Design Lift Coefficient Research Articles

Design of Hybrid-Laminar-Flow-Control Wing and Suction System for Transonic Midrange Aircraft

Hybrid laminar flow control (HLFC) has shown significant promise in the viscous drag reduction of aircraft. However, the use of HLFC for commercial applications requires further simplification. The current study proposes tools for the conceptual design of transonic HLFC wing and suction system. In the first part of the study, airfoil sections for the wing are optimized for minimum total drag using a multi-objective genetic algorithm approach at six spanwise locations. The induced drag of the wing is estimated using a vortex lattice method solver. In the second part of the study, suction system design is performed using ASPeCT, an in-house solver for HLFC system design. A simplified inner structure for the suction system is proposed, which can be integrated easily within the wing structure. A total drag penalty approach is proposed to establish a tradeoff between matching the target suction distribution and the complexity of the suction system. Finally, the additional weight and off-design performance of the suction system are analyzed for a ±0.1 change in the design lift coefficient. A maximum fuel reduction of 7% can be expected with the HLFC system taking into account the additional weight added and power off-take from the engine.

Experimental Flutter Analysis over Different Selected Wing Planforms by Varying the Wing Cross Section Geometry

Flutter is a phenomenon that occurs in structures which are subjected to aerodynamic forces. As the wing model flies at increasing speeds and increasing angle of attack the vibrations get increased and the frequency of these modes coincide with each other which leads to resonance, this is called Flutter and this may lead to catastrophic failures in the aircraft flight. An appropriate wing model design includes various parameters that need to be selected according to the wind-tunnel test conditions. The material used for skin is monocot, spars are made of aluminium, ribs are made of balsa wood. We follow an iterative approach in which angle of attack and true airspeed are constant per iteration. In the present note, parameters we are going to use are design lift coefficient and location of maximum camber, the flutter response of the wing models is detected experimentally with the help of accelerometers placed at the leading edge and trailing edge of the aero elastic models. The aero elastic models we use in the present experiment have two degrees of freedom, these wing models with accelerometer setup are placed in the test section of the wind tunnel where Arduino UNO gives the code to encrypt the flutter response to save the values from each iteration; by the observation of this iterative approach we can reach a conclusion. This experimental flutter analysis on aircraft wings ensures that flutter does not occur if we make sure the model strictly operates in its design limitations.

Aerodynamic Optimization and Fuel Burn Evaluation of a Transonic Strut-Braced-Wing Single-Aisle Aircraft

This paper presents an assessment of the potential fuel burn savings offered by the transonic strut-braced-wing configuration within the single-aisle class of aircraft relative to a modern conventional tube-and-wing aircraft through aerodynamic shape optimization based on the Reynolds-averaged Navier–Stokes equations. A representative strut-braced-wing aircraft is first developed through conceptual multidisciplinary design optimization based on the Airbus A320neo, with current technology levels assumed. A concept for the conventional tube-and-wing configuration is also developed to represent the Airbus A320neo as a performance baseline. Single-point aerodynamic shape optimization is then performed on wing–body–tail models of each aircraft to address aerodynamic design challenges and to provide more accurate performance estimates. Results indicate that shock formation can be mitigated from the wing–strut junction of the strut-braced wing at Mach 0.78 and a relatively high design lift coefficient of 0.750, providing an 8.2% reduction in block fuel over a 1000 n mile nominal mission when compared to the conventional tube-and-wing aircraft. Multipoint aerodynamic shape optimization is then performed to build toward a more credible estimate of fuel burn performance, with results showing a reduction in the fuel burn savings to 7.8% at the nominal design point relative to the conventional tube-and-wing aircraft to maintain a 7.6–8.0% improvement over the envelope of operating conditions, which includes design points at even higher Mach numbers and lift coefficients. These results demonstrate the viability of the transonic strut-braced-wing configuration for transport aircraft within the single-aisle class and its potential for reducing commercial fleet fuel burn.

