Blade Airfoil Research Articles

Rapid method of Predicting the Subsonic Flutter Stability of AGTE Axial-Flow Compressor Blade Cascades. Part 2. Mathematical Implementation of Method and its Potentional Application

The paper considers the implementation of the rapid method of predicting the dynamic stability of the compressor blade assemblies against subsonic flutter. The first flexural mode of blade vibrations is analyzed at the design stage for a wide range of the angle of attack based on the developed database of the critical values of the reduced vibration frequency in straight cascades of blade airfoils. The multiple regression equation is developed that depends on the relative blade spacing and stagger angle of the straight cascade of blade airfoils, coefficient of the flexural-torsional coupling of the blade, and angle of attack with the correlation factor of the studied parameters in the range of 0.92–0.98. Using the obtained equation, the numerical program has been developed for the determination of the dynamic stability limit against subsonic flutter for the first flexural mode of the blade vibrations. The program allows one to find the numerical values of critical reduced frequencies as the characteristics of its dynamic stability and determine their dependence on the angle of attack. The results of practical application of the developed program are presented using the assessment of the dynamic stability of the flexural mode of axial compressors in four modern aircraft gas-turbine engines. It is shown that at the design engine stage it is possible to select the reduced vibration frequencies of the blade assembly for the specified geometry of its peripheral sections and angle of attack of the inflow upon the condition of the occurrence of subsonic flutter.

РЕЗУЛЬТАТЫ ОЦЕНКИ ДИНАМИЧЕСКОЙ УСТОЙЧИВОСТИ К ДОЗВУКОВОМУ ФЛАТТЕРУ ЛОПАТОЧНЫХ ВЕНЦОВ КОМПРЕССОРОВ НЕКОТОРЫХ АВИАЦИОННЫХ ГАЗОТУРБИННЫХ ДВИГАТЕЛЕЙ

The paper outlines the results of the investigation on the verification of the express method of prediction of dynamic stability for subsonic flutter using the blade assemblies of individual stages of the compressor of some types of aircraft gas-turbine engines at different modes of their operation. The paper gives a brief overview of the basic concepts of the developed express estimation method, possibilities of the determination of the stability limit for the blade assemblies for a subsonic flutter, as well as the results of the assessment of the dynamic stability of the compressor stages of some modern aircraft gas-turbine engines. Firstly, the reduced frequencies of vibrations of the blade assemblies under investigation and their critical values coincide practically. The mentioned critical values were determined from the test data for the straight cascades of the blade airfoils corresponding to two sections of the height of the blade airfoil portion. Hence it follows that the task can be solved employing only gas-dynamic parameters of the flow for one of the sections of the airfoil within the specified range of its height. Secondly, the prediction of dynamic stability for the subsonic flutter of the blade assemblies of separate compressor stages of some types of aircraft gas-turbine engines and the comparison of the obtained results with the data of bench tests, as well as the data obtained using other methods, were made. It was implied that the developed method allows one to determine the flutter limit with high accuracy, as well as make an optimal selection of the values of the reduced frequency of the blade vibrations for the specified range of the angle of attack of the sections of the blade assemblies upon the condition of its occurrence. Thirdly, the possibility to determine the nature of vibration excitation for the blade assemblies is considered using the analysis of the initiation of cracks in the blade root of the first compressor stage of the high-pressure gas-turbine engine. Moreover, it is shown that at large angles of attack (≥ 10°) an insignificant displacement of the dynamic stability limit of the blade assemblies may occur in the direction of large values of the reduced frequency of their vibrations.

