Lift Reduction Research Articles

Unsteady RANS and IDDES studies on a telescopic crescent-shaped wingsail

ABSTRACT Over the years, several research projects have evaluated different concepts for wind-assisted propulsion, generally concluding that it can lead to significant fuel savings. The time-averaged propulsive performance of a single rigid wingsail has been analysed in previous studies. However, the unsteady characteristics of the external loads which may induce structural vibration are also important to be considered. In this study, full-scale simulations, with both unsteady RANS and IDDES methods, are performed to analyze the flow field. The paper's analysis includes flow separation and vortex shedding, the development and dissipation of wake vortices, and the lift reduction due to tip vortices. It also studies the telescopic function of the wingsail by analyzing sails with different heights and wind conditions. The paper concludes that the unsteady RANS and IDDES simulations make similar predictions for time-averaged loads but disagree on the unsteady characteristics. The IDDES simulations indicate more complex vortex-shedding phenomena.

Design and Analysis of Wing Tip Twist on a Forward Swept Wing Using Prandtl-d Wing Concept

Our project is all about the implementation of a wing tip twist for Prandtl-D wing to a Forward swept wing. The innovative idea is that the Prandtl-D wing is used only for a glider till date whereas, we implied this concept for a commercial aircraft. The phenomena of twisting the tip of the wing leads to the change in geometry which results in drag reduction and increase in lift to drag ratio. With the help of a reference project, a wing geometry is chosen and the model is scaled down according to our test section. By using CATIA V5 R20, our model is drawn and analyzed with the help of ANSYS Fluent 16.0. The geometry with the best result is 3-D printed and tested in the low speed subsonic wind tunnel. Both the analytical and experimental results are validated. In general, the forward swept wing aircraft possess good aerodynamic performance in subsonic range. We look into that whether our project increases the efficiency or not.

Exploring synchronization and lift suppression in fluid flow around vibrating cylinder: a parallel CFD and global optimization investigation

In this study, we employ a parallel Computational Fluid Dynamics (CFD) code integrated with the VTDIRECT95 algorithm, a parallel deterministic global optimization method, to conduct global optimization for an oscillating circular cylinder. We conduct numerical simulations for the flow at a Reynolds number of 500 within the parameter range of 0.1≤Ax≤0.3 and 0.5fst≤fex≤2.5fst where Ax represents the inline oscillating amplitude, fex denotes the forcing oscillation frequency, and fst corresponds to the frequency of a stationary cylinder. To enhance computational efficiency, a combination of VTdirect and a CFD solver is utilized to efficiently identify the synchronization region, thereby reducing computational resources. The results reveal a significant reduction in the lift coefficient within the synchronized region compared to unsynchronized regimes. Furthermore, the study delves into the underlying flow physics behind synchronization and lift suppression. By synchronizing the shedding of vortices, their detrimental effects are nullified, resulting in a reduction in lift. Moreover, the research examines the influence of three-dimensional (3-D) flow by comparing 2-D and 3-D simulations at two different Reynolds numbers. It demonstrates that accounting for 3-D effects yields more accurate predictions of fluid behavior. Synchronization maps and root mean square (rms) lift coefficient plots illustrate the impact of Reynolds number and movement frequency on lift suppression. The findings indicate that achieving synchronization in 3-D flow necessitates stronger amplitudes and higher frequencies. At higher Reynolds numbers, the wake structures become unstable, leading to intricate vortical patterns. Consequently, the synchronization curve shifts towards higher amplitudes and frequencies in 3-D simulations. Understanding these phenomena is vital for reducing lift force in practical applications. This research significantly contributes to knowledge regarding synchronization and lift suppression in fluid flow around vibrating cylinders.