Performance Investigation of Airfoils for Axial Flow Fans in Low Solidity Cascades Operating at High Inlet Flow Angles

Abstract Axial flow fans are usually characterized by blade sections with low solidity and high inlet flow angles. Two main approaches are followed in the preliminary design phase, to take into account blade interaction effects: the use of available airfoil cascades data (or related correlations) and that of isolated airfoil data together with interference coefficients. The working conditions of low solidity airfoil cascades with highly tangential inflow are not widely studied in the literature, leaving the designer the possibility to rely on limited cascade data or often on the use of isolated airfoil data, with the assumption of negligible interference effects. A systematic investigation of the above working conditions for airfoil cascades is performed with Reynolds-averaged Navier–Stokes simulations. Three different airfoils are used to evaluate the influence of the design lift coefficient and maximum blade thickness. The results provide a better insight into the aerodynamic behavior of airfoil sections in such operating conditions, showing that interactions cannot be neglected. The use of metamodeling coupled with computational fluid dynamics (CFD) simulations is presented as a suitable tool for treating interference effects within the fan design process. The main findings of the present work can be used as a support for design choices as well as for developing design strategies both for the fan blades and for the airfoil sections.

Research on Comparative Monitoring Method of Aerodynamic Coefficient Applied to Artificial Ice Flight Test

Abstract In the implementation of the artificial ice flight test, artificial ice shapes must be installed to the test aircraft, which reduces the aerodynamic performance of the aircraft and leads to a high risk. In order to reduce the risk of artificial ice flight test, starting from the flight test requirements, this paper proposes a real-time comparative monitoring scheme of the design lift coefficient and the actual lift coefficient of the test aircraft, and develops a comparison model of aerodynamic coefficients accordingly. Verified by the flight test data, the model can figure out reasonable design lift coefficient and actual lift coefficient, which lays a foundation for the subsequent application in the artificial ice flight test.

An Aerodynamic Design Method to Improve the High-Speed Performance of a Low-Aspect-Ratio Tailless Aircraft

This paper puts forward an aerodynamic design method to improve the high-speed aerodynamic performance of an aircraft with low-aspect-ratio tailless configuration. The method can ameliorate the longitudinal moment characteristics of the configuration by designing and collocating the key section airfoils with the constrains of fixed parameters of planform shape and capacity. Firstly, the effect of twisting the wing, fore-loading and aft-reflexing key section airfoils on the high-speed aerodynamic performance of the configuration is evaluated by high-fidelity numerical methods, and quantified by defining trimming efficiency factors. Then, a linear superposition formula is obtained by analyzing the effect rule of trimming efficiency factor, and based on the formula the design and collocation methods of key section airfoils are achieved. According to the methods, a trimmed configuration is obtained. The results of computational fluid dynamics (CFD) and wind tunnel tests show that the trimmed configuration has smaller zero-lift pitching moment and higher available lift-to-drag ratio than the initial configuration at cruise, besides the trimmed configuration achieves the design principle raised for tailless configuration, which can be described as the zero-pitching moment, cruising design lift coefficient, and maximum lift-to-drag ratio are coincident. In addition, at off-design conditions, the trimmed configuration shows favorable drag divergence characteristics, satisfactory aerodynamic characteristics at medium-altitude maneuvering condition, and good stall and pitching-moment performance at low speed state.

Design of Low-Speed Slotted, Natural-Laminar-Flow Airfoil Reproducing Transonic Behaviors

Airfoils tested at low speeds generally produce surface pressure distributions that differ substantially from those measured at transonic conditions, which in turn results in very different boundary-layer characteristics even for the same Reynolds number. A methodology is presented for mapping transonic pressure gradients to an equivalent low-speed airfoil. It is applied to the design of a low-speed, slotted, natural-laminar-flow (SNLF) airfoil intended to emulate the pressure gradients of a SNLF airfoil designed for a transonic commercial transport with a Reynolds number of 13.2 million. The on-design cruise operating condition of the original airfoil was chosen as the reference condition; however, the design lift coefficient of the new airfoil was lowered to account for both compressibility effects and suitability for low-speed wind-tunnel testing. The overall design process mirrors the development of the transonic airfoil by beginning with a single-element airfoil and then modifying it to include an aft element. An inverse design method based on conformal mapping was developed and employed to determine the necessary geometry of the low-speed single-element airfoil. Analysis of the new SNLF airfoil confirms that the design objectives were met, and the airfoil is found to be well behaved down to a Reynolds number of 1 million.

