Lift-drag Ratio Research Articles

Optimizing Airfoil Aerodynamic Characteristics by Using Proposed CSA-KJ Method

Combined with the cuckoo search algorithm (CSA) and the Kutta–Joukowski (KJ) theorem, a CSA-KJ optimization method was proposed to improve the airfoil aerodynamic characteristics in this work. The fourth-order constant-free polynomial function was employed to describe the airfoil profile. The KJ loop lift of the airfoil was taken as the objective function, and the CSA was applied to iteratively update this method, which was used to optimize the NACA4412 airfoil. The results demonstrate that the optimized effect of the CSA-KJ method on the lift-drag ratio becomes increasingly more significant with the increase of incoming wind speed, and it has the best performance at an angle of attack of 0°. Compared with the NACA4412 airfoil, the average and the maximum lift-drag ratio coefficients of the CSA-KJ4412 airfoil have increased. Meanwhile, the pressure difference distribution is improved, and the aerodynamic characteristic is better. From this, it can be seen that the CSA-KJ method can provide an effective way to optimize the aerodynamic performance of other airfoils.

Lift Airfoils Close to the Airfoils in a Flow with the Maximum “Critical” Mach Numbers

The lift airfoils close to the airfoils optimal with respect to the critical Mach numbers М* of two-dimensional bodies optimal with respect to М* are constructed using the direct method. Their almost zero wave drag coefficients сх remain the same not only at the free-stream Mach numbers М0 which are lower than М* but also at М0 perceptibly higher than М*. These new lift airfoils differ from the supercritical lift airfoils whose сх grow extremely rapidly when М0 becomes higher than the designed values. At identical thicknesses and М0 = М* the supercritical lift airfoils implement the greater lift coefficients су. However, due to the difference in the behavior of сх at М0 which are higher than the designed ones, the lift-drag ratio of the supercritical airfoils can become lower for the ratio of су not to сх, but even to the coefficient of total drag.

Correction of a Strapdown Inertial Navigation System During Descent in the Atmosphere

The article deals with the problem on determining the angular position during descent on an apparatus with low lift-drag ratio. A solution is presented using the least squares method, which reduces to determining the orientation quaternion using a system of linear algebraic equations. The proposed method is based on the algebraic properties of quaternions. A vibrating string accelerometer and a fiber optic gyroscope are used to obtain acceleration and angular velocity measurements. Data on the speed and coordinates of the device are available according to the readings of the satellite navigation equipment.

Aerodynamic Interaction between a Rotor and a Wing on Compound Helicopter in Forward Flights

This paper investigates the influence on aerodynamic performance of the rotor/winged-body configuration due to change of advance ratio and the lift share ratio between a rotor and a wing through numerical simulations. A computational model of compound helicopter is constructed with a main rotor of UH-60A helicopter and a winged-body configuration where the fuselage is designed by JAXA and the wing is rectangular. Flight conditions at various cruising speed corresponding to an advance ratio of 0.1 to 0.7 is simulated. As a result, the flow around the wing is deflected in a direction of decreasing angle of attack. This trend becomes stronger as the advance ratio decreases. The lift share of the rotor increases between 0.05 and 0.08 at the advance ratio of 0.1 to 0.7. The total effective drag coefficient increases due to the aerodynamic interaction, the increase of the rotor effective drag coefficient is greater than that of the winged-body. The drag coefficient of the wing of the winged-body becomes negative at the advance ratio of 0.1 and 0.15. The rotor effective drag coefficient and the winged-body drag coefficient increase significantly at high advance ratio. Therefore, the total effective lift-to-drag ratio decreases as the advance ratio increases, and it decreases by 18% at the advance ratio of 0.7. In addition, the advance ratio of the maximum total lift-drag ratio is smaller than that designed without aerodynamic interaction between the rotor and wing-body.

