Numerical/experimental investigations on reducing drag penalty of passive vortex generators on a NACA 4415 airfoil

Abstract

A study emphasizing the effects of passive vortex generators (VGs) on aerodynamic characteristics of a NACA 4415 airfoil is presented. Both experimental and numerical works have been carried out on an array of VGs attached to a NACA 4415 airfoil. Lift and drag measurements are made at various angles of attack by using three-axis component balance system. On the numerical side, Reynolds-averaged Navier-Stokes (RANS) equations have been solved with ANSYS FLUENT 14.5 commercial code with fully structured mesh and three turbulence models (realizable k-ε, k-ω shear stress transport [SST] and the Spalart-Allmaras model) at Reynolds number Re = 2 × 10 5 .Parametric studies have been conducted to find out optimal configurations with respect to span-wise separation distance between VGs, along with their location along the chord. A very good agreement has been obtained between experimental and computational results indicating that this optimized configuration is robust for the considered parameters. It turns out that increasing the span-wise separation length increases the aerodynamic performances (lift-to-drag ratio) at low attack angles for which low parasitic drag is achieved but conversely degrades it at higher ones. For the stream-wise location along the chord, upstream position of VGs degrades the lift-to-drag ratio at low attack angles and conversely improves it at higher ones. KEYWORDS computational fluid dynamics, flow control, NACA 4415 airfoil, passive vortex generators, Spalart-Allmaras turbulence model, wind tunnel 1 | INTRODUCTIONOwing to the continuous increase in energy consumption and persisting demand from governments and citizens for a more sustainable energy production the wind energy has experienced considerable growth in the past decade.The prospects and main challenges of wind applications are to reach the target of 1000 GW of wind energy by 2030. 1 For the offshore market, this has led to race in building the largest wind turbines, but one now faces critical limits from a technical point of view along with prohibitive prices toward the goal to reduce the energy cost for the end-user (CoE). 2,3 For the onshore market, size upgrade is not a promising strategy owing to environmental issues related to higher noise levels and visual inconveniences. Therefore, for this latter market, engineers investigate the way to increase the aerodynamic efficiency from classical wind turbines. However, studying aerodynamic performance of full size wind turbine remains a difficult task since relevant metrology in rotating frame of such sizes is incredibly expensive and difficult. On the computational fluid dynamics side, their related large size 3-D highly turbulent flows around moving bodies are also very challenging, so very few works have been published up to now. 4

A review of commercial numerical modelling approaches for axial hydrokinetic turbine wake analysis in channel flow

“…For BEM-VD rotor modelling a sensitivity analysis was done using drag (C D ) and life (C L ) coefficients comparing experimental [112,113] and numerical data (XFOIL data). The results indicated a significant variation in turbine performance, wake formation and wake dissipation rate in the near and far wake.…”

Experimental Investigation on Hover Performance of a Ducted Coaxial-Rotor UAV

“…Most of the prior studies tended to either focus on the hover performance in order to seek out an optimal configuration by a series of experimental measures (including wind tunnel tests), or adopt the numerical simulation to determine clear characteristics related to the complicated aerodynamic environments such as the tip vortex, induced inflow, mutual interference, etc. [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Both of the two methods above obviously require extensive effort.…”

The Effect of Location and Shape of Vortex Generators on Aerodynamic Characteristics of a NACA 4415 Airfoil

“…However, the introduction of micro VGs led to some increase in parasitic drag. Another study by Fouatih et al [5] investigated the influence of passive VGs on the aerodynamic properties of the NACA 4415 airfoil using experimental and numerical approaches. The results demonstrated a strong agreement between experimental and computational findings, highlighting the optimized VG configuration that enhanced aerodynamic performance.…”