Lian Y, Shyy W (2007) Laminar-turbulent transition of a low Reynolds number rigid or flexible airfoil. Laitone E (1997) Wind tunnel tests of wings at Reynolds numbers below 70 000. Jacobs EN (1932) The aerodynamic characteristics of eight very thick airfoils from tests in the variable density wind tunnel (No. Hu H, Yang Z (2008) An experimental study of the laminar flow separation on a low-Reynolds-number airfoil. Genç MS, Karasu I, Açıkel HH (2012) An experimental study on aerodynamics of naca2415 aerofoil at low Re numbers. Gaster M (1969) The structure and behaviour of laminar separation bubbles. įitzgerald EJ, Mueller TJ (1990) Measurements in a separation bubble on an airfoil using laser velocimetry. Int J Heat Fluid Flow 52:84–96ĭemir H, Genç MS (2017) An experimental investigation of laminar separation bubble formation on flexible membrane wing. Prediction of Aerodynamic Characteristics for Elliptic Airfoils in Unmanned Aerial Vehicle Applications, New YorkĬhoudhry A, Arjomandi M, Kelso R (2015) A study of long separation bubble on thick airfoils and its consequent effects. Exp Fluids 44(4):609–622Ĭarmichael B (1981) Low Reynolds number airfoil survey, vol. 1 (NASA-CR-165803)Ĭhitta V, Walters DK, Dhakal TP (2012) Prediction of aerodynamic characteristics for elliptic airfoils in unmanned aerial vehicle applications. Exp Fluids 45(4):675–691īurgmann S, Dannemann J, Schröder W (2008) Time-resolved and volumetric PIV measurements of a transitional separation bubble on an sd7003 airfoil. Phys Fluids 24(8):084105īurgmann S, Schröder W (2008) Investigation of the vortex induced unsteadiness of a separation bubble via time-resolved and scanning PIV measurements. Master’s thesisīoutilier MS, Yarusevych S (2012) Separated shear layer transition over an airfoil at a low Reynolds number. J Flow Control Meas Vis 6(03):185īoutilier MSH (2011) Experimental investigation of transition over a NACA 0018 airfoil at a low Reynolds number. Exp Fluids 48(1):81–103Īnyoji M, Wakui S, Hamada D, Aono H (2018) Experimental study of owl-like airfoil aerodynamics at low Reynolds numbers. Graphical abstractĪlam MM, Zhou Y, Yang H, Guo H, Mi J (2010) The ultra-low Reynolds number airfoil wake. The aerodynamic performance was correlated with the observed flow features around the airfoils. The cambered airfoil showed some Reynolds number dependence but performed better than its symmetrical counterpart. Symmetric NACA airfoils exhibited nonlinear lift behavior at Reynolds number below \(4\times 10^4\) as well as abrupt changes in lift values. The results showed that the airfoil thickness and camber significantly influence the aerodynamic performance and a strong dependence on the Reynolds number was observed. A high-precision load cell was utilized to characterize the performance of the airfoils, and the hydrogen bubble flow visualization was used to assess the flow over the airfoils. For this purpose, NACA-0009, 0012, 0021, and 6409 airfoils were used, and all experiments were performed in a water tunnel. The objective of this study is to investigate the impact of airfoil thickness and camber for canonical NACA airfoils at Reynolds numbers in this range and to correlate the observed aerodynamic behavior with the flow patterns. However, there are limited data sets characterizing the airfoil performance at Reynolds number spanning \(2\times 10^4 \le Re_c \le 5\times 10^4\). This implies that the vortex coherence during upstroke is higher than downstroke, which is evidenced by a more coherent vortex during the upstroke.Some unmanned aerial vehicles, micro-air vehicles, and small-scale wind turbines operate at Reynolds number values less than \(5 \times 10^5\) based on chord length. The magnitude of noise emission during the upstroke is higher than that during the downstroke in the hysteresis loop, although the velocity fluctuation magnitude is smaller. Flow measurements near the leading edge and trailing edge by particle image velocimetry show that the airfoil noise trend vs AoA is dominated by the trailing-edge flow features. The trend of overall sound pressure level vs AoA shows two local peaks: one at 4.4° with high tonal noise and a second one at 12.6° where the maximum lift coefficient is observed. A map of the noise emission vs AoA is presented revealing tonal noise emission at low AoA, and broadband noise beyond the linear range of lift coefficient. In order to investigate this effect, a NACA 0012 airfoil is investigated during upstroke and downstroke between zero and post-stall AoA at a constant Reynolds number of 5.1 × 10 5. In contrast, the effect of hysteresis on the noise emission has not been reported before. The effect of hysteresis on the lift coefficient of an airfoil is well-known, i.e., the lift coefficient is higher during the upstroke than during the downstroke for the same angle of attack (AoA).
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