Australian Journal of Basic and Applied Sciences

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1 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: AENSI Journals Australian Journal of Basic an Applie Sciences ISSN: Journal home page: Velocity Distribution Downstream compoun Weirs Mahmou Ali R. Eltoukhy an Mohamma Ibrahim Civil Engineering Department, Faculty of Engineering, Banha University, Cairo, Egypt A R T I C L E I N F O Article history: Receive 19 September 014 Receive in revise form 19 November 014 Accepte December 014 Available online January 015 Keywors: Compoun weir, compoun notch, coefficient of ischarge, velocity istribution. A B S T R A C T Weirs are the common an important structures which are use in controlling an measuring the flow in irrigation channel. This stuy carrie out experimental runs to survey the velocity istributions in each vertical an longituinal irections, ownstream compoun weirs. It uses compoun sharp-creste weirs consisting of two triangular parts with ifferent weir angles. All parameters, such as hea over the weir, h, ownstream water epth, y, be type, an the shape of the compoun weir, which affect the velocity istribution were stuie. Three weirs, 90/90, 90/10, an 90/150, two bes, san an plastic, four heas, 6, 9, 1, an 15 cm, an three ownstream epths, 10, 14, an 18 cm were use. The results show that the vertical an longituinal velocity istributions increase with water hea an with plastic be case. The velocity istributions ecrease for larger wie weir an higher ownstream water epth. 015 AENSI Publisher All rights reserve. To Cite This Article: Mahmou Ali R. Eltoukhy an Mohamma Ibrahim., Velocity Distribution Downstream compoun Weirs. Aust. J. Basic & Appl. Sci., 9(1): 38-45, 015 INTRODUCTION Applications of weir in measurement of ischarge through large an small open channels in the fiel or in the laboratory remains an age ol practice. Compoun sharp-creste weirs are more commonly use ue to their simplicity, easy maintenance, an goo flow measurement precision. Many types of weirs more commonly use are the sharp weirs with a notch of rectangular an triangular shapes, use particularly where the coefficient of ischarge C starts from 0.55 in case of rectangular notch an 0.59 for the v- notch. These transactions are affecte by viscosity an surface tension, roughness of the plate an weir shape. A weir that causes significant change of water level behin it, will give an accurate inication of the flow rate. Backgroun: A weir is built as an overflow structure perpenicular to an open channel axis to measure the ischarge. There are mainly two types of weirs: sharp-creste weirs an broa-creste weirs. For a weir to be consiere sharp creste, the top thickness of the crest an sie plates shoul be between 1 an mm. If the plates are thicker than specifie, the plate eges nee to be bevele to an angle of at least 45 ; 60 is highly recommene for a V- notch, (Bos 1989). The overflow sheet or nappe shoul touch only the upstream faces of the crest an sie plates an not cling to the ownstream face of the weir. Regaring the flow of water over weirs, many stuies have been reporte in the literature such as Ackers et al. (1978), Bos (1989), Swamee et al. (1998), Borghei et al.(1999), Johnson (000), Clemmens et al. (001), an Ayin et al.(00). Effect of the ownstream transition region of a flow measurement flume of rectangular compoun cross section on flow properties an vertical velocity istribution in open-channel flow with rigi vegetation were stuie by Mustafa Gogus et al (013) an Changjun Zhu et al (014). Also, experimental investigation on ischarge coefficient for a combine broa creste weir-box culvert structure was stuie by A. Guven et al (013), J. Martínez (005) carrie out esign an calibration of a compoun sharp-creste weir an Anees Kahum (013) Stuy coefficient of ischarge for a combine free flow over weir an uner Gate for Multi Cases. Flow equations for sharp-creste weirs are usually obtaine by the mathematical integration of elemental flow strips over the nappe (Bos 1989). Each strip is consiere an element with a ifferent hea. The triangular or V-notch sharp-creste weir is often use for flow measurement, particularly when accurate measurement of low flow rates is require. For triangular weirs, the flow equation is as follows (Henerson 1966): Corresponing Author: Mahmou Ali R. Eltoukhy, Civil Engineering Department, Faculty of Engineering, Banha University, Cairo, Egypt Emahmou_ali@hotmail.com

