Oscillating water column wave energy converters require self-rectifying turbines capable of maintaining stable performance under bidirectional airflow. This study numerically investigates the aerodynamic performance and internal flow characteristics of an axial-flow impulse turbine using OpenFOAM under both uniform and reciprocating airflow conditions. Rotor motion was modeled using the Multiple Reference Frame approach, and the numerical model was validated against experimental data for one-way flow at an inlet velocity of 8.71 m s−1 and rotational speeds ranging from 300 to 1300 rpm. The CFD results successfully reproduced the experimental efficiency trend, yielding a peak efficiency of η = 0.4269 at 700 rpm and ϕ ≈ 0.95, which closely aligns with the experimental peak efficiency of η = 0.4425. Validation metrics demonstrated a high degree of accuracy, with an RMSE of 0.0219, a mean absolute error of 0.0197, a maximum absolute error of 0.0399, a squared Pearson correlation coefficient of 0.826, and a peak-efficiency difference of 3.5%. Flow-field analysis revealed that low rotational speeds resulted in high outlet velocities and incomplete energy extraction, whereas excessive rotational speeds caused flow misalignment, downstream vortex formation, and additional aerodynamic losses. Under reciprocating flow conditions, characterized by a sinusoidal velocity amplitude of 8.71 m s−1 and periods of 0.5–2.0 s at 700 rpm, both input and torque coefficients exhibited hysteresis, with the strongest loops observed at the shortest periods. Examinations of streamline, pressure, and velocity distributions indicated that residual flow during flow reversal alters the effective inlet direction in the subsequent half-cycle, resulting in flow memory and a phase-dependent turbine response. As the present computational domain excludes the OWC chamber, these findings characterize turbine-level aerodynamic performance rather than the complete system power coefficient.
Recovering unused kinetic energy from urban and industrial airflow systems provides a potential approach for decentralized renewable energy generation. This study investigated the performance of a Persian Panemone vertical-axis wind turbine (VAWT) integrated with a diffuser and adjustable deflector for airflow energy recovery in confined environments. Computational fluid dynamics (CFD) simulations and laboratory experiments using fan-generated airflow were conducted to evaluate the effects of blade number and airflow conditions on turbine performance. Five- and six-blade configurations were evaluated under different wind speeds. CFD results showed that the 5-blade configuration achieved the highest power coefficient (Cp) of 0.2332 at 2 m/s and maintained a tip speed ratio (TSR) of approximately 1.9. Velocity and pressure contours indicated that the diffuser accelerated the incoming airflow and improved momentum transfer to the rotor. In the experiments, the 6-blade configuration exhibited better starting characteristics, reaching a maximum no-load rotational speed of 260 rpm compared with 213 rpm for the 5-blade configuration. The difference between CFD and experimental results was attributed to non-uniform fan-generated airflow, mechanical friction, electrical loading, and idealized numerical assumptions. The results indicate that the 5-blade configuration provides more favorable aerodynamic performance, whereas the 6-blade configuration provides better starting and rotational characteristics under the tested laboratory conditions. The diffuser–deflector system therefore provides a potential approach for recovering energy from confined urban ventilation and industrial exhaust airflow.
Halim Sobri, F. Arifin, C. Rs· Jurnal POLIMESIN· 0 citations
This research is a numerical investigation into the two-dimensional configuration of a Savonius vertical axis wind turbine (VAWT) using computational fluid dynamics (CFD). Transient analysis has been performed on this turbine using rotatable domains in COMSOL Multiphysics to capture the unsteady aerodynamic characteristics. A transient analysis was also performed using the incompressible Navier-Stokes equations to determine the following performance characteristics: velocity distribution; pressure distribution; torque generated by turbine; and acceleration of rotor. The results showcase how blade flow asymmetry between advancing and returning blades creates periodic vortex shedding patterns, and how the torque generated is also fluctuating. For the purpose of this analysis, the torque increases from near zero torque to approximately 0.45 N·m., while the angular velocity grows from 0 rad/sec (initially) to roughly 37 rad/sec (maximum velocity achieved) during the transient analysis. During the simulation, the rotor speed achieved during transient analysis is approximately 350 rpm, with a corresponding mechanical power value ranging from approximately 16 to 17 W. The results obtained from the transient analysis suggest that the flow separation and wake behaviour associated with unsteady states are critical to determining the overall turbine performance. Furthermore, the CFD model created through this investigation establishes a solid methodology for determining the performance of Savonius vertical axis wind turbines relative to predicted aerodynamic characteristics and design optimization criteria.