Simulation research on hydrodynamic performance of wave glider airfoil

To improve the wave energy utilization rate of the wave glider as the research goal, research on the improvement of the hydrodynamic performance of the airfoil of the wave glider was carried out. First, we extract the bionic airfoil A and the standard airfoil C and draw the design airfoil B and the regular airfoil D. Secondly, using ANSYS Fluent, the hydrodynamic performance of the four airfoils under different inflow velocities and angles of attack is studied. Finally, data analysis shows that under the same attack angle, the lift coefficient, drag coefficient, and lift-drag ratio of the airfoil are not affected by the incoming flow velocity. Under the same incoming flow velocity, when the attack angle is 5°-13°, the bionic wing Type A is slightly better than the design airfoil B, obviously better than the standard airfoil C and regular airfoil D. Considering the hydrodynamic performance and material cost, it can be seen that the B airfoil is the optimal airfoil in this study. The comparative analysis of four airfoils provides a research basis for improving the wave energy utilization rate of the wave glider.

Optimization of the Bionic Wing Shape of Tidal Turbines Using Multi-Island Genetic Algorithm

In this study, we improved the energy acquisition efficiency of tidal turbines with bionic airfoils by optimizing the seagull, long-eared owl, sparrowhawk, and two-dimensional airfoils, thereby obtaining a better lift–drag ratio. We used Isight software to integrate the Integrated Computer Engineering and Manufacturing (ICEM) software and used Fluent simulation software, batch operation file, and multi-island genetic algorithm to maximize the lift–drag ratio as the objective function for optimizing the original airfoil. The optimized upper airfoil profile was distributed upward from the starter wing, and the thickness of the upper wing was the greatest. Meanwhile, the lower airfoil profile was thinner and more curved. The thickness of the three airfoils was distributed backward from the front of the wing, with the maximum thickness at the front, and the maximum camber was distributed backward from the front. The three optimized wings exhibited a maximum lift–drag ratio at an angle of attack of approximately 5°, with the sparrowhawk wing having a maximum lift–drag ratio of 80.87 at an angle of attack of 6°, the seagull wing having a maximum lift–drag ratio of 76.82 at an angle of attack of 4°, and the long-eared owl wing having a maximum lift–drag ratio of 68.43 at an angle of attack of 5°.

Analysis on aerodynamic performance of mine horizontal axis wind turbine with air duct based on breeze power generation

Developing wireless sensor networks based on breeze power generation is of great significance to promote the development of intelligent mines. In this paper, a small horizontal axis wind turbine with air duct was designed for the underground environment of coal mine. The aerodynamic performance of the wind turbine was analyzed by constructing a three-dimensional solid model of the wind turbine. The results show that under the condition of low wind speed underground, the air flow entering the air duct in the outer basin is accelerated and rectified, and the velocity near the impeller increases. The pressure value at the front end of the blade is the largest and the pressure value at the rear end of the blade is the smallest. A certain range of negative pressure zone is formed at the rear end of the impeller, which is conducive to the operation of the wind turbine. After the air flow passes through the impeller, the speed decreases and the speed is the lowest near the rotating shaft of the impeller. Inner basin: the air flow velocity increases gradually along the radial direction of the impeller centre. The pressure at the front end of the blade is greater than the atmospheric pressure, which is conducive to promoting the stability and sustainability of the wind flow and facilitating the operation of the wind turbine. When the wind speed reaches the rated wind speed of the wind turbine, the power, torque and output power of the wind turbine increase, which can provide effective power generation. Compared with other aerofoils, NACA5505 air foil has higher lift drag ratio and thrust coefficient, and is more suitable for downhole low wind environment. Compared with the wind turbine without air duct, the wind turbine with air duct has higher wind energy conversion and output power at low Reynolds number, which verifies the feasibility of the wind turbine with air duct. In the case of low incoming wind speed and no expansion of the size of the wind turbine, improve the output power of the wind turbine and meet the intrinsic safety requirements of the wind turbine. The research can provide technical support for the continuous power supply of wireless intelligent sensors in the mine environment, and provide scientific basis for mine safety production and fine management, which has long-term economic and social benefits.

