WATER SUPPLY FLOW MEASUREMENT USING EXPERIMENTAL DATA AND CFD MODELING

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1 WATER SUPPLY FLOW MEASUREMENT USING EXPERIMENTAL DATA AND CFD MODELING Martim, A.L.S.S. 1, Costa Filho, L. S. 2, Brentan, B.M. 3, Dalfré Filho, J. G. 4 1,2,4 School of Civil Engineering, Architecture and Urban Design University of Campinas UNICAMP Campinas, Brazil 3 CRAN Université de Lorraine, Vandoeuvre-les-Nancy, France 1 sotero@fec.unicamp.br ABSTRACT The use of CFD models associated with physical models is always useful to better understand the hydraulic phenomena and allows finding new applications to existing methods. In addition, the results of the CFD model are generally faster and with lower costs. In contrast, the results of the physical model allow the validation of the results of the CFD model. Whereas that in systems of water supply, both for operation and for water loss control, the information of the inflows and outflows of the systems is fundamental, which makes the presence of a flowmeter mandatory. And even though it is not always possible to have a meter in the pipeline, the insertion meters of the Cole Pipe type can be an alternative for flow measurement. It occurs that the use of Pitot to measure the flow traditionally requires the complete determination of the velocity profile and this, in general, requires that measurements and adjustments be made in order to determine the velocity profile of the site. This work presents an application through an alternative way for computation water flow, based on the center velocity determined using Pitot Cole Tube, and the correction factor obtained from the profiles of velocity modeled with Computational Fluid Dynamics (CFD) on an experimental bench with three different assemblies: a 90 elbow, two orthogonally 90 elbows, and, finally, downstream of a gate valve, 50% opening. Keywords: Pitot Cole Tube, Flow Measument, Velocity Profile 1. Background Water distribution systems assure water for consumers, however, it is subject to deterioration over time that usually leads to problems such as the reduced utility of main purposes of network water systems. [1] Water loss, service disruption, and lower water quality. Moreover, the gradual increase in consumer demand for water creates problems as low pressure [2]. These changes, usually raises the entrance water pressure of the water distribution system, which in turn increases the number of leakage [3] and [4]. The solution of problems in water supply systems, in general, need for water measurement, and for this, flow meters. In turn, these flow meters need calibration and corrective work plans [5]. The leakage water ratio, that is, the ratio between water loss and water entering the network, measured with a flowmeter, is a factor deteriorating waterworks management and holds the greatest influence over the non-revenue water ratio. These parameters affect directly the network performance, and depending on the flow meter and its accuracy [1]. And, these parameters are directly linked to the evaluations that are often performed, sometimes, only in field calibration. 1

2 Water balance of the network is the basis for evaluating the operation of the water distribution system in terms of water consumption and loss, and depends directly on the flow meters information [6]. Moreover, for higher accuracy and to avoid the errors, flow meter calibration is needed, and this involves checking of each measuring instrument against accurate standards to determine any deviation and correct for errors. This process is time consuming and very costly [7]. In this sense, field calibration techniques, and alternating flow measurement techniques are very well accepted. In addition, hydraulic studies become easier the identification of where traditional meters may not function properly [8], and one of the alternative insertion meters that allow the use for flow measurement and field calibration widely used by water facilities companies is Pitot Cole. Pitot Cole tubes are widely used in the measurement of water flow in mains of water supply companies with application also in measurement of gas flow. There are also applications in biogas systems, in the field calibration of mass-thermal meters [9] and [10]. The great advantage of insertion meters is that they do not require interruptions in the system for installation and removal of equipment, allowing the evaluation of several locations with only one equipment, and also allowing the development of calibration techniques for flow meters in the field. Another relevant aspect of the use of Pitot tubes for flow measurement is the wide range of pipe diameters that can be evaluated, ranging from 100mm to 3000 mm, [10] and [11]. The Pitot tube is an insertion meter, which calculates the point velocity by the differential pressure measurement. The meter pressure taps are inserted into the pipe line. There are a static pressure outlet, and a dynamic or full pressure outlet. The flow rate is defined, as in other pressure meters, proportional to the square root of the measured pressure difference. This work presents an alternative methodology for the use of Pitot Cole with the objective of determining the flow in forced conduits, from the use associated with the CFD (Computational fluid dynamics) modeling. Using the CFD tools, to determine the velocity profiles of the installation, and from these profiles obtain a correction factor, as a function of the relationship between the average flow velocity and the velocity in the center of the tube, to finally be applied to the velocity value in the center measured with the Pitot Cole Tube (physical model). Thus, from the CFD modeling and the single-velocity measurement in the center of the pipeline it is possible to calculate the average flow velocity and consequently the flow rate. In order to evaluate the methodology, the velocity profiles were determined with Computational Fluid Dynamics (CFD), and also in an experimental bench, both for different installation conditions, comparing the results. 2. Methods 2.1 Laboratory Facilities In laboratory facilities at the Laboratory of Hydraulics and Fluid Mechanics (LHMF) of the School of Civil Engineering, Architecture and Urbanism of UNICAMP, velocity profiles were determined, from a test stand set up specifically for this purpose. The bench is formed by a line of PVC pipe with 0,1 m diameter. A centrifugal pump recirculates water from a lower reservoir in a forced pipe line with 160KPa of operating pressure with section completely filled by water. In the pipeline is installed in series with the Pitot tube, a witness flow meter of the type Venturi Tube Inserted. The facilities can be seen in Figure 2 (a) which represents the assembly with a 90 bend and in Figure 2 (b) with two orthogonal 90 bends. The section where the Pitot is installed is formed by 0,1m diameter PVC pipes. All the tests were performed with the pipes presented and the equipment used are all described in this work, identified with their respective serial numbers, allowing at any time the reproduction of the tests. 2

