Airfoil Section Research Articles

Coupled Aeroelastic Prediction of the Effects of Leading-Edge Slat on Rotor Performance

A coupled computational fluid dynamics and computational structural dynamics methodology is developed to analyze the effects of a leading-edge slat on rotor performance. The multielement intermesh connectivity was handled by implicit hole cutting overset implementation. The three-dimensional coupled computational fluid dynamics/computational structural dynamics model is extensively validated against a UH-60 flight-test condition: C9017. The solver is then used to successfully demonstrate the effectiveness of a leading-edge slat in mitigating (or eliminating) dynamic lift and moment stall on a modified UH-60A blade with a 40%-span slatted airfoil section. This results in a reduction of torsional structural loads (up to 73%) and pitch link loads (up to 62%) as compared to the baseline C9017 values. A dynamically moving slat strategy, actuating between slat positions S-1 and S-6 with 1 per revolution harmonic, is considered for stall mitigation. Further, it is shown that using slats with up to 10% higher thrust beyond the limit imposed by McHugh’s stall boundary (C9017) can be achieved. Stall mitigation due to the slat results in a reduction of torsional load up to 54% and a reduction of pitch link load up to 32% as compared to the baseline C9017 flight-test values, even for an increase in thrust of 10%.

Plasma-Based Control of Transition on a Wing with Leading-Edge Excrescence

Large-eddy simulations are carried out to investigate plasma-based flow control that is used to delay transition generated by excrescence on the leading edge of a wing. The wing airfoil section has a geometry that is representative of modern reconnaissance air vehicles and has an appreciable region of laminar flow at design conditions. Modification of the leading edge, which can be caused by the accumulation of debris, insect impacts, microscopic ice crystal formation, damage, or structural fatigue, may result in premature transition and an increase in drag. A dielectric barrier discharge plasma actuator, located downstream of the excrescence, is employed to mitigate transition, decrease drag, and increase energy efficiency. Numerical solutions are obtained to the Navier–Stokes equations that were augmented by source terms used to represent the body force imparted by the plasma actuator on the fluid. A simple phenomenological model provided this force resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity numerical scheme and an implicit time-marching approach. An overset mesh system is employed to represent excrescence in the leading-edge region. Solutions are generated for both uniform and distributed excrescence geometries, as well as for the clean wing configuration without leading-edge modification. Results are obtained for two different values of the plasma field strength. Features of the computational flowfields are elucidated, and the effectiveness of control is quantified by comparison with baseline results without plasma actuation. It is found that plasma control can reestablish the laminar flow region lost to excrescence-generated transition and increase the lift-to-drag ratio by up to 8.7%.

Computational fluid dynamics analysis of the vertical axis wind turbine blade with tubercle leading edge

The performance of a vertical axis wind turbine (VAWT) blade with NACA0015 airfoil section has been investigated using the commercial computational fluid dynamics software ANSYS FluentTM. The Semi Implicit Method for Pressure Linked Equations algorithm is chosen to solve the incompressible Navier-Stokes equations. The k-ω shear stress transport turbulence model was selected for the turbulence flow simulations. The simulation results of lift and drag coefficients between angles of attack of 0° and 40° were first validated with the experimental data in order to confirm the boundary layer distributions. The grid numbers and time step sizes were then examined to confirm the simulation accuracy. To exam the 3D effect, a 2.5D model was additionally developed and compared with 2D model. Finally, the predictions of thrust obtained from the blade with tubercle leading edge were compared with the ones from the straight blade. Overall, the thrusts of VAWT with modified turbine blades were lower than the ones with straight blade. The values of the thrust decreased with increasing amplitudes and decreasing wavelengths, mainly due to the structure of the vortices generated at the leading edge of the turbine blade.

