Total Lift Research Articles

The Effect of Folding Wing on Aerodynamics and Power Consumption of a Flapping Wing

Experimental study on the unsteady aerodynamics analysis and power consumption of a folding wing is accomplished using a wind tunnel testing. A folding wing model is fabricated and actuated using servo motors. The flapping wing consists of an inboard main wing and an outboard folding wing. The aerodynamic forces and consumed powers of the flapping wing are measured by changing the flapping and folding wings inside a low-speed wind tunnel. In order to calculate the aerodynamic forces, the measured forces are modified using static test data. It was found that the effect of the folding wing on the flapping wing's total lift is small but the effect of the folding wing on the total thrust is larger than the main wing. The folding motion requires the extra use of the servo motor. Thus, the amount of the energy consumption increases when both the wings are actuated together. As the flight speed increases, the power consumption of the folding wing decreases which results in energy saving.

Effect of Different Types of Wing-Wing Interactions in Flapping MAVs

Wing-Wing Interaction (WWI), such as the Clap and Fling Motion (CFM), occurs when two wings are flapping close together, improving performance. We intend to design a hovering Flapping Micro Aerial Vehicle (FMAV) which makes use of WWI. We investigate the effects of flexibility, kinematic motions, and two- to six-wing flapping configurations on the FMAV through numerical simulations. Results show that a rigid spanwise and flexible chordwise wing produces the highest lift with minimum power. The smoothly varying sinusoidal motion, which is visually similar to the CFM, produces similar lift in comparison to the CFM, while having lower peak power requirement. Lastly, lift produced by each wing of the two-, four-, six-wing configurations is approximately equal. Hence more wings generate higher total lift force, but at the expense of higher drag and power requirement. These results will be beneficial in the understanding of the underlying aerodynamics of WWI, and in improving the performance of our FMAV.

Wind loads and load-effects of large scale wind turbine tower with different halt positions of blade

In order to investigate the influence of different blade positions on aerodynamic load and wind loads and load-effects of large scale wind turbine tower under the halt state, we take a certain 3 MW large scale horizontal axis three-blade wind turbine as the example for analysis. First of all, numerical simulation was conducted for wind turbine flow field and aerodynamic characteristics under different halt states (8 calculating conditions in total) based on LES (large eddy simulation) method. The influence of different halt states on the average and fluctuating wind pressure coefficients of turbine tower surface, total lift force and resistance coefficient, circular flow and wake flow characteristics was compared and analysed. Then on this basis, the time-domain analysis of wind loads and load-effects was performed for the wind turbine tower structure under different halt states by making use of the finite element method. The main conclusions of this paper are as follows: The halt positions of wind blade could have a big impact on tower circular flow and aerodynamic distribution, in which Condition 5 is the most unfavourable while Condition 1 is the most beneficial condition. The wind loads and load-effects of disturbed region of tower is obviously affected by different halt positions of wind blades, especially the large fluctuating displacement mean square deviation at both windward and leeward sides, among which the maximum response occurs in <TEX>$350^{\circ}$</TEX> to the tower top under Condition 8; the maximum bending moment of tower bottom occurs in <TEX>$330^{\circ}$</TEX> under Condition 2. The extreme displacement of blade top all exceeds 2.5 m under Condition 5, and the maximum value of windward displacement response for the tip of Blade 3 under Condition 8 could reach 3.35 m. All these results indicate that the influence of halt positions of different blades should be taken into consideration carefully when making wind-resistance design for large scale wind turbine tower.

