A Review of Blowing: as an Active Flow Control Strategy

Upper surface flaps commonly referred to as spoilers or drag brakes can increase maximum lift, and improve aerodynamic efficiency at high, near-stall angles of attack. This phenomenon was studied experimentally and computationally using a 0.307626 m chord length NACA 2412 airfoil in six different configurations, and one baseline clean configuration. A wind tunnel model was placed in the Ryerson Low Speed Wind Tunnel (atmospheric, closed-circuit, 3 ft × 3 ft test section) at a Reynold’s number of approximately 780,000 and a Mach number of 0.136. The wind tunnel study increased the lift coefficient by 0.393%-2.497% depending on the spoiler configuration. A spoiler of 10% chord length increased the maximum lift coefficient by 2.497 % when deflected 8º, by 2.110% when deflected 15º, and reduced the maximum lift coefficient by 2.783% when deflected 25º. A spoiler of 15% chord length produced smaller maximum lift coefficient gains; 0.393% when deflected 8º, by 1.760% when deflected 15º, and reduced the maximum lift coefficient by 4.475% when deflected 25º. Deflecting the spoiler increased the stall angle between 37.658% and 87.544% when compared with the clean configuration. The drag coefficient of spoiler configurations was lower than the clean configuration at angles of attack above 18º. The combination of the increased lift and reduced drag at angles of attack above 18º created by the spoiler configurations resulted in a higher aerodynamic efficiency than the clean configuration case. A 10% chord length spoiler deflected at 8º produced the highest aerodynamic efficiency gains. At low angles of attack, the computational study produced consistently higher lift coefficients compared with the wind tunnel experiment. The lift-slope was consistent with the wind tunnel experiment lift-slope. The spoiler airfoil stall behaviour was inconsistent with the results from the wind tunnel experiment. The drag coefficient results were consistent with the wind tunnel experiment at low angles of attack. However, the spoiler equipped airfoils did not reduce drag at high angles of attack. Therefore, the computational model was not valid for the spoiler configurations at high angles of attack.

In this research, the flow physics and aerodynamic performance of dragonfly cross sections, used in Micro Aerial Vehicles (MAVs), in low Reynolds are investigated. The main objective of the research is to study the performance of dragonfly wing cross-sections flapping motion in Reynolds 5000 and 10,000. Pitching motion is one of the most important mechanisms in force lifting generation, and the effects of Reynolds number and mean angle of attack on aerodynamic coefficients have been extensively investigated for the pitching motion. In the present study, the geometry of two cross sections of dragonfly was extracted. Incompressible, two-dimensional and unsteady Navier–Stokes equations have been used to simulate the flow. k − ɛ RNG model was used for turbulence modeling. To simulate the wing pitching motion, the dynamic mesh method was used. The results showed that in flapping motion, pitching-up rotation has caused a rapid increase in lift coefficient. Furthermore, it was found that the absence of stall does not increase the lift and drag coefficients, while formation of new strong vorticity layers have caused an increase in lift coefficient. On the other hand, corrugations on the cross sections of the dragonfly in the pitching motion cause the delay of separation and increasing the lift coefficient. In flapping motion and the pitching motion, the lift coefficients of three cross sections were increased due to stronger vorticity layers by reducing the Reynolds number. Due to the existence of corrugations, the first and the second cross sections have good aerodynamic performance, compared to the flat plate. The comparison carried out in the current research showed that the second cross section is a proper replacement for the flat plate in MAVs.