Smooth Curvature of Airfoils Meanline for a General Turbomachinery Geometry Generator

The blade geometry design process is integral to the development and advancement of compressors and turbines in gas turbines or aeroengines. An airfoil section design feature has been added to a previously developed open source parametric 3D blade design tool. The second derivative of the mean-line (related to the curvature) is controlled using B-splines to create the airfoils. This is analytically integrated twice to obtain the mean-line. A smooth thickness distribution is then added to the airfoil with two options either the Wennerstrom distribution or a quartic B-spline thickness distribution. B-splines have also been implemented to achieve customized airfoil leading and trailing edges. Geometry for a turbine, compressor, and transonic fan are presented along with a demonstration of the importance of airfoil smoothness.

Numerical Study of Rotating Cylinder Effects on the Performance of a Symmetrical Airfoil Section

Numerical studies of a NACA 0024 airfoil section with a leading edge rotating cylinder are made using ANSYS CFX 14. Three different turbulence models, SST k-ω, Standard k-ω and k-e were utilized to investigate the flow field of the airfoil section. The lift, drag and lift to drag ratios are obtained for each turbulence model. The time dependent simulations gave the mean values of lift and drag coefficients in addition to the pressure distributions and the velocity profiles on the airfoil surfaces. The lift increased approximately 77% and the stall angle increased from 10 to 18 degrees with the use of a rotating cylinder. This is a proof that the rotating cylinder had a desirable effect on the performance of this airfoil section.

Computational analysis of insect impingement patterns on wind turbine blades

AbstractWind turbines experience significant power loss due to insect contamination on the blades. In order to estimate power losses, computational fluid dynamics software or empirical models are used to compute drag increases due to roughness‐induced boundary‐layer transition. These models require knowledge of the expected levels and location of insect contamination on the blade surface. This is generally unknown, making power loss predictions unreliable. The present study develops a computer simulation to predict this information and uses this tool to simulate insect impingement for a variety of turbine operating conditions. The simulation code combines an invsicid panel method with a Lagrangian insect particle simulation module to first solve for the turbine velocity field and then track insect paths through this field. The effects of blade thickness, angle of attack and insect size are studied for 2D airfoil sections. The simulations show that increasing blade thickness leads to a larger chordwise extent of insect impingement yet lower maximum levels of contamination. Increasing insect mass is also found to increase the chordwise extent of impingement. These results are consistent with previous wind tunnel results and theoretical predictions. The model is then applied to a representative 5‐MW turbine model to determine spanwise variation in contamination. Results agree qualitatively with field observation, suggesting that this technique may be used in the future to more accurately predict power losses on turbines. Copyright © 2015 John Wiley & Sons, Ltd.

Structural changes and damage of single-crystal turbine blades during life tests of an aviation gas turbine engine

The irreversible structural changes of the single-crystal ZhS32-VI nickel superalloy blades of a high-pressure turbine that occur during life tests of a gas turbine engine are studied. The main operation damages in the hottest section of the blade airfoil are found to be the fracture of the heat-resistant coating in the leading edge and the formation of thermomechanical fatigue cracks. The possibility of reconditioning repair of the blades is considered.

A transformation-based formulation of an airfoil cloak using Joukowski mapping

Since its introduction in 2006, the transformation approach to cloaking has been extensively explored for electromagnetic and acoustic fields, due to its intuitive nature as well as the methodology. In this approach, the construction of invisibility cloaks consists of exploiting a change of coordinates to create a void region within a finite space while keeping the outer boundary of the considered space unchanged. Such changes in physical coordinates can be interpreted as a transformation of material properties related to electromagnetics and acoustics, given the invariance of the respective field equations to coordinate change. Based on the transformation, properties of an invisibility cloak can be inferred using available formulae. To this date, this approach has been successfully applied to various two-dimensional geometries including circular and square cylinders. In this work, as an extension, the authors present initial results obtained for the cloaking of a two-dimensional airfoil section. They take advantage of the mapping properties of the well-known Joukowski transformation, a complex mapping that is used in aerodynamics applications.