Method for fitting wind turbine blade airfoil profile with function curve

This paper analyzed the characteristics of a midline -thickness function, and gave the influence of the change of the constant value in the function on the change of the function graph. A method for fitting a wind turbine blade airfoil profile with a midline -thickness function curve was demonstrated by three examples, and some limitations of this method were pointed out. Studies have shown that the airfoil profile can be generated by using the midline -thickness function. The shape of the airfoil profile can also be changed in the desired direction by adjusting the constant value in the function. As a result, new airfoil profiles can be created, and the airfoil design can be improved. For existing wind turbine airfoil profiles, the midline -thickness function can be used for fitting. The main method is to adjust the constant value in the function to compare with the airfoil profile bitmap. Since the constants have a clear geometric meaning, the fitting process is relatively simple, but there are minor errors.

COMPARISON OF HINT WIND TINES OF AIRFOIL TYPE NACA 4412, NACA 23012, and NACA 16-212 USING QBLADE SOFTWARE

Wind energy as one of the new renewable energies that has considerable potential in Indonesia is known by the rapid development of wind power plants in Indonesia. The windmill blade which is one of the main components of the windmill has a role as the conversion of wind potential energy into motion energy to eventually become electrical energy that is influenced by the shape of the windmill blade of the windmill. NACA (National Aeronautical Committee Advisory) in charge of aeronautics has standards regarding varying airfoil shapes. A comparison of variations of 4-digit type airfoils (NACA 4412), 5 digits (NACA 23012) and series 16 (NACA 16-212) to determine the value of Cl / Cd from the variation of NACA airfoil types. The results of simulations carried out using Qblade software showed that the value of Cl / Cd to the highest alpha of the three types of airfoils was NACA 4412 with a value of 134, alpha 6 and the Cp value for the highest TSR was 0.44 at TSR 5.5. Furthermore, the NACA 4412 airfoil blades can be developed by making lighter material variations so that the windmill blades are easier to spin so that the resulting power becomes more maximal.

Effect of Gurney Flap Geometry on a S809 Airfoil

In this paper, the effect of Gurney flap shapes on wind turbine blade airfoil S809 has been studied by numerical simulation. First, the O-type grid is used in the numerical simulation. By comparing with experimental data, such as the lift force, the drag coefficient, and the pressure distribution, the accuracy of the simulation method is validated. Second, the research on the widths of three kinds of rectangular Gurney flaps at the trailing edge of the S809 airfoil is carried out. Rectangular Gurney flaps can considerably increase the lift in both the linear and nonlinear sections, and the maximum lift coefficient can be increased by 20.65%. In addition, the drag and the pitching moment are increased. However, the width of the rectangular Gurney flap has a small impact on the lift, the drag, and the pitching moment. Finally, the effects of rectangular and triangular Gurney flaps on the aerodynamic characteristics of the S809 airfoil are compared. The results show that the triangular flaps can obtain an increase of maximum lift coefficient by 28.42%, which is better than 16.31% of the rectangular flaps.

Simulation Analysis on the Blade Airfoil of Small Wind Turbine

The selection of the blade airfoil of wind turbine has a crucial impact on the overall efficiency of wind turbine and wind energy utilization. Aiming at the small 300W household wind turbine on the market, based on its known design parameters and using the software of Profili and SolidWorks, the 3D solid modeling of the blade has been achieved in three common airfoils (NACA4412, NACA0009 and NACA 23012). Then, by using the Fluent module of the finite element analysis software ANSYS, the actual working environment of the blade is simulated. The results show that the blades under the NACA0009 airfoil can produce a relatively maximum axial torque of 3.7808 Nm. Finally, based on the above research method, the new airfoil Icarus was discovered by improving the existing airfoil, which has a relatively low manufacturing cost, and the average pressure difference per unit area of the blade is 4.95% higher than that of the NACA0009 airfoil. This research can provide reference for the improvement of airfoil of small wind turbines, which has certain practical significance and practical value.

