EXPERIMENTAL WORK AND CFD MODEL FOR FLOWRATE ESTIMATING OVER OGEE SPILLWAY UNDER LONGITUDINAL SLOPE EFFECT

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 13, December 2018, pp , Article ID: IJCIET_09_13_042 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed EXPERIMENTAL WORK AND CFD MODEL FOR FLOWRATE ESTIMATING OVER OGEE SPILLWAY UNDER LONGITUDINAL SLOPE EFFECT Sadiq Salman Muhsun Assistant Professor, Department of Water Resources, College of Engineering, University of Al-Mustansiriya, P.O. Box 14150, Bab-al-Mu'adhem, Baghdad, Iraq Zainab T. Al-Sharify Lecturer, Department of Environmental Engineering, College of Engineering, University of Al-Mustansiriya, Baghdad, Iraq Academic visitor, School of Chemical Engineering, University of Birmingham, Birmingham, United Kingdom. ABSTRACT The basic purpose of the spillway is to provide a means of controlling the flow and providing conveyance from reservoir to tail water for all flood discharges up to the spillway design flood. In this paper, an OGEE spillway model was developed to study the effect of the longitudinal slope So on the depth of the spillway crest Y og and its relationship with the critical depth Y c and flowrate. A laboratory experiment was conducted to determine the relationship between the two depths by considering ten different values of the slope ranging from 0 to 0.02.Statistical regression analysis indicates that the relationship between Yc and Y og is about 1.2 and has insignificant change with changes in the value of the longitudinal slope So. Using this relationship, a new flowrate formula over an OGEE spillway was obtained. Comparing the results of the traditional formula with that of the ogee spillway, it was found that the latter agrees quite well with all of the experimental flowrate data for the ten different slope values. The average error of estimating the flowrate by the new and traditional formula respectively was found to be about 3.37% and 9.93% respectively. The problem was also simulated using computational fluid dynamic techniques with ANSYS Ver. 15 program. The simulation model provided a very good representation of the stream flow pattern and had a very agreement results with respect to the suggested formula. Existing such power formula provides engineers with another tool in the estimating of flow rate in additional to the design and analysis of OGEE spillways. Key words: Ogee spillway, critical depth, crest depth, flow measurement, CFD editor@iaeme.com

2 Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect Cite this Article: Sadiq Salman Muhsun, Zainab T. Al-Sharify, Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect, International Journal of Civil Engineering and Technology (IJCIET) 9(13), 2018, pp INTRODUCTION The OGEE shape was first comprehensively investigated [1], many authors studied the physical model data from USACE and USBR [2-6]. Even since the first half of the 1950s, the US Army Corps of Engineers has through its Waterways Experiment Station, focused greatly on the behavior of water discharged over spillways [7]. In this regard, the documentation and preservation of numerous hydraulic design charts has been conducted. To aid with the design of a spillway profile for different flooding scenarios [8] prepared a detailed manual for engineers and professionals. The drawback of this manual is the lack of wide ranging flood scenarios covered by the design charts which in turn results in its applicability for only limited spillway profiles. The Overflow (or OGEE) spillway as it is known can be described as an S-shape control weir possessing spillway in terms of its profile. Functioning similar to a dam, a spillway as part of the dam itself provides an avenue for the safe passage of water over it. In various civil engineering applications such as barrages and weirs, spillways also function as diverting agents for excess amounts of water that is diverted to different canals, thereby prevent flooding. This spillway uses the additional water from the top part of the pool for diversion. Spillways are extremely important for maintaining river systems as they prevent any harm from occurring during flow from upstream to downstream points. In engineering terms, they can be compared in function to safety vales in boilers. Generally, ogee spillways are utilized as ''flood release structures on dams'' [9]. Several authors [10, 11] have stressed upon the need to continuously update the criteria required for safe hydraulic structures to keep pace with the changes in climate and potentially hazardous after effects on structural integrity and capacity. This has resulted in the need for continuous expansion and upgrade of spillway capacities to meet the increasing discharge volumes and heads respectively. They have noted that these requirements have resulted in the global need for measures such increasing the dam height or individual spillway modifications to cope with the increased capacity requirements. In the case of a gated OGEE spillway, one technique to improve its capacity is to remove the parapet wall which directly improves the functioning of the lower outlet. Cost and hydraulics are two important aspects that need to be taken into account when deciding how to improve capacity. For this purpose, the use of a hydraulic model for optimizing crest modification and the resulting downstream flow effects is critical. These physical tests investigate spillway alterations, sediment control, wave movements, energy losses and turbulent motions to name a few parameters [11]. One of the key aspects of past research has focused on the determination of the crest shape for an overflowing spillway dependent upon the slope of the upstream face and the relative height [5]. Another author used an analytical functional boundary value to expand upon the potential flow theory to describe a spillway characterised by a free drop [12]. However, others built upon their work by modifying and achieving a solution to the Reynolds-averaged Navier-Stokes (RANS) equations in both 2D and 3D computational scenarios [13]. The authors utilized the standard k-ε equations to model turbulence and the results showed a promising level of agreement with a specified set of flows in terms of discharge coefficients and the water body surface. Using both a physical and computational OGEE-crested spillway editor@iaeme.com