3 Figure 2 Facilities in LHMF second set up M2 (a) and third set up M3 (b) In all configurations, a 6,0m (60DN) straight line is maintained between the singularity under study and the nearest singularity upstream to eliminate any distortion of the existing velocity profile, except for the distortions caused by the singularity whose effect is being studied. In the first setup (M1), to guarantee a fully developed profile, the Pitot tube meter was installed in a straight pipeline, in standard recommended conditions. In second setup (M2) the Pitot tube meter is installed downstream a 90º bend. In third setup (M3) the Pitot tube meter is installed downstream a two 90º bend, and in the last setup (M4) the Pitot tube meter is installed downstream a gate valve. 2.2 Velocity profile plotting For the velocity profile determine, the recommendations found in the technical standards [11] and the standard [12] are followed, and the Pitot Cole Tube inserted in the piping, as can be seen in figure 3. According to [11]for diameters smaller than 100mm recommends to consider the errors due to the blocking of the section area of the pipe due to the insertion of the Pitot tube stem, this factor can be calculated through the corrected area of the section. According to [13] and [14] errors for diameters smaller than 100mm may exceed 2%. For this study, an electronic pressure transducer is used to measure the differential pressure. The positions adopted for plotting with the Pitot Tube follow the Linear Log distribution, suggested by ISO 3966 (1977), and determine by [Eq 1]. V Cd 2 g h [Eq 1] where: V: local flow velocity (m/s); Cd: Pitot tube calibration factor (= 0.87); g: acceleration of gravity (m/s 2 ); h: measured pressure differential (mmh2o); ρ: density of water kg/m 3. The coefficient used for this study is a standard value presented by [15] and [16], for the Pitot Cole tube of the manufacturer MECALTEC. For the case of the linear Log distribution adopted, it is given by equation [Eq 2], where Vc is the velocity in the center, Vm is the mean velocity, and Vij is the point velocity in each position studied by the Log-linear distribution: 3

