Increase In Lift Force Research Articles

Cavitation analysis of plunging hydrofoils using large eddy simulations

This study employs numerical analysis to investigate the behavior of the National Advisory Committee for Aeronautics (NACA)66 modified (mod) hydrofoil under plunging motion, considering various cavitation numbers. The Large Eddy Simulation (LES) method is utilized to model turbulence. The hydrofoil's plunging motion leads to an increase in lift force and a decrease in drag force. Our research indicates that increasing the speed of the hydrofoil's heaving motion delays the onset of cavitation and enhances the formation of cavity clouds. Furthermore, during the peak oscillatory motion of the hydrofoil in the plunging phase, the detachment length of cavitation bubbles decreases. Additional investigations reveal that cavitation on the hydrofoil's surface accelerates the transition from a laminar to a turbulent boundary layer, strengthening the turbulent boundary layer and postponing the onset of flow separation. This research involves an in-depth investigation of the terms in the vorticity transport equation in cavitation inception, finding a correlation between vapor volume fraction and vorticity dilatation near the hydrofoil surface. This correlation proves crucial to the initial stages of the cavitation inception process.

Power Output Enhancement of Straight-Bladed Vertical-Axis Wind Turbines with Surrounding Structures

Wind tunnel experiments were conducted by installing wind-acceleration structures on both sides of a straight-bladed vertical-axis wind turbine (VAWT) to improve the output performance of the turbine. In the case of Venturi-shape structures, a curved shape with a large outlet opening produced a higher power output than straight or brimmed Venturi shapes. More importantly, two simple flat plates installed upstream of the wind turbine achieved the highest power enhancement of 2.4 times the power of the bare wind turbine. From the analysis of the flow visualization results, the power enhancement was attributed to the increase in lift force on the blades in the upstream region due to the acceleration of the gap flow between the flat plates, and the decrease in drag force on the blades toward the upstream region due to stagnation of the flow behind the plates.

Numerical study of the aerodynamic characteristics of airfoil with high-lift devices

The subject matter of this article is the aerodynamic profile of the wing with high-lift devices in the aircraft transport category. When high-lift devices are released, the aerodynamic flow of the wing changes significantly, this changes the stress-strain state of the wing. This relates not only to an increase in lift force due to a change in the curvature of the wing and an increase of the wing area, but also due to a change of the position of the center of pressure relative to the chord of the wing. The goal is to study the influence of wing high-lift devices on the aerodynamic characteristics of the profile during take-off, cruise, and landing cases using numerical methods. The obtained data will be used to determine the loads on the wing in various flight cases. The task is to determine the aerodynamic coefficients of lift and drag forces, changing the position of the pressure center during flight cases: take-off, cruise, and landing. The aerodynamic profile b737c-il was used in the analysis. The single-slot slat and double-slots flap were used in the analysis model. The numerical methods with the CAE system ANSYS Fluent were used. The solver models k-epsilon and transition SST were used for comparison. The use of numerical methods in the process of designing aircraft structures is widely used to accurately determine the aerodynamic parameters of the wing in various flight cases. The following results were obtained: the dependence of the lift coefficient on the angle of attack, the lift coefficient on the drag coefficient, and the position of the center of pressure along the chord of the profile for cruise, take-off, and landing flight cases. Conclusion. The scientific novelty of the results obtained is as follows: the use of numerical methods for determining the aerodynamic characteristics of a wing with high-lift devices in particular, determining the dependence of the position of the center of pressure relative to the chord and at different angles of attack. The obtained results will be used to determine the load on the wing, in particular the distributed load on the slats and flaps, to clarify the torque moment in the wing section where high-lift devices are used.

