Mahmashani, Ahmad Wildan Mahmashani (2025) Pemanfaatan Passive Flow Control Pada Turbin Hidrokinetik Aksis Vertikal Tipe Darrieus. Doctoral thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Disertasi ini membahas upaya peningkatan kinerja turbin hidrokinetik aksis vertikal jenis Darrieus melalui penerapan passive flow control menggunakan passive flap. Pada kecepatan aliran rendah turbin Darrieus memiliki kendala performa seperti kesulitan self-start dan efisiensi turbin yang lebih rendah. Penelitian ini bertujuan mengkaji secara menyeluruh pengaruh pemasangan passive flap pada bilah turbin terhadap karakteristik kinerja turbin dan fenomena aliran yang terjadi. Penelitian dilakukan secara eksperimen di flume-tank dan simulasi numerik dengan CFD. Model turbin Darrieus tiga bilah berprofil NACA 0018 pada tiga kecepatan arus berbeda 0.17 m/s, 0.21 m/s dan 0.29 m/s. Konfigurasi yang diuji meliputi: baseline (NACA 0018 tanpa flap), inner flap, outer flap, serta combine flap. Passive flap didesain mampu bergerak terbatas dengan bergantung pada interaksi fluida tanpa memerlukan energi eksternal tambahan. Parameter eksperimen yang diukur antara lain kecepatan putar rotor (RPM), torsi poros turbin, serta kecepatan arus inlet. Simulasi CFD berbasis RANS (model turbulensi k–ω SST) dilakukan dalam 2D untuk melengkapi data eksperimen dan memahami fenomena aliran secara detail. Hasil simulasi meliputi distribusi tekanan, kontur kecepatan, jalur arus (streamlines), serta gaya – gaya sepanjang rotasi.
Hasil penelitian menunjukkan bahwa passive flap dapat meningkatkan torsi hidrodinamis yang dihasilkan turbin, sehingga kemampuan self-start turbin Darrieus membaik. Pada simulasi kondisi TSR 0,7 konfigurasi inner flap dengan sudut bukaan 90° meningkatkan puncak koefisien torsi (Ctorque) mencapai 137% (dari 0,039 menjadi 0,092) pada azimuth 70º dan menaikkan titik terendah CTorque sebesar 153% dibanding profil NACA 0018 tanpa flap pada azimuth 180º. Kenaikan torsi maksimum dan minimum ini memperbesar rata-rata torsi satu rotasi turbin sekitar 2,37 kali lebih besar dibanding baseline NACA 0018 tanpa flap. Konfigurasi combine flap (flap sisi dalam+luar) memberikan tren serupa dengan peningkatan torsi puncak naik 76% dan fluktuasi torsi yang lebih rendah dibandingkan inner flap, sedangkan outer flap justru menurunkan torsi turbin (puncak CTorque turun 65% dari baseline) karena menambah resistansi hidrodinamis. Dengan demikian, konfigurasi inner flap 90° terbukti sebagai konfigurasi paling efektif untuk meningkatkan torsi awal turbin, sementara flap sisi luar tidak direkomendasikan karena berdampak negatif pada performa dan self-start turbin. Oleh karena itu, kontribusi utama penelitian ini adalah diperolehnya konsep desain passive flap baru pada bilah Darrieus yang mampu secara otomatis meningkatkan daya pada arus lambat dengan mekanisme sederhana. Inovasi desain ini berpotensi mengatasi kelemahan klasik turbin Darrieus (yakni kesulitan self-start dan efisiensi rendah pada TSR < 1), sehingga penelitian ini memiliki novelty dalam pengembangan turbin hidrokinetik aksis vertikal.
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This dissertation discusses performance enhancement of a vertical-axis hydrokinetic Darrieus turbine through the application of passive flow control utilizing passive flaps. At low flow velocities, the Darrieus turbine encounters performance challenges such as difficulties in self-starting and inherently low efficiency. This study comprehensively examines the effects of integrating passive flaps on turbine blades, analyzing both turbine performance characteristics and associated flow phenomena. Research methods involve experimental investigations conducted in a flume tank, complemented by numerical simulations using computational fluid dynamics (CFD). A three-bladed Darrieus turbine employing NACA 0018 airfoil profiles was tested at three different inlet velocities: 0.17 m/s, 0.21 m/s, and 0.29 m/s. The configurations examined include: baseline (without flap), inner flap, outer flap, and combined flap. The passive flap is designed to rotate passively within defined angular limits under hydrodynamic forces, requiring no external energy input. Experimental parameters measured include rotor rotational speed (RPM), shaft torque, and inlet flow velocity. Two-dimensional CFD simulations using Reynolds-Averaged Navier-Stokes (RANS) equations with the k–ω SST turbulence model were performed to complement experimental data and provide detailed insights into flow dynamics, including pressure distribution, velocity contours, streamlines, and flap motion dynamics during turbine rotation. Results indicate that incorporating passive flaps significantly enhances hydrodynamic torque output, improving the turbine’s self-starting capability. Under simulated conditions at TSR 0.7, the inner flap configuration with a 90° maximum opening angle increased the peak torque coefficient (CTorque) by approximately 136% (from 0.039 to 0.092), and improved the minimum torque coefficient by 153% compared to the baseline NACA 0018 profile. Consequently, average torque throughout one turbine rotation increased by approximately 2.37 times relative to the baseline, translating proportionally into higher power output. The combined flap configuration (inner and outer flap) exhibited a similar torque improvement trend, increasing the peak torque by about 76% with slightly lower torque fluctuations compared to the inner flap alone. Conversely, the outer flap configuration negatively impacted performance, decreasing peak torque by about 65% due to additional hydrodynamic resistance. Thus, the 90° inner flap configuration emerged as the most effective design for improving initial turbine torque, whereas the outer flap configuration is not recommended due to adverse effects on both self-starting capability and turbine performance.In conclusion, the primary contribution of this research is the development of a novel passive flap design concept on Darrieus blades capable of automatically enhancing power generation in low-flow conditions through a simple passive mechanism. This design innovation addresses classical limitations of Darrieus turbines (poor self-starting and low efficiency at TSR < 1), thereby representing a novel advancement in vertical-axis hydrokinetic turbine technology.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Uncontrolled Keywords: | turbin hidrokinetik aksis vertikal, passive flow control, flap, koefisien performansi, fenomena aliran, vertical axis hydrokinetic turbine, passive flow control, flap, performance coefficient, flow phenomena |
| Subjects: | T Technology > TA Engineering (General). Civil engineering (General) > TA357 Computational fluid dynamics. Fluid Mechanics T Technology > TJ Mechanical engineering and machinery > TJ808 Renewable energy sources. Energy harvesting. T Technology > TJ Mechanical engineering and machinery > TJ870 Hydraulic turbines. |
| Divisions: | Faculty of Industrial Technology > Physics Engineering > 30001-(S3) PhD Thesis |
| Depositing User: | Ahmad Wildan Mahmashani |
| Date Deposited: | 16 Sep 2025 03:11 |
| Last Modified: | 16 Sep 2025 03:11 |
| URI: | http://repository.its.ac.id/id/eprint/128251 |
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