Unexpected trends of lift for hydrofoils with superhydrophobic coating

In this paper, the physics of external flow past a superhydrophobic SD7003 hydrofoil is studied at Reynolds number of 105. We used Navier’s slip length to model the superhydrophobic surfaces, and investigated the effect of different slip lengths on hydrofoil performance by means of RANS (Reynolds-averaged Navier–Stokes) simulations. The slip length boundary condition is imposed on upper, or/and lower side(s), to study the effect of each superhydrophobic region on lift coefficient. By increasing the slip length (ls), it was expected to see lift enhancement and drag reduction. However, the lift enhancement trend had some exceptions. The unexpected trends were explained by studying the location of laminar separation and reattachment for different angles of attack (AOA) and slip lengths. For example, the lift coefficient of a full superhydrophobic hydrofoil at AOA = 2° does not change monotonically against slip length. By increasing the slip length, separation and reattachment points are shifted towards the trailing edge and at slip length 200 μm, there is separation with no reattachment which results in lift reduction. By further increasing the slip length, the separation is shifted further down and eventually there would be no separation n\\and flow becomes fully attached.

A novel R744 multi-temperature cycle for refrigerated transport applications with low-temperature ejector: Experimental ejector characterization and thermodynamic cycle assessment

A novel vapor-compression system concept employing carbon dioxide as the refrigerant is proposed to serve the needs of a typical medium-size refrigerated truck used for multi-temperature (MT and LT) goods delivery. The system design is based on the implementation of an ejector as the only component increasing the refrigerant pressure from the LT evaporation pressure to the MT evaporation pressure, thus providing cooling effect at two different temperature levels with only one stage of compression. The ejector was experimentally tested and its ability to effectively entrain mass flow rate from low pressure suction conditions (corresponding to a LT evaporation temperature of −25 °C) was assessed. Lower external ambient temperatures and consequent lower expansion energy available at the ejector motive nozzle leads to a reduction of the maximum achievable pressure lift. Moreover, a significant degradation of the ejector performance towards the highest pressure lifts is experienced. Based on the ejector experimental data, a numerical evaluation of the proposed cooling unit performance has been performed, highlighting that in design conditions (LT evaporation at −25 °C) the cooling unit provides a LT freezing power ranging between 1.1 kW and 2.3 kW and a corresponding minimum MT cooling power ranging between 5.1 kW and 3.8 kW, depending on the chosen ejector lift. The MT cooling power can be further increased by increasing the compressor mass flow rate. The system COP is maximized at the maximum available lift provided by the ejector.

Lift alleviation in travelling vortical gusts

AbstractLift alleviation by a mini-spoiler on aerofoils, unswept and swept wings encountering an isolated counter-clockwise vortical gust was investigated by means of force and velocity measurements. The flow separation region behind the spoiler remains little affected during the gust encounter. The maximum lift reduction is found for the static stall angle of attack. The change in the maximum lift during the gust encounter is approximately equal to that in steady freestream. The comparison with plunging aerofoils reveals that, for the same maximum gust and plunge velocity, the effectiveness of the mini-spoiler is much better in travelling gusts. This reveals the importance of the streamwise length scale of the incident gust. For the unswept wing, there is some three-dimensionality of the flow separation induced by the mini-spoiler near the wing tip. The magnitude of the lift reduction can be estimated using the aerofoil data and by making an aspect ratio correction for the reduced effective angle of attack. For the swept wing, the mini-spoiler can disrupt the formation of a leading-edge vortex induced by the incident vortex on the clean wing and can still reduce the maximum lift.

Numerical and experimental investigation of the in-phase and out-phase plasma actuation effects on the wake flow for Re = 1000

The aim is to characterize the role of symmetry pattern on the flow control induced by dielectric barrier discharge plasma actuators. Two DBD actuators are employed for in-phase excitation with duty cycle 50% leading to symmetric wake pattern and out-phase excitation for two pulsing frequencies St=0.2 and St=1 at Re=1000 which forms quasi-symmetric and asymmetric flow structures respectively. The modes deduced from POD and DMD methods represent the competition between symmetric (S) and asymmetric mode (K) in all cases. The harmonic in-phase plasma actuation with 50% duty cycle is the most effective flow control method with lowest power consumption. The harmonic out-phase excitation is not much effective; however adjustment of the actuator position can form the symmetric pattern with minimum power consumption. The superharmonic out-phase plasma actuation reduces the wake region however is not effective in lift reduction significantly and consumes high amount of energy. This indicates that phase difference and plasma location influence on the size and symmetry of the vortical structure. Then, based on the symmetry properties of the designed wake pattern created by frequency and phase difference of the plasma actuator, the effective active flow control can be performed. The numerical results are validated with experiments.