Effect of posture on the aerodynamic characteristics during take-off in ski jumping

The purpose of this study was to investigate the effects of posture of a ski jumper on aerodynamic characteristics during the take-off using computational fluid dynamics (CFD). The CFD method adopted for this study was based on Large–Eddy Simulation. Body surface data were obtained by 3-D laser scanning of an active ski jumper. Based on video analysis of the actual take-off movement, two sets of motion data were generated (world-class jumper A and less-experienced jumper B). The inlet flow velocity that corresponds to the in-run velocity in actual ski jumping was set to 23.23m/s in the CFD. The aerodynamic force, flow velocity, and vortexes for each model were compared between models. The total drag force acting upon jumper A was lower than that acting upon jumper B through the whole movement. Regarding the total lift force, although jumper A׳s total lift force was less in the in-run posture, it became greater than that of jumper B at the end of the movement. In the latter half of the movement, low air-speed domain expansion was observed at the model׳s back. This domain of jumper B was larger. There were two symmetric vortexes in the wake of jumper A, but the disordered vortexes were observed behind the jumper B. In the case of jumper A, these two distinct vortexes generated by the arms produced a downwash flow in the wake. It is considered that the positioning of the arms in a very low position strongly influences the flow structure.

Numerical study of flow-induced oscillations of two rigid plates elastically hinged at the two ends of a stationary plate in a cross-flow

The flow-induced oscillation (FIO) of bluff bodies is commonly encountered in the fluid structure interaction (FSI) problems. In this study, we use an unstructured moving grid strategy and simulate the FIO of two rigid plates, which are elastically hinged at the two ends of a fixed flat plate in a cross-flow. We use a hybrid finite-element-volume (FEV) method in an arbitrary Lagrangian–Eulerian (ALE) framework to study FIO of the two hinged plates. The current simulations are carried out for wide ranges of flow Reynolds number (50–175), spring stiffness coefficient, and the two hinged plates' moment of inertia magnitudes. The influences of these parameters are investigated on the magnitudes of maximum deflection angle, the amplitude of oscillation, the total lift and drag coefficients, and so on. The study is also carried out in the transition period to describe the in-phase and out-of-phase angular oscillations occurring for the two elastically hinged plates with respect to each other. After the transition period, the two hinged plates eventually arrive to a similar periodic oscillation; however, with some phase lags. We find that the achieved phase lag is equal to the phase lag between the two pairs of flow vortices, which are alternatively shed into the flow from the upper and lower hinged plates. Similar to past FIO problems, the current model also exhibits two important lock-in and phase-switch FSI phenomena; however, in angular directions. There is a phase jump of approximately 170° between the aerodynamic lift coefficient and angular oscillations of hinged plates, which nearly occurs in the middle of lock-in region. Indeed, our literature review shows that this is the first time to report the phase-switch phenomenon in angular oscillations of three-element bluff bodies in a FSI problem.

The gust-mitigating potential of flapping wings

Nature’s flapping-wing flyers are adept at negotiating highly turbulent flows across a wide range of scales. This is in part due to their ability to quickly detect and counterract disturbances to their flight path, but may also be assisted by an inherent aerodynamic property of flapping wings. In this study, we subject a mechanical flapping wing to replicated atmospheric turbulence across a range of flapping frequencies and turbulence intensities. By means of flow visualization and surface pressure measurements, we determine the salient effects of large-scale freestream turbulence on the flow field, and on the phase-average and fluctuating components of pressure and lift. It is shown that at lower flapping frequencies, turbulence dominates the instantaneous flow field, and the random fluctuating component of lift contributes significantly to the total lift. At higher flapping frequencies, kinematic forcing begins to dominate and the flow field becomes more consistent from cycle to cycle. Turbulence still modulates the flapping-induced flow field, as evidenced in particular by a variation in the timing and extent of leading edge vortex formation during the early downstroke. The random fluctuating component of lift contributes less to the total lift at these frequencies, providing evidence that flapping wings do indeed provide some inherent gust mitigation.

