arXiv subjects

Ahmad Nabhani

Publications and source records attributed to Ahmad Nabhani.

3 recordsLinked to original sources

arXiv2026

Influence of Turbulence Length Scale and Platform Surge Motion on Wake Dynamics in Tandem Floating Wind Turbines

Wake interaction is a key factor limiting the performance of floating offshore wind turbine arrays, yet the combined influence of inflow turbulence structure and platform motion on wake dynamics remains poorly understood. This study examines how the integral length scale of inflow turbulence and platform surge motion shapes wake development and power performance in a tandem configuration of two aligned floating offshore wind turbines separated by five rotor diameters. High-fidelity computational fluid dynamics simulations are performed using OpenFOAM, based on Large-Eddy Simulation with an Actuator-Line Model and the Wall-Adapting Local Eddy-Viscosity subgrid-scale closure. Synthetic turbulent inflows are generated using the Divergence-Free Synthetic Eddy Method, with prescribed integral length scales spanning 0.25-1.25 times the rotor radius. Over this range, increasing the integral length scale naturally leads to higher freestream turbulence intensity, which increases from approximately 1.9% to 7.2%. The corresponding dominant inflow frequencies are extracted from time-resolved velocity signals, yielding Strouhal numbers in the range St approx 0.71 to 0.12. Wake evolution is analyzed through disk-averaged velocity deficits, turbulent kinetic energy distributions, spectral characteristics, vortex topology, and time-averaged power coefficients. The results show that the inflow turbulence integral length scale is the primary parameter controlling wake recovery. Larger integral scales introduce energetic, low-frequency eddies that destabilize the tip-vortex system, enhance lateral and vertical entrainment, and accelerate wake mixing. These mechanisms lead to substantial reductions in the inter-turbine velocity deficit and translate directly into increased downstream power output...

physics.flu-dyn↗

arXiv2024

Large-Scale Horizontal Axis Wind Turbine Aerodynamic Efficiency Optimization using Active Flow Control and Synthetic Jets

Efficiency increase is seen as one of the main goals in any energy converting device. In this direction, the present study aims to demonstrate that large-scale wind turbines can still be improved in order to generate larger amounts of energy. The research presented in this manuscript consists of two main blocks. Initially, it analyzes via Computational Fluid Dynamics (CFD) the boundary layer dynamics on a set of pre-determined airfoils cut along the DTU-10MW reference blade by using the 2D URANS k omega SST turbulence model. The aim of this initial stage is to identify the boundary layer separation point, its associated frequency, and peak to peak amplitude for each airfoil cut along the blade, evaluating as well their respective aerodynamic characteristics. The second main goal of the present research consists of implementing the Active Flow Control (AFC) technology and, when employing synthetic jets, to reattach the boundary layer in all airfoils where it is separated. To accomplish this second goal efficiently, the five parameters associated to the AFC implementation performed to each airfoil will be obtained through respective genetic algorithm optimizations. An energy assessment is finally undertaken at each airfoil to validate the respective energy gain obtained. When comparing the net power gain, before and after AFC implementation, generated by each of the airfoils evaluated, net power gains between 23 and 36KW are obtained in all airfoils analyzed, clarifying that the proposed technology is capable of improving the performance of the wind turbines, very likely at any operating condition.

physics.flu-dyn↗

arXiv2024

Wind turbine enhancement via Active Flow Control Implementation

The present research aims to enhance the efficiency of a DTU-10MW Horizontal Axis Wind Turbine (HAWT) via Active Flow Control (AFC) implementation and using Synthetic Jets (SJ). In the initial part of the study the flow around two airfoil sections cut along the wing turbine blade and for a wind speed of 10m/s is simulated using CFD-2D-RANS-Kω-SST turbulence model, in order to obtain the time averaged boundary layer separation point and the associated vortex shedding frequency. This information is used, on a second stage of the paper, to set, in one of these two airfoils where the boundary layer is having an early separation, two of the AFC parameters while optimizing the remaining three. The optimization is performed employing a parametric analysis and demonstrates that a considerable WT power increase can be obtained when managing to reattach the former separated boundary layer. This is further clarified thanks to the energy assessment presented in the final part of the paper. Although the AFC optimization needs to be extended for the rest of the blade sections, the procedure outlined in the present research clarifies the different steps to be followed to optimize the performance of any HAWT under any operating conditions. The Reynolds numbers associated to the respective airfoil sections analyzed in the present manuscript are Re = 14.088 e6 and Re = 14.877 e6, the characteristic length being the corresponding chord length for each airfoil.

physics.flu-dyn↗