Aircraft post-flight reduction is one of the most important research topics, since post-reduction is effective in all parameters of bird performance, such as maximum speed, fast acceleration, shortening the runway required, high maneuverability, and reduced fuel consumption. Therefore, it is important to examine how the force applied to the airfoil changes in different streams from an industrial point of view. In this study, NACA( National Advisory Committee for Aeronautics) Airfoil 0012 has been studied. Numerical solution is used for the study. In the simulations, the air fluid and Mach number 0.5 are considered and the lift, drag and pressure coefficients at different attack angles are investigated. The results show that this airfoil has a lift factor of 0 due to its symmetric geometry at angle of attack 0 but its drag coefficient is about 0.01384 and its pressure coefficient is about -0.483. By varying the angle of attack from -12 to +12, it was observed that for the positive attack angle the lift coefficient increases and for the negative attack angle increases the lift coefficient decreases. Also with increasing angle of attack the drag coefficient always increases and the coefficient of pressure coefficient decreases. Cite this Article Ali Kamranpay, Alireza Mehrabadi. Numerical Analysis of NACA Airfoil 0012 at Different Attack Angles and Obtaining its Aerodynamic Coefficients. Journal of Mechatronics and Automation. 2019; 6(3): 8–16p.

This paper presents an evaluation of five different turbulence models by comparing the numerical data derived from these models using ANSYS Fluent with experimental data at a Reynolds number and a Mach number of 0.05 × 106 and 0.015 respectively based on the centerline chord of the airfoil for the flow over NACA 0012 and NACA 2412 airfoils. Moreover, the aim of the present study is to demonstrate the difference in aerodynamic characteristics of the airfoils in order to find aerodynamically more advantageous airfoil. It is concluded that Spalart-Allmaras model and k-ω SST model are capable of providing the most accurate prediction for lift coefficient at a low angle of attack for both airfoils. Standard k - ε model gives a slightly low value of lift coefficient at low angle of attack and slightly high value of lift coefficient at high angle of attack for both airfoils. k-ω SST model, Spalart-Allmaras model, Transition k-kL - ω model, and γ-Rⅇθ Transition SST model can predict drag coefficient reasonably at low angle of attack. At a high angle of attack, however, no turbulence model is able to give a satisfactory prediction for lift coefficient as well as drag coefficient, which implies that these models are unable to predict post-stall characteristics. NACA 2412 airfoil produces more lift coefficient than that of the NACA 0012 airfoil at all angles of attack. Moreover, the drag coefficient of NACA 2412 airfoil is less than that of the NACA 0012 airfoil, which implies that NACA 2412 airfoil exhibits better aerodynamic performance. The lift to drag coefficient ratio of NACA 2412 airfoil is also higher than that of the NACA 0012 airfoil indicating NACA 2412 airfoil to be more fuel economic.

A biomimetic wing is designed by considering the wing of a natural flyer ( Passer domesticus) as a reference. Since the birds have thin wings, Bergey BW-3, a thin and highly cambered airfoil, is used to design the wing cross section. To investigate the aerodynamic characteristics of the biomimetic wing, numerical and experimental studies are carried out at low Reynolds number (Re) ranging from 2.5 × 104 to 1 × 105. It is observed that the numerical findings have the similar trend as that of the experimental observations. The performance of the biomimetic wing is compared with rectangular and elliptical wings at Re = 5 × 104. It is observed that the separation bubble formed over the surface of the biomimetic wing at Re = 2.5 × 104 is not strong enough to influence the lift coefficient but increases the drag coefficient dramatically when the mean angle of attack exceeds 18°. It is observed that the drop in the lift coefficient of rectangular wing is higher than that of the other wings due to the presence of sharp edges in the planform. The lowest drag coefficient is witnessed in the elliptical wing but it also has the lowest lift coefficient due to the interaction between the separation bubble and tip vortices. On the other hand, the biomimetic wing offers the highest lift coefficient with a considerable amount of drag. Overall, a 57.9% increase in lift coefficient is observed for the biomimetic wing than that of the elliptical wing under the same conditions. A 22.4% increase in the lift to drag ratio of the biomimetic wing is observed over that of the rectangular wing. It is also observed that the flow separates dramatically as the mean angle of attack increases beyond the stall angle in the rectangular and elliptical wings. But a delay in the flow separation is observed in case of the biomimetic wing after the stall angle. It is also observed that the suction over the wing surface of the biomimetic wing is more at the wing root (fixed end) than that at the wing tip (free end), which may provide good stability during flight conditions. The enhanced aerodynamic performance of the biomimetic wing is due to change in shape of the wing along the span which has a strong influence over its effective angle of attack with respect to the incoming flow.