Numerical flow simulation of mechanism of increase and method for suppressing increase in lift force of pantograph head of conventional line pantograph under crosswind

Numerical flow simulation of mechanism of increase and method for suppressing increase in lift force of pantograph head of conventional line pantograph under crosswind

Computational Fluid Dynamics and Experimental Analysis of a Wind Turbine Blade’s Frontal Section with and without Arrays of Dimpled Structures

Horizontal axis wind turbines are used for energy generation at domestic as well as industrial levels. In the wind turbines, a reduction in drag force and an increase in lift force are desired to increase the energy efficiency. In this research work, computational fluid dynamics (CFD) analysis has been performed on a turbine blade’s frontal section with an NACA S814 profile. The drag force has been reduced by introducing an array of dimpled structures at the blade surface. The dimpled structures generate a turbulent boundary layer flow on its surface that reduces the drag force and modifies the lift force because it has greater momentum than the laminar flow. The simulation results are verified by the experimental results performed in a wind tunnel and are in close harmony with the simulated results. For accurate results, CFD is performed on the blade’s frontal section at the angle of attack (AOA) with a domain of 0° to 80° and at multiple Reynolds numbers. The local attributes, lift force, drag force and pressure coefficient are numerically computed by using the three models on Ansys fluent: the Spalart-Allmaras, the k-epsilon (RNG) and the k-omega shear stress transport (SST).

Feasibility Study of Concave Wing Design for Subsonic Aircraft (NACA 2412)

In this current world of technology, airfoil has been produced for concave wing in many different shapes in terms of root size, tip, existence of winglet and different thickness.Concave wing isthe tendency of a wing to bend during flying at a certain height of deflection. Itincreased higher velocity of the aircraft,mainly due to the increase of lift force produced above the wing.However bySolidWorks,airfoil design for concave wing with NACA 2412 has been choosen.In this study, 0.2m deflection shows the highest lift coefficient andlift drag ratio compared to other height of deflection.The maximum value of CLobtained is 1.517, while for CL/CDis 37.708. This indicates that the airfoil can produce high lift even at low angle of attack, which is beneficial when aircraft wants to take-off, climbing and landing.

横風を受ける在来線パンタグラフの舟体揚力増加の抑制手法に関する数値流体解析

Methods for reducing lift force of conventional pantographs in a crosswind were investigated using large-eddy simulations (LESs). In our previous study, wind tunnel tests and numerical simulations using a full-scaled pantograph were carried out, and the mechanism how the lift force increase in a crosswind was clarified. There are mainly two mechanisms: one is a stational large-scale vortex generated on the upper surface of the pantograph head, and the other is positive pressure generated on the lower surface of the pantograph head. In this study, LESs were carried out using a modified pantograph head shape based on the mechanisms described above, in order to investigate methods for reducing the lift force of the pantograph head. As a result, the lift force decreased in the cases of a shape with a diagonal cut on the lower surface of the pantograph head, and a shape with an opening sections on both the upper and lower surface of the pantograph head. The former shape generates a negative pressure area under the pantograph head, while the latter shape attenuates the large-scale vortex on the upper surface of the pantograph head. Thus, they achieve the lift reduction by different mechanisms and can be used together. The lift reduction rate reaches approximately 60% when both methods are used together, indicating that this is an effective method for lift force reduction.

Design by adaptive infill sampling with multi-objective optimization for exploitation and exploration

A surrogate-based design optimization with an adaptive sampling technique based on the innovative infill sampling criteria (ISC) is developed, where key issues are mathematically formulated on where in the design space and how many sample points are infilled to guarantee desirable accuracy at minimal computational cost. The ISC developed in the study involve multi-objective optimization (MOO) to determine infilling sample points separately for exploitation and exploration of the design space, which represent the global and the local accuracy of the surrogate model, respectively. The infill samples are found by the MOO on the Pareto front in terms of variance of estimation uncertainty and a predicted function value. To dynamically control the location and the count of the infilling points per iteration for the sample infilling, two criteria of the balancing and the dynamic switching approach are developed.The balancing approach selects infill sample points equally from the two far ends of the Pareto front as well as on the middle of it. The dynamic switching approach uses cut-off variance of uncertainty estimation to dynamically switch the ISC exclusively from the exploration to the exploitation, or vice versa adaptively to the accuracy of the model. Solution optimality and computation efficiency of the present method for the EGO, are compared for two analytic functions with those of the EGO with a conventional, multi-point Expected Improvement (q-EI) ISC and a Latin Hypercube Sampling (LHS) method. The gradient-based optimization without using the surrogate model was also carried out independently for the comparison purpose on the solution accuracy and efficiency. The proposed method shows the greatest efficiency, requiring the smallest number sample points in the training set and becomes even compatible with the gradient-based optimization method. For the practical design problem, high-life multi-element airfoil is chosen to maximize a lift coefficient with non-increasing drag constraints. The proposed method showed about 18% increase of lift force.