3 Sadiq Salman Muhsun, Zainab T. Al-Sharify model [14-16]. It was reported that a two-dimensional investigation was adequate and time efficient computationally to determine the key flow parameters [17]. Although the literature may appear exhaustive, few studies have focused on the effect of the longitudinal slope S o on the depth over the OGEE spillway. Therefore, the objective of this work is to study this effect and to find a relationship between the depth over the spillway Y ogee and the critical depth Y c. 2. MATERIALS AND METHODS The experimental facility is a self-contained tillable laboratory flume 170 cm in length and 5 cm wide. The OGEE spillway was located in the middle of the flume. A movable point gauge and a vernier assembly was located above the crest of the spillway to measure the water depth Y ogee. The flume was located above a hydraulic bench to estimate the flow rate as in [18]. Ten tests for slopes for values ranging from 0 to 0.02 were conducted. Each test had eight different values of flowrate where the depth over the spillway was measured at each value. The experimental tests were conducted in the Al- Mustansiriya University Hydraulic Engineering Laboratory. Figure 1 exhibits the different devices that were used during the experiment. The set up consisted of a main open canal flue of 1.5 m length and 0.51 m width. The canal was fitted above an Armfield, F1-10 Hydraulic Bench. A steel model of OGEE spillway of m height and 0.51 m width was used to achieve the experimental tests in additional to a vernier and stop watch. A simulated model based on the principles of computational fluid dynamics (CFD) technique was also designed and used to simulate the problem. The results of the simulated model were then used with the help of the experimental results to verify and check the target formula for flowrate estimation. Figure 1:Photograph of the a) hydraulic bench and flume, b) Vernier and OGEE spillway. 3. RESULTS AND DISCUSSION In this Section, all of the results of the experimental investigation will be explained and discussed in more detail. Table 1 shows the methodology for finding the critical depth (Y c )and the actual depth over the OGEE spillway (Y c ) for a nill horizontal longitudinal slope i.e. S o = 0. Figure 2 shows the relationship between the critical depth and the actual depth for the same slope S o Effect of longitudinal slope So on the Y c Y og Relationship The results of the critical depth (Y c ) versus the actual depth over the OGEE spillway (Y c ) have been plotted in Figure 2. It can be seen that a linear relationship exists between the theoretical critical depth (Y c ) and the actual depth over the crest of spillway (Y og ).Therefore, the relationship may be expressed in the following form: editor@iaeme.com