Non-uniform stator loss reduction design strategy in a transonic axial-flow compressor stage under inflow distortion

In a boundary layer ingesting (BLI) propulsion system, the fans/compressors continuously operate at a highly distorted inflow condition due to ingesting the boundary layers on the aircraft fuselage. The BLI inlet distortion induces non-uniform whirl and axial velocities at the rotor outlet, leading to a circumferential and radial non-uniform incidence distribution for the downstream stator. One of the main challenges for the compressor performance is a bad match between the rotor outflow and the stator inlet geometry, which would cause flow separations in blade passages. This paper has employed a non-uniform stator loss reduction design strategy to make a redistribution of stator incidence at the compressor off-design working point so as to reduce the potential separation loss and enhance the stage aerodynamic performance. Firstly, three-dimensional full-annulus unsteady numerical simulations are carried out to reveal the specific flow features of the non-uniform incidence distribution at the stator inlet. Then, according to the circumferential and radial non-uniform incidence distribution, a spatial non-uniform stator loss reduction design strategy based on adjusting the local inlet metal angles of the blade airfoil sections is utilized to make it a good match between the rotor outflow and the stator inlet geometry. Finally, the inner flow fields are analyzed to test the effectiveness of the non-uniform loss reduction design strategy. The computational results indicate that the high-incidence regions at the stator inlet are notably reduced and a more uniform incidence distribution has been achieved along both the circumferential and radial directions. Moreover, the non-uniform loss reduction design has successfully suppressed the flow separations at both the hub and tip regions. As a result, the stator has achieved an 18.2% reduction of the aerodynamic loss at the re-designed point and the stage efficiency has been improved by 0.83%. In the meanwhile, the re-designed stator has decreased the aerodynamic losses over the whole compressor operating range, and the re-designed stage has also achieved a higher efficiency than the baseline one while maintaining the total pressure ratio.

Investigation of Blade Geometry and Airfoil for Small Wind Turbine Blade

Investigation of Blade Geometry and Airfoil for Small Wind Turbine Blade

Influence of the stressed state of the surface layer on the endurance of gas turbine engine compressor blades

Different types of final strengthening treatment of gas turbine engine (GTD) compressor blades are considered. The influence of each type of treatment on the formation of roughness of the surface with favorable microrelief, as well as on the level and depth of distribution of residual compressive stresses in the compressor blade airfoil is analyzed. The causes of blade fatigue failure are described and methods of controlling this kind of failure are presented. The results of testing special specimens made of VT9 titanic alloy are presented to establish the influence of final strengthening treatment modes on the compressor blade resistance to fatigue stress. The results of testing residual stress distribution along the thickness of compressor blade airfoil are presented. A method of improving dynamic strengthening of specimens due to the protection of compressor blade edges is discussed. The results of semi-graphical analysis of the stressed state of low-pressure and medium-pressure compressor blades made of VT9 alloy are presented. They take into account residual stresses, as well as operating load stresses in the process of operation. We show that it is possible to increase the limit of the blade endurance due to the optimization of residual stress diagrams by improving the final strengthening technology with the use of dust blasting.

Perancangan dan Pemodelan Turbin Darrieus untuk Pembangkit Listrik Tenaga Arus Laut (PLTAL)

<em>Sea current energy is one of the new and renewable energy that is currently being developed to replace fossil energy which is starting to deplate its availability. Sea current energy research continues to be developed. One of the studies that can be developed is modeling laboratory-scale sea currents, so that it is necessary to design a model of Sea Current Power Plants that aims to improve the process of understanding the energy. In this design, a model of Sea Current Power Plant with a capacity of 150 Watt is designed using the Darrieus Turbine. The design results some data such as : diameter of 428 mm for turbine rotor, height of 327 mm for turbine rotor, chord length of 0.04 m for 3 NACA 0018 airfoil blades, and a transmission ratio of 1 : 5 for transmission systems using a straight gear gearbox. In addition, the turbine generated 205.5 rpm rotation at flow rate of 1.15 m/s with turbine efficiency of 40%.</em>

Investigation of pre-stall flow control on wind turbine blade airfoil using roughness element

