1,721,007 research outputs found
Experimental Investigation of a Trailing Edge L-shaped Tab on a Pitching Airfoil in Deep Dynamic Stall Conditions
Full text linkAn L-shaped tab was tested at the trailing edge of an oscillating airfoil to evaluate its effects on blades aerodynamic performance. The tests were conducted on a NACA 23012 pitching airfoil in deep dynamic stall conditions with the L-shaped tab fixed in two different positions. When deployed the tab is attached to the airfoil upper surface so that the end prong protrudes at the airfoil trailing edge. In retracted position the tab features an angle of 9.1° with the airfoil upper surface, since its prong tip touches the airfoil trailing edge. The airloads time histories during a pitching cycle were evaluated by pressure measurements carried out on the airfoil midspan contour. The phase-averaged flow field at the trailing edge region was investigated by means of particle image velocimetry to evaluate the detailed flow physics involved in the use of the device. The experimental results indicate that the use of such a pivoting L-shaped tab can introduce similar effects to those that can be obtained by the use of an active Gurney flap. Thus, the L-shaped tab can be considered an attractive device due to its easier integration on helicopter blades
Experimental Evaluation of an L-Shaped Tab to be Used as an Active Gurney Flap for Dynamic Stall Control
No full textThe present paper describes an experimental activity carried out in the frame of research about dynamic stall control. In particular, an L-shaped tab was tested on the trailing edge of a pitching airfoil in deep dynamic stall condition. The L-shaped tab was tested on a NACA 23012 pitching blade section model in two different fixed positions: deployed and retracted. When deployed the tab is flush to the airfoil upper surface and its end prong behaves as a Gurney flap at the airfoil trailing edge. When retracted the tab features an angle of 9.1 deg. with the airfoil upper surface since its prong tip touches the airfoil trailing edge. The experimental activity includes both unsteady pressure measurements on the airfoil midspan contour to evaluate the airloads time histories and Particle Image Velocimetry (PIV) carried out at the trailing edge region. The experimental results shows that the use of such a pivoting L-shaped tab can introduce similar advantages for dynamic stall alleviation to the ones that can be obtained by the use of an active Gurney flap. Therefore, due to an easier integration on helicopter blades, the tested L-shaped tab can be considered an attractive device to be used on helicopter blades for dynamic stall control
Cycling Aerodynamics
No full textA general introduction presents the main concepts about biker and bicycle aerodynamics. A decription of the drag reduction problem is presented and the athlete position effects as well as the main bicycle components effects are examinated. Advices are proposed to improve performances (taking the international regulations as a constant reference)
Experimental Evaluation of an Active Controlled L-Shaped Tab for Dynamic Stall Alleviation
No full textAerodynamic and aeroacoustics investigation of tandem propellers in hover for eVTOL configurations
Full text linkThe present study investigates the aerodynamic interactions and the aeroacoustic footprint of a tandem propellers configuration typical of a multi-rotor eVTOL aircraft in hover conditions. In particular, an experimental campaign was conducted to collect a comprehensive aerodynamic and aeroacoustic database over two scaled propellers models in tandem. Aerodynamic loads and acoustic measurements were performed in an anechoic test chamber. Measurements also included flow field surveys using stereoscopic PIV technique. The configurations tested included twin propellers in side-by-side and staggered configurations with partial overlap between rotor disks. The activity was completed by numerical simulations performed with the mid-fidelity aerodynamic solver DUST. The analysis of experimental and numerical results enabled to provide a robust comprehension of the different flow mechanisms that characterise aerodynamic interaction between propellers wakes by changing longitudinal and lateral distances as well as blades sense of rotation. In particular, the effects of these interactions on both the aerodynamic performance and aeroacoustic footprint was investigated. Specifically, the partial overlap between propellers disks leads to a conspicuous reduction of aerodynamic performance of the propeller invested by front propeller slipstream as well as an increase of the acoustic emission of the dual propeller system
Wake Measurements behind an Oscillating Airfoil in Dynamic Stall Conditions
Full text linkThe unsteady flow field in the wake of an NACA 23012 pitching airfoil was investigated by means of triple hot-wire probe measurements. Wind tunnel tests were carried out both in the light and deep dynamic stall regimes. The analysis of the wake velocity fields was supported by the measurements of unsteady flow fields and airloads. In particular, particle image velocimetry surveys were carried out on the airfoil upper surface, while the lift and pitching moments were evaluated integrating surface pressure measurements. In the light dynamic stall condition, the wake velocity profiles show a similar behaviour in upstroke and in downstroke motions as, in this condition, the flow on the airfoil upper surface is attached for almost the whole pitching cycle and the airloads show a small amount of hysteresis. The deep dynamic stall measurements in downstroke show a large extent of the wake and a high value of the turbulent kinetic energy due to the passage of strong vortical structures, typical of this dynamic stall regime. The comprehensive experimental database can be considered a reference for the development and validation of numerical tools for such peculiar flow conditions
Experimental Method for Drag Measurement of an Oscillating Airfoil in Dynamic Stall Condition
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