Design of Efficient Propellers Using Variable-Fidelity Aerodynamic Analysis and Multilevel Optimization

A multilevel design optimization framework was developed for the aerodynamic design of an electric aerial vehicle propeller in cruise conditions. The objective was to determine the optimum propeller shape to minimize torque at a given required thrust level and thus maximize overall propeller efficiency. A key concept of the design is the sequential application of a three-dimensional planform and two-dimensional section designs iteratively to make the best use of the complementary characteristics of gradient-free and gradient-based optimization strategies and the corresponding parameterization of the design space. Variable-fidelity aerodynamic analyses of blade element momentum theory and Navier–Stokes solutions were used to achieve computational efficiency and high accuracy. First, the optimal planform shape was determined by adjusting radius, twist angle, and chord lengths of the blade. Subsequently, the sectional airfoil design was performed at several spanwise locations. Given the new airfoil sections, the planform was redesigned to consider three-dimensional flow effects. The final optimized propeller design was validated using three-dimensional Navier–Stokes flow solvers and was tested in a wind-tunnel facility. Propeller efficiency was found to be improved by 5.7%. Finally, the fluid–structure interaction was analyzed to confirm that a required safety factor was ensured.

Effect of Taper Ratio at Low Reynolds Number

A low speed wind-tunnel investigation is presented documenting the impact of taper ratio at low Reynolds number. An wing using a S8036 section was tested at and 150,000. Taper ratio was varied from 1 down to 0.2 in 0.2 increments. An analytic prediction method as well as extended numerical lifting line theory incorporating nonlinear section data was implemented to compare with experiment. The experimental results indicated a weak dependence of peak lift to drag ratio on taper ratio for both Reynolds numbers. Surface flow visualization showed the presence of a large laminar transitional bubble on the upper wing surface. The relative extent of the bubble was observed to increase towards the tip region for tapered planforms. Agreement between theory and experiment in terms of lift and drag estimation was good. Planform optimization using the extended numerical lifting line theory indicated that at the test conditions and using the selected airfoil section, a planform that differs from straight taper or elliptic may be most efficient.

Aeroelastic Dynamic Response and Control of an Airfoil Section with Hysteresis Nonlinearity

Aeroelastic Dynamic Response and Control of an Airfoil Section with Hysteresis Nonlinearity

Three-dimensional suction flow control and suction jet length optimization of NACA 0012 wing

A three-dimensional suction flow control study was performed to investigate the aerodynamic characteristics of a rectangular wing with a NACA 0012 airfoil section. In addition, the optimum suction jet length was determined. In this study, the Reynolds-averaged Navier–Stokes equations were employed in conjunction with a k–ω SST turbulent model. Perpendicular suction was applied at the leading edge of the wing’s upper surface, with two different types of slot distributions: i.e., center suction and tip suction. The suction jet lengths were varied by 0.25–2 of the chord length, and the jet velocity was selected to be 0.5 times the freestream velocity. Most importantly, in both cases, the results indicated that the lift-to-drag ratio increased as the suction jet length rose. However, the improvement in aerodynamic characteristics was more pronounced with center suction, and these characteristics were extremely close to those of the case considering suction over the entire wing such that the jet length was equal to wingspan. Moreover, in the center suction case, vortexes frequently abated or moved downstream. Interestingly, under similar conditions, a greater number of vortexes were removed with center suction than with tip suction. Ultimately, when the jet length is less than half the wingspan, tip suction is the better of the two alternatives, and when the jet length is greater than half the wingspan, center suction is better suited.