This work describes the aerodynamic characteristics of an aircraft wing model with a Rüppell’s griffon vulture (RGV)-type winglet. A computational fluid dynamics (CFD) study using ANSYS 15.0 was conducted to study the effect of the RGV winglet on a rectangular wing. The NACA 65(3)-218 wing consists of 660 mm span and 121 mm chord length where the aspect ratio is 5.45. Eight different winglet configurations have been studied. Furthermore, the study is extended to study effect of cant angle and different angles of attack (AOA) to the winglet. A comparative study is done on aerodynamic features such as lift coefficient (CL), drag coefficient (CD), lift/drag ratio (CL/CD) and tip vortices to get the best RGV winglet design. The RGV winglet achieved highest CL compared to other types of winglets configuration. Based on contour plot analysis, the RGV winglet shows lower vortex formation compared to without winglet. The results show about 15 to 30% reduction in drag coefficient and 5 to 25% increase in lift coefficient by using an RGV winglet.

An in-depth study on the dynamic aerodynamic performance of the pitching oscillating airfoil is carried out in the two-dimensional test section of the NF-3 low-speed wind tunnel of Northwestern Polytechnical University. The experimental model is a span-wise three-section force measuring model, and the force measure is only performed in the middle section of the model to reduce the influence of the sidewall interference of the wind tunnel. In the experiment, the transient angle of attack of the model is collected, the inertial force and pitching moment on the middle section of the model are calculated, and the data collected from the balance is subtracted to correct the influence of the model's inertia on the results. The results show that the angle of attack exceeding the positive or negative static stall angles of attack is a necessary condition for the lift and pitch moment coefficients to produce a large hysteresis loops. As the oscillation reduced frequency increases, the dynamic stall is delayed, the lift coefficient hysteresis loop increase, the drag coefficient increase, and the pitch moment coefficient near the maximum angle of attack decrease. When the angle of attack is less than the static angle of attack of stall or exceeds a small range, with the increase of the reduced frequency of the airfoil oscillation, the pitch moment coefficient of the airfoil decreases when it goes up and increases when it goes down. With the increase of the oscillation amplitude, the hysteresis loops of both dynamic lift coefficient and pitching moment coefficient of the oscillating airfoil increase. As the average angle of attack increases, the angle of attack of airfoil enters the positive stall zone more, the lift coefficient hysteresis loop increases, and the minimum pitch moment coefficient decreases. The Reynolds number has no obvious effect on the hysteresis loop of lift, drag and pitch moment coefficients; however, in the downward process, as the Reynolds number increases, the lift recovery advances, and the hysteresis loop decreases.KeywordsAirfoilWind tunnel testDynamic aerodynamic performanceDirect force measurementInertia correction

Airfoil performance data is regarded as highly valuable data in its wide area of application since it will help the designer, for examples; to predict the influence of rear spoiler mounting to the maneuverability and top speed of racing car, the thrust and fuel consumption needed for an aircraft to take off and cruise, or the power delivered by a wind turbine rotor at certain wind speed. The performance of airfoil, which is measured with its lift and drag coefficient, is greatly affected by its geometry and operating condition. The influence of various geometric and operational parameters to the airfoil performance is needed to be studied experimentally and the airfoil performance data obtained can be added to enrich the airfoil performance data base. The experiment was done by testing airfoil models by lift force direct measurements in a sub-sonic wind tunnel. The type of airfoil used in this experiment is the symmetric airfoil with maximum thickness location as the geometric parameter and angle of attack with wind speed as the operational parameter being investigated for their influence to the lift and drag coefficient. The maximum thickness location was varied in 30%, 40%, and 50% of chord length measured from leading edge. The angle of attack was varied from 0^o to 20^o with 4^o increments. The wind speed was varied from 10 m/s to 20 m/s with 2 m/s increments. Parameters being measured were the free stream velocity, and the lift force. The result of the research shows that the best airfoil performance with lift coefficient 3,16 is achieved by the airfoil that has maximum thickness location in 40% of its chord length measured from its leading edge and operates at 20^o angle of attack and 8,9 m/s free stream velocity.