Aerodynamic Design of Megawatt Wind Turbine Blades with NPU-WA Airfoils

The NPU-WA airfoils were designed at high design lift coefficient and high Reynolds number, with small sensitivity of the maximum lift coefficient to leading edge roughness and excellent geometric compatibility. Compared to the widely used airfoils, the NPU-WA airfoils have higher lift-to-drag ratio and higher maximum lift coefficient. This paper aims to design a megawatt wind turbine blade in order to demonstrate the advantage of the NPU-WA airfoils. The distributions of chord length and twist angle for a 2 MW wind turbine blade are optimized by a kriging surrogate model-based optimizer, with aerodynamic performance being evaluated by blade element-momentum theory. Results show that compared with the baseline blade, the maximum power coefficient of the optimized NPU blade is larger, and the chord lengths at all span-wise sections are smaller, which is benefit to structural weight reduction. It is shown that the NPU-WA airfoils feature excellent aerodynamic for the design of megawatt wind turbine blades.

Design Optimization of a Multi-Megawatt Wind Turbine Blade with the NPU-MWA Airfoil Family

A new airfoil family, called NPU-MWA (Northwestern Polytechnical University Multi-megawatt Wind-turbine A-series) airfoils, was designed to improve both aerodynamic and structural performance, with the outboard airfoils being designed at high design lift coefficient and high Reynolds number, and the inboard airfoils being designed as flat-back airfoils. This article aims to design a multi-megawatt wind turbine blade in order to demonstrate the advantages of the NPU-MWA airfoils in improving wind energy capturing and structural weight reduction. The distributions of chord length and twist angle for a 5 MW wind turbine blade are optimized by a Kriging surrogate model-based optimizer, with aerodynamic performance being evaluated by blade element-momentum theory. The Reynolds-averaged Navier–Stokes equations solver was used to validate the improvement in aerodynamic performance. Results show that compared with an existing NREL (National Renewable Energy Laboratory) 5 MW blade, the maximum power coefficient of the optimized NPU 5 MW blade is larger, and the chord lengths at all span-wise sections are dramatically smaller, resulting in a significant structural weight reduction (9%). It is shown that the NPU-MWA airfoils feature excellent aerodynamic and structural performance for the design of multi-megawatt wind turbine blades.

Airfoil design for large horizontal axis wind turbines in low wind speed regions

Abstracts Low wind speed technology helps to reduce the cost of energy, but also creates huge challenge on the wind turbine blade design. To essentially address the particular blade requirements in low wind speed regions with high inflow turbulence, this study extends previous airfoil design optimization methods. Firstly, special design criteria were proposed besides traditional considerations, concerning efficiency, loads, noise and in particular the high inflow turbulence effects on the enlarged blades. Then through improved mathematic models and modified auto optimization platform, an extended airfoil design optimization framework dedicated to low wind speed sites was established. The case design results show that key features of the new airfoil tailed to low wind speed sites are effectively enhanced: the design lift coefficient and lift-to-drag ratio are fairly increased, and the maximum lift coefficient is well constrained. In addition, the acoustic parameter of the new airfoil is successfully reduced. More important is that the airfoil performance sensitivity to surface roughness and inflow turbulence intensity are evidently eliminated. These finally contribute to an improved overall performance. The rotor blade performance evaluation with the new design airfoil in further verified the case design. Results indicate the proposed framework is able to design special airfoils suited for site-specific blade requirements, contributed by the customized considerations, parameterization model, robust calculation method and global algorithms.

Optimal Hyperelliptic Cambered Span Configurations for Minimum Drag

The current study considers an analysis of hyperelliptic cambered span wing configurations, optimized for minimum drag. This study encompasses a multidimensional design optimization approach wherein the wing geometries are optimized with respect to both span load and spanwise camber to achieve minimum aerodynamic drag. A discrete vortex element method was coupled with a constrained gradient-based optimization routine to achieve these drag-optimal design configurations. Optimum drag configurations were obtained at a fixed design lift coefficient as well as a fixed bending moment constraint. Navier–Stokes simulations were also performed, which revealed an gain of 29.01 and 25.35% at design conditions, relative to an elliptically loaded planar wing for the upward and downward cant configurations, respectively. Different wake trace characteristics for the two hyperelliptic cambered span configurations were observed along with surface flow features indicating different wake vortex and boundary-layer transition behaviors for the two hyperelliptic cambered span configurations.