In the current study, the aerodynamic performance of NACA 4412 airfoil with sandpaper which was used as an alternative control device instead of vortex generators was investigated. It was especially considered how the sandpaper affected the growth of the separation bubble. Regarding the flow visualization, the smoke-wire experiment was done at different angles of attack and Reynolds numbers. Moreover, the hot-wire experiment was employed to measure velocity as well as the values of the turbulence statistics over and near wake of the airfoil. Besides the mentioned experiments, the force measurement was performed to obtain aerodynamic forces, and quasi-wall shear stress was measured by means of a hot-film sensor. With the roughness, the instability in the long transition region at low Reynolds number was bypassed. Flow momentum was increased in the boundary layer on the airfoil surface, and the flow over the roughened airfoil exhibited more resistance against adverse pressure gradients. The flow triggered by the roughness element suppressed the bubble, which meant pre-stall flow control carried out with resulting CL increment and CD reduction. Finally, using the sandpaper over the airfoil provided prominent benefits in terms of postponing of the stall and enhancement of aerodynamic performance for wind turbine blades.

Improved performance of a slotted blade using a novel slot design

Efficient capture of wind energy requires optimal dynamic performance of turbine blades, desirably including delaying stall to higher angles of attack (AoAs). Stall is associated with flow separation close to the leading edge on the suction side of a blade so that delaying flow separation mitigates this condition. Merits of passive slots in wings for increasing their lift are well known. Typically, however, the increase in lift is accompanied by a corresponding increase in drag so that the overall aerodynamic efficiency is at most marginally improved. Here, we discuss application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. Delaying flow separation, results in increase in lift and decrease in drag at significantly high angles of attack. Slot width and inclined angle were varied to determine the optimum configuration. Dynamic performance of the blade was investigated both numerically and experimentally, with angles of attack in the range 0o≤AoA≤30o at a Reynolds number of 105. Lift and drag coefficients of the slotted airfoils predicted from the computational fluid dynamics (CFD) study correlate well with the corresponding coefficients determined via experiments. Experimental results show that a 58% increase in maximum lift coefficient and an 14% increase in maximum lift-to-drag ratio could be achieved with the optimum design case. Flow details obtained from the CFD study provide better insight into the underlying control mechanism of the internal slot. The findings could have significant implications for aeronautics and for improving capture of renewable energy from wind.

Effects of Offset Blade on Aerodynamic Characteristics of Small-Scale Vertical Axis Wind Turbine

A new way of connecting blade to rotor shaft named offset blade method was proposed for straight-bladed vertical axis wind turbine (SB-VAWT) in this study. In order to invest the efficiency of this method and effects of main parameters including offset length and blade airfoil on improving the output power performance and static starting characteristics, numerical simulations and wind tunnel tests were carried out. Four kinds of blade airfoil including NACA0012, NACA0018, NACA0024 and S809 were selected to analyze the influence of blade thickness and symmetry on SB-VAWT with offset blade. Numerical simulations were firstly carried out on output power for the rotor with 6 kinds of offset length for each airfoil. Wind tunnel tests were also carried out to compare with the results of simulations. The flow fields of rotor with different offset lengths were simulated and the effects of offset blade were analyzed. The optimum offset length among all studied for output power performance was found. Furthermore, the static starting torque and aerodynamic force characteristics of the rotor with optimum offset length were researched. According to the results, appropriate offset length can improve the output power characteristics and smooth the fluctuations of the static torque during one rotational period. The best offset length varies with the airfoil.

Comparison of low wind speed aerodynamics of unsymmetrical blade H-Darrieus rotors-blade camber and curvature signatures for performance improvement