Numerical investigations of three-dimensional flows around a cylinder attaching with symmetric strips

Minor changes to the surface of a cylinder can significantly influence the associated flow characteristics. This paper describes a three-dimensional numerical investigation of a cylinder attached with symmetric strips in a uniform flow at Re=3900. The location (20°≤α≤130°), thickness (0.01D≤t≤0.08D), and coverage (5°≤β≤100°) of the strips are selected for study. Two flow modes, patterns A and D, can be characterized in the flow around this passive turbulence control cylinder by their vortex enhancement and suppression effects. The Strouhal number of pattern A is very close to the response of a smooth cylinder. For cylinders with the upper strip located at α≤90° from the front stagnation point, the lift force correlation in the spanwise direction is enhanced by the forced flow separation. When the front edge of the upper strip is fixed at α=60°, the thickness of the strips plays a vital role: the drag and lift force increase linearly as the thickness increases, whereas the Strouhal number and the vortex shedding frequency decrease.

A novel V-shaped layout method for VIV hydrokinetic energy converters inspired by geese flying in a V-Formation

A novel bio-inspired V-shaped layout is proposed to enhance energy conversion performance for VIV hydrokinetic energy converters. The layout method is inspired by wild geese flying in a V-formation. In this paper, 2-dimensional RANS equations with the SST k-ω turbulence model are used to simulate the VIV responses at various distances. The numerical method is verified by comparing with experiments. Two-cylinder and five-cylinder V-shaped layout are investigated separately to analyze multi-cylinder interactions. The main conclusions are: (1) The VIV response of the upstream cylinder is suppressed due to the blockage effect when at small distance. (2) The energy recovery area of downstream cylinders is identified and located on the edge of the wake. (3) In the energy recovery area, the enhancement mechanism of this novel layout is the upstream and downstream vortices coalesce, resulting in a significant increase in lift force on the downstream cylinder. (4) The converted power of downstream cylinders in the energy recovery area is increased by up to 6.3%–8.4%. Future work is directed to optimize the distance among the cylinders for optimal energy conversion.

Effect of aerodynamic force change caused by car-body rolling on train overturning safety under strong wind conditions

Understanding the relationship between car-body vibration and train aerodynamic forces is very important for developing a reasonable operation plan when the train passes through the complex terrain under strong wind conditions. In this study, car-body vibration under strong wind conditions was initially investigated with a full-scale test. Then the train aerodynamic forces for different rotation configurations with a train speed of 250 km/h and a wind speed of 25 m/s were further studied using a Computational Fluid Dynamics simulation. The results revealed that the car-body vibration was primarily a low-frequency and large-amplitude rolling and transverse coupling motion in windy conditions, and the roll angle of the car-body with respect to the bogie frame was greater than that of the bogie frame with respect to the track. The train aerodynamic force coefficients are sensitive to the car-body rolling motion in windy conditions. When the car-body rolling from the windward side to the leeward side, the significant reduction in the negative pressure at the bottom of the car-body was the dominant reason for the train lift force increase, and the effect of the aerodynamic force change caused by car-body rolling on the train overturning risk was not significant.