How to Avoid Pseudoptosis after Lifting and Breast Reduction Mammaplasties

Pseudoptosis or “bottoming-out” is a common complication following breast reduction. It is secondary to five causal phenomena: improper determination of nipple placement, dissociation of the nipple from the gland, dissociation between different parcels of a reconstituted breast, improper evaluation of the skin to be resected and weakness of the inferior dermal arch. The total posterior pedicle breast reduction technique was described by Richard Moufarrege in 1982. It consists of dissecting the skin away from the breast tissue offering free access to all breast quadrants. This technique is known for its robust blood supply to the nipple areolar complex, the preservation of the nipple areolar complex sensation, and for the conservation of the breastfeeding function. In this article, we also elucidate the reasons why the Moufarrege Total Posterior Pedicle breast reduction technique has a lowest rate of postoperative pseudoptosis.

How to Avoid Pseudoptosis after Lifting and Breast Reduction Mammaplasties

How to Avoid Pseudoptosis after Lifting and Breast Reduction Mammaplasties

Numerical study on the aerodynamic performance of the three-dimensional wing of a jellyfish-like flyer

The jellyfish-like flying machine is a new development direction of the future bionic flapping-wing aircraft besides the insect-mimic and bird-mimic micro air vehicles (MAVs). To better understand the underlying fluid mechanisms of the jellyfish-like flyer, we numerically simulated the aerodynamic forces of the three-dimensional flapping wings under different control parameters. The effects of flapping amplitude, vortex wake, up-flight speed, and wing–wing interaction on aerodynamic performance were investigated. The results show that, at hovering, the mean lift rises rapidly at first and then tends to be stable with the increase in flapping amplitude. The vortex wake can improve the lift at large flapping amplitudes, while it reduces the lift at very small flapping amplitudes. With the increase in up-flight speed, the lift decreases. However, the sources of lift reduction are different for different flapping amplitudes. When the two wings flap together and the distance between the wings is small enough, the wing–wing interaction can improve the lift by about 15% compared with that of a single wing, but much higher power is required, resulting in lower efficiency. The results of this study provide new insights into the flight mechanism of the jellyfish-like aircraft and have important guiding significance for the design and optimization of the jellyfish-like flying machine.

Aerodynamic Load Reduction on a Supercritical Airfoil Using Tilted Microjets

Microjets arranged on the wing surfaces of civil transport aircraft have been shown to have great potential in suppressing high-frequency gust loads. This paper presents a study of aerodynamic load reduction on a supercritical airfoil using tilted microjets by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The numerical method was first validated against the experimental and previous numerical data. Afterward, the subsonic and transonic flowfields around the supercritical airfoil were simulated with various angled microjets. The results show that both the lift reduction and the power efficiencies significantly increase as the blowing direction shifts downstream to upstream. The movement and weakening of the shock due to the jet are observed at α > 2 ∘ in transonic flow, resulting in a drag reduction compared to the baseline airfoil. However, the transient subsonic results revealed that the upstream jet induces a strong vortex shedding, which is suppressed in transonic flows. During jet deployment, there are three distinct phases: time lag, vortex rolling-up, and rebalancing, in that order. Once it reaches the trailing edge in subsonic flows, the starting vortex rapidly modifies the load and induced a strong roll-up vortex from the pressure surface. Nevertheless, in transonic flow, the rebalancing stage contributes to a greater reduction in lift due to the additional shock movement and weakening effect.

Assessing the Impact of COVID-19 on Facial Aesthetic Surgery Search Interest.