Unsymmetrical blade Vertical axis wind turbine (VAWT) can be nicely adapted in the built environment because of its improved performance, self-starting ability, simple construction, easy maintenance and capability to adapt to wind direction changes. For proliferation of such VAWT installations, the challenge is to improve its efficiency in low wind speed condition (usually less than 10 m/s) of the built environment, which depends on its blade profile design. In an unsymmetrical blade, blade thickness-to-chord ratio, percentage camber, blade curvature around aerodynamic moment center are the controlling parameters for effective blade-fluid interactions for performance improvement, thus requiring a detailed investigation of the aerodynamics of unsymmetrical blade VAWT. The objective of this paper is to compare low wind speed aerodynamics of two different unsymmetrical airfoil blade profiles to obtain design information of blade camber and blade curvature around aerodynamic moment center for performance improvement of H-Darrieus VAWT, which is hardly available in the existing literature. Detailed blade-fluid interactions are analysed by Ansys Computational Fluid Dynamics (CFD) software for different low wind speeds between 4 m/s and 8 m/s. It is found that more rounded curvature of the suction side surface of advancing S815 blade around aerodynamic moment center and thicker blade profile (maximum thickness is 26.2% at 25.7% chord) has a distinct influence for performance improvement of the rotor in the power stroke. In the returning stroke, the VAWT is benefited from higher camber of EN0005 blade (maximum camber percentage of 10% at 55% chord) and lesser blade curvature of the blade suction side. Next, vorticity structures of each blade profile have also been monitored at different azimuthal positions and necessary performance insights with regards the development of static/deep stall vortices and other boundary layer features have been drawn. Further, blade polars, power performance, and blade loading have also been obtained and compared with published results. Overall better designs of unsymmetrical blade profiles have also been recommended. The present study leads to the understanding of the design blade camber and curvature signatures in both power and returning strokes for possible performance improvement of small-sized VAWT in low wind speed condition.

A novel method for preform die design in forging process of an airfoil blade based on Lagrange interpolation and meta-heuristic algorithm

In this paper, a new method is introduced for optimization of a two-stage forging process of an airfoil blade. Geometrical dimensions of preform shape and cavity of the intermediate die were selected as input variables and uniformity of strain distribution, flash volume, and lateral forces were considered as objective functions. Design parameters of the intermediate die cavity were defined by Lagrange interpolation method. Then, using the design of experiments and implementation of proposed tests by the finite element method, the objective function values were obtained and afterwards artificial neural network modeling were applied for extracting the effectiveness of the input variables on the objectives. Finally, optimal amount of preform and intermediate die parameters was achieved using a multi-objective genetic algorithm based on a fuzzy method. Also, by using physical modeling of the optimal conditions, experimental tests of the forging process were executed. Results show that the trained artificial neural network model estimates the process with good accuracy and also, comparison of optimized and non-optimized two-stage forging reveals that in the former condition, flash volume and strain non-uniformity reduced more by 51% and 42%, respectively.

Flow Analysis of the Symmetric Airfoil NACA0015 Blade at Different Angles of Attack and Mixing Velocities in a Continuous Stirred Tank Reactor (CSTR)

Biogas produces from the degradation of organic compounds of garbage and water wastes from various sources such as ranch and agricultural industries, usually by the fermentation process with anaerobic microorganisms. Layers of sediment are often occurred that can block the flow and longer mixing time is required for a more homogenous mixing. The objective of this study is to solve the non-uniform and non-homogenous as well as to save the mixing time in the fermentation process of biogas production using a model-mixing reactor. Flow analysis using an image processing technique of the symmetric airfoil NACA0015 blade at different angles of attack and mixing velocities in a Continuous Stirred Tank Reactor (CSTR) was examined. The CSTR was equipped with two and three airfoil blades at the angles of attack 0, 10, 16(stall angle) and 20° operated at the mixing velocities at 80, 110, 140 and 190 rpm. The mixing efficiency was evaluated from the homogenous appearance of plastic particles (5 mm diameter) dispersed in water by an image processing technique. The results showed that the mixing efficiencies of CSTR with three blades were higher than that of the CSTR with two blades of about 1.3 folds. The mixing efficiency increased with increasing mixing velocities and angles of attack, and was almost constant when the blade angles of attack increased from 16° to 20° and the mixing velocity increased from 140 to 190 rpm. This may be due to the airfoil blade stall and the saturation of the mixing. A new blade design for the CSTR system from this study can give a more efficient stir and mixing flow which will not only be beneficial for biogas production in the laboratory scale, but also a model design for the industrial biogas production as well.