Baxtiyor Rustamov, Habibullo Goyibnazarov, Nodirabegim Rajabova et al.· EPJ Web of Conferences· 0 citations
The Wells turbine is a key component in an Oscillating Water Column (OWC)-based ocean wave energy conversion system, yet its limited operating range due to leading-edge stall constrains overall system efficiency. This study presents an independent CFD benchmark of the performance of the Wells turbine with and without a passive flow control device, a stall fence, as investigated by Das and Samad (2020). Steady Reynolds-Averaged Navier-Stokes (RANS) simulations using the SST k-ω turbulence model were performed in ANSYS CFX v22.1 by replicating the original geometry, boundary conditions, and mesh density for direct comparison. The reference turbine (eight NACA 0015 blades, solidity 0.64) and the configuration with a stall fence (fences at 40% and 80% span) were evaluated over a flow coefficient range of φ = 0.075-0.275. Grid independence study using quantitative (non-dimensional torque T*) and qualitative (tip-vortex topology) criteria resulted in the selection of a 3.5-million-element mesh. For the reference turbine, a mean absolute percentage error (MAPE) of 2.0% for T* and 3.1% for efficiency was obtained in the pre-stall range (φ ≤ 0.225), confirming strong numerical reproducibility. However, steady RANS failed to predict the stall onset for the reference configurations and overpredicted torque by up to 508% in the post-stall region. The stall point at φ = 0.250 was successfully reproduced with a deviation approaching zero, proving that the vorticity induced by the fence geometry enhances the reliability of RANS stall predictions. The pre-stall MAPE for the fence configuration was 4.4% for T*, slightly higher due to local vortex interactions around the fence. These findings establish steady RANS as a reliable design tool in the pre-stall range and demonstrate that passive fence stalls not only extend the turbine’s operating range but also improve the accuracy of CFD predictions. Keywords: Wells turbine, Stall fence, CFD benchmark, Steady RANS, Ocean wave energy conversion.
Muhammad Nurfajriansyah Muslich, A. Prabowo, R. Adiputra et al.· Research in Education, Techn...· 0 citations
To address the low efficiency and unclear internal loss mechanisms of azimuth waterjet propulsion (AWP) systems operating under shallow and complex flow conditions, this study investigates an AWP unit at 950 rpm with a thrust of 1.63 kN. Steady numerical simulations are conducted under mooring and low-speed conditions, focusing on thrust coefficient, impeller efficiency, pump efficiency, and diffuser flow characteristics, with comparisons to a conventional mixed-flow pump. The results show that the propeller hydraulic efficiency at the design condition is approximately 52%, significantly lower than the 80–93% typical of mixed-flow pumps. The diffuser contributes nearly 80% of the total hydraulic loss, dominated by secondary flow effects. From the perspective of radial equilibrium in the guide vanes, secondary flow development is closely linked to spanwise momentum non-uniformity and deviation from equilibrium. The inclined outflow from the impeller induces strong spanwise imbalance, while the nearly 180° turning in the diffuser suppresses conventional force terms and establishes a pressure-gradient-dominated inertial balance associated with streamline curvature. This mechanism drives transverse migration and entrainment, promoting the formation of counter-rotating vortex pairs and secondary flows. Four major vortex concentration regions are identified, where interactions between secondary flow and recirculation generate complex three-dimensional vortex structures, including induced and spiral separation vortices. These vortices locally block the flow passage, causing pressure fluctuations and energy dissipation. The mid-span region of the guide vanes is identified as the primary location of loss accumulation. These findings provide theoretical and engineering guidance for diffuser optimization in AWP systems. It should be noted that the present study is based solely on numerical simulations, and no experimental validation for the investigated AWP configuration is currently available. Future experimental studies are needed to further verify the predicted hydraulic performance and flow structures.