The global COVID-19 pandemic reshaped many components of modern health care practice. Before the pandemic, research was beginning to demonstrate the impact of self-facing cameras, selfie images, and webcams on patient interest in head and neck (H&N) aesthetic surgery. We sought to determine temporal changes in patient interest in aesthetic surgery of the H&N as compared with the rest of the body because of COVID-19, and the subsequent surge in Web-conferencing and telecommunication. The 2020 Plastic Surgery Trends Report produced by the American Society of Plastic Surgeons was used to identify the 5 most common aesthetic surgical procedures performed on the H&N and the rest of the body for 2019: blepharoplasty, face lift, rhinoplasty, neck lift, cheek implant, and breast lift, liposuction, tummy tuck, breast augmentation, and breast reduction, respectively. Google Trends filters, which provide relative search interest for greater than 85% of Internet searches, were applied to gauge interest from January 2019 to April 2022. Relative search interest and mean interest were plotted as a function of time for each term. Our findings demonstrate a sharp decline in online aesthetic surgery interest in March 2020, coinciding with the beginning of the COVID-19 pandemic for both the H&N and the rest of the body. Search interest increased shortly after March 2020 and reached values greater than those of the prepandemic year (2019) in 2021 for rest of the body procedures. After March 2020, there was a brief, sharp increase in search interest for rhinoplasty, neck lift, and facelift, whereas patient interest in blepharoplasty increased more gradually. There was no increase in search interest for H&N procedures as a result of COVID-19 when using the mean values of the included procedures, although current interest has returned to prepandemic levels. The COVID-19 pandemic caused a disruption of normal trends in aesthetic surgery interest, with a sharp decline in search interest in March 2020. Afterward, there was a sharp increase in rhinoplasty, face lift, neck lift, and blepharoplasty interest. Patient interest in blepharoplasty and neck lift has remained elevated compared with 2019. Interest in rest of the body procedures has returned to and even surpassed prepandemic levels.

Numerical investigation of flow past a circular cylinder modified with a single groove at low Reynolds number

Flow past a circular cylinder modified by grooves is one of the passive control techniques to control the drag and lift forces. The presence of grooves tends to reduce the hydrodynamic drag and lift. The aim of this work was to numerically investigate the influence of a single groove modification on a circular cylinder and how it was impacting the hydrodynamic coefficients based on its position and shape at low Reynolds numbers. Three types of grooves were considered, namely, dimple, square, and triangular, with identical width and depth which is 0.1 times the diameter. The Reynolds numbers considered were 100, 150, and 200. The computational domain was set to a blockage ratio of 0.01 after carrying out a detailed domain independence test. It was observed that the drag and lift reduction was maximum at groove location 90° with the decrements being more for the square groove shape. The viscous drag showed a decrease in its values for all the groove positions located on the flow-facing side of the cylinder; however, the pressure drag showed an increment in its values for these groove locations, and these increments were relative of larger magnitudes, thus influencing a net increase in the total mean drag when compared to the smooth case; this was evident at groove locations 120° and 150°. The vorticity patterns for the grooves located on the front side showed large irregularities in magnitude between the anticlockwise and the clockwise vortices with the groove side vortices being of larger magnitudes, and for the wake side, the irregularities were negligible. The coefficient of pressure and separation angles were also investigated. The CP vs θ plots showed discontinuity at groove locations with abrupt variations at the front face of the cylinder; for the wake side grooves, these discontinuities were low and almost coincided with the CP vs θ plots of the smooth cylinder. The grooves located at 90° showed a delay in separation and at 60° the boundary layer tends to detach earlier.

