Maximum Lift Research Articles

Wind tunnel experiments on a NACA 633‐418 airfoil with different types of leading edge roughness

AbstractThe NACA 633‐418 airfoil has been tested in the new Poul la Cour Wind Tunnel at the Technical University of Denmark, Risø campus, to expand the publicly available data of airfoils with leading edge roughness. The airfoil was constructed with an exchangeable leading edge. The clean airfoil showed good agreement with results from other high‐quality wind tunnels. The airfoil was equipped with three heights of zigzag tape, a trip strip, three sandpaper types, and leading edge cavities with different modifications. In general, increasing zigzag tape heights reduce the maximum lift, whereas the increase in drag is less affected by the zigzag tape height. Almost the same reduction in maximum lift is seen for the different sandpaper types. However, the drag increases with the coarseness of the sandpaper. The highest zigzag tape and coarsest sandpaper resulted in the highest penalty on the aerodynamics. A combination of sandpaper and cavities showed the largest reduction in maximum lift and the highest increase in drag.

Modeling the Flow State Sensitivity of Actuation Response on a Stalled Airfoil

In this work, we perform direct numerical simulations of leading-edge momentum injection of a NACA0009 airfoil at poststall angles of attack. It is found that the lift response is highly dependent upon the instantaneous state of the wake at the time of actuation, which is characterized by the phase of the vortex-shedding limit cycle present in the unactuated system. In particular, we find that actuating at a phase of the limit cycle corresponding to the maximum lift gives the largest maximum in transient lift response, whereas actuating near the lift minimum gives a smaller initial transient lift enhancement and can lead to a significant reduction in the amplitude of the limit cycle. As well as characterizing this phase dependency, we develop a reduced-order model that can capture this behavior. This is achieved by applying dynamic mode decomposition with control to a concatenation of velocity and lift measurements from several training datasets. The resulting models can accurately capture the dynamics of the training datasets as well as for phases not included in the training data. We show that for this method of actuation, multiple control objectives with the same actuator can be achieved.

An experimental study of an ejector-boosted transcritical R744 refrigeration system including an exergy analysis

The field of refrigeration witness a massive transition in the supermarket with a strong focus reflected on energy consumption. The use of ejector allows for overcoming the significant exergy destruction lays on the expansion processes of the cooling systems and led to spark improvement in the system performance by recovering some of the expansion work. In this study, a detailed experimental work and exergy analysis on the R744 transcritical ejector cooling system was investigated. The experiment was implemented on the commercial ejector cartridge type (032F7045 CTM ELP60 by Danfoss). The impact of different operating conditions determined by exit gas cooler pressure and temperature, evaporation temperature and receiver pressure was examined. The ejector performance of the pressure lift, mass entrainment ratio, work rate recovery and efficiency were evaluated. In addition, exergy efficiency and the variation of exergy produced, consumed, and destruction were assessed based on the transiting exergy. The result revealed better overall performance when the ejector operated at transcritical conditions. The ejector was able to recover up to 36.9% of the available work rate and provide a maximum pressure lift of 9.51 bar. Moreover, it was found out that the overall available work recovery potential increased by rising the gas cooler pressure. Out of the findings, the ejector could deliver maximum exergy efficiency of 23% when working at higher motive nozzle flow temperatures along with providing lower exergy destruction. The experiment results show that the amount of the exergy consumed and destruction were gradually increased with higher gas cooler pressure and, in contrast, decreasing with higher motive nozzle flow temperature.