4 Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect Y = M * Y c og Where M is a constant value that represents the slope of the best-fit line of the linear relationship. From Figure 2 the statistical method of the linear regression analysis indicates that the value of M is approximately Equation 1 now becomes: Y c =1.1802* Y og (1) for S o = 0 (2) All other values of M corresponding to their slopes are listed in Table 2. Figure 3 presents the relationship between the longitudinal slopes o and the value of M for all ten experiential tests when S o varies from 0 to As shown in the figure, the longitudinal slope S o has no significant effect on the values of the constant M for the Yc Y og relationship. Therefore, it can be stated that the value of M equals the average value of 1.2 as indicated in Table 2, i.e., Y =1.2016* Y for any slope S o (3) c og This means that the actual depth over the OGEE spillway has a significantly lower value than the critical depth Y c by approximately 20%.From hydraulic principles, the flowrate can be estimated depending upon the critical condition formula [19, 20]. b g 2 3 for any slope S 2 o (4) 2 3 gb Y c (5) In the case of a spillway, Eq. 5 must be adapted to determine Y c (from Eq. 3) before usage. Eq. 5 will now take the following form for any value of So: gb ( Y og ) (6) Where is the flow rate in m 3 /s or ft 3 /s depending on whether g = 9.81 m/s 2 or g = 32.2 ft/s 2 respectively. Y og is the depth over the crest of the OGEE spillway and b is the channel width in meters or feet. Figure 4 shows the verification of equation 6 corresponding to the actual flowrate for all slopes. As the figure shows, the formula indicates an excellent agreement for all cases Traditional formula of an overflow spillway The discharge over a spillway can be computed by the traditional formula from Figure 5: C 2g LH 32 e d (7) Where H e is the total energy head on the crest in meter including the velocity head in the approach channel= H + V 2 /2g, L is the length of the spillway in meters and C d is the discharge coefficient which depends on H e and the height of the spillway P. The discharge coefficient C d is the most important factor in Eq.7 because it varies with the total energy head on the crest and it is not easy to estimate. More information about the formula can be found in literature [2, 21-26]. Under the conditions of our model with P/H d greater than 2 (where H d is the design head excluding the velocity head), the value of C d can be calculated as [27]. With this value of C d and for a horizontal slope So as an example, the flowrates were estimated and compared with the corresponding values obtained by Eq.6, as illustrated in Error! Reference source not found.. As shown in the editor@iaeme.com

5 Sadiq Salman Muhsun, Zainab T. Al-Sharify figure, results using Eq.6 are more accurate than the results obtained by the traditional formula (Eq.7); and the error increases as the flow rate increases as shown in Table 1. Vol. (L) Time ( sec) Actual ( l/s) Table 1: Experimental work results for S o =0 Y c b g Y og (cm) He (cm) Eq.6 Er. % Eq.7 Er. % (cm) Average error 3.37% 9.93% Table 2: The values of the constant M corresponding to the longitudinal slope S o. No. Longitudinal slope S o M - values Average Figure 2: Y c vs Y og Relationship for S o =0. Figure 3: The effect of longitudinal slope S o on the values of the constant M editor@iaeme.com

6 Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect Figure 4: Verification of the Equation6 corresponding to the actual flowrate for all slopes. Figure 5: OGEE spillway, where H is the height and P is the height of the spillway, Y og is the Figure 6:Comparison between Equation6 and traditional formula for S o = COMPUTATIONAL FLUID DYNAMIC SIMULATION Computational fluid dynamics (CFD) technique is a very powerful tool to simulate various fluid dynamic problems [16, 28, 29]. In this study, ANSYS V was considered to simulate the flow over ogeespill way as shown in Figure (7) and Tables (3 & 4). For the case study of a horizontal slope with flow rate of (0.609 l/s), Figure (8 & 9) explain the water volume fraction and the stream flow pattern while the Figure (9) shows the velocity distribution over the crest of the spillway. As the figures indicated, the simulation model provides a very good simulation for the stream flow pattern. Table 5 shows another verification of Eq.6 with respect to the results of the simulation model and the experimental value for some elective tests. The table shows a very good agreements of the suggested formula of (Eq.6) for all cases with a percentage error less than 10% editor@iaeme.com

7 Sadiq Salman Muhsun, Zainab T. Al-Sharify Figure 7: Simulation model meshing. Figure 8: Simulation model for water volume fraction pattern. Figure 9: Simulation model for stream flow pattern. Figure 10: Velocity distribution over crest spillway from simulation model results

