Simulasi Numerik Pengaruh Sudut Pitch dan Arc Angle terhadap Kinerja Turbin Hibrida Savonius-Darrieus pada Arus Laut Kecepatan Rendah

Adinata Raharja, Ir. Muhammad Agung Bramantya, S.T., MT., M.Eng., Ph.D., IPM., ASEAN Eng.

2026 | Skripsi | TEKNIK MESIN

Ketergantungan terhadap bahan bakar fosil yang tinggi di Indonesia memicu urgensi transisi menuju Energi Baru Terbarukan. Sebagai negara maritim, Indonesia memiliki potensi energi kinetik arus laut yang masif mencapai 60 GW, namun pemanfaatannya hingga saat ini masih berada di angka nol. Penggunaan teknologi Vertical Axis Hydrokinetic Turbine (VAHT) hibrida tipe Savonius-Darrieus menjadi solusi relevan untuk perairan berkecepatan rendah. Desain hibrida ini mengombinasikan keunggulan rotor Savonius (drag-driven) yang menghasilkan torsi awal tinggi untuk mengatasi inersia diam sistem (self-starting), dengan rotor Darrieus (lift-driven) yang memiliki efisiensi tinggi pada kecepatan putar besar. Penelitian ini bertujuan untuk menganalisis secara numerik pengaruh interaksi variasi geometri sudu terhadap performa hidrodinamika sistem turbin hibrida koaksial tersebut. 
Metodologi penelitian dilakukan secara komputasional menggunakan pendekatan Computational Fluid Dynamics (CFD) dua dimensi (2D) aliran transien melalui software ANSYS Fluent, dengan perancangan model geometri menggunakan Autodesk Inventor Professional 2026. Variabel bebas yang diuji mencakup variasi arc angle rotor Savonius (160°, 170°, 180°), sudut pitch rotor Darrieus (80°, 85°, 90°), free stream velocity (0,5 m/s; 1,0 m/s; 1,5 m/s), serta Tip Speed Ratio atau TSR (0,5; 1,0; 1,5). Variabel terikat yang diamati meliputi nilai torsi, daya, koefisien torsi (Ct), koefisien daya (Cp), serta visualisasi kontur tekanan, kecepatan, dan Energi Kinetik Turbulensi (Turbulent Kinetic Energy/TKE).
Hasil simulasi numerik menunjukkan bahwa performa turbin hibrida sangat sensitif terhadap perubahan geometri sudu dan parameter operasional. Kombinasi geometri paling optimal ditemukan pada Model 90-160 (sudut pitch Darrieus 90° dan arc angle Savonius 160°) yang mencatatkan nilai Cp dan Ct tertinggi. Pengurangan arc angle Savonius menjadi 160° sukses mereduksi zona tekanan tinggi pada returning blade, sehingga mampu meminimalkan efek pengereman (braking effect) atau torsi lawan akibat gaya hambat fluida. Sementara itu, sudut pitch Darrieus 90° berhasil merekayasa sudut serang (angle of attack) secara ideal dengan mengarahkan resultan gaya dominan ke arah tangensial untuk memutar poros, berbeda dengan sudut pitch kecil (80°) yang menghasilkan gaya radial penyumbat aliran (blockage effect). Karakteristik hidrodinamika terbaik dicapai pada kondisi TSR tinggi (TSR 1,5) dan kecepatan arus 1,5 m/s, di mana lonjakan bilangan Reynolds secara drastis menunda gejala stall, menjaga fluida tetap menempel pada permukaan sudu (attached flow), serta menghasilkan intensitas ekstraksi energi kinetik air yang maksimal. 

The high dependence on fossil fuels in Indonesia triggers an urgent transition toward Renewable Energy. As a maritime country, Indonesia possesses a massive marine current kinetic energy potential of up to 60 GW, yet its utilization currently remains at zero. The utilization of hybrid Savonius-Darrieus Vertical Axis Hydrokinetic Turbine (VAHT) technology serves as a relevant solution for low-velocity waters. This hybrid design combines the advantages of the Savonius rotor (drag-driven), which generates high starting torque to overcome the system's static inertia (self-starting capability), with the Darrieus rotor (lift-driven), which exhibits high efficiency at high rotational speeds. This study aims to numerically analyze the interaction effect of blade geometric variations on the hydrodynamic performance of the coaxial hybrid turbine system.
The research methodology was conducted computationally using a two-dimensional (2D) transient flow Computational Fluid Dynamics (CFD) approach via ANSYS Fluent software, with geometric model design executed using Autodesk Inventor Professional 2026. The independent variables tested include variations in the Savonius rotor arc angle (160°, 170°, 180°), Darrieus rotor pitch angle (80°, 85°, 90°), free stream velocity (0.5 m/s; 1.0 m/s; 1.5 m/s), and Tip Speed Ratio or TSR (0.5; 1.0; 1.5). The observed dependent variables include torque, power, coefficient of torque (Ct), coefficient of power (Cp), as well as contour visualizations of pressure, velocity, and Turbulent Kinetic Energy (TKE).
The numerical simulation results indicate that the performance of the hybrid turbine is highly sensitive to blade geometric changes and operational parameters. The most optimal geometric combination was found in Model 90-160 (Darrieus pitch angle of 90° and Savonius arc angle of 160°), which recorded the highest Cp and Ct values. Reducing the Savonius arc angle to 160° successfully reduced the high-pressure zone on the returning blade, thereby minimizing the braking effect or counter-torque caused by fluid drag forces. Meanwhile, the 90° Darrieus pitch angle successfully engineered an ideal angle of attack by directing the dominant resultant force in the tangential direction to rotate the shaft, unlike the small pitch angle (80°) which produced radial forces that caused a flow blockage effect. The best hydrodynamic characteristics were achieved under high TSR conditions (TSR 1.5) and a current velocity of 1.5 m/s, where a drastic surge in the Reynolds number delayed stall phenomena, maintained attached flow on the blade surfaces, and yielded maximum water kinetic energy extraction intensity. 

Kata Kunci : Turbin Hibrida, Savonius-Darrieus, Computational Fluid Dynamics, Sudut Pitch, Arc Angle, Arus Laut Kecepatan Rendah