Assessment on flow characteristics of dam spillway structure using physical laboratory model and computational fluid dynamics / Che Mohamad Amirus Shafiq Che Ismail
Alur limpah ialah suatu struktur yang melepaskan air lebihan dari empangan ke kawasan hilir. Tanpa alur limpah, air yang melepasi akan menyebabkan empangan runtuh ketika musim hujan lebat. Ketika melepaskan aliran air yang besar, profil permukaan air yang tinggi dan halaju yang tinggi akan berlaku. Situasi ini cenderung untuk aliran melepasi dan keluar dari alur limpah. Halaju yang tinggi menyebabkan tekanan yang rendah atau negatif berlaku di lantai alur limpah dan hakisan di kawasan hilir. Tekanan negatif menyebabkan peronggan dan mungkin menyebabkan kerosakan yang teruk di kawasan hilir. Matlamat kajian ini dijalankan untuk mengkaji ciri-ciri aliran hidraulik alur limpah seperti kedalaman air, halaju, tekanan dan pelesapan tenaga di penenang lembangan. Kajian ini menggunakan model fizikal dan Pengkomputeran Dinamik Bendalir (CFD). Satu model fizikal alur limpah berskala 1:20 telah dibina dandipasang di Makmal Hidraulik, Universiti Sains Malaysia. Kajian ini telah dilakukan terhadap empat kadar alir yang berbeza (0.012 m3/s, 0.017 m3/s, 0.021 m3/s dan 0.067 m3/s) dengan sebanyak 62 titik pengukuran untuk setiap kes. Data diambil dan direkodkan di setiap titik yang dipilih. Untuk memastikan air yang dilepaskan selamat daripada menyebabkan kerosakan yang teruk, kajian ini kemudiannya difokuskan ke kawasan penenang lembangan. Untuk CFD, ANSYS FluentTM digunakan sebagai penyelesai untuk kajian ini. Selepas mendapat keputusan dari CFD, nilai-nilai itu dibandingkan dengan data yang diperoleh dari model fizikal untuk pengesahan. Berdasarkan kepada reka bentuk asal, panjang dan kedalaman lompatan hidraulik melebihi dinding tepi model untuk lepasan air. Penurunan halaju untuk semua empat jenis susunan penenang lembangan berada dalam lingkungan 54% ke 64%. Panjang dan kedalaman lompatan hidraulik turun seperti yang dicadangkan pada perubahan kedua. Untuk pelesapan tenaga, susunan asal menghasilkan nilai tertinggi secara purata. Dengan pengesahan keputusan untuk kedua-dua kaedah, persetujuan yan baik telah dicapai. Untuk hubungan plotan berselerak antara dat ujikaji dan simulasi, nilai pekali regresi (R2), berada dalam julat 0.97 ke 0.99 telah diperoleh. Keputusan akhir telah menunjukkan halaju air dihujung alur limpah boleh dikurangkan lebih banyak dengan mempunyai blok penampan yang bersaiz lebih besar sementara mengekalkan panjang penenang lembangan yang sedia ada. Kesimpulan yang boleh dibuat daripada kajian ini ialah, CFD dapat digunakan untuk simulasi atau menggantikan model fizikal kepada aliran alur limpah.
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Spillway is a structure that release surplus water from a dam into downstream area. Without spillway, water will be overtopping the dam and collapse during heavy raining season. During releasing large flow discharge, higher water surface profile and high velocity flow occur. This situation have the tendency for the flow to overtopping and breaching out the spillway. High velocity cause low or negative pressure on the spillway slab, scouring and erosion at downstream area. Negative pressure leads to cavitation and may cause critical damage on spillway structure. This study aims to investigate the flow characteristics along spillway such as water depth, velocity, pressure and energy dissipation on the stilling basin. The study were attempt on the physical experiment and Computational Fluid Dynamic (CFD). A 1:20 scaled spillway physical model was constructed and assembled in Hydraulic Laboratory of Universiti Sains Malaysia. This study has been conducted on four different flow rate (0.012 m3/s, 0.017 m3/s, 0.021 m3/s and 0.067 m3/s) with total of 62 measurement points for each case. The data were measured and recorded on the selected points. To ensure the release flow is safe from causing severe damage on the downstream area, the study then was focused on stilling basin. For CFD, ANSYS FluentTM used as the solver for this study. After obtaining the required results from CFD, the values were compared to the physical model data for validation. Based on the original design, hydraulic jump length and depth were overtopping the side bank wall of the model for all flow discharge. Three modifications on the stilling basin were suggested to reduce the depth and length of hydraulic jump. The velocity reduced from these four tested stilling basin ranging from 54% to 64%. The length and depth of the hydraulic jump reduce as suggested on the 2nd modification. As for energy dissipation, original configuration yield the most value averagely compare to the others. By validating the results for both method, a good agreement was achieved for the water surface profile, velocity and pressure. The scatter plot relationship between physical experiment and numerical analysis having the regression coefficient (R2) ranging from 0.97 to 0.99. End results shows that the velocity, length and depth of hydraulic jump at the end of spillway can be reduce more by having a bigger dimension with additional row of buffer blocks while having the same length of stilling basin. Thus, it can be concluded that CFD can be used to simulate the flow characteristics in spillway as an alternative to physical experiment of spillway.
Assessment on flow characteristics of dam spillway structure using physical laboratory model and computational fluid dynamics / Che Mohamad Amirus Shafiq Che Ismail
Assessment on flow characteristics of dam spillway structure using physical laboratory model and computational fluid dynamics_Che Mohamad Amirus Shafiq Che Ismail_A9_2017