PENGARUH TANDEM STAGGER CYLINDER TERHADAP PERFORMA HIDRODINAMIKA DRAG TURBINRAFIAKMALauthorTurbin Savonius memiliki konstruksi sederhana dan kemampuan self-starting yang baik, tetapi performanya masih terbatas akibat drag negatif pada returning blade serta pembentukan wake yang menyebabkan kehilangan energi. Penelitian ini bertujuan menganalisis pengaruh empat circular cylinder dalam konfigurasi tandem-stagger terhadap performa hidrodinamika turbin Savonius menggunakan simulasi Computational Fluid Dynamics dua dimensi. Simulasi dilakukan menggunakan pendekatan Unsteady Reynolds-Averaged Navier–Stokes dan model turbulensi SST kω dengan fluida kerja air, kecepatan aliran bebas 1 m/s, bilangan Reynolds 3,6 × 10⁵, serta sudut stagger 45°. Variasi spacing ratio yang digunakan adalah S/D = 0,8; 0,9; 1,0; dan 1,1. Model numerik diverifikasi melalui uji grid independence dan divalidasi dengan membandingkan kecenderungan hasil simulasi terhadap penelitian sebelumnya. Parameter yang dianalisis meliputi distribusi tekanan, pola aliran, karakteristik wake, coefficient of moment, dan coefficient of power. Hasil penelitian menunjukkan bahwa seluruh variasi cylinder mampu meningkatkan performa dibandingkan turbin konvensional. Konfigurasi S/D = 0,9 menghasilkan performa terbaik dengan Cm maksimum sebesar 0,515 dan Cp maksimum sebesar 0,373, yang meningkat masing-masing sekitar 41,5% dan 62% dibandingkan turbin konvensional. Konfigurasi tersebut mampu mengarahkan aliran menuju advancing blade, mengurangi drag negatif pada returning blade, serta menghasilkan pola wake yang lebih teratur. Dengan demikian, konfigurasi tandem-stagger cylinder efektif digunakan sebagai metode passive flow control untuk meningkatkan performa hidrodinamika turbin Savonius. Kata kunci: turbin Savonius, tandem-stagger cylinder, hidrodinamika, CFD,coefficient of moment, coefficient of power. =========================================================== The Savonius turbine has a simple construction and good self-starting capability, but its performance remains limited due to negative drag on the returning blade and wake formation that causes energy losses. This study analyzes the effect of four circular cylinders arranged in a tandem-stagger configuration on the hydrodynamic performance of a Savonius turbine using two-dimensional Computational Fluid Dynamics simulations. The simulations were performed using the Unsteady ReynoldsAveraged Navier–Stokes approach and the SST k-ω turbulence model, with water as the working fluid, a free-stream velocity of 1 m/s, a Reynolds number of 3.6 × 10⁵, and a stagger angle of 45°. The tested spacing ratios were S/D = 0.8, 0.9, 1.0, and 1.1. The numerical model was verified through a grid-independence test and validated against previous studies. The evaluated parameters included pressure distribution, flow patterns, wake characteristics, coefficient of moment, and coefficient of power. The results showed that all cylinder configurations improved turbine performance compared with the conventional design. The S/D = 0.9 configuration produced the best performance, with a maximum Cm of 0.515 and a maximum Cp of 0.373, representing improvements of approximately 41.5% and 62%, respectively. Therefore, tandemstagger cylinders are effective passive flow-control devices for improving the torque and power performance of a hydrokinetic Savonius turbine. Keywords: Savonius turbine, tandem-stagger cylinder, hydrodynamics, CFD, coefficient of moment, coefficient of power.TL Motor vehicles. Aeronautics. Astronautics2026-07-15Tugas Akhir