Aerodynamic drag reduction of high-speed maglev train based on air blowing/suction

The significant increase in aerodynamic drag is still a key problem restricting the further speed increase of maglev trains. The Improved Detached Eddy Simulation (IDDES) turbulence model based on the Shear Stress Transport (SST) k-ω model was employed to explore the potential and effect of blowing/suction control on the aerodynamic drag reduction of the maglev train. In this study, the aerodynamic characteristics of the train's wake region, and the interference mechanism of blowing/suction on the flow field were studied. The results indicate that the best drag reduction rate ζd of 8.69% of the train and the lift reduction rate δl of 30.4% of the tail car are achieved when blowing along the normal direction of the surface at 0.5 times of the train speed at the separation region near the tail nose. In this case, the ζd and δl grow with the increase of blowing speed; however, the growth rate of ζd decreases when the blowing speed reaches 0.2 times to 0.5 times of the train speed. Studies in this paper propose an effective active flow control method to reduce the train aerodynamic drag, and provide theoretical guidance for the development of drag reduction technology for maglev trains.

Flow structures around a circular cylinder with bilateral splitter plates and their dynamic characteristics

Flow structures around a circular cylinder with bilateral splitter plates and their dynamic characteristics are numerically investigated at a low Reynolds number of 100. The two splitter plates with the same length as the half of cylinder diameter are symmetrically placed beside the cylinder. In this work, three gap ratios of G/D = 0, 0.5 and 1.0 (G is the gap distance between the cylinder surface and the near end of plate, D is the diameter of circular cylinder) and inclination angle (α, between splitter plate and wake centerline) ranging from 0° to 90° are examined. According to flow characteristics, five vortex shedding regimes are identified, including "2S" (two vortices are alternatively shed per cycle) regime, single-sided regime, wake-flapping regime, steady regime and irregular regime. Apart from the main vortices, some special vortices such as subordinate vortices, tip vortices and persisted vortices are recognized. Additionally, local "2S″ and "4S" (four vortices are shed per cycle) regimes are observed behind the cylinder and the plates, respectively. The dynamic mode decomposition (DMD) results show that the first mode possesses the majority of energy of the flow field. As α increases, the splitter plates contribute to the lift reduction, especially when a gap is introduced. By contrast, the bilateral plates lead to a significant growth in the drag coefficient when α ≥ 15°.

Design Analysis of Open and Ducted Propellers in UAV Application

The aim of the study was to determine the feasibility of implementing a ducted propeller system for small scale drones. 5” propeller drones are common in first person view (FPV) drone racing and cinematography, increasing the likelihood of injury due to untrained pilots, of which the majority are laceration injuries due to the propeller blades. Furthermore, the addition of a duct improves the thrust output of the entire system. A few key parameters are identified, of which were manipulated to determine the optimum values through a series of ANSYS Fluent CFD simulations. Introducing a duct is shown to reduce the lift a propeller produces; however, the reduction is offset by the lift generated by the duct. Blade tip clearance was investigated, with the optimum value found to be 0.25 mm, producing the most lift from the duct and least reduction of propeller lift, and with thrust outputs up to 35.568% more in some cases compared to open propeller. It was observed that increasing the BTC significantly reduced duct lift. Diffuser length simulations provided unconclusive results, with the duct lift varying depending on the diffuser length. However, the optimum diffuser length was determined to be 65 mm with respect to thrust outputs. In comparison, inlet lip radius shows a clear pattern, deviating from the optimum value of 16.5 mm reduces the duct lift produced, with smaller values severely decreasing performance.

Separation Control for a Transonic Convex Corner Flow Using Ramp-Type Vortex Generators

A flap can be used to control wing camber and as a high-lift device. A convex corner is a simplified model of the upper surface of a flap. At transonic speeds, shock-induced boundary layer separation (SIBLS) occurs at greater freestream Mach numbers and deflection angles. This results in energy losses and a reduction in aerodynamic performance. This study installs ramp-type vortex generators (VGs) upstream of a convex corner, and the effect of the height of the VG on SIBLS is determined. As the height of the VG increases, the magnitude of the mean surface pressure upstream of the corner increases and downstream expansion decreases, which results in a reduction in lift. A reduction in peak surface pressure fluctuations, the separation length, and the frequency of shock oscillation is also determined. For flow control and lift enhancement, micro-VGs are more effective.