Optimization of Variable-Camber Continuous Trailing-Edge Flap Configuration for Drag Reduction

The variable-camber continuous trailing-edge flap is a novel control surface technology designed to serve as an aeroelastic wing shaping control device. Capable of minimizing drag throughout an aircraft flight envelope, use of the variable-camber continuous trailing-edge flap technology is examined on a flexible-wing transport aircraft configuration known as the NASA generic transport model. Drag reduction studies at various flight conditions are conducted in order to examine the performance of different flap configurations with selected camber deflection profiles. Rapid optimization of the design space is achieved by using aerodynamic–structural modeling based on a vortex lattice method coupled with transonic small disturbance and integral boundary-layer solutions. The begin cruise optimization results show that a parabolic flap deflection profile configuration with three-cambered-segments achieves the largest drag reduction of 8.4% as compared to a clean wing configuration. The configuration is used to run additional optimizations measuring performance benefits at different flight conditions including 20% fuel end cruise, a design lift coefficient, and a Mach overspeed condition. The optimization framework and initial results produce insights that can be used to refine the optimization of variable-camber continuous trailing-edge flap configurations with higher-fidelity aerodynamic tools.

Numerical simulation of VAWT on the effects of rotation cylinder

Based on Finite Element Analysis Method, studying on Vertical Axis Wind Turbine (VAWT) which is added rotating cylinder in front of its air foils, especially focusing on the analysis of NACA6 series air foils about variation of lift to drag ratio. Choosing the most suitable blades with rotary cylinder added on leading edge. Analysis indicates that the front rotating cylinders on the VAWT is benefit to lift rise and drag fall. The most suitable air foil whose design lift coefficient is 0.8, the blades relative thickness is 20%, and the optimistic tip speed ratio is about 7.

Power Properties of Two Interacting Wind Turbine Rotors

In the current experiments, two identical wind turbine models were placed in uniform flow conditions in a water flume. The initial flow in the flume was subject to a very low turbulence level, limiting the influence of external disturbances on the development of the inherent wake instability. Both rotors are three-bladed and designed using blade element/lifting line (BE/LL) optimum theory at a tip-speed ratio, λ, of 5 with a constant design lift coefficient along the span, CL = 0.8. Measurements of the rotor characteristics were conducted by strain sensors installed in the rotor mounting. The resulting power capacity has been studied and analyzed at different rotor positions and a range of tip-speed ratios from 2 to 8, and a simple algebraic relationship between the velocity deficit in the wake of the front turbine and the power of the second turbine was found, when both rotors have the coaxial position.

A new optimization approach to improve the overall performance of thick wind turbine airfoils

A crucial problem of designing thick airfoils is balancing structural and aerodynamic requirements. This paper documented a new idea to deal with the thick airfoil's design. Firstly, the relative thickness of the original airfoil was increased to enhance its structural property. Then the overall aerodynamic performance was improved by the optimization design method. Specifically, this paper put forward a mathematical model of the overall optimization employing airfoil's performance evaluation indicators which represent modern rotor blades' aerodynamic requirements of “high efficiency, low extreme load, wide range of operating angle of attack and stability with varying operating conditions”. Based on this model, an integrated optimization platform for thick airfoils' overall design was established. Through an optimization experiment, a new 35-percent relative thickness airfoil was obtained. The new airfoil was predicted with high design lift coefficient, acceptable maximum lift to drag ratio, moderate stall parameter, and desirable stability parameters. These characteristics contribute to a high overall performance which could be competent with commonly used thick DU airfoils. Lift characteristics of the new airfoil have been validated by tests. These results confirmed the proposed method has effectively balanced airfoil's complicated requirements and successfully improved the new airfoil's overall performance.