2 39 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: / Q C h g tan( ) (1) 15 Where; Q = ischarge, C = ischarge coefficient, g = gravitational acceleration, Kinsvater an Shen (USBR 1997) consiere the surface tension an the viscous effects aing a correction factor to the hea, so that the coefficient C epene exclusively on the notch angle. Weirs are the common an important structures which are use in controlling an ajusting the flow in irrigation channel. Weirs wiely use for flow measurements. Weirs, however, require to be cleane an seiments remove perioically. Sluice gates are use extensively for flow control an water measurement for long time. One isavantage of the sluice gates is they retain the floating materials. In orer to maximize their avantages, weirs an gates can be combine together in one evice, so that water coul pass over the weir an below the gate simultaneously. Figure 1 shows this structure, this compoun evice create new hyraulic conitions in compression with weir or gate. Alhami (1999) stuie combine flow over V-notch weir an below contracte rectangular gate. Ferro (000) reporte the results of an investigation carrie out to establish the stage ischarge relationship for a flow simultaneously ischarging over an uner a sluice or a broa creste gate. Samani an Mazaheri (007) presente a new physically base approach for estimating the stage ischarge relationship of combine flow over the weir for semi submerge an fully submerge conitions. The publishe materials about the flow over the compoun weirs are mostly relate to the investigations on ischarge coefficient for it. There are a no stuies concerning the velocity istributions in vertical an longituinal irections ownstream the compoun weirs. In this backrop, this stuy surveys the velocity istributions in each vertical an longituinal irections ownstream the compoun weirs, an presents its results in the forms of curves to show the velocity istributions in vertical an longituinal irections, for ifferent bes, water heas, ownstream water epth, an ifferent weirs. Experimental Apparatus: The experimental work of this stuy was conucte in a flume locate at the Hyraulics Research Institute (HRI) experimental hall of the National Water Research Center, Egypt. The flume channel is 1 m long, 0.6 m wie, 0.5 m eep, an the sie walls along the entire length of the flume were mae of brick. The flume is associate with a steel wooen gate with an orifice with a rectangular shape, also has movable ownstream gate is locate at the en of the flume. Centrifugal pump riven by inuction motor to re-circulate the flow from an unergroun reservoir to the flume. Electromagnetic current meter was use for measuring the velocities in each vertical an longituinal irections, an the ischarge was measure using flow meter. The weir moels were mae of steel with a 0.0 m thick 0.3 m height an 0.6 m with. Compoun sharp-creste weirs consisting of two triangular parts with ifferent weir angles were use changing the upper weir angle as 90, 10, an 150 egrees, refer as 90/90, 90/10, an 90/150 respectively, Fig. 1. The teste upstream water heas have values of 6, 9, 1, an 15 cm measure from the compoun weir vertex, while the values of weir ownstream water epths, y varie as 10, 14, an 18 cm. San an plastic flume bes were use in the this stuy experimental program A m.00m 3.35m A 4.5m 8.30m 1- Pump Fig. 1: Experimental Apparatus. - Inlet pipe 3- Stone box 4- First weir 5- Secon Weir 6- Movable Be 1.00m 7- Control Gate Sec (A-A) 0.10m Experimental Work: The experimental work consists of two main sets of experiments. The first set consists of twenty four runs using plastic be, for ifferent heas, h, ifferent ownstream water epths, y, an ifferent weir moels. The secon set also, consists of twenty four runs using san be for ifferent pervious parameters, as summarize in the following Tables 1 an. The velocities were measure at epths function of the ownstream epth as 0. y, 0.4 y, 0.6 y, an 0.8 y from the water surface.

3 V 90/90 San V 90/150 San V 90/10 San V 90/10 Plastic V 90/90 Plastic V 90/150 plastic 40 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: Experimental Proceure: 1- Place the specific weir plate which is to be teste first, using plastic be. Ensure that the square ege of the weir faces upstream. - Start the pump an slowly open the flume regulating valve until the water level reaches the crest of the weir an measure the water level to etermine the atum level. 3- Ajust the flume regulating valve to give the first require hea level of approximately 6 cm. Measure the flow rate using the flow meter, an the velocity istributions in each vertical an longituinal irections were surveye by the electromagnetic current meter. In the vertical irection, velocities were measure at epths of 0. y, 0.4 y, 0.6 y, an 0.8 y from Table 1: First set of experimental runs outline, for plastic be. First Set Run No. h (cm) V-notch Y (cm) First Set Run No. h u.s (cm) V-notch Y (cm) Table : Secon set of experimental runs outline, for san be. Secon Set Run No. Upstream hea h (cm) Y (cm) Secon Set Run No. Upstream hea h (cm) Y (cm) the free surface, at ifferent longituinal sections,.5, 3.6, 5, 6.5, 7.5, 10, an 1.5 times of the weir height, y, which may take values of 10, 14, an 18 cm. The X / H for ifferent ownstream water epths, ownstream epth may be ajuste by the ownstream gate is locate at the en of the flume. 4- Increase the flow by opening the flume regulating valve to set up heas above the atum level in steps of approximately 3.0 cm until the regulating valve is fully open. At each conition measure the flow rate an observe the shape of the nappe, an the velocity istributions in each vertical an longituinal irections are measure. 5- Close the regulating valve, stop the pump an then replace the weir with the next weir to be teste. Repeat the test proceure. 6- The above proceures are repeate for using sa be. RESULTS AND DISCUSSION