Comparative analysis and manufacturing of airfoil structures suitable for use at low speeds

An aerodynamic technique to calculating lift and drag coefficients is one of the required instruments in the wing design process. During the last decades, several tools and software have been developed according to aero-dynamics and numerical methods. Nowadays, aeronautical architecture requires many calculations. Today’s techno-logists use a variety of simulation techniques to avoid a expensive model testing. This paper explains how wing profiles can be modelled using ANSYS Fluent and tested by low-speed tests considering experimental literature re-sults. With the selected wing profile, the geometry is shaped in two dimensions and designed in three dimensions. Computational fluid dynamics (CFD) was adopted as the method for studying wing profiles. Wing profiles created at 0 to 20-degree attack angles are calculated in the simulation area equal to the actual wind tunnel scale, and equations are solved using the RNG k-Epsilon turbulence model. The process of developing the grids was realized with Ansys Mesher software. The solution stage and the result show operations were carried out with the CFD Post software. The study of the low velocity and high transport wing profiles, the drag coefficient, the lift coefficient, and the effect on the lift-drag ratio were studied using a numerical procedure. After determining the high efficiency of wing profi-les, production of a selected profile began with a static examination.

Numerical study of transient aerodynamic forces acting on a ski jumper considering dynamic posture change from takeoff to landing

ABSTRACT This study was designed to develop a computational fluid dynamics (CFD) method for unsteady analysis of a series of ski jump movements with attitude changes, and to analyse the aerodynamic characteristics of an expert jumper over the entire ski jump movement. Two ski jumpers participated in this study. A sensor-based motion capture suit was used to capture the jumper’s posture during the actual ski jump. A three-dimensional computer graphics animation was created by superimposing the joint angles obtained from the motion measurements of the 3D shape of the athlete. The unsteady aerodynamic forces acting on the ski jumper, from the takeoff to the landing, were then calculated using CFD. A time-varying spatially uniform flow was specified as the inflow boundary condition of the computational domain. The results indicated that both the lift and drag forces of the expert jumper increase rapidly during the initial flight when the jumper’s posture changes drastically. Thereafter, drag force decreased considerably, but the decrease in the lift force was less drastic. Later in the flight phase, the lift force acting on the expert jumper increased, and throughout the flight phase, the lift-drag ratio of the expert jumper remained higher than that of the unskilled jumper.

Numerical Modeling of Surface-Piercing Flexible Hydrofoils in Waves

_ Hydrofoils made of metal alloys were broadly used on high-speed boats in the past. Nowadays, much lighter hydrofoils made of composite materials are finding increasingly more applications on sailing yachts and powerboats. However, these hydrofoils are usually rather flexible, and their design requires computationally demanding analysis, involving hydroelastic calculations. In this study, exploratory high-fidelity simulations have been carried out for surface-piercing hydrofoils in unsteady conditions with help of a computational fluid dynamics solver for fluid flow coupled with a finite element solver for the foil structure. To model unsteady foil deformations, the morphing mesh approach was utilized, and the volume-of-fluid method was applied for multiphase flow simulations. The computational setup, as well as verification and validation study, is described in this paper. Three hydrofoils of different stiffness, including a perfectly rigid foil, were simulated in both calm water conditions and regular head waves. Representative examples of foil deflections and wave patterns, as well as time-dependent structural and hydrodynamic characteristics, are presented. Introduction Hydrofoils are efficient lift-generating devices intended for application in water flows. Hydrofoils have streamlined shapes, and when operating at small incidence angles, they can produce high lift forces at relatively low drag, when moving in a certain speed range. Due to this ability, hydrofoils and their derivatives are commonly used as control and propulsive devices, e.g., as rudders, fins, and propeller sections. In the second half of the last century, hydrofoils found broad applications on fast boats, such as passenger ferries and military ships (McLeavy 1976; Matveev & Duncan 2005). These craft were able to achieve high speeds at lift–drag ratios (LDR) around 12–15, significantly higher than LDR of other hulls, such as planing boats. However, due to rather limited favorable operational conditions with regard to speed and payload, popularity of hydrofoils somewhat receded. One of drawbacks was that hydrofoils were usually made of metal alloys, thus being relatively heavy and difficult to service.