4 11 Vij i 1 Vc Vm 1,1 [Eq 2] Figure 3 shows the scheme of insertion of the Pitot tube in the pipeline, and illustrates the adopted positioning of the meter, which was used both vertically and horizontally. Figure 3 Relative position Horizontal and Vertical Traverse with Pitot Cole Tube. 2.3 Building Profiles Using CFD CFD is used to generate velocity profiles for each assembly, and since the model determines the velocity at any point in the part section that is requested, the average velocity value is calculated based on all values of velocity of a section. SOLIDWORKS is the software used for the computational simulations of this work. The mesh generated automatically in CFD is rectangular shape and its cells are parallelepiped, cells that are close to the limit of the geometry of the part or the contact between the fluid and the geometry are cut by these limits, thus becoming polyhedral. For this study different meshes are generated, one for each configuration of the system. For the M1 configuration a mesh is generated with 630,958 cells, for the M2 configuration with 206,081 cells, for the M3 configuration with 161,762 cells and finally, for the M4 configuration with 126,260 cells. The difference in the number of cells depends on the specificities of each configuration of the system tested. The CFD model uses, for fluid flow, the Navier-Stokes (continuity, moment and energy) equations with Favre mean, which are solved based on the finite volume method. For the turbulence study, it uses the turbulence model k-ε, two basic turbulence properties, where K is the turbulent kinetic energy portion and ε the turbulent dissipation portion. The pipe dimensions and distances of the singularities of the installation up to the point of measurement of velocities obeyed faithfully those used in the physical experiment in the facilities, to reflect with fidelity, the same conditions. The boundary conditions used in the CFD software were the inlet pressure and the flow at the system. And the requested results were the velocity at the same points tested in the facilities and the average velocity in the pipe section. 2.4 The essentials of the method Since the velocity profiles are plotted (measuring and plotting the all point velocity) for all the bench setups, in physical and in CFD model. The values of the Vm/Vc ratio of the CFD model were then compared with the values obtained with the physical model. In both, four profiles are defined in each of the three flows tested, for the same conditions for the physical installation, and CFD 4

5 model. From these values, it is possible to define a very simple processing for the associated use of the Pitot Cole tube and CFD modelling, to determine the mean velocity and the flow with the measurement of a single velocity with the Pitot tube. Once the pipe line and the installation geometry (position and details of valves, curves and other line singularities) are known, it is possible to determine the Vm / Vc ratio from the CFD, indicated by KCFD, and from it to calculate the value of Vm from the value of Vc measured with the Pitot tube, and from Vm determine the flow rate. Where Vm is the average flow velocity and Vc is the velocity at the center of the pipe. The schematic summary of this proposal is shown in Figure 4. Figure 4 - Schematic summary of the proposed method 2.5 Results and discussion From the velocity profiles measured with the Pitot Cole tube (physical model), and the velocity profiles constructed through CFD modeling, the comparative graphs shown in Figures 5 to 7, which simultaneously present the values obtained by the mathematical simulation and the data measured in the model for the same installation conditions. Figure 5 shows the results obtained in the first configuration of the assembly, with 60 D of straight upstream pipeline. Figure 5 Velocity profile in real model and CFD model in first assembly. 5

6 In this work, the Vm / Vc ratio obtained for the Reynolds range from 1.6x10 5 to 2.8x10 5 is to depending on the singularity of the studied facility. In [3] and [17] show the Prandtl's experiences values for this ratio close to for the Vm / Vc ratio in the Reynolds 10 5 range. Figure 6 shows the result by the modeling in the second assembly configuration, in which a 90º curve was installed upstream of the section, located 7 D downstream of the curve. Figure 6 - Velocity profile in real model and CFD model downstream of a 90º bend. In the third assembly, in which two orthogonal 90º curves were installed, the results obtained with the real model using Pitot tube and the results with the CFD model are shown in figure 7. The velocity profiles obtained with Pitot tube present greater differences in relation to the mean velocity, than the values obtained by the CFD. The relationship Vm (average velocity of the flow) and Vc (velocity in the center of the tube) present values closer to the bibliographical references for the results obtained with the CFD modelling. Based on the profiles presented, the average velocity is calculate using the data obtained with the Pitot tube in the physical model, and the KCFD values is determined for each assembly. From these values the average velocities based on the velocity of the center multiplied by the KCFD could be calculated. The results obtained showed some differences and are presented in figure 8 (a). Figure 7 V-profile in real model and CFD model downstream of two 90º bend. Figure 8 (b) shows the relationship Vm / Vc (obtained in CFD model and Physics model) plotted versus the Reynolds Number for each test run in the facilities, these values represent the value of 6