Owls have an incredibly unique ability to fly in silence, and this ability has significant potential to reduce noise pollution from aircraft engines. For decades, researchers have been studying the noise abatement system in conventional aircraft, but only a few of them had looked into the owl’s ability to reduce the aircraft noise level, especially on the serrated wing. The present study aims to investigate the lift and drag coefficient of the serrated wings including leading-edge serrations, trailing-edge serrations, both-edge serrations, and the original/baseline wing model from the NACA 0012 airfoil. The experimental testing was performed in a wind tunnel at Reynolds numbers of 20,000 and 40,000 and angle of attack from 2° to 30°, in 2° angle intervals. In general, the results showed that each wing model produced a similar lift and drag coefficient profiles, which were proportional to the angle of attack. At Reynolds number of 40,000, the lift coefficient increases from 0.45 to 1.5, as the angle of attack increases from 2° to 24°. Afterward, it decreased as the angle of attack exceeded 24°. According to the data, the trailing-edge serrations model showed the lowest drag coefficient at a Reynolds number of 40,000. Meanwhile, the highest lift coefficient at Reynolds number of 40,000 had been produced by the baseline wing model. This result is beneficial in reducing the noise generation produced by wing structure and at the same time enhancing aerodynamic efficiency.

Flow control on a circular cylinder using streamwise-oriented Dielectric Barrier Discharge (DBD) plasma actuators was examined. These actuators generated pairs of counter-rotating streamwise vortices that influence overall flow characteristics. Particle Image Velocimetry (PIV) and aerodynamic force measurements were performed to analyze the flow control effectiveness. PIV measurements show that a streamwise-oriented DBD plasma actuator produced good suppression of flow separation at ReD = 3300 and the actuation effect was still discernible at higher ReD = 6530. However, this remarkable result was limited to region directly downstream of the exposed electrode where a downwash was present. Subsequent force measurements reveal a rise in both lift and drag acting on the cylinder when DBD plasma actuation was implemented. A maximum increase in lift coefficient ∆CL and drag coefficient ∆CD of 0.04 and 0.16 (+16%) were recorded, respectively. Surface pressure distributions estimated from PIV measurements indicate a pressure drop on the downstream-facing surface of the cylinder. The increase in streamwise pressure differential across the cylinder signifies a rise in drag acting on the cylinder.

Windborne debris is one of the main factors that damage building structures in typhoon-prone areas, and plate-type debris is more common and concerning. Wind tunnel tests were conducted to study the aerodynamic characteristics of the rotating plate under the influence of tilt angle, chamfer form, and mass eccentricity. The aerodynamic characteristics including rotational speed, lift, drag, and moment coefficients were studied. Two states of steady speed and of a variant rotational speed increasing from 0 to a steady value were analyzed. The experimental results show that, in the steady state, the rotational speed and lift coefficient change slowly at first and then increase rapidly as the tilt angle increases (when the aspect ratios are greater than 1), and increase with the presence of the chamfers. The effects of different symmetrical chamfer forms on rotational speed and force coefficients are varied. In the acceleration state, the chamfers lead to the reduction of lift coefficient and the increase of moment coefficient at the same dimensionless rotational speed. The influence of mass eccentricity on rotational speed and force coefficients in both states is not obvious. Particularly, when both the buoyancy coefficient and eccentricity position are large, the plate cannot enter into full cycle. The Magnus effects of rotational plates with higher aspect ratios have been studied, and the aerodynamic data are useful for improving plate-type debris motion models. • Two states of accelerated and steady rotation are analyzed. • Complex rotation at different tilt angles is considered. • Chamfer increases the average rotational speed and lift coefficient at steady state. • Plates cannot rotate full circle when both buoyancy coefficient and eccentricity are large.