Study on heat reduction and lift-to-drag ratio increase of two-dimensional wedge-shaped waverider blunt leading edges and high pressure capture wing[1] combined configuration

In this paper, the aerodynamic and aerothermal performance of the simplified two-dimensional wedge-shaped waverider bluntness leading edge and high pressure capture wing(HCW) combined configuration in a hypersonic continuous flow basin is numerically simulated by the Computational Fluid Dynamics (CFD) method, the flow field structure of the model is analyzed, and the law of anti-thermal rise is revealed. The main contents of the study include the surface heat flux and lift-drag ratio characteristics of the bluntness leading edge under different bluntness radii, the lift-to-drag ratio, and surface heat flux characteristics of the composite configuration of the bluntness leading edge and the high pressure capture wing under different bluntness radius. Within the scope of the study: 1. The larger the bluntness radius is, the more effective it is to reduce the heat flux of the head. When the bluntness radius is 2mm, the decrease is about 82.5%;2. The larger the bluntness radius is, the more serious the lift-drag ratio decreases. When the bluntness radius is 2mm, the lift-drag ratio decreases by about 72.4%;3. The combined configuration of the bluntness leading edge and the high pressure capture wing can effectively reduce the head heat flux under the premise of ensuring a certain lift-drag ratio. The optimal bluntness radius is 1mm, the head heat flux decreases by about 76% and the lift-drag ratio only decreases by 24%.

Study on aerodynamic force and aerothermal effect of two-dimensional wedge wave rider with different passivation shape of the head

With the rapid development of space technology, hypersonic vehicles flying at altitudes of 20-100 km near space are showing more and more important application value, and how to solve the serious aerodynamic heating problem caused by hypersonic vehicles in the process of flight is the focus of current research. In this paper, the simplified two-dimensional wedge-shaped waveride is treated with the passivation leading edge by the Computational Fluid Dynamics (CFD) method, and the aerodynamic and aerothermal properties of the hypersonic continuous flow basin are numerically simulated. The flow field structure of the model is analyzed, and the law of heat-resistant rise is revealed. The research contents mainly include the characteristics of body head heat flux and body lift-drag ratio under different passivation shapes. Within the research scope: 1. The larger the passivation radius, the more effective it is to reduce the head heat flux. When the passivation radius is 2 mm, the reduction is about 82.5%. 2. The larger the passivation radius, the more serious the lift-drag ratio reduction. When the passivation radius is 2mm, the maximum reduction is about 72.4%; 3. The four passivation leading edge modes have the best thermal protection effect when the passivation radius R is the same, and the lift-drag ratio of the Bezier curve passivation leading edge mode is the largest.

Surrogate-assisted hierarchical learning water cycle algorithm for high-dimensional expensive optimization

Excessive function evaluations are the main obstacle preventing the application of metaheuristic algorithms to expensive real-world problems. Although many surrogate-assisted metaheuristic algorithms have been proposed to tackle this challenge, most of them still suffer from low prediction accuracy on high-dimensional problems. This article presents a surrogate-assisted hierarchical learning water cycle algorithm (SA-HLWCA) for high-dimensional expensive optimization problems. SA-HLWCA utilizes two searching modes, namely, global search and local search, to cooperatively search for the optimal solution. A global search is conducted by a surrogate using a global diverse subset and aims to locate promising optimal areas. A local search is conducted by a surrogate built in the neighboring region of the current best and aims to refine the optimal solution. To validate the performance, comprehensive studies of the impacts of major components of SA-HLWCA are conducted. The proposed algorithm is then compared with three state-of-the-art algorithms on a series of tests on problems that range from 20 dimensions to 100 dimensions, and the results show that SA-HLWCA performs better in terms of both effectiveness and robustness. In addition, SA-HLWCA is applied to the shape optimization of a blended-wing-body underwater glider (BWBUG), and the lift-drag ratio of the optimized shape is improved by 7.66% compared with that of the initial shape.