7 the KCFD used to calculate the average flow velocity from the central velocity measured with the Pitot tube. As can be observed, the values are practically constant in the Reynolds range that was evaluated 1.5 to 2.7x10 5. The figure shows also the difference between average velocity and velocity in the center, for the data collected in the physical model, compared with the results obtained in the CFD model. To illustrate, the difference was presented in terms of correction factor, VPHYSICAL / VCFD. 3. Conclusions Figure 8 (a) Vm determined by KFCD relation. - (b) Vm/Vc ratio versus Reynolds Number in physical model and CFD model. With the results of variation Vm / Vc the relationship between the values obtained physically and the values obtained by CFD show stability in range of Reynolds number studied from 1.6x10 5 to 2.8x10 5. This range of Reynolds corresponds to the usual values of operation of pipelines by facilities companies, and also foreseen in the technical standards, as well as mentioned by [18]. The Vm / Vc ratio obtained in this study represents an adherence to what is presented by [3] and [17] and [18], for the Reynolds range of 10 5, in that referring to the Prandtl study is of The relation Vm / Vc presents stability values with low variability of results, with values approximately constant for each configuration studied, with results in the range of to depending on the singularity of the studied installation. From the pipeline data (internal diameter, material, roughness) and installation configuration, it is possible to generate from the CFD model a result set that represents a standard of the installation (as if it are installation fingerprint) that can then be used in practice to predict the behavior of the installation and allow measurement of the flow at the site studied and previously modelled in the CFD from a single velocity measurement at the center of the pipe using a Cole Pipe Tube or any other method of point velocity measurement. Thus, it is possible to define the expected Vm / Vc factors and which correction factor to be applied in the measured Vc, allowing, from the measurement of this velocity, to define the flow rate. 7

8 4. References [1] D. Jang, H. Park, and G. Choi, Estimation of Leakage Ratio Using Principal Component Analysis and Artificial Neural Network in Water Distribution Systems, Sustainability, 10, 750; [2] J.G. Saldarriaga, S. Ochoa, M.E. Moreno, N. Romero, and O.J. Cortes, Prioritized Rehabilitation of Water Distribution Networks Using Dissipated Power Concept to Reduce Non-Revenue Water Urban Water J. 2010, 7, , [3] G. J. Delmée, Manual de Medição de Vazão, 3ª Ed. São Paulo, Brasil; Edgard Blucher, [4] S.E. Galaitsi, R. Russell, A. Bishara, J.L. Durant, J. Bogle, and A. Huber-Lee, Intermittent Domestic Water Supply: A Critical Review and Analysis of Causal-Consequential Pathways Water, 8, 274; [5] D. Jang, and G. Choi, Estimation of Non-Revenue Water Ratio Using MRA and ANN in Water Distribution Networks, Water, 10, 2; [6] A.O. Kubicka, K. Wilczak,; Water Loss Reduction as the Basis of Good Water Supply Companies Management, E3S Web of Conferences 19, (2017), EEMS, [7] M. B. Salamah, A. Kapoor, M. Savsar, M. Ektesabi, and A. Abdekhodaee, The importance of accurate water metering in resource management - WIT Transactions on Ecology and the Environment, Vol 120, Sustainable Development and Planning IV, Vol [8] L. H. Maldonado, E. C. Wendland, R. M. Porto, Evaluation of low cost methods for flow measurement in streams - Revista Ambiente & Água, Vol 10, No2, 2015 [9] I.O. Buscarini, P.S.J. Barsaglini, N.M. Taira and G. Nader, Impact of Pitot tube calibration on the uncertainty of water flow rate measurement - 3rd International Congress on Mechanical Metrology, IOP Publishing, Journal of Physics: Conference Series, 648, 2015 [10] G. Nader, O.S. Yoshida and N.M.Taira, Analise da influência da mudança de ângulos de Roll e Yaw de tubo de Pitot Cole na medição da velocidade do escoamento II International Congress on Mechanical Metrology, Natal, Brazil, November 27-30, [11] ISO 3966:2008, Measurement of fluid flow in closed conduits -- Velocity area method using Pitot static tubes, International Organization for Standardization - ISO, Geneva, Switzerland, [12] BS 1042, Measurement of fluid flow in closed conduits. Pressure differential devices, British Standards, [13] E.S. Cole, "The Pitot Tube in Current Practice, Civil Engr., vol. 5, 1935, pp [14] Cole, E. S. "Pitot Tube Practice", Trans. ASME, vol. 57 (Hyd-57-8), 1935, pp [15] J. A. Pedrazzi, Critérios de projeto para um novo tip do Pitot Cole. Master Thesis, São Paulo, USP, Brazil, [16] SABESP, Manual de Pitometria Technical Guide, Companhia de Saneamento Básico do Estado de São Paulo SABESP, São Paulo, Brazil, [17] V.E. Senecal and R.R. Rothfus, Transition flow fluids in smooth tubes. Chem. Eng. Prog. Vol. 49, no10, p533, [18] J. P. Tullis, Hydraulics of Pipelines: Pumps, Valves, Cavitation, Transients, John Wiley & Sons, Inc.,