Numerical Study on Drag Reduction by Micro-Blowing/Suction Compounding Flow Control on Supercritical Airfoil

Micro-Suction technique(MST) is proposed by the development of micro-blowing technique(MBT). Current experiments and numerical studies are mostly focusing on MBT, micro-suction flow control in turbulent boundary layer remains unstudied. Thus, based on 2D-RAE2822 supercritical airfoil, numerical research on MST and MB/ST compounding flow control have been carried out. And Micro-Porous Wall Model(MPWM) is used to represent the real effects that the blowing and suction of the micro-porous wall has on the surface flow.The numerical results of micro-suction indicate that micro-suction control is capable of inducing a lower pressure zone in front of the micro-porous zone, and a higher pressure zone in the rear end. Given that micro-porous zone is placed on the particular section of airfoil, where the pressure drag direction is backward parallel to free-stream direction, the reduction of the pressure induced by micro-suction control can result in the decrease of pressure drag. Finally, combining the previous study on the MBT, a compounding configuration of micro-blowing/suction flow control on RAE2822 airfoil is proposed. The compounding configuration can take the advantage of both micro-blowing and micro-suction, over 20% increase of the lift and up to 15% decrease of the drag can be realized. Therefore, the compounding flowing control of micro-blowing/suction shows a great potential for the flow control on aircraft.

擬似逆行列を用いた修正PARSEC法による三次元遷音速主翼形状の推定法

Modified PARSEC (PARametric SECtion Method) is used as a parameterization method to describe airfoil shapes by few number of parameters, which is suitable for airfoil design optimization. To calculate these parameters, GA (Genetic Algorithm) is usually used. However, it has been observed that for some airfoils, Modified PARSEC method generates irregular shapes when GA is used. To overcome this issue, a new method using Pseudo-Inverse Matrix is developed. The proposed method is applied to various airfoils including the airfoil sections of the CRM (Common Research Model) wing, and a two-dimensional CFD code is used to carry out the aerodynamic analysis. Subsequently, the three-dimensional CRM wing is reproduced using the proposed method and its aerodynamic characteristics are analyzed with Euler equations. The results show that reproduced geometry is almost identical to that of the original CAD data in terms of aerodynamic characteristics, which shows the applicability and usefulness of the method.

Aeroelastic Dynamic Response and Control of an Aeroelastic System with Hysteresis Nonlinearities

A state feedback control law based on the sliding mode control method is derived for the aeroelastic response and flutter suppression of a two-dimensional airfoil section with hysteresis nonlinearity in pitch. An observer is constructed to estimate the unavailable state variables of the system. With the control law designed, nonlinear effect of time delay between the control input and actuator is investigated by a numerical approach. The closed-loop system including the observer and nonlinear controller is asymptotically stable. The simulation results show that the observer can give precise estimations for the plunge displacement and the velocities in pitch and plunge and that the controller is effective for flutter suppression. The time delay between the control input and actuator may jeopardize the control performance and cause high-frequency vibrations.

Effect of pseudoelastic hysteresis of shape memory alloy springs on the aeroelastic behavior of a typical airfoil section

The literature on aeroelasticity includes studies on the use of smart materials as sensors and actuators in vibration control problems. Although different smart materials are available, shape memory alloys have received growing attention in aerospace applications. The hysteretic response of shape memory alloys exhibiting pseudoelasticity provides energy dissipating and damping capabilities for these materials, and therefore, the effectiveness of the pseudoelastic behavior of shape memory alloys has been investigated for passive structural vibration control. However, its effect on the aeroelastic behavior of lifting surfaces has not been covered in the literature. Hence, this article addresses the modeling and analysis of a 2-degree-of-freedom typical aeroelastic section with shape memory alloy springs introduced through the pitch degree of freedom. A state-space model is employed for the simulations of the coupled system, and a two-state approximation to Theodorsen aerodynamics is used for the determination of the aerodynamic loads. The effects of the hysteretic behavior of the shape memory alloy springs on the aeroelastic behavior of the typical section are investigated at the flutter boundary and at post-flutter regime.