Airfoil design: Finding the balance between design lift and structural stiffness

When upscaling wind turbine blades there is an increasing need for high levels of structural efficiency. In this paper the relationships between the aerodynamic characteristics; design lift and lift-drag ratio; and the structural characteristics were investigated. Using a unified optimization setup, airfoils were designed with relative thicknesses between 18% and 36%, a structural box height of 85% of the relative thickness, and varying box widths in chordwise direction between 20% and 40% of the chord length. The results from these airfoil designs showed that for a given flapwise stiffness, the design lift coefficient increases if the box length reduces and at the same time the relative thickness increases.Even though the conclusions are specific to the airfoil design approach used, the study indicated that an increased design lift required slightly higher relative thickness compared to airfoils with lower design lift to maintain the flapwise stiffness. Also, the study indicated that the lift-drag ratio as a function of flapwise stiffness was relatively independent of the airfoil design with a tendency that the lift-drag ratio decreased for large box lengths.The above conclusions were supported by an analysis of the three airfoil families Riso-C2, DU and FFA, where the lift-drag ratio as a function of flapwise stiffness was decreasing, but relatively independent of the airfoil design, and the design lift coefficient was varying depending on the design philosophy. To make the analysis complete also design lift and lift- drag ratio as a function of edgewise and torsional stiffness were shown.

PIV and LDA measurements of the wake behind a wind turbine model

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 – 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

Performance estimation of HAWT blade using NACA airfoils

Wind energy is one of the developing resources of renewable energy. In order to increase the use of wind energy, development of wind turbine blade with higher power coefficient plays a vital role. The work being presented here is to give new design of blade for VESTAS V82-1.65MW (HAWT). In this work, NACA airfoils are used for the determination of aerodynamic performance characteristics of horizontal axis wind turbine blade. Optimal rotor theory is used here, which is simple enough and accurate enough for blade design. Four different airfoils are used to investigate the changes in performance of the designed blade. The airfoils taken are same from root to tip in every blade. The design lift coefficient taken is 1.1. A computer programme is developed to automate the entire design procedure for optimisation. Consequently after optimisation chord and twist distributions are obtained for the blade from root to tip. It is found that the elemental power coefficient of the designed blade is maximum between the interval r/R = 0.2 to r/R = 0.6. Therefore, the proposed method of new design for blade can be efficiently used for optimisation of wind turbine blade performance.

Effect of wing-box structure on the optimum wing outer shape

AbstractA new method for wing shape optimisation is presented, in which the wing shape is optimised not only for the best aerodynamic properties but also for minimum structural weight. An advanced structural sizing method for wing structural weight estimation is developed. The method is based on elementary, physics based analyses of simplified structure to determine the amount of required material to resist the applied loads. The sizing loads are determined based on the airworthiness regulations using advanced aerodynamic analysis tools. In this new weight estimation method, the effect of wing outer (aerodynamic) shape on the wing-box structural weight is taken into account. A mathematical equation is derived, which relates the wing-box structural weight to the wing outer shape. The weight estimation method is validated for several existing passenger aircraft. A series of optimisations is performed to optimise the wing shape for a general objective function, which includes both aerodynamic and structural properties of the wing. The aircraft fuel weight is used as the objective function. Different structures are tested both metal and composite ones. The latter includes different composite layups. In order to find the effect of the internal structure on the optimum wing outer shape, the design lift coefficient is assumed to be constant for all the test cases. The results of the optimisations showed that the optimum wing shape is depending on the structural concept (metal alloys versus different composite layups) for different internal structures.

A study on performance influences of airfoil aerodynamic parameters and evaluation indicators for the roughness sensitivity on wind turbine blade

The roughness increase on horizontal axis wind turbine (HAWT) blade surface, especially on the leading edge, can lead to an aerodynamic performance degradation of blade and power output loss of HAWT, so roughness sensitivity is an important factor for the HAWT blade design. However, there is no criterion for evaluating roughness sensitivity of blade currently. In this paper, the performance influences of airfoil aerodynamic parameters were analyzed by the blade element momentum (BEM) method and 1.5 MW wind turbine blade. It showed that airfoil lift coefficient was the key parameter to the power output and axial thrust of HAWT. Moreover, the evaluation indicators of roughness sensitivity for the different spanwise airfoils of the pitch-regulated HAWT blade were proposed. Those respectively were the lift-to-drag ratio and lift coefficient without feedback system, the maximum lift-to-drag ratio and design lift coefficient with feedback system for the airfoils at outboard section of blade, and lift coefficient without feedback, maximum lift coefficient with feedback for the airfoils at other sections under the pitch-fixed and variable-speed operation. It is not necessary to consider the roughness when HWAT can be regulated to the rated power output by the pitch-regulated and invariable-speed operation.