Aerodynamic Analysis of Large Aspect Ratio Parafoil

Large aspect ratio parafoils are more attractive compared with moderate ones less than 3.5, since they either improves load-carrying capacity with the same aero-dynamical area or decreases taxing speed with the same load. Based on its original airfoil, one open-source elliptical parafoil with 4.7 AR is modified while scaling the canopy geometric parameters, then CFD simulations, solving the incompressible Reynolds time-averaged Navier-Stokes equation with the (SST) K-ω turbulence model in the finite volume method, are adopted to analyze its aerodynamics in forward taxing mode as well as steering mode with lateral wind. With the numerical simulation results of this canopy, lift and drag are analyzed according to their attack angle profiles for taxing. The steering mode with the deflection of one-side flap increases the drag coefficient significantly, even it raises its lift simultaneously, reduces the lift-drag ratio, and generate rolling and yaw moments; The rolling moment due to lateral wind during steering mode has two phases of rising linked by a short straight line when sideslip angle increases, while yaw moment increases to a peak value then reduces, finally followed by a relatively stable trend. Compared with the above two moments, the pitching moment changes moderately with the increase of the sideslip angle, although it has an overall decreasing trend; The simulation of the modified canopy provides a calculation basis for its following manufacture and dynamical modelling.

Modeling and Simulation of Flight Profile and Power Spectrum for Near-Space Solar-Powered UAV

Currently, several solar-powered unmanned aerial vehicles (UAVs) have achieved 24 h uninterrupted cruise. However, models that can cruise for weeks or even months without interruption are in the minority. The technological progress requires the improvement of subsystems and also depends on the accurate planning of flight profile and power spectrum in a long working cycle. Combined with the test data obtained during the development of a solar-powered UAV, this paper establishes systematic mathematical and physical models of aerodynamic, energy, and propulsion systems, which can reflect the change in performance parameters with flight conditions and the performance attenuation with time. Further, a track control strategy based on the principle of maximum energy utilization is proposed, and the energy balance model of each flight stage is established. On the basis of the strategy, the typical flight profile and power spectrum of a solar-powered UAV are analyzed. Finally, the input parameters are decomposed into task parameters (takeoff time window, flight season, flight latitude, takeoff weight) and performance parameters (lift–drag ratio, secondary battery density), and their effects on mission feasibility are studied respectively. The research methods and conclusions of this paper have reference significance for the mission and track planning of solar-powered UAVs.

Cooperation of Trailing-Edge Flap and Shock Control Bump for Robust Buffet Control and Drag Reduction

At transonic flight conditions, the buffet caused by the interaction between the shock waves and the boundary layers can degrade an aircraft’s aerodynamic performance and even threaten its safety. In this paper, the shock control bumps, originally designed to reduce the wave drag at cruise speeds, are applied to enhance the robustness of the closed-loop buffet control system using the trailing-edge flap. For the OAT15A supercritical airfoil, a closed-loop buffet control system is first designed with a feedback signal of lift coefficient. Then, the shock control bumps designed for drag reduction are integrated into the active buffet control system. The results show that the closed-loop flap control can be greatly enhanced by coupling with the shock control bumps. At the steady state under control, the shock control bumps can slightly increase the airfoil lift–drag ratio. More importantly, the ranges of control parameters that can effectively suppress the buffet are significantly enlarged with the help of the bumps; thus, the robustness of the control system is greatly enhanced.

Research on the Hydrodynamic Performance of a Horizontal-Axis Tidal Current Turbine with Symmetrical Airfoil Blades Based on Swept-Back Models

For the design of a horizontal-axis tidal current turbine with adaptive variable-pitch blades, both numerical simulations and physical model experiments were used to study the hydrodynamic performance of symmetrical airfoil blades based on backward swept models. According to the lift–drag ratio of symmetrical airfoils, variable airfoil sections were selected for each part of the blade in the spanwise direction. Then, three kinds of blades were designed by using different swept-back models from wind turbines. A rotation model with a multi-reference frame was employed to conduct a three-dimensional steady numerical simulation of the turbine model based on the CFD method. The axial thrust and energy-capturing efficiency under different tip speed ratios, as well as the corresponding starting torque under different flow rates, were analyzed. The simulation results indicate that model 2 has optimal start-up performance, and model 3 has the largest power coefficient. The thrust coefficient of model 1 is the smallest. In all, model 2 has better comprehensive performance. The experiments of model 2 show that it has suitable hydrodynamic performance to capture bidirectional energy via passively variable pitch. This research provides an important solution for the design and optimization of horizontal-axis turbines to harvest bidirectional tidal current energy.