Characteristics of aerodynamic forces exerted on a twisted cylinder at a low Reynolds number of 100

Laminar flow over a twisted cylinder is numerically simulated at a Reynolds number of 100. The flow past a smooth cylinder is calculated for comparison. Jung and Yoon (J. Fluid Mech., 759, 2014) showed the considerable suppression of force coefficients at the subcritical Reynolds number of 3000. The present results verify that the twisted shape of the cylinder can be used to reduce the force coefficients at a low Reynolds number containing the laminar flow. This suppression of the force coefficients is supported by a longer vortex formation length produced by the twisted cylinder. We investigated the characteristics of the local force coefficients for a twisted cylinder. The simple periodic oscillation of the time histories of total and local lift coefficients for the twisted cylinder exhibits the same pattern as that of a smooth cylinder. However, the time history of drag for the twisted cylinder reveals the presence of multi-frequency oscillations, resulting in harmonic behavior of the power spectra. This is confirmed by a time sequence of the instantaneous flow fields during the half-period of the time histories of force coefficients. The nature of the three-dimensional (3-D) twisted shape forms the 3-D vortical structures along the spanwise direction, which leads to the harmonic behavior of the drag time trace power spectra.

Computational aerodynamic modeling for flight dynamics simulation of ram-air parachutes

This work presents a step toward bridging the gap between flight dynamics simulation of ram-air parachutes and high-fidelity computational fluid dynamics. Today's parachute design codes mainly rely on the empirical or semi-empirical methods generated from wind tunnel experiments and drop tests. The outcome of this study will hopefully help to reduce the cost of experiments and drop testing in the design of future canopies and to better understand the aerodynamic characteristics of these geometries. In this work, the parachute geometries were modeled as rigid rectangular wings with an aspect ratio of two and zero anhedral angle. The wings have seven opening cells and the trailing edge is deflected or not deflected. To validate computational methods, the aerodynamic predictions of similar wings, but with closed and round inlets, are compared with experimental data available from the Subsonic Wind Tunnel at United States Air Force Academy. Total lift and drag force coefficients were measured at a Reynolds number of 1.4 million. The results show that computational predictions of fine (closed-inlet) grids match the experimental data very well up to the stall angle. Both experiments and simulations show that closed wings have sharp stalling characteristics. The aerodynamics of closed wings up to stall can be approximated by linear functions and their derivatives. The closed wings show a negative static stability with respect to changes in the angle of attack. The open wings, on other hand, have positive static stability in the longitudinal and lateral directions. The open wings exhibit highly nonlinear unsteady aerodynamic characteristics; they also stall earlier and have higher drag values than the closed wings. The aerodynamic derivatives of open and closed wings were estimated using a linear regression method and training data simulated in small-amplitude oscillations in pitch, yaw, and roll directions. While the open wings have large oscillations in aerodynamic coefficients over the yawing and rolling hysteresis loops, lateral aerodynamic derivatives of the open and closed wings are similar. Finally, the results show that model predictions are reasonably accurate for use in flight-dynamics simulations.

Vortex dynamics and new lift enhancement mechanism of wing–body interaction in insect forward flight

The effects of wing–body interaction (WBI) on aerodynamic performance and vortex dynamics have been numerically investigated in the forward flight of cicadas. Flapping wing kinematics was reconstructed based on the output of a high-speed camera system. Following the reconstruction of cicada flight, three models, wing–body (WB), body-only (BD) and wings-only (WN), were then developed and evaluated using an immersed-boundary-method-based incompressible Navier–Stokes equations solver. Results have shown that due to WBIs, the WB model had a 18.7 % increase in total lift production compared with the lift generated in both the BD and WN models, and about 65 % of this enhancement was attributed to the body. This resulted from a dramatic improvement of body lift production from 2 % to 11.6 % of the total lift produced by the wing–body system. Further analysis of the associated near-field and far-field vortex structures has shown that this lift enhancement was attributed to the formation of two distinct vortices shed from the thorax and the posterior of the insect, respectively, and their interactions with the flapping wings. Simulations are also used to examine the new lift enhancement mechanism over a range of minimum wing–body distances, reduced frequencies and body inclination angles. This work provides a new physical insight into the understanding of the body-involved lift-enhancement mechanism in insect forward flight.

