Effect of Downstream Expansion of a Long-Throated Flume on Flow Properties

Abstract

Long throated flumes are widely used flow measurement devices that not requiring site-specific level to flow curves and therefore laboratory experiments. In this study, downstream expansion effect of the long throated flumes with rectangular cross section were analysed for the dimensionless parameters derived from Buckingham’s pi theorem and some other known hydraulic quantities such as discharge coefficient, approach velocity coefficient, submergence ratio of the flow etc. Therefore, five downstream transitions with different expansion angles were tested. In each test, the critical depth yc, the flow head at the depth measurement section h1, minimum required energy dissipater length Lt and the head after hydraulic jump y2 were measured for both modular and free flow conditions. The relation of hydraulic quantities of calculated dimensionless parameters with relevant parameters; modular limits, approach velocity coefficients and discharge coefficients etc. were graphed to represent the design relationships for long throated flumes.Long throated flumes are widely used flow measurement devices that not requiring site-specific level to flow curves and therefore laboratory experiments. In this study, downstream expansion effect of the long throated flumes with rectangular cross section were analysed for the dimensionless parameters derived from Buckingham’s pi theorem and some other known hydraulic quantities such as discharge coefficient, approach velocity coefficient, submergence ratio of the flow etc. Therefore, five downstream transitions with different expansion angles were tested. In each test, the critical depth yc, the flow head at the depth measurement section h1, minimum required energy dissipater length Lt and the head after hydraulic jump y2 were measured for both modular and free flow conditions. The relation of hydraulic quantities of calculated dimensionless parameters with relevant parameters; modular limits, approach velocity coefficients and discharge coefficients etc. were graphed to represent the design relationships for long throated flumes.

Keywords

• Long-throated flumes
• Downstream expansion
• Modular limit
• Discharge coefficient

References

1. [1] Bos, M.G., “The use of long-throated flumes to measure flows in irrigation and drainage canals”, Agricultural Water Management, 1(2):111-126, (1977). https://doi.org/10.1016/0378-3774(77)90035-X
2. [2] Nashta, C.F. and Garde, R.J., “Subcritical flow in rigid-bed open channel expansions”, Hydraulic Research, 26(1):49-65, (1988). https://doi.org/10.1080/00221688809499234
3. [3] Swamee, P.K. and Basak, B.C., “Design of rectangular open-channel expansion transitions”, Irrigation and Drainage Engineering, 117(6):827-838, (1991). https://doi.org/10.1061/(ASCE)0733-9437(1991)117:6(827)
4. [4] Bhallamudi, S.M. and Chaudhry, M.H., “Computation of flows in open-channel transitions”, Hydraulic Research, 30(1):77-93, (1992). https://doi.org/10.1080/00221689209498948
5. [5] Krueger, S. and Rutschmann, P., “Modelling 3D supercritical flow with extended shallow-water approach”, Hydraulic Engineering, 132(9):916-926, (2006). https://doi.org/10.1061/(ASCE)0733-9429(2006)132:9(916)
6. [6] Mazumder, S.K. and Hager, W.H., “Supercritical expansion flow in rouse modified and reversed transitions”, Hydraulic Engineering, 119(2):201-219, (1993). https://doi.org/10.1061/(ASCE)0733-9429(1993)119:2(201)
7. [7] Stamou, A.I., Chapsas, D.G. and Christodoulou, G.C., “3-D numerical modelling of supercritical flow in gradual expansions, Hydraulic Research, 46(3):402-409, (2008). https://doi.org/10.3826/jhr.2008.3162
8. [8] Gogus, M., Al-Khatib, I.A. and Atalay, A.E., “Effect of the downstream transition region of a flow measurement flume of rectangular compound cross section on flow properties”, Flow Measurement and Instrumentation, 33(1):88-95, (2013). https://doi.org/10.1016/j.flowmeasinst.2013.05.006

9. [9] Nasser, A.N.N. and Li, S.S., “Reduction of flow separation and energy head losses in expansions using a hump”, Irrigation and Drainage Engineering, 141(3):04014057, (2015). https://doi.org/10.1061/(ASCE)IR.1943-4774.0000803
10. [10] Asnaashari, A., Akhtari, A.A., Dehghani, A.A. and Bonakdari, H., “Experimental and numerical investigation of the flow field in the gradual transition of rectangular to trapezoidal open channels”, Engineering Applications of Computational Fluid Mechanics, 10(1):272-282, (2016). https://doi.org/10.1080/19942060.2016.1149102
11. [11] Bos, M.G. and Reinink, Y., “Required head loss over long-throated flumes”, Irrigation and Drainage Division, 107(1):87-102, (1981).