Effects of blade aspect ratio and taper ratio on hovering performance of cycloidal rotor with large blade pitching amplitude

In recent years, a lot of research work has been carried out on the cycloidal rotors. However, it lacks thorough understanding about the effects of the blade platform shape on the hover efficiency of the cycloidal rotor, and the knowledge of how to design the platform shape of the blades. This paper presents a numerical simulation model based on Unsteady Reynolds-Averaged Navier–Stokes equations (URANSs), which is further validated by the experimental results. The effects of blade aspect ratio and taper ratio are analyzed, which shows that the cycloidal rotors with the same chord length have quite similar performance even though the blade aspect ratio varies from a very small value to a large one. By comparing the cycloidal rotors with different taper ratios, it is found that the rotors with large blade taper ratio outperform those with small taper ratio. This is due to the fact that the blade with larger taper ratio has longer chord and hence better efficiency. The analysis results show that the unsteady aerodynamic effects due to blade pitching motion play a more important role in the efficiency than the blade platform shape. Therefore we should pay more attention to the blade airfoil and pitching motion than the blade platform shape. The main contributions of this paper include: the analysis of the effects of aspect ratio and taper ratio on the hover efficiency of cycloidal rotor based on both the experimental and numerical simulation results; the finding of the main influencing factors on the hover efficiency; the qualitative guidance on how to design the blade platform shape for cycloidal rotors.

Numerical research on the turbulent drag reduction mechanism of a transverse groove structure on an airfoil blade

The optimization of the airfoil has a significant impact on the reduction of energy consumption for a rotary machine. In this paper, ANSYS Fluent is used to study the influence of different groove structure sizes on the turbulence drag of NACA0012 airfoil blades, and the drag reduction mechanism is analyzed. The results show that the groove structure can significantly reduce the drag during the working speed of the fan. The optimal groove size is s = 0.1 mm and the drag is reduced by 9.65%. The secondary vortices reduce the normal velocity gradient at the top of the groove structure, resulting in a reduction in viscous drag. However, as the groove size increases, the drag reduction effect decreases, and even the drag increases. The overall shear stress of the airfoil surface with the transverse groove structure is smaller than the original airfoil, and the velocity gradient of the airfoil surface is reduced. The two sides work together to reduce the turbulence drag of the airfoil. Besides, the spacing between the grooves increases the shear stress in some areas, but reduces the mutual interference of the vortices, so there is an optimum value for the groove spacing.

Shape Optimization of Blade Airfoil for a Small Vertical Axis Wind Turbine Considering Uncertainties

Shape Optimization of Blade Airfoil for a Small Vertical Axis Wind Turbine Considering Uncertainties

Predicting the volume shrinkage while manufacturing the GTE turbine blades

The process analysis of manufacturing the castings of turbine moving blades demonstrated that approximately 5% of the blade blanks from a lot are rejected to a considerable geometric distortion of the blade airfoil. The turbine moving blade casting manufactured by the casting method with directed crystallizing may differ in its geometric and dimensional-accuracy parameters from the design model. The casting geometry varies as a result of high temperature and structural shrinkage deformations which are manifested as the hindered volumetric shrinkage and contraction during crystallizing and upon the casting knockout from the ceramic mould. High-temperature deformations may result in contraction of the casting mould and ceramic core shaping the inner blade cooling channels. As a result, to obtain the blade of the geometric form as set by the designer, it becomes necessary to predict the stress-deformed state of the moving blade casting in order to consider the volumetric shrinkage and deformation in advance. Therefore, predicting and considering the total volumetric shrinkage during the manufacture of the moving blade castings ensuring the minimum contraction of the process system “ceramic mould – casting – ceramic core” is a relevant problem for the modern blank production.