8 Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect Table 3: Model Meshing No. Item properties No. Item Properties 1 Object Name Mesh 26 View Advanced Options No 2 State Solved 27 Assembly Meshing 3 Defaults 28 Method None 4 Physics Preference CFD 29 Patch Conforming Options 5 Solver Preference Fluent 30 Triangle Surface Program Mesher Controlled 6 Relevance 0 31 Patch Independent Options 7 Sizing 32 Topology Checking Yes 8 Use Advanced Size Function On: Curvature 33 Advanced 9 Relevance Center Fine 34 Shape Checking CFD 10 Initial Size Seed Active Assembly 35 Element Midside Nodes Dropped 11 Smoothing Medium 36 Number of Retries 0 12 Span Angle Center Fine 37 Extra Retries For Assembly Yes 13 Curvature Normal Angle 14 Min Size 15 Max Face Size 16 Max Size Default (18.0 ) 38 Rigid Body Behavior Default (2.0523e- 004 m) Default (2.0523e- 002 m) Default (4.1046e- 002 m) Dimensionally Reduced 39 Mesh Morphing Disabled 40 Defeaturing 41 Use Sheet Thickness for Pinch 17 Growth Rate Default (1.20 ) 42 Pinch Tolerance Minimum Edge Generate Pinch on 18 7.e-003 m 43 No Length Refresh 19 Inflation 44 Sheet Loop Removal No Use Automatic Automatic Mesh Based 20 None 45 On Inflation Defeaturing 21 Inflation Option Smooth Transition 46 Defeaturing Tolerance 22 Transition Ratio Statistics 23 Maximum Layers 2 48 Nodes Growth Rate Elements Inflation Algorithm Pre 50 Mesh Metric None Table 4: Model Geometry Parts Material Fluid/Solid Defined By Geometry (Solid) Bounding Box Length X 1.4 m Length Y m Properties Volume 0. m³ Centroid X m Centroid Y e-002 m Surface Area(approx.) m² Statistics Nodes 9565 Elements 9204 Mesh Metric None No Default (1.8471e- 004 m) Default (1.0262e- 004 m) editor@iaeme.com

9 Sadiq Salman Muhsun, Zainab T. Al-Sharify Table 5 Verification of the Eq.6 according to the actual and simulated model results. So Actual (L/s) of Eq.6 (L/s) of Simulation model (L/s) Error % of Eq.6 based on actual Error % of Eq.6 based on Simulated CONCLUSIONS The results of the experimental work and mathematical analysis show that the ratio of the value of critical depth (Yc) and crest depth (Y og ) is constant and the former undergoes insignificant change with changes in the value of the longitudinal slope S o. Where the relation between them (Yc / Yog) is about 1.2 maintaining about this value however the longitudinal slope So has been changed. The study indicates the ability of adapting the depth over the crest of an OGEE spillway to estimate the flowrate over the spillway itself. The resultant formula gives a very good agreement in comparison with the traditional formula with the average error of the former being 3.37% compared to 9.93% to the latter respectively. Also, the formula has insignificant errors comparing with the results of the computational fluid dynamic simulation model with a percentage error less than 10% in a worst case. ACKNOWLEDGMENTS The authors acknowledge the support of Mustansiriyah University, College of Engineering and the Hydraulic Laboratory staff for their for their support with the experiments. REFERENCES [1] Bazin H. E. (1888), Recent experiments on the flow of water over weirs, Proceedingl, EngiMel'8' Club of Philadelph.ia, 16:(6): Ba.zin's data were reprinted almost eutirely by G. W. Rafter in Report on special water-supply investigation, Congressional Documents 4146 and 4147, WaShington, D.C., pp , l990; and Hydrology of the State of New York, 'l'few York State musuem Bulletin 85, Albany, N.Y.,1905. [2] Chow, V. T., (1986), Open-channel hydraulics, McGraw-Hill, New York, [3] Murphy, T. E. (1973), Spillway crest design. MP H-73-5, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. [4] Design of small dams (1977). U.S. Bureau of Reclamation, U.S. Government Printing Office, Washington, D.C. [5] Maynord, S. T. (1958), General spillway investigation. Tech. Rep. HL-85-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. [6] U.S. Army Corp of Engineers (USACE), (1990). Hydraulic design of spillways. EM , Dept. of the Army, Washington, D.C. [7] US Army Corps of Engineers Waterways Experiment Station revised in subsequent years. Corps of Engineers Hydraulic Design Criteria editor@iaeme.com