LDV measurement of boundary layer on rotating blade surface in wind tunnel

Wind turbines generate electricity due to extracting energy from the wind. The rotor aerodynamics strongly depends on the flow around blade. The surface flow on the rotating blade affects the sectional performance. The wind turbine surface flow has span-wise component due to span-wise change of airfoil section, chord length, twisted angle of blade and centrifugal force on the flow. These span-wise flow changes the boundary layer on the rotating blade and the sectional performance. Hence, the thorough understanding of blade surface flow is important to improve the rotor performance. For the purpose of clarification of the flow behaviour around the rotor blade, the velocity in the boundary layer on rotating blade surface of an experimental HAWT was measured in a wind tunnel. The velocity measurement on the blade surface was carried out by a laser Doppler velocimeter (LDV). As the results of the measurement, characteristics of surface flow are clarified. In optimum tip speed operation, the surface flow on leading edge and r/R=0.3 have large span-wise velocity which reaches 20% of sectional inflow velocity. The surface flow inboard have three dimensional flow patterns. On the other hand, the flow outboard is almost two dimensional in cross sectional plane.

CFD aerodynamic analysis of non-conventional airfoil sections for very large rotor blades

The aerodynamic performance of flat-back and elliptically shaped airfoils is analyzed on the basis of CFD simulations. Incompressible and low-Mach preconditioned compressible unsteady simulations have been carried out using the k-w SST and the Spalart Allmaras turbulence models. Time averaged lift and drag coefficients are compared to wind tunnel data for the FB 3500-1750 flat back airfoil while amplitudes and frequencies are also recorded. Prior to separation averaged lift is well predicted while drag is overestimated keeping however the trend in the tests. The CFD models considered, predict separation with a 5° delay which is reflected on the load results. Similar results are provided for a modified NACA0035 with a rounded (elliptically shaped) trailing edge. Finally as regards the dynamic characteristics in the load signals, there is fair agreement in terms of Str number but significant differences in terms of lift and drag amplitudes.

Microstructural Degradation of Thermal Barrier Coatings on an Integrated Gasification Combined Cycle (IGCC) Simulated Film-Cooled Turbine Vane Pressure Surface Due to Particulate Fly Ash Deposition

Research is being conducted to study the degradation of thermal barrier coatings (TBC) employed on IGCC turbine hot section airfoils due to particulate deposition from contaminants in coal syn-thesis gas (syngas). West Virginia University (WVU) had been working with US Department of Energy, National Energy Technology Laboratory (NETL) to simulate deposition on the pressure side of an IGCC turbine first stage vane. To simulate the contaminant deposition, several TBC coated, angled film-cooled test articles were subjected to accelerated coal fly ash, which was injected into the flow of a combustor facility with a high pressure (approximately 4 atm) and a high temperature (1560 K) environment. To investigate the degradation of the TBCs due to particulate deposition, non-destructive tests were performed using scanning electron microscopy (SEM) evaluation and energy dispersive X-ray spectroscopy (EDS) examinations. The SEM evaluation was used to display the microstructure change within the layers of the TBC system directly related to the fly ash deposition. The SEM micrographs showed that deposition-TBC interaction made the YSZ coating more susceptible to delamination and promoted a dissolution-reprecipitation mechanism that changed the YSZ morphology and composition. The EDS examination provided elemental maps of the shallow infiltration depth of the fly ash and chemical composition spectrum results which showed yttria migration from the YSZ into the deposition.

A Pareto optimal multi-objective optimization for a horizontal axis wind turbine blade airfoil sections utilizing exergy analysis and neural networks

In this study a multi-objective genetic algorithm is utilized to obtain a Pareto optimal set of solutions for geometrical characteristics of airfoil sections for 10-meter blades of a horizontal axis wind turbine. The performance of the airfoil sections during the process of energy conversion is evaluated deploying a 2D incompressible unsteady CFD solver and the second law analysis. Artificial neural networks are trained employing CFD obtained data sets to represent objective functions in an algorithm which implements exergetic performance and integrity characteristics as optimization objectives. The results show that utilizing the second law approach along with Pareto optimality concept leads to a set of precise solutions which represent minimum energy waste, maximum efficiency, and topmost stability. Furthermore, enhanced rotor performance coefficients are observed through a BEM study which compares conventional designs with the second law obtained configurations. Exergy analysis is believed to be an efficient tool in the optimal design of wind turbine blades with the capability of determining the amount of lost opportunities to do useful work.