Numerical Investigation of Aerodynamic Characteristics of NACA 4312 Airfoil with Gurney Flap

This paper presents a two-dimensional Computational Fluid Dynamics (CFD) analysis on the effect of gurney flap on a NACA 4312 airfoil in a subsonic flow. These numerical simulations were conducted for flap heights 1.5%, 1.75%, 2% and 3% of chord length at fixed Reynold Number, Re (5×105) for different angle of attack (0o ~16o). ANSYS Fluent commercial software was used to conduct these simulations. The flow was considered as incompressible and K-omega Shear Stress Transport (SST) model was selected. The numerical results demonstrate that lift coefficient increase up to around 12o AoA (angle of attack) for NACA 4312 with and without gurney flap. For every AoA lift coefficient and drag coefficient presented proportionate behavior with flap height. However, lift co-efficient was decreased after around angle of attack due to flow separation. Maximum lift to drag ratio was found at around 4o AoA for every flap length and airfoil with flap of 1.5%C (chord length) had shown the most optimized aerodynamic performance through the analysis. This study concluded that airfoil with gurney flap displayed enhanced aerodynamic performance than the airfoil without gurney flap due to the delay in flow separation.

Design and computational fluid dynamics analysis of bio-inspired non slender cropped delta wingsuit

This study examines the effect of bio-inspired serrations on aerodynamic performance of a Non Slender cropped delta wingsuit model. In this study, Gottingen 228 aerofoil is used for designing the wingsuit model having AR of 1.00 using CAD software Solidworks. Ansys Fluent solver has been utilised to solve the Reynolds Averaged Navier–Stokes (RANS) equations with a k− $$\omega$$ turbulence model. The flow velocity was kept at 45 m/s with Re ~ 2.6 × 106 and angle of attack was varied from 0° to 45°. Computations revealed that the wingsuit with serrations in comparison with clean basemodel had a notable increase in maximum lift coefficient. The results were compared with the experimental and CFD results of existing literature in the open domain. The serrated non slender delta wingsuit performs extremely well giving a lift coefficient of 2.74 and $$C_{{\text{L}}}$$ / $$C_{{\text{D}}}$$ of 9.72. The results were validated by comparing them with flat plate and non slender cropped delta wing results available in the existing literature. A good agreement in terms of trends was obtained for $$C_{{\text{L}}}$$ and $$C_{{\text{D}}}$$ which indicates that proposed wingsuit should perform well aerodynamically under typical wingsuit flying conditions.

Flying With Damaged Wings: The Effect on Flight Capacity and Bio-Inspired Coping Strategies of a Flapping Wing Robot

Insects wings are subject to wear and tear from collisions and environmental disturbances during flight. They can tolerate both symmetrical and asymmetrical wing damages while maintaining flight capability to some extent. Drawing inspiration from nature's adaptation capabilities, we investigated the consequences of wing damage on a flapping wing micro air vehicle by quantifying the changes in wing kinematics, lift generation, control torque offset, and aerodynamic damping variations in flight tests with intact and damaged wings. For the proposed vehicle, the wing damage affected the lift generation significantly. Compared to the intact wings, the damaged ones result in increased stroke angle amplitude in order to compensate for lift loss and torque imbalance, which causes an increase in power consumption accordingly. Furthermore, asymmetric damages usually require a larger amount of additional control effort for flight stabilization compared to symmetric cases. In addition, aerodynamic damping varies as the wing areas change. All these aspects pose challenges in flight control. An adaptive controller is proposed to cope with the wing damage induced detrimental effects on flight capacity. Flight tests were conducted to validate the control performance. As a result, the robot can effectively overcome such challenges even in the case of a maximum unilateral lift loss of up to $\approx$ 22%. Such a result matches the performance of hovering hawkmoths, which can handle torque asymmetry up to 22.3 $\pm$ 7.8%. To the best of our knowledge, this is the first demonstration of FWMAVs to handle significant wing asymmetry in hover flight.

Experimental Determination of the Impact of Floats on the Aerodynamic Characteristics of an OSA Model in Symmetric Flow

This paper presents the results of experimental determination of the impact of floats on the aerodynamic characteristics of an OSA model in symmetric flow. The studies have been performed in the low-speed wind tunnel at the Military University of Technology (MUT, Warsaw, Poland). The aircraft model was examined at the dynamic pressure q = 500 Pa in the following angle of attack range = -2828. The investigations have been performed for an aircraft model under plain configuration with floats and without floats. The influence of elevator and flap inclination on the aerodynamic characteristics of the model has also been analysed. The obtained values of aerodynamic drag coefficient, lift coefficient, pitching moment coefficient and lift-to-drag ratio have been presented in the form of tables and graphs. The studies performed demonstrated that the use of floats causes the increase of aerodynamic drag coefficient CD, maximum lift coefficient CLmax as well as critical angle of attack cr. The decrease of lift-to-drag ratio has also been observed. Its value in the case of the model with floats was up to 20% lower than in the model without floats. The studies also showed that the model equipped with floats had a lower longitudinal static stability margin than the model without floats.