Aerodynamic Analysis of Flexible Flapping Wing Micro Aerial Vehicle Using Quasi-Steady Approach

In recent times flexible flapping-wing aerodynamics has generated a great deal of interest and is the topic of contemporary research because of its potential application in micro aerial vehicles (MAVs). The prominent features of MAVs include low Reynolds Number, changing the camber of flapping wings, development of related mechanisms, study of the suitability airfoil shape selection and other parameters. Generally, low Reynolds Number is similar to that of an insect or a bird (103–105). The primary goal of this project work is to perform CFD analysis on flexible flapping wing MAVs in order to estimate the lift and drag by using engineering methods such as quasi-steady approach. From the wind tunnel data, 3-D deformation is obtained. For CFD analysis, two types of quasi-steady methods are considered. The first method is to slice the wing section chord-wise and span wise at multiple regions, frame by frame, and obtain the 2-D corrugated camber section for each frame. This 2-D corrugated camber is analysed using CFD techniques and all the individual 2-D corrugated camber results are summed up frame by frame, to obtain the total lift and drag for one wing beat. The second method is to consider the 3D wing in entirety and perform the CFD analysis to obtain the lift and drag for five wing beat.

Seeking key meteorological parameters to better understand Hector

Abstract. Twelve Hector events, a storm which develops in northern Australia, are analyzed with the aim of identifying the main meteorological parameters involved in the storm's convective development. Based on Crook's ideal study (Crook, 2001), wind speed and direction, wind shear, water vapor, convective available potential energy and type of convection are the parameters used for this analysis. Both the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and high-resolution simulations from the Fifth-Generation Mesoscale Model (MM5) are used. The MM5 simulations are used to connect the mean vertical velocity to the total condensate at the maximum stage and to study the dynamics of the storms. The ECMWF analyses are used to evaluate the initial conditions and the environmental fields contributing to Hector's development. The analysis suggests that the strength of convection, defined in terms of vertical velocity, largely contributes to the vertical distribution of hydrometeors. The role of total condensate and mean lifting versus low-level moisture, convective available potential energy, surface wind and direction is analyzed for shear and no-shear conditions to evaluate the differences between type A and B for real events. Results confirm the tendency suggested by Crook's analysis. However, Crook's hypothesis of low-level moisture as the only parameter that differentiates between type A and B can only be applied if the events develop in the same meteorological conditions. Crook's tests also helped to assess how the meteorological parameters contribute to Hector's development in terms of percentage.

Combination of Treatments in Nonsurgical Facelift Performance to Conduce a Case of Severe Photoaging

Introduction: Combination of techniques enables access to different depths in skin improving performance in nonsurgical face lift. Objective: To determine the effectiveness of the combination: intraoral 2940 nm erbium, followed by microneedled radiofrequency and microfocused ultrasound in severe photoaging. Materials and methods: Split-face study assessing combination combination of Intraoral Erbium: Yag Laser (IEL) 2940 nm pro-collagen, Microfocused Ultrasound and Microneedled Radiofrequency (Total Lift). Improvement was evaluated through photographic record. Results: After forty days of one laser treatment, significant improvement of photoaging from baseline was observed. The laser side showed, through the photographic record, great improvement in skin laxity, skin texture and wrinkles. Conclusion: The combination of techniques (Total Lift) is a promising new technology in the treatment of photoaging in patients with contraindications or do not want to perform surgery.

