Studi Numerik Pengaruh Inclined Inlet Draft Tube Terhadap Performa Turbin Francis

Wanda, Sabrila (2025) Studi Numerik Pengaruh Inclined Inlet Draft Tube Terhadap Performa Turbin Francis. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Pembangkit listrik yang dahulu menggunakan bahan bakar fosil, diganti dengan pembangkit listrik yang menggunakan sumber energi baru terbarukan. Pengembangan sistem operasi PLTA banyak dilakukan untuk mencapai efisiensi tertinggi dalam segala kondisi, terutama pada beban sebagian. Penelitian ini berfokus pada analisis pengaruh desain dan konfigurasi draft tube terhadap efisiensi operasional turbin Francis pada Pembangkit Listrik Tenaga Air (PLTA). Draft tube berfungsi untuk mengubah energi kinetik sisa dari aliran fluida yang keluar dari runner menjadi energi tekanan, yang berkontribusi pada peningkatan efisiensi sistem secara keseluruhan. Salah satu masalah yang muncul pada draft tube adalah fenomena Rotating Vortex rope (RVR), yang terjadi pada operasi beban parsial dan berpotensi menimbulkan fluktuasi tekanan serta kavitasi yang menyebabkan penurunan efisiensi sistem. Penelitian menggunakan metode simulasi numerik Computational Fluid Dynamics (CFD) dengan perangkat lunak ANSYS Fluent 2023 R2 untuk memodelkan aliran fluida dalam berbagai konfigurasi draft tube. Simulasi dilakukan pada debit Best Efficiency Point sebesar 121 m³/s, 96 m³/s, 72,60 m³/s, dan 48,40 m³/s dengan kecepatan 187,5 rpm. Meshing menggunakan unstructed tetrahedon dengan jumlah sebanyak 1.843.592. Pemodelan dilakukan secara steady dengan model turbulensi SST (Shear Stress Transport) k-ω. Simulasi ini memvariasikan sudut inclined draft tube sebesar 9.50°, 11.08°, 13.23°, 16.27°, and 21.40°, selain draft tube tradisional. Pada inlet boundary condition yang digunakan dalam simulasi adalah pressure inlet dan pada outlet boundary condition yang digunakan dalam simulasi adalah massflow outlet. Hasil dari simulasi menghasilkan efisiensi pada desain draft tube tradisional sebesar 121 m³/s sebesar 96,61% , 96 m³/s sebesar 94,9%, 72,60 m³/s sebesar 92,6%, 48,40 m³/s sebesar 92,02%. Setelah dilakukan variasi sudut inclined, sudut inclined sebesar 11.08° adalah yang paling efektif menaikkan efisiensi pada tiga kondisi operasi, yaitu 96 m³/s sebesar 95%, 72,60 m³/s sebesar 94,3%, dan 48,40 m³/s sebesar 92,8% dengan rata – rata kenaikan sebesar efisiensi sebesar 0,86% . Pada kondisi BEP (100%Q) tidak terlihat kemunculan vortex rope, sedangkan pada 0,4Q terlihat adanya vortex rope. Modifikasi pada inclined draft tube berhasil mengurai vortex rope tetapi tidak menghilangkan vortex rope.
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Power plants that previously used fossil fuels have been replaced with power plants that use new renewable energy sources. The development of hydroelectric power plant operating systems is widely carried out to achieve the highest efficiency in all conditions, especially at partial loads. This study focuses on the analysis of the effect of draft tube design and configuration on the operational efficiency of Francis turbines in Hydroelectric Power Plants (HPP). The draft tube functions to convert the residual kinetic energy of the fluid flow exiting the runner into pressure energy, which contributes to increasing the overall system efficiency. One of the problems that arises in the draft tube is the Rotating Vortex Rope (RVR) phenomenon, which occurs in partial load operations and has the potential to cause pressure fluctuations and cavitation, which cause a decrease in system efficiency. The study uses the Computational Fluid Dynamics (CFD) numerical simulation method with ANSYS Fluent 2023 R2 software to model fluid flow in various draft tube configurations. Simulations were performed at Best Efficiency point (BEP) flowrate or 121 m³/s, 96 m³/s, 72.60 m³/s, and 48.40 m³/s with a speed of 187.5 rpm. Simulation meshing uses unstructured tetrahedra with a total cells 1,843,592. Modeling was performed using steady model with the SST (Shear Stress Transport) k-ω turbulence model. This simulation varies the inclined draft tube angles of 9.50°, 11.08°, 13.23°, 16.27°, and 21.40°, in addition to the traditional draft tube. The inlet boundary condition to be set of pressure inlet and the outlet boundary condition to be set as massflow outlet. The results of the simulation so that the turbine with traditional draft tube design have efficiencies of 96.61%, 94.9%, 92.6%, and 92.02% for the flowrates of 121 m³/s, 96 m³/s, 72.60 m³/s, and 48.40 m³/s, respectively. The inclined angle of 11.08° is the most effective in increasing efficiency in three operating conditions, namely 96 m³/s with efficiency of 95 %, 72.60 m³/s with efficiency of 94.3%, and 48.40 m³/s with efficiency of 92.8% with an average increase in efficiency of 0.86%. At BEP conditions (100%Q), there was no vortex rope, while at 0.4Q, there was a vortex rope. Modifications to the inclined draft tube at the inlet section succeeded in unraveling the vortex rope but they did not eliminate the vortex rope.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	PLTA, turbin Francis, kondisi part load , vortex rope, efisiensi turbin.
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering T Technology > TJ Mechanical engineering and machinery > TJ164 Power plants--Design and construction T Technology > TJ Mechanical engineering and machinery > TJ870 Hydraulic turbines.
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21101-(S2) Master Thesis
Depositing User:	Sabrila Wanda
Date Deposited:	04 Feb 2025 10:06
Last Modified:	04 Feb 2025 10:06
URI:	http://repository.its.ac.id/id/eprint/118183

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