Design of wind-turbine blades for improving aerodynamic performance using hybrid blades

The blade airfoil significantly influences the performance of wind turbine. This study designs a new hybrid blade airfoil (abbreviated as HBA) based on the previous airfoils (S809 and NACA 63215). The surface-flow modes, wake-flow characteristics, and aerodynamic performance of HBA were tested using various Reynolds numbers and angles of attack. The experimental methods involved (1) the smoke-wire visualization at low wind speeds, (2) the surface-oil flow visualization at high wind speeds, (3) the hot-wire anemometry, and (4) the six force–moment balancer. At blade stall, the lift coefficient of 2.12 for HBA is approximately twice that of 1.07 for S809 and NACA63215. The maximum lift–drag ratio of 6.11 for HBA is approximately twice those (3.63 and 3.13) of S809 and NACA 63215. Moreover, the HBA has a higher stall angle than those of the other two blades. The (pitch) moment coefficient of HBA is also higher than those of S809 and NACA 63215.

Aerodynamic Performance Enhancement of Tiltrotor Aircraft Wings Using Double-Row Vortex Generators

To improve the aerodynamic performance of tiltrotor aircraft, the flow characteristics of the V-22 airfoil without and with one, two parallel rows of vortex generators (VGs) were investigated using numerical simulation methods. The results were obtained with three-dimensional compressible Reynolds-averaged Navier–Stokes equations, and the turbulence was simulated with the SA-based DES model. The influence of the chordwise installation of VGs was emphatically discussed. First, the single-row VGs are, respectively, mounted at the 10, 20, and 40% chord positions, denoted as VGs1, VGs2, and VGs3. The results indicate that with the addition of the optimal configuration (VGs1), the maximum lift coefficient is extended from 1.43 to 2.44, and the stall angle of attack increases from 10° to 22° with respect to the clean airfoil. The drag coefficient of the airfoil with VGs1 is 60.8% lower than that of the airfoil without VGs at an angle of attack of 24°. On this basis, the double-row VGs’ arrangements are located at the 10 and 30% chord positions (VGs4), the 10 and 50% chord positions (VGs5) and the 10 and 70% chord positions (VGs6). Compared to single-row VGs, double-row VGs have the greater potential to suppress the flow separation. Due to the effect of VGs4, the maximum value of lift coefficient has increased to 2.61. However, the case of VGs6 degrades the overall aerodynamic performance as compared to VGs1. Further research suggest that with the increase in the height of the second row of vortex generators (VGs7), the aerodynamic characteristics of airfoil A821201 can be effectively enhanced at large angles of attack.

A High-Lift Optimization Methodology for the Design of Leading and Trailing Edges on Morphing Wings

Morphing offers an attractive alternative compared to conventional hinged, multi-element high lift devices. In the present work, morphed shapes of a NACA 64A010 airfoil are optimized for maximum lift characteristics. Deformed shapes of the leading and trailing edge are represented through Bezier curves derived from locally defined control points. The optimization process employs the fast Foil2w in-house viscous-inviscid interaction solver for the calculation of aerodynamic characteristics. Transitional flow results indicate that combined leading and trailing edge morphing may increase maximum lift in the order of 100%. A 60–80% increase is achieved when morphing is applied to leading edge only—the so-called droop nose—while a 45% increase is obtained with trailing edge morphing. Out of the stochastic optimization algorithms tested, the Genetic Algorithm, the Evolution Strategies, and the Particle Swarm Optimizer, the latter performs best. It produces the designs of maximum lift increase with the lowest computational cost. For the optimum morphed designs, verification simulations using the high fidelity MaPFlow CFD solver ensure that the high lift requirements set by the optimization process are met. Although the deformed droop nose increases drag, the aerodynamic performance is improved ensuring the overall effectiveness of the airfoil design during take-off and landing.