Hydrodynamics of the interceptor on a 2-D flat plate by CFD and experiments

AbstractNowadays, the use of interceptor by both partial and total dynamic lift crafts is quite common. In this article, a lot of evidence is given regarding the effectiveness of interceptor. The interceptor, when placed at the stern region, changes the pressure distribution around the craft. Its presence affects drag force, lifting force and the position of pressure's center leading to a new trim. This study focuses on hydrodynamic effects of interceptors on a 2-D flat plate based on both computational fluid dynamic (CFD) and experimental approaches. The Reynolds average Navier-Stokes (RANS) equations are used to model the flow around a fixed flat plate with an interceptor at different heights and attack angles. Based on finite volume method and SIMPLE algorithm which uses static structures, this model can be analyzed and the RANS results can be compared with the experimental data obtained in the current channel of the laboratory of waves and current of COPPE/UFRJ (LOC in Portuguese acronym). According to the results, the increase of pressure at the end of the flat plate was proportional to the interceptor height. In addition, the existence of interceptors can significantly increase the lift force coefficient at high angles of attack also proportional to the interceptor height. The presence of interceptor at the end of the flat plate increased both the lift coefficient and the drag coefficient but hydrodynamic drag did not grow as fast as the lift coefficient did. The lift coefficient increased much more. Furthermore, the results showed that the interceptor effectiveness is proportional to the boundary layer thickness at the end of the flat plate. As the interceptor was inside the boundary layer alterations of flow speed led to changes in boundary layer thickness, directly affecting interceptor's efficiency. Optimum choice of interceptor height had a great effect on its efficiency, and in choosing it the flow speed and length of the boat must be taken into consideration.

Energy efficient active control of the flow past an aircraft wing: RANS and LES evaluation

Numerical simulations of the flow past a NACA 0015 wing with active control have been performed. The Reynolds number of the flow based on the wing's chord is Re = 2.5 × 106. The configuration proposed in this study does not follow the conventional active control methodology past wings. Large blowing surfaces and low jet velocity magnitudes are considered and the energy efficiency of such configuration is examined for a number of variants. Although the momentum coefficient of the injected fluid is similar to most of the referenced studies, the effects on the flow-field are quite pronounced. Strategies for drag reduction and lift increase of the wing are proposed by varying some of the actuation parameters. The present active flow control could be energy efficient at all angles of attack, while in the same time could be able to reduce significantly the total drag of the wing, increase the total lift or combine effectively those favorable effects for better flight performance. The present actuation reduces the profile drag of the wing and influences the flow mainly in two dimensions. Maximum drag decrease could be close to 40% at low angles of attack, with still positive energy income. Supportive Large Eddy Simulations at Re = 2.2 × 105 verify the trends of this control, which are predicted by Reynolds Averaged Navier–Stokes modeling and it is shown that the mechanism of drag reduction or lift increase, does not depend crucially upon the unsteadiness and turbulence of the flow close to the actuation area.

On the Estimation of Time Dependent Lift of a European Starling (Sturnus vulgaris) during Flapping Flight.

We study the role of unsteady lift in the context of flapping wing bird flight. Both aerodynamicists and biologists have attempted to address this subject, yet it seems that the contribution of unsteady lift still holds many open questions. The current study deals with the estimation of unsteady aerodynamic forces on a freely flying bird through analysis of wingbeat kinematics and near wake flow measurements using time resolved particle image velocimetry. The aerodynamic forces are obtained through two approaches, the unsteady thin airfoil theory and using the momentum equation for viscous flows. The unsteady lift is comprised of circulatory and non-circulatory components. Both approaches are presented over the duration of wingbeat cycles. Using long-time sampling data, several wingbeat cycles have been analyzed in order to cover both the downstroke and upstroke phases. It appears that the unsteady lift varies over the wingbeat cycle emphasizing its contribution to the total lift and its role in power estimations. It is suggested that the circulatory lift component cannot assumed to be negligible and should be considered when estimating lift or power of birds in flapping motion.

Aerodynamic and overall parameters analysis of buoyancy-lifting hybrid airship

In order to balance the aerodynamic performance and buoyancy-lifting characteristics of airship,to make full use of their advantages and to strengthen the controllability,a hybrid airship configuration which has combined envelopes that are based on high lift NACA airfoil was proposed. With computational fluid dynamics( CFD) and FLUENT computing modeling,the lift-drag characteristics,longitudinal static stability and buoyancy-lifting property under different velocities and attack angles of the airship were simulated,furthermore,its overall performance was evaluated and lastly it was compared with conventional airship. The results show that the airship configuration with combined envelopes has good aerodynamic performance and efficiency. It can produce three times aerodynamic lift than that of conventional airship under the same condition.When the magnitude of cruise velocity is greater than 26 m / s,hybrid airship begins to have a higher total lift efficiency and better buoyancy-lift property. Besides,the hybrid airship's size is smaller than conventional airship under the same design load,which contributes to increasing payloads. This can provide a reference for low-attitude large hybrid airship's research.