Role of synthetic jet control in energy harvesting capability of a semi-active flapping airfoil

The role of synthetic jet (SJ) control in the energy harvesting capability of a semi-active flapping airfoil is numerically investigated in this study. An elliptic airfoil with ratio of 8, which is placed in a two-dimensional laminar flow, is employed to harvest energy from the flow field. The airfoil undergoes an imposed pitching motion, and then an induced plunging motion can be achieved. A pair of SJs with the same frequency and strength is integrated into the upper and lower surfaces of flapping airfoil. As a result, the flow field around the airfoil would be modified by the SJs. At the Reynolds number of 1100 and the pitching axis location of one-third chord, the effects of the inclined angle between the jet direction and the chord line, the phase angle between the SJs and the pitching motion as well as the position of SJ slot on the energy harvesting capability are systematically examined. With the help of SJs, it is demonstrated that the enhancement of energy harvesting efficiency can be achieved. Based on the numerical analysis, it is indicated that the jet flow on the airfoil surfaces with suitable working parameters, which results in the obvious increase of lift force, can benefit the energy extraction performance of the flapping airfoil.

Study on Influence of Environmental Parameters on Dynamic Stall Characteristics of Wind Turbine Blades

Wind turbines in complex environments could encounter dynamic loads that deviate from design values, while the dynamic stall problem could reduce the reliability and safety of wind turbines. In order to accurately evaluate the aerodynamic characteristics of wind turbine blades, the influence on the dynamic stall characteristics of wind turbine airfoil under complex wind farm environmental factors is studied. The variation law of lift coefficient under different working conditions is obtained, and the pressure coefficient and flow field distribution with times are given. The evolution characteristics of vortex on airfoil surface are analyzed. The results show that when the unsteady effect is significant, the closed-loop area of the blades lift coefficient is gradually larger, and the angle of attack for the maximum lift is proportional to it; when the oscillation angle becomes larger, the upper and lower extreme values of the lift force increase, and the lift curve is more obvious in the shape of the oblique “$$\infty$$.” When the blade appears to be in dynamic stall, the lift coefficient increases quickly and has a hysteresis effect. The maximum increase is up to 46.15%, and the hysteresis effect occurs. The instability of the shear layer, the formation and quenching of the trailing edge vortex are the main causes of the hysteresis effect for the blade lift coefficient. Reasonable evaluation of its value is of great significance for wind turbine blade design in complex wind farm environment.

Numerical Investigation of Lift Force Increase in a Hovercraft by Changing the Geometrical Parameters of Flow Transfer Part and Air Channel

Numerical Investigation of Lift Force Increase in a Hovercraft by Changing the Geometrical Parameters of Flow Transfer Part and Air Channel

Study of Round Jet Impingement in Proximity of Ground and Water Surface

The goal of this paper is to study the difference in aerodynamics and flow physics of an air jet impinging on a solid ground and a water surface at low subsonic Mach numbers with different heights above the ground. Single air jet impingement on solid ground and water surface with baffle plate around the jet exit is simulated by employing the incompressible Reynolds-averaged Navier–Stokes equations with turbulence model, and volume of fluid tracking method for air–water interface. The simulation results show that, at the same (small) impingement height, there is increase in lift force on the baffle plate due to impingement on the water surface, which is contrary to the lift loss experienced in the presence of solid ground. Furthermore, in case of impingement on water surface, the simulation results at the same velocity but at different heights above the water surface show that the lift increase at lower height tends to become smaller as the height above the water surface increases, finally showing a loss in lift as the jet exit moves from small distance to very large distance.

Static and dynamic stall control by NS SDBD actuators

In the last two decades, nonequilibrium plasmas have demonstrated the ability to affect a variety of flows of aeronautical interest, including mitigation of stall on steady airfoils as it is a nonintrusive, active control method. Plasma actuation also shows promise to address dynamic stall in rotorcraft because of the absence of moving parts, extremely lightweight and flexible assembly, extremely fast turn-on time and wide range of actuation frequency. In this paper, we summarize the recent advances in flow control both for static and dynamic flow separation control using nanosecond pulsed surface dielectric barrier discharge plasma devices. Topics of discussion include the mechanism of NS plasma actuation, results of experiments at different Reynolds and Mach numbers, dynamics of flow reattachment, and boundary layer separation control on a pitching airfoil. The common issue of retreating blade stall, as experienced in helicopters, was also considered in this study by experimenting with a reverse flow over an airfoil. Increases in lift are demonstrated for separated flows for reduced frequencies up to k = 0.05, angle of attack up to 32°. Instantaneous increase in lift with plasma control was demonstrated to be up to 55%. The 20% integral lift force increase of a helicopter model in hover mode using a constant engine power is also demonstrated with NS SDBD actuation of the flow on the rotating blades.