Computational evaluation of geometric effects on aerodynamic performance of circulation control airfoils

The geometric effects of Coanda trailing edges on the aerodynamic performance of an airfoil are numerically evaluated for a range of different freestream Mach numbers and momentum coefficients. A Circulation control (CC) airfoil with a circular trailing edge (ACTE) proves to have better control effectiveness at low subsonic freestream speeds (Mach = 0.1). A CC airfoil having an elliptic trailing edge (AETE) outperforms the ACTE at high subsonic flow conditions. The occurrence of C μ-stall for the AETE is greatly postponed, and meanwhile the maximum net lift coefficient increment achieved for the AETE (Δ C L = 0.51) is slightly higher than that of the ACTE (Δ C L = 0.50) at Mach 0.6. Compared to the ACTE, the AETE is found to have better control consistency at different operating velocities and better control stability when the Coanda jet is supersonic. Through careful consideration of the aerodynamic performance and the control effects, the most appropriate axial ratio for an AETE ellipse is within the interval from 1.5 to 2. Finally, the flow field instability phenomenon and the jet detachment induced by the supersonic Coanda jet are investigated. A self-sustained shock-wave instability phenomenon without jet detachment is first observed in this paper.

Effects of Micro-Tab on the Lift Enhancement of Airfoil S-809 with Trailing-Edge Flap

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use of TEF with Micro-Tab in wind turbine blades using NREL’s S-809 as a model airfoil. In particular, the benefits generated by TEF with Micro-Tab may be of great interest in the design of wind turbine blades. In this paper, an attempt was made to evaluate the influence of TEF with Micro-Tab on the performance of NREL’s S-809 airfoils. Firstly, a computational fluid dynamics (CFD) model for the airfoil NREL’s S-809 was established, and validated by comparison with previous studies and wind tunnel experimental data. Secondly, the effects of the flap position (H) and deflection angle (αF) on the flow behaviors were investigated. As a result, the effect of TEF on air-flow behavior was demonstrated by augmenting the pressure coefficient at the lower surface of the airfoil at flap position 80% chord length (C) and αF = 7.5°. Thirdly, the influence of TEF with Micro-Tab on the flow behaviors of the airfoil NREL’s S-809 was studied and discussed. Different Micro-Tab positions and constant TEF were examined. Finally, the effects of TEF with Micro-Tab on the aerodynamic characteristics of the S-809 with TEF were compared. The results showed that an increase in the maximum lift coefficient by 25% and a delay in the air-flow stall were accomplished due to opposite sign vortices, which was better than the standard airfoil and S-809 with TEF. Therefore, it was deduced that the benefits of TEF with Micro-Tab were apparent, especially at the lower surface of the airfoil. This particularly suggests that the developed model could be used as a new trend to modify the designs of wind turbine blades.

An Experimental Analysis on the Effects of Stagger on the Aerodynamic Forces of Tandem Wings

This study is inspired by the flapping motion of natural flyers: insects. Many insects have two pairs of wings referred as tandem wings. Literature review indicates that the effects of tandem wing are influenced by parameters such as stagger (the stream-wise distance between the aerodynamic center of the front and the rear airfoil), angle-of-attack and flow velocity. As a first stage, this study focuses on the effects of stagger (St) on the aerodynamic performance of tandem wings. A recent numerical study of stagger on tandem airfoils in turbulent flow (Re = 6000000) concluded that a larger stagger resulted in a decrease in lift force, and an increase in drag force. However, for laminar flow (Re = 2000), increasing the stagger was not found to be detrimental for aerodynamic performance. Another work also revealed that the maximum lift coefficient for a tandem configuration decreased with increasing stagger. The focus of this study is to perform an experimental analysis of tandem two-dimensional (2D) NACA 0012 airfoils. The two airfoils are set at the same angle-of-attack of 0° to 15° with 5° interval and three variations of stagger: 1c, 1.5c and 2c. The experiments are conducted using an open-loop-subsonic wind tunnel at a Reynolds number of 170000. The effects of St on the aerodynamic forces (lift and drag) are analyzed