A combined experimental and numerical study on aerodynamic load reduction for a swept wing by using jets

This paper presents a combined experimental and numerical investigation on aerodynamic load reduction through steady blowing on the suction surface of a swept wing. In the experiment, a swept wing with an array of jet exit holes near the wing tip was studied in a low-speed wind tunnel. Numerical studies based on solving the Reynolds-averaged Navier-Stokes equations provide further insight into aerodynamic load and bending moment reduction and the associated flow physics caused by the surface jets with various jet parameters, including blowing direction, blowing strength and jet velocity distribution. It is found that the upstream blowing causes a much larger reduction in both lift and bending moment than that caused by the normal blowing. Both the experiment and numerical simulations confirm that the aerodynamic load reduction increases as the jet momentum increases. It is also found that the linear jet velocity distribution, with the lowest blowing velocity at the outer end (y/b=0.98) of jets region and the highest blowing velocity at the inner end (y/b=0.755), achieves the maximum aerodynamic load reduction among the six different distributions studied. In addition, three key flow mechanisms associated with aerodynamic load reduction are identified, including the pressure rise on the suction surface caused by the flow separation, the wingspan shortening effect caused by the large drop in lift in the tip region of a three-dimensional swept wing as well as the jet reaction force.

Aerodynamic Study of a Drag Reduction System and Its Actuation System for a Formula Student Competition Car

This work presents a computational fluid dynamic (CFD) analysis of a drag reduction system (DRS) used in a Formula Student competition vehicle, focusing on the interaction between the triple wing elements, as well as on the electrical actuators used to provide movement to the upper two flaps. The S1123 wing profile was chosen, and a 2D analysis of the wing profile was made. The trailing edge was rounded off to conform to Formula Student competition safety rules, resulting in around a 4% decrease in the lift coefficient and around a 12% increase in the drag coefficient for an angle of attack of 12°, compared to the original wing profile. The multi-element profile characteristics are: wing main plate with 4°, first flap 28°, and second flap 60°. To evaluate the wing operation, end plates and electrical linear actuators were added, generating a maximum lift coefficient of 1.160 and drag coefficient of 0.397, which provides around a 10% reduction in lift and a 9% increase in drag compared to the absence of the linear actuators. When activating the DRS, the flap rotation generates about a 78% decrease in the aerodynamic drag coefficient and 53% in the lift coefficient for the minimum aerodynamic drag setting.

Nucleation effects on cloud cavitation about a hydrofoil

The dynamics of cloud cavitation about a three-dimensional hydrofoil are investigated experimentally in a cavitation tunnel with depleted, sparse and abundant free-stream nuclei populations. A rectangular planform, NACA 0015 hydrofoil was tested at a Reynolds number of $1.4\times 10^{6}$ , an incidence of $6^{\circ }$ and a range of cavitation numbers from single-phase flow to supercavitation. High-speed photographs of cavitation shedding phenomena were acquired simultaneously with unsteady force measurement to enable identification of cavity shedding modes corresponding to force spectral peaks. The shedding modes were analysed through spectral decomposition of the high-speed movies, revealing different shedding instabilities according to the nuclei content. With no active nuclei, the fundamental shedding mode occurs at a Strouhal number of 0.28 and is defined by large-scale re-entrant jet formation during the growth phase, but shockwave propagation for the collapse phase of the cycle. Harmonic and subharmonic modes also occur due to local tip shedding. For the abundant case, the fundamental shedding is again large-scale but with a much slower growth phase resulting in a frequency of $St=0.15$ . A harmonic mode forms in this case due to the propagation of two shockwaves; an initial slow propagating wave followed by a second faster wave. The passage of the first wave causes partial condensation leading to lower void fraction and consequent increase in the speed of the second wave along with larger-scale condensation. For a sparsely seeded flow, coherent fluctuations are reduced due to intermittent, disperse nuclei activation and cavity breakup resulting in an optimal condition with maximum reduction in unsteady lift.