Computational Fluid Dynamic Modeling of the Desander: A Case Study from Pakistan

Authors: Ali Heidari, Hosain Ardalan

Abstract:

A CFD model was developed for a desander on the waterway of the Madyan Hydro Power Plant. An underground desander was designed to settle the sediments before the headrace tunnel, which is 14 km long. The desander chamber consists of two caverns, each including two basins with a flushing-type desander, adopted in the feasibility design on the left bank of the river. Eleven scenarios were defined for different configurations of the desander, including the transition vertical slope, symmetric and asymmetric entrance, the basin net length, and tranquilizer racks specifications. The CFD results confirmed the symmetric entrance configuration, desander net length of 135 m, and a transition angle of 34° to the horizon as the optimum configuration. The configuration provides a removal efficiency of 97% for a particle size of 0.2 mm. The CFD results also show that horizontal tranquilizing racks are risky and do not help sediment trapping in the basin. 

Keywords: CFD, Computational Fluid Dynamic, sediment, desander, Madyan.

References:

[1] Bouvard, M., Mobile barrages and intakes on sediment transporting rivers. IAHR Monograph, A.A. Balkema, Rotterdam, pp. 205-222, 1992.
[2] Central Water & Power Research Station-CWPRS, Guidelines for the Design of Desilting Basins, 2005.
[3] Construction Site Best Management Practices Manual, Sediment/Desilting Basin, Caltrans Storm Water Quality Handbooks, 2003.
[4] Graf, W.H., Hydraulics of Sediment Transport McGraw-Hill Book Company, 1971.
[5] Paschmann, C., VAW-Mitteilungen 247, Design Optimization of Desanding Facilities for Hydropower Schemes, Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie (VAW), (R. M. Boes, ed.), ETH Zürich, Schweiz, PP 210, 2018.
[6] Lysne, D., Glover, B., Stole, H., and Tesakar, E., Hydraulic Design, Series 8 on Hydropower Development. Published by the Department of Hydraulic and Environmental Engineering of the Norwegian University of Science and Technology (NTNU), Trondheim, Norway, 2003.
[7] The Nile Basin Capacity Building Network (NBCBN), Numerical Modeling for Settling Basin Design, 2010.
[8] Weerakoon S.B., Rathnayake U.S., Effect of the entrance zone on the trapping efficiency of desilting tanks in run-of-river hydropower plants. In: Proc. international conference on small hydropower, Department of Civil Engineering, University of Peradeniya, Peradeniya, Sri Lanka, 2007.
[9] Shah C.M., Verma M.K., Deolalikar P.B., Transition for desilting basin with open channel flow. ISH J Hydraul Eng 14:117–125, 2008.
[10] Qamar M.Z., Verma M.K., Meshram A.P., Importance of desilting basins in run-of-river hydro projects in Himalayan region. Int J Emerg Technol Adv Eng 4:407–412, 2014.
[11] Simanjuntak T., Boeriu P., Roelvink J.D., Consideration on the sedimentation process in a settling basin. J Hydrol Hydromechanics 57:16–25, 2009.
[12] Bråtveit K., Brevik O., Olsen N.R.B., Three-dimensional numerical study of an unlined pressurized rockblasted sand trap. In: 35th IAHR World Congress, Chengdu, China, 2013.
[13] Nøvik H., Dudhraj A., Olsen N.R., et al, Numerical modeling of nonuniform flow in settling basins. Hydro Nepal J Water, Energy Environ 14:27–35, 2014.
[14] Paschmann, C.; Vetsch, D.F.; Boes, R.M. Design of Desanding Facilities for Hydropower Schemes Based on Trapping Efficiency. Water 2022, 14, 520. https://doi.org/10.3390/w14040520, 2022.
[15] Daneshvari M., Münch-Alligné C. and De Cesare G., Numerical Simulation of a New Sand Trap Flushing System, 4th IAHR International Symposium on Hydraulic Structures, Porto, Portugal, ISBN: 978-989-8509-01-7, 9-11 February 2012.
[16] Dhemi H., Dantje K. N., Mohammad B. A., Hernawan M., and Fitra A., 3D Numerical Modeling of Flow in Sedimentation Basin, SIBE 2017, MATEC Web of Conferences 147, 03012, 2018.
[17] Singh T.P., Chandrashekhar J., Agrawal A.K., Analysis of water and sediment flow in desilting basin of a run-of-river hydroelectric project. In: International conference on small hydropower-hydro Sri Lanka. p 24, 2007.
[18] Qamar M.Z., Verma M.K., Meshram A., Isaac N., Model studies for desilting basin for Teesta-VI HE project, Sikkim–a case study. Brazilian J Dev 10:1157–1170, 2024.
[19] Azrulhisham E., Azri M.A., Desilting Basin Efficiency Estimation for Run-of-River Small Hydropower Plants. Int J Recent Technol Eng 8, 2020.
[20] Flow Science (2011). Flow-3D User's Manual, Flow Science Inc.