performed by the use of Hardy Cross Method and Newton-Raphson algorithm. The comparison of the numerically obtained results by these two methods to those obtained by the use the commercial software Pipe Flow Expert has shown a good concordance between them. The numerical analysis has shown that the convergence of Newton-Raphson method is more rapid than that of the classic Hardy Cross Method.

Transient Flow Analysis through Centrifugal Pumps

A theoretical study has been carried out on the transient flow through a centrifugal pump during the starting period. The problem is governed by two hyperbolic partial differential equations which the continuity and the motion equations. The mathematical model is solved numerically by using the method of characteristics with specified time intervals. The comparison between the obtained numerical results and those obtained by experiment has shown a good concordance. In this study, the effect of the starting time, the impeller diameter, the number and the height of blades on the pressure increase were analyzed. The numerical results have shown that the pressure increase is inversely proportional to the starting time. However, during the starting period, these results have shown that the number of blades has no significant effect on this pressure increase.

Numerical Study of Anti-ram of Hydraulic Lines by an Additional Viscoelastic Pipe

The purpose of this paper is to study numerically the effect of adding a short viscoelastic pipe in series with a main quasi-rigid pipe on water hammer phenomenon. The model takes into account the viscoelastic behaviour of the added pipe. The governing equations of such phenomenon are two coupled, non linear, hyperbolic, partial equations. The fluid pressure and velocity are considered as two principal dependant variables. The problem has been solved by the non linear method of characteristics. The obtained results show that the deformability of the additional pipe reduces the celerity of pressure waves and significantly alleviates the pressure fluctuations.