10 Experimental Work and CFD Model for Flowrate Estimating Over Ogee Spillway Under Longitudinal Slope Effect [8] US Army Corps of Engineers. (1995) Hydraulic Design of Spillway. Technical Engineering and Design Guides as adapted form the US Army Corps of Engineers, No. 12 ASCE. [9] Peltier, Y., Dewals, B., Archambeau, P., et al. (2017) Pressure and velocity on an ogee spillway crest operating at high head ratio: Experimental measurements and validation. Journal of Hydro-environment Research. [10] Millet, J. C., Chambon, J., Soyer, G., & Lefevre, C. (1988). Augmentation de la capacité des ouvrages d évacuation de divers barrages 63 R78. 16ème Congrès des Grands Barrages. San Francisco, USA. [11] Xlyang, J., Cederström, M., Modification of spillways for higher discharge capacity. J. Hydraul. Res. 45 (5), [12] Yakun, G., Xianyun, W., Chigong, W., et al. (1998) Numerical modelling of spillway flow with free drop and initially unknown discharge. Journal of Hydraulic Research, 36: (5): [13] Olsen, N. R., and Kjellesvig, H. M, (1998), Three-dimensional numerical flow modeling for estimation of spillway capacity, J. Hydr. Res.,Delft, The Netherlands, 36(5), [14] Rodi, W. (1993) Turbulence models and their application in hydraulics. Monograph, International Association for Hydraulic Research, Delft, The Netherlands, 27 30,. CRC Press. [15] Rodi, W. (1980), Turbulence models and their application in hydraulics, Monograph, International Association for Hydraulic Research, Delft, The Netherlands, [16] AL-SHARIFY, Z. T. (2017). Flow and mixing of complex fluids. PhD Thesis. University. Birmingham of [17] Savage, B.M. and Johnson, M.C. (2001) Flow over ogee spillway: Physical and numerical model case study. Journal of Hydraulic Engineering, (127): (8): [18] Humberto Avila, (2007), Water Resources Engineering laboratory files for Open Channel Hydraulic Experiments. The University of Alabama [19] Vennard, K. and Street, L., (1996), Elementary Fluid mechanics, McGraw-Hill [20] Subramanya, K., 1998, "Flow in open channel", Tata McGraw Hill, New Delhi [21] Sturm, T. W., (2001), Open Channel Hydraulics, McGraw-Hill, New York [22] Modi, P. N., (2004), Irrigación Water Resources and power Engineering, 6 th Edition [23] Modi, P., (2008), Irrigation water resources and water power engineering. Standard Book House [24] Chin, D.A,(1986), Water Resources Engineering, 2 nd edition, Prentice Hall, 2006 [25] Rajput R. K., (2008),A textbook of fluid mechanics and hydraulic machines, Ram nagar, New dalhi. [26] Sharma R. K. and Sharma T. K., 2008, "Irrigation engineering ", Ram nagar, New dalhi [27] Roberson. J. A., John J. Cassidy and Hanif Chaudhry M., (1998), Hydraulic engineering, John wiley& Sons, Inc [28] Al-Sharify, Z.T, Zhao Y. and Barigou M., (2014) Comparing The Performance Of Different Impellers In Mixing Viscoplastic Fluids: CFD, Theory And Experiment. The 5th Birmingham Environment for Academic Research (BEAR) Conference, Birmingham, UK [29] Aal, G. M. A., Sobeah, M., Helal, E., & El-Fooly, M. (2017). Improving energy dissipation on stepped spillways using breakers. Ain Shams Engineering Journal. doi.org/ /j.asej editor@iaeme.com