Leading-Edge Vortex Characteristics of Low-Aspect-Ratio Sweptback Plates at Low Reynolds Number

A sweptback angle can directly regulate a leading-edge vortex on various aerodynamic devices as well as on the wings of biological flyers, but the effect of a sweptback angle has not yet been sufficiently investigated. Here, we thoroughly investigated the effect of the sweptback angle on aerodynamic characteristics of low-aspect-ratio flat plates at a Reynolds number of 2.85 × 104. Direct force/moment measurements and surface oil-flow visualizations were conducted in the wind-tunnel B at the Technical University of Munich. It was found that while the maximum lift at an aspect ratio of 2.03 remains unchanged, two other aspect ratios of 3.13 and 4.50 show a gradual increment in the maximum lift with an increasing sweptback angle. The largest leading-edge vortex contribution was found at the aspect ratio of 3.13, resulting in a superior lift production at a sufficient sweptback angle. This is similar to that of a revolving/flapping wing, where an aspect ratio around three shows a superior lift production. In the oil-flow patterns, it was observed that while the leading-edge vortices at aspect ratios of 2.03 and 3.13 fully covered the surfaces, the vortex at an aspect ratio of 4.50 only covered up the surface approximately three times the chord, similar to that of a revolving/flapping wing. Based on the pattern at the aspect ratio of 4.50, a critical length of the leading-edge vortex of a sweptback plate was measured as ~3.1 times the chord.

Experimental study on unsteady aerodynamic characteristics of deformed blades for vertical axis wind turbine

Based on the self-deforming blade model and the related wind tunnel test platform, the experiments with synchronous deformation and pitch of the blade were carried out to simulate the operating condition of the blade on the vertical axis wind turbine (VAWT). Taking NACA0012 as the reference blade, the unsteady aerodynamic characteristics of the blade deformation at different deformation frequencies and amplitudes were investigated at low Reynolds number of 2.5 × 105. It is found that the maximum lift force of the blade with deformation amplitude of 0.06c is raised by nearly 60% compared with that of the rigid blade. Secondly, by applying the same deceleration frequency, same pitch amplitude and different initial angles of attack to the blade, it is observed that the flow hysteresis phenomena are obviously different from that of applying various synchronous pitch and deformation amplitudes, and the special aerodynamic characteristic curves are obtained. The lift force increases significantly with the rise of deformation amplitude and drag force, while the lift-drag ratio increases in one cycle. The study in this paper proves the applicability of the blade with this deformation law in the VAWT, and provides a reference for its application on the design of VAWT.

Numerical Investigation of The Effect of Airfoil Trailing Edge Inflation at low Reynolds Number

To investigate the effect of airfoil shape design on aerodynamics of the airfoil, a new modified airfoil shape design is introduced in this paper. Thick symmetrical NACA 0021 airfoil is used as base model in this study that the trailing edge end curvature was altered in design shape to be inflated to have 25%, 50% and 100% scaled of the leading-edge curvature at the same cord length and same maximum thickness data. Numerical investigation, using shear-stress transport kω-SST turbulence model, is performed to study the effect of airfoil trailing edge inflation on the aerodynamic characteristics at low Reynolds Number. The base airfoil model, NACA0021, is validated numerically and shows a good agreement with previous experimental results. The results show that the new modified airfoil with 100% inflation delays the flow separation to higher angle of attack and increases the maximum lift coefficient about 40% compared with the base NACA0021 airfoil.