Design optimization of a blunt trailing-edge airfoil for wind turbines under rime ice conditions

A new optimization method is developed for the design of a blunt trailing-edge airfoil for wind turbines under rime ice conditions. The parametric representation of the airfoil is given using the profile integration theory and B-spline function. The rime ice shape from wind tunnel tests is fitted using a linear interpolation algorithm with equidistant and equiangular steps to preserve the same number of ice shape feature points. The blunt trailing-edge thickness and distribution ratio on the upper side of the middle arc are included in the design variables. The optimizer, based on the Bare-Bones Multi-Objective Particle Swarm Optimization (BB-MOPSO) algorithm integrated with ICEM-CFD and FLUENT software, seeks the solutions maximizing the lift coefficient and lift-drag ratio. A new airfoil NACA0012BT (with BT denoting the blunt trailing-edge) with the trailing-edge thickness of 2.2004 %c (with c denoting the chord length) and distribution ratio of 1:55.8482 is obtained, and the lift and drag coefficients, lift-drag ratios, pressure distributions, and flow characteristics are investigated using the Computational Fluid Dynamics (CFD) method. Significant improvements of the NACA0012 airfoil design are achieved in this process, confirming that the developed method constitutes a valuable tool for designing and optimizing the wind turbine airfoil operating in icing conditions.

Numerical Calculation Method of Spanwise Icing Characteristics and Performance Loss of Three-Dimensional Vertical Axis Wind Turbine Blades

Most icing studies use 2D or quasi-3D models, ignoring the effects of blade span and tip icing. In this paper, a new model for predicting 3D vertical axis wind turbine blades icing by supplementing the blade span is established, the icing characteristics of blades under multiple working conditions are simulated step by step from the time scale, and the unsteady icing laws are compared and analyzed. Ice properties and surface temperature distribution determine the corresponding deicing power. The analysis results show that the unfrozen water film flows in the spanwise direction of the blade, resulting in a smaller icing limit on the pressure surface than the two-dimensional model, which indicates that the chordwise anti-icing structure can be set in a small range. At the same time, the annular ridge ice formed at the end of the blade slows down the reduction rate of the lift-drag ratio of the blade, effectively reducing the influence of the leading edge ice shape on the aerodynamic performance of the blade. Finally, the critical ice melting power density required to reach equilibrium temperature at the leading edge of the blade is reduced by about 11% compared to the trailing edge due to the increased thermal resistance of the gas-to-blade matrix interface by the ice layer.

Parametric research and aerodynamic performance analysis of wind turbine airfoil with added flap

A self-popped up flap is added to the airfoil (S809) suction surface to improve aerodynamic performance under large angle of attack (AOA) inspired by the slightly popped up feathers on the trailing edge of a bird’s wing. The response surface methodology (RSM) optimization of H, D, and θ is conducted. The lift–drag ratio of an airfoil is taken as the optimization response target, and the Box–Behnken design is adopted to design the experiment scheme for H, D, and θ. Multivariate quadratic polynomials are used to carry out equation regression analysis on the combined results of 17 sample schemes, and the mathematical surrogate model between the flap structure parameters and the airfoil lift–drag ratio and the optimal design parameter combination of the flap structure are obtained. The clean airfoil and the airfoil with optimal flap are compared and analyzed from the static and dynamic aerodynamic characteristics by numerical simulation. The calculation results show that the optimal flap obtained by RSM increases the pressure difference between the suction and the pressure surfaces at large AOA, suppresses flow separation on the suction surface, and delays the stall AOA. The airfoil with optimal flap leads to a smaller separation vortex and wake vortex, therefore delaying the dynamic stall effect.