4 41 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: First of all, the flume was calibrate through measuring the ischarge coefficient, C. Fig. shows that the ischarge coefficient for ifferent weirs are consistent with literature work. The coefficient of ischarge, C, was calculate as; Qact C () Q th Where; Q act is the actual ischarge, which was measure in each run, an Q th is the theoretical ischarge, which was calculate through the following conclue formula; Q 8. th tan( 1 ) h 5 g for h h1 (3) Q tan ( ) tan( ) ( ) tan th h1 g g h1 h h1 h h for h1 h h (4) where: 1 is the compoun weir lower part angle, is the compoun weir upper part angle, h 1 is the height of the lower part, h 1 is the upper part height, an h is the hea over the compoun weir vertex. Velocity Distributions at the Compoun Weir ownstream: The velocity istributions were measure by the electromagnetic current meter, ownstream the compoun weir. The vertical velocities were measure at epths of 0. y, 0.4 y, 0.6 y, 0.8 y from the water surface. These velocity istributions were measure at ifferent istances ownstream the weir, X = 50, 75, 100, 15, 150, 00, an 50 cm. The Fig. : Coefficient of Discharge for ifferent weir moels. Effect of water heas h, ownstream water epths y, bes (san an plastic), an weir moels on the velocity istributions in each vertical an longituinal irections were stuie. It was foun that, the vertical velocity istributions ownstream the compoun weir have the same tren at ifferent istances from the weir, X. Figs.3 an 4 are examples for ownstream water epth, y = 14 cm, upstream water hea h 1 cm, san be, an for 90/10 weir moel. Fig.3. represents the vertical velocity istributions at ifferent longituinal istances as a ratio of the weir height, H, i.e. at X / H of.5, 3.75, 5, 6.5, 7.5, 10, an 1.5. Fig.4 shows the longituinal variations in velocity values at ifferent water epths. The figures show that, the variations in the velocity values at ifferent istances is ue to the non uniformity of flow at the weir ownstream. The ifference in the velocity values at the same epth, ecreases as the ownstream istance, X increases, an the flow will be uniform after X / H = 1.5. Figs.5 shows the velocity istributions in the vertical irection at ifferent heas, for longituinal istance, X = 15 cm, y = 14 cm, san be, an 90/10 weir moel. Fig.6 shows the longituinal velocity istributions for the same parameter values. The upstream water hea was measure as function of the total compoun weir height, h / H. The values of h / H were taken as 0.36, 0.45, 0.60, an It was foun that, as the upstream water hea, h increases the velocity values at ifferent epths increases. For example; changing h from 6 to 1 cm the velocity at 0.6 y from the water surface increases from to m/s.

5 4 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: Also, changing the weir moel affecting the vertical an longituinal velocity istributions ownstream it. This stuy foun that, for y = 14 cm, h = 1 cm, an san be, increasing the upper part angle, the velocity values in the vertical irection ecreases, Figs.7 an 8. This is ue to increasing the flow area as a result of increasing the upper part angle,. So, 90/90 weir moel gives velocity values more than 90/10, an 90/150 moels for h = 1 cm, y = 14 cm, an san be. Fig. 3: Vertical Velocity Distribution at ifferent istances own stream the weir, for y = 14 cm, h=1 cm, san be, an for 90/10 weir. Fig. 4: Longituenal Velocity Distribution at ifferent Depths, for y = 14 cm, h=1 cm, san be, an for 90/10 weir. Fig. 5: Vertical Velocity at Different Water Heas, for X = 15 cm, ytai l = 14 cm, san be, an 90/10 weir. Fig. 6: Longituinal Velocity Distribution at ifferent Heas for X = 15 cm, ytai l = 14 cm, san be, an 90/10 weir.

6 43 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: Fig. 7: Vertical Velocity Distribution for Different Compoun weir moels, for ytai l= 14 cm, h = 1 cm, an san be. Fig. 8: Longituinal Velocity Distribution for Different weir, for y = 14 cm, h = 1 cm, an san be. Fig. 9: Vertical Velocity Distribution at Different Downstream water epths, for h = 1 cm, san be, an 90/10 weir. Fig. 10: Lonituinal Velocity Distribution at ifferent Downstream water Depths, for h = 1 cm, san be, an 90/10 weir. Several experimental runs were carrie out to stuy the effect of the ownstream water epth, y on the vertical an longituinal velocity istributions. All other parameters have constant values, i.e. h = 1 cm, san be, an 90/10 weir moel. The velocity in vertical an longituinal irections ecreases as the ownstream water epth, y increases, Figs.9 an 10. This result is because the flow area increases, which results in ecreasing in the velocity.