Comparison of aerodynamic performances of various airfoils from different airfoil families using CFD

In this study, three airfoil families, NACA, FX and S, in each case three from each series with different shapes were investigated at different angles of attack using Computational Fluid Dynamics (CFD) method. To verify the CFD model, simulation results of the NACA 0012 airfoil was compared against the available experimental data and k-ω SST was used as the turbulence model. Lift coefficients, lift to drag ratios and pressure distributions around airfoils were obtained from the CFD simulations and compared each other. The simulations were performed at three Reynolds numbers, Re=2x105, 1x106 and 2x106, and angle of attack was varied between -6 and 12 degrees. According to the results, similar lift coefficient values were obtained for symmetric airfoils reaching their maximum values at similar angles of attack. Maximum lift coefficients were obtained for FX 60-157 and S 4110 airfoils having lift coefficient values around 1.5 at Re=1x106 and 12 degrees of angle of attack. Flow separation occurred close to the leading edge of some airfoils at higher angles of attack, while some other airfoils were more successful in keeping the flow attached on the surface.

Wind Tunnel Testing Study of Segmented Slat with Simulated Icing for Civil Aircraft

Icing accretion on civil aircraft have a severe impact on safety and performance, and the leading edge icing of wing resulting in maximum lift coefficient reduction, drag increasing, stalling incidence forward, control and stability worsening and even stalling. This article is to explore aerodynamic characteristics variation of civil aircraft with simulated icing accretion on different segmented slats through the means of wind tunnel testing, and the typical aerodynamic characteristic parameters involve maximum lift coefficient, stalling incidence and lift-to-drag ratio. Forces and moments measurement for configurations of the cruising, take-off and landing had been carried out, the results and analysis of testing data could be used for anti-icing design and operation strategy making.

Multiscale instabilities of Magnus–Robins effect for compressible flow past rotating cylinder

In the present research, the instability suffered by flow past a rotating cylinder with very high rotation rates is studied. Special emphasis is given on exploring the effects of compressibility by solving two-dimensional Navier–Stokes equations. The first account of this instability has been provided in “T. K. Sengupta, K. Gupta, and M. T. Nair, “Lift generation and limiting mechanism via unsteady flow development for Magnus-Robins effect,” Proceedings of the 8th Asian Congress of Fluid Mechanics, Shenzhen, China (1999).” Subsequently, there have been other efforts on the same with different numerical models based on incompressible and compressible flow formulation. Apart from the efforts reported by the present group, other reported results did not identify this as a phenomenon of flow instability. The perceived temporal variations of lift and drag by both the incompressible and compressible flow formulation have been correlated with each other, without highlighting the role of compressibility in triggering the flow instability. Here, we report the sensitive dependence of the temporal instability on the accuracy of the simulation for the growth of the disturbance field during the transient monotonic variations of lift and drag. Of specific interest is the role of compressibility in promoting the disturbance growth and limiting the maximum lift that is generated. The compressibility effects have been incorporated by considering lower Mach numbers for the oncoming uniform flow, so that nowhere in the flow field there is the formation of a supersonic pocket.

Numerical investigation into rotational augmentation with passive vortex generators on the NREL Phase VI blade

Passive vortex generators (VGs) have been widely used on wind turbines to improve the aerodynamic power. Nevertheless, most studies of VGs are conducted on flat plates and airfoils rather than rotating blades. The effect of VGs on rotational blade flow therefore remains unclear. This paper presents a comparative study between the NREL S809 airfoil flow and NREL Phase VI blade flow, to highlight rotational augmentation with VGs. There are 36 pairs of rectangular VGs installed at about 20% c between 25% and 50% spans of the blade. Fully-resolved RANS simulations are used to identify the airfoil and blade flow characteristics with VGs. Although VGs greatly increase the maximum lift coefficient of airfoil by almost 60%, they cause unexpected decreases in aerodynamic forces on the inboard blade. This is mainly because VGs can reduce the radial flow and thus undermine rotational augmentation. Furthermore, increasing VG size amplifies the VG effect on radial flow and enlarges the separation bubble at 30% span from 43% c to 57% c in height. Positioning VGs in a skewed layout, however, effectively diminishes this negative VG effect and reduces the separation bubble height to 28% c. These findings indicate a huge difference between the airfoil flow and blade flow with VGs due to rotational effects. This work might deepen the understanding of rotational augmentation with VGs on a rotating blade.