Plasma actuators operating under atmospheric conditions show great promise for flow control due to their unique physical characteristics, such as the body force generated by a strong electric field. This study numerically examines the effect of low-powered plasma actuation on the aerodynamic performance of a NACA 2412 airfoil. Utilizing the Shyy plasma actuation model, the study simulates its effects through defined functions. The analysis investigates the lift and drag coefficients at various angles of attack, with a freestream velocity of 14.5 m/s. Without plasma actuation, the airfoil experiences common aerodynamic challenges, such as flow separation near the trailing edge, which reduces efficiency. However, plasma actuation accelerates the airflow over the upper surface, delaying flow separation and decreasing drag. This results in smoother airflow and increased lift, particularly at higher angles of attack. The use of plasma actuation achieved approximately a 21% increase in the lift coefficient. Overall, plasma actuators enhance airflow control, reduce drag, and boost lift, improving the airfoil’s aerodynamic performance. This improvement is supported by pressure contour analysis, which demonstrates a more favorable pressure distribution with plasma actuation.

A high-performance Ishii airfoil was analyzed using both a wind-tunnel and large-eddy simulations at a low-Reynolds-number condition (). The design guidelines for an airfoil shape with a high lift-to-drag ratio under the aforementioned condition are described by analyses of flowfields and aerodynamic characteristics of the Ishii airfoil. Compared with conventional airfoils, such as the NACA 0012 and NACA 0002, the shape characteristic effects of the Ishii airfoil on its flowfield and aerodynamic characteristics are discussed. The shape on the suction side of the Ishii airfoil can cause delays in the flow separation at low angle of attacks. The separated flow reattaches, and a separation bubble forms even when trailing-edge separation changes to leading-edge separation. The separation bubble contributes to an increase in lift coefficient. In addition, the Ishii airfoil can gain a high positive pressure on the pressure side as compared with the other two symmetric airfoils due to the camber near the trailing edge. On the other hand, the pressure drag of the Ishii airfoil, which is a dominant factor of total drag, is considerably smaller than those of the other two airfoils. It was found that the shape on the suction side as well as that on the pressure side (such as the leading-edge roundness and the camber) are very significant in the low-Reynolds-number airfoil with a high lift-to-drag ratio.

Analytical prediction of trajectories of ice pieces after release in an airstream

Wing configuration is a parameter that affects the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic characteristics of a new compound wing were investigated during ground effect. The compound wing was divided into three parts with a rectangular wing in the middle and two reverse taper wings with anhedral angle at the sides. The sectional profile of the wing model is NACA6409. The experiments on the compound wing and the rectangular wing were carried to examine different ground clearances, angles of attack, and Reynolds numbers. The aerodynamic coefficients of the compound wing were compared with those of the rectangular wing, which had an acceptable increase in its lift coefficient at small ground clearances, and its drag coefficient decreased compared to rectangular wing at a wide range of ground clearances, angles of attack, and Reynolds numbers. Furthermore, the lift to drag ratio of the compound wing improved considerably at small ground clearances. However, this improvement decreased at higher ground clearance. The drag polar of the compound wing showed the increment of lift coefficient versus drag coefficient was higher especially at small ground clearances. The Reynolds number had a gradual effect on lift and drag coefficients and also lift to drag of both wings. Generally, the nose down pitching moment of the compound wing was found smaller, but it was greater at high angle of attack and Reynolds number for all ground clearance. The center of pressure was closer to the leading edge of the wing in contrast to the rectangular wing. However, the center of pressure of the compound wing was later to the leading edge at high ground clearance, angle of attack, and Reynolds number.