Aerodynamic Performance of Trains with Different Longitudinal Section Lines under Crosswind

Aerodynamic analysis of trains with different longitudinal section lines under crosswind was studied using the CFD methods in this paper. The slopes of five different longitudinal section lines are 0.58, 0.54, 0.5, 0.46, 0.42, respectively. The results show that the drag coefficient increases 27.6% and the lift force increases 12.3% with the slope of longitudinal section line increases from 0.42 to 0.58, but the lateral force varies little. The drag coefficient and lift force increase logarithmically with the slope of longitudinal section lines. With the increase of the slope of longitudinal section line, the surface pressure coefficient of the windward side is basically unchanged, but the surface pressure coefficient of the leeward side is decreasing. Comparing the flow field around the train, it is found that the longitudinal section line has no obvious influence on the flow field structure of the lead car, the vortex of the leeward of the middle car and the tail car increases with the slope of longitudinal section line increases.

Wake effect on a semi-active flapping foil based energy harvester by a rotating foil

The wake effect on a semi-active flapping foil based energy harvester by a rotating foil is numerically investigated in this work. A NACA0015 airfoil, which is placed in a two-dimensional laminar flow, is adopted to harvest energy from the flow. It executes a forced pitching motion, which subsequently induces a plunging motion. An auxiliary smaller foil pitching about its center is arranged in the upstream of the flapping foil. As a consequence, the generated wake influences the dynamic performance of the flapping foil. At a Reynolds number of 1100 and the position of the pitching axis at one-third chord, the effects of the distance between two foils, the phase difference between the rotating motion and the pitching motion as well as the frequency of pitching motion on the power extraction behavior are examined in detail. It is shown that compared with the single flapping foil, the efficiency improvement of overall power extraction for the flapping foil together with the rotating foil can be obtained under some specific conditions. Based on the numerical analysis, it is demonstrated that the wake effect, which leads to the increase of lift force and the decrease of torque, can benefit the overall power extraction of the flapping foil.

The estimated aerodynamic characteristics of a closed carrying surface finite element method

The article the calculation of the basic aerodynamic characteristics of a closed carrying surface using FEM. The modeling of flow around the object of research by using the finite element method having higher accuracy. Compliance with the results of FEM calculation and the results of physical experiment for aircraft of various schemes repeatedly confirmed in practice, aerodynamic design, which is clearly represented in the works. Polar CLS presented in the form of dependency, suggest that the proposed new form of the CLS without any additional boundary layer control means provides a steady airflow around the bole in a much wider range of angles of attack than the wing of the aircraft of the classical scheme. The increment of the resistance caused by the increase in lift force, certain FEM and PVM is almost identical. This allows for a simpler and less demanding of computing means PVM for calculating the aerodynamic characteristics of complex layout.

Self-Noise Effects on Aerodynamics of Cambered Airfoils at Low Reynolds Number

Aerodynamics of cambered airfoils are investigated numerically, using a NACA four-digit series of 6% thickness at low Reynolds number and moderate Mach number , by focusing on the relation of aeroacoustic effects and hydrodynamic flow unsteadiness. Two-dimensional numerical simulations show that the onset of an acoustic feedback loop leads to an abrupt increase in lift force. Associated with the feedback process, the evolution of two-dimensional vortices in the suction-side boundary layer shifts a separation bubble toward the leading edge, which causes a relatively steep pressure recovery near the trailing edge. Through a parametric study on airfoil shape, the aerodynamically favorable feature of aft camber is further enhanced with the presence of an acoustic feedback loop. In addition, the aft camber airfoil successfully forms a laminar separation bubble in three-dimensional calculations at the present Reynolds number, developing transitional behavior on the suction side, supposedly prompted by the airfoil tones. Although the boundary layer shows three-dimensional complexity, still the formation of an acoustic feedback loop is strongly suggested, via the comparison of spanwise correlations.