Manuscript title: Effect of spanwise groove on the dynamic stall characteristics of an airfoil

Numerical simulations are conducted to investigate the effect of triangular groove on the dynamic stall characteristics of a NACA 0012 airfoil at a Reynolds number of 135,000. The right-angled triangular grooves are placed at either 10%, 25%, or 50% chord locations on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The solutions that are second order accurate in time and space are obtained using pressure-based finite volume solver and the 4-equation transition SST turbulence model viz. γ- Re θt is used to predict transition and viscous stresses accurately. The airfoil is in harmonic pitch motion about its quarter-chord with a maximum circular frequency of 18.67 rad/s. The results suggest that the presence of a groove, except for the deeper grove at 0.5c, quickens the dynamic stall, but with smaller rise in C l,max and a less severe fall in lift at the stall. The mean C l value during the downstroke is improved by up to 8% for the deeper groove at 0.25c, reducing the hysteresis in lift significantly. The grooves at 0.1c, 0.25c, and 0.5c also reduce the drag by 4%, 7%, and 9% during a complete cycle, with subsequent improvements of 54%, 69%, and 63% in the l/d ratio. The current finding can be thus used to enhance the performance of flapping wing MAVs, helicopter rotors, and wind turbine blades as these applications encounter the dynamic stall phenomena frequently.

Perfiles de microaerogeneradores HAWT a bajo número de REYNOLDS

Este trabajo consiste en el estudio aerodinámico de 8 perfiles alares distintos; NACA 0012, NACA 4412, NREL S822, NREL S823, NREL S833, CLARK Y, SD7080 (9.2%), Wortmann FX 63-137 a bajo número de Reynolds. De manera de poder seleccionar el perfil ideal para el diseño de los álabes de un aerogenerador de baja potencia de ≈ 1 kW. Mediante el software QBlade se han analizado los valores de los coeficientes adimensionales de sustentación (CL) y arrastre (CD) a un Reynolds de 109.007 y un rango de ángulos de ataque (α) de 0° a 20°. Mientras que utilizando el software SolidWorks® se ha simulado el comportamiento del flujo de aire alrededor de los perfiles bajo distintas condiciones de cálculo, variando el refinamiento en búsqueda de la convergencia de los resultados.Finalmente, se realizó una comparación de los resultados de simulación numérica obtenidos con Flow Simulation con los del software QBlade®. De esta forma se pretende verificar las simulaciones obtenidas, a fin de seleccionar el perfil adecuado para las condiciones de estudio.

Experimental investigation of NACA-0012 airfoil instability noise with sawtooth trailing edges

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

Lift Force of Airfoil (NACA 0012, NACA 4612, NACA 6612) With Variation of Angle of Attack and Camber: Computational Fluid Dynamics Study

Airfoil is a cross section from air plane wings can affect aerodynamic performance to lift force (FL). The lift force generated by airfoil has different values due to several external and internal factors, including angle of attack, flow rate and camber. To find the lift force of airfoils with different cambers and variations angle of attack and then flow rate can use computational fluid dynamics simulation. Computational fluid dynamics is simulation on a computer that can complete systems for fluid, heat transfer and other physical processes. This research using computational fluid dynamics simulation performed by SolidWorks, with NACA airfoil type which has different camber NACA 0012, NACA 4612 and NACA 6612. The angle of attack used in research was 0o, 4o, 8o, 12o, 16o and 20o. Flow rate used in research was 20m/s, 40 m/s, 60 m/s, 80 m/s and 100 m/s. From this research will be the bigger camber can produce a greater force lift. In addition, the greater airfoil flow rate can produce a greater force lift. This research also that the connection between force lift with coefficient lift (CL) is nonlinear quadratic form.

On the performance of RANS turbulence models in predicting static stall over airfoils at high Reynolds numbers

Purpose This paper aims to conduct, a detailed investigation of various Reynolds averaged Navier–Stokes (RANS) models to study their performance in attached and separated flows. The turbulent flow over two airfoils, namely, National Advisory Committee for Aeronautics (NACA)-0012 and National Aeronautics and Space Administration (NASA) MS(1)-0317 with a static stall setup at a Reynolds number of 6 million, is chosen to investigate these models. The pre-stall and post-stall regions, which are in the range of angles of attack 0°–20°, are simulated. Design/methodology/approach RANS turbulence models with the Boussinesq approximation are the most commonly used cost-effective models for engineering flows. Four RANS models are considered to predict the static stall of two airfoils: Spalart–Allmaras (SA), Menter’s k – ω shear stress transport (SST), k – kL and SA-Bas Cakmakcioglu modified (BCM) transition model. All the simulations are performed on an in-house unstructured-grid compressible flow solver. Findings All the turbulence models considered predicted the lift and drag coefficients in good agreement with experimental data for both airfoils in the attached pre-stall region. For the NACA-0012 airfoil, all models except the SA-BCM over-predicted the stall angle by 2°, whereas SA-BCM failed to predict stall. For the NASA MS(1)-0317 airfoil, all models predicted the lift and drag coefficients accurately for attached flow. But the first three models showed even further delayed stall, whereas SA-BCM again did not predict stall. Originality/value The numerical results at high Re obtained from this work, especially that of the NASA MS(1)-0317, are new to the literature in the knowledge of the authors. This paper highlights the inability of RANS models to predict the stall phenomenon and suggests a need for improvement in modeling flow physics in near- and post-stall flows.