Aerodynamics of biplane and tandem wings at low Reynolds numbers

Experiments were performed to investigate the aerodynamic characteristics of two-wing configurations at a low Reynolds number of 100,000. The wing models were rectangular flat plates with a semi-aspect ratio of two. The stagger between the wings was varied from ∆X/c = 0 to 1.5; the gap was varied from ∆Y/c = 0 to 2 and ∆Y/c = −1.5 to 1.5 for biplane and tandem configurations, respectively, with the decalage angle fixed at 0°. Lift, drag, aerodynamic efficiency and power efficiency ratios show that for small incidence angles, performance compared with the single wing is degraded. However, for single-wing post-stall angles of attack, lift performance improves and stall is delayed significantly for many configurations with nonzero gap, i.e., ∆Y/c ≥ 0. For a fixed angle of attack, there are optimal gaps between the wings for which total lift becomes maximum. Particle image velocimetry measurements show that performance improvement relies heavily on the strength of the inter-wing flow and the interaction of the separated shear layers from the leading edge and trailing edge of the leading wing with the trailing wing. Unsteady forces are found to intensify for certain two-wing configurations. A switching between the stalled and unstalled states for the trailing wing as well as a switching between the merged and distinct wakes is shown to have high flow unsteadiness and large lift fluctuations.

Numerical study on the 3-D complex characteristics of flow around the hull structure of TLP

Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier–Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a “beating” behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.

Effects of 28 Days of Two Creatine Nitrate Based Dietary Supplements on Body Composition and Exercise Performance in Recreationally Active Males

We examined 28d of randomly assigned of (1) Placebo (PL), (2) Creatine (CR, 3 g), (3) Creatine Nitrate (CrN; 1 g CR; 0.5 N) and (4) CrN2X (2 g CR; 1.0 g N) on exercise performance and body composition. Participants (N=48; 21 ±3 y) presented for fasting (12h) testing after abstaining from exercise and alcohol for 48h. Performance (reps at 70% of bench press 1 RM [BP] and repeated sprints on cycle ergometer) was measured at 0 &amp; 4 wks. Body composition (DXA) was measured at 0, 1, &amp; 4 wks. We used GLM to examine mean change (95% CI) from baseline. While all three treatment groups significantly increased BP repetition at 4 wks, total BP lifting volume was greater at 4 wks for CrN2X (294.6 lbs; 95% CI, 196, 393) vs CrN (164.2 lbs; 95% CI, 25, 304) and PL (187.1 lbs;95% CI, 37, 336, both p=0.02). No treatment effects were observed for cycle ergometry testing (peak or mean power, fatigue slope, and total work). While no difference in fat mass were observed for any treatment group, CrN2X did augment lean mass (1.2 lbs; 95% CI, 0.3, 2.1) and fat‐free mass (1.1 lbs; 95% CI, 0.2, 2). Our results indicate that CrN2X can increase muscular endurance, and lean and fat‐free mass.

Global optimization for ducted coaxial-rotors aircraft based on Kriging model and improved particle swarm optimization algorithm

To improve the operational efficiency of global optimization in engineering, Kriging model was established to simplify the mathematical model for calculations. Ducted coaxial-rotors aircraft was taken as an example and Fluent software was applied to the virtual prototype simulations. Through simulation sample points, the total lift of the ducted coaxial-rotors aircraft was obtained. The Kriging model was then constructed, and the function was fitted. Improved particle swarm optimization (PSO) was also utilized for the global optimization of the Kriging model of the ducted coaxial-rotors aircraft for the determination of optimized global coordinates. Finally, the optimized results were simulated by Fluent. The results show that the Kriging model and the improved PSO algorithm significantly improve the lift performance of ducted coaxial-rotors aircraft and computer operational efficiency.