7 44 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: Fig. 11: Vertical Velocity Distribution for ifferent bes, for h = 1 cm, y = 14 cm, an 90/10 weir. Fig. 1: Longituinal Velocity Distribution for Different Bes for h = 1 cm, ytai l = 14 cm, an 90/10 weir. On the other han, the effect of the be materials on the velocity istributions in the vertical an longituinal irection were stuie for h = 1 cm, y = 14 cm, an 90/10 weir moel. Figs 11 an 1 show that, the velocity in the two irections have more values in case of plastic be than san be. The ifference in the velocity values are large near the be an ecrease near the free surface. The reason of this result is that, the plastic be has less friction than the san be. From the analysis of the obtaine results, this stuy foun that the velocity istributions in vertical an longituinal irections, ownstream compoun weirs are varie with the variation of the upstream water hea, the ownstream water epth, the compoun weir moel, an the be materials. Conclusions: In this stuy, a series of laboratory experimental runs were conucte in orer to investigate the effect of upstream water hea, weir ownstream water epth, be material, an the weir moel on the ownstream velocity istributions in vertical an longituinal irections. The following conclusions are obtaine: The ischarge coefficient, C values obtaine from the experimental runs performe on the compoun weirs has have the same values of the pervious stuies. Increasing the upstream water hea results in increasing the ownstream velocities at vertical an longituinal irections. Oppositely, the velocities ownstream the weir ecrease as the ownstream water epth increase. Also, as the weir moel with upper part angle increases, the velocities ecreases in their values. It was foun that, the flume plastic be gives larger velocities than san be. REFERENCES Guven, A., M. Hassan an Shahin Sabir, 013. Experimental investigation on ischarge coefficient for a combine broa creste weir-box culvert structure, Journal of Hyrology, 500: Ackers, P., W.R. White, J.A. Perkins an A.J.M. Harrison, Weirs an flumes for flow measurement. Wiley, New York. Alhami, A.A., Analysis an formulation of flow through combine V-notch gate evice. J. Hyraul. Res., 37(5): Anees Kahum Irees AL-Saai, 013. Stuy Coefficient of Discharge for a Combine Free Flow over Weir an uner Gate for Multi Cases. Euphrates Journal of Agriculture Science, 5(4): Ayin, I., A. Metin Ger an O. Hincal, 00. Measurement of small ischarges in open channels by slit weir. J. Hyraul. Eng., 18():

8 45 Mahmou Ali R. Eltoukhy an Mohamma Ibrahim, 015 Australian Journal of Basic an Applie Sciences, 9(1) January 015, Pages: Borghei, S.M., M.R. Jalili an M. Ghosian, Discharge coefficient for sharp-creste sie weir in subcritical flow. J. Hyraul. Eng., 15(10): Bos, M.G., Discharge measurement structures. International Institute for Lan Reclamation an Improvement (ILRI) Publication 0, Wageningen, The Netherlans. Changjun Zhu, Wenlong Hao, an Xiangping Chang (014).Vertical Velocity Distribution in Open- Channel Flow with Rigi Vegetation. The Scientific Worl Journal, Article ID 14689, 6. Clemmens, A.J., T.L. Wahl, M.G. Bos an J.A. Replogle, 001.Water measurement with flumes an weirs. International Institute for Lan Reclamation an Improvement (ILRI) Publication 58, Wageningen, The Netherlans. Ferro, V., 000. Simultaneous flow over an uner a gate. J. Irrig.Drain. Eng, 16(3): Henerson, F.M "Open channel flow", Prentice Hall, Englewoo Cliffs, N.J. Martínez, J., J. Reca, M.T. Morillas an J.G. López, 005. Design an Calibration of a Compoun Sharp- Creste Weir. J. Hyraul. Eng, 131: Johnson, M.C., 000..Discharge coefficient analysis for flat-toppe an sharp-creste weirs. Irrig. Sci., 19: Mustafa Gogusa, Issam, A. Al-Khatib, Ahmet, E. Atalay, 013. Effect of the ownstream transition region of a flow measurement flume of rectangular compoun cross section on flow properties. Flow Measurement an Instrumentation, 33: Samani M.V., Jama, M. Mazaheri, 007. Combine flow over weir an uner gate. 7 th Iranian hyraulic conference, Power an Water University of Technology, Tehran, Iran, Swamee, P. K., C.S.P. Ojha an S. Kumar, Discharge equation for rectangular slots. J. Hyraul. Eng., 14(9): Unite States Department of the Interior, Bureau of Reclamation(USBR), Water measurement manual, 3r E., Denver.