Impact of Blade-Flapping Vibration on Aerodynamic Characteristics of Wind Turbines under Yaw Conditions

Although the aerodynamic loading of wind turbine blades under various conditions has been widely studied,the radial distribution of load along the blade under various yaw conditions and with blade flapping phenomena is poorly understood.This study aims to investigate the effects of second-order flapwise vibration on the mean and fluctuation characteristics of the torque and axial thrust of wind turbines under yaw conditions using computational fluid dynamics(CFD).In the CFD model,the blades are segmented radially to comprehensively analyze the distribution patterns of torque,axial load,and tangential load.The following results are obtained.(i)After applying flapwise vibration,the torque and axial thrust of wind turbines decrease in relation to those of the rigid model,with significantly increased fluctuations.(ii)Flapwise vibration causes the blades to reciprocate along the axial direction,altering the local angle of attack and velocity of the blades relative to the incoming wind flow.This results in the contraction of the torque region from a circular shape to a complex“gear”shape,which is accompanied by evident oscillations.(iii)Compared to the tangential load,the axial load on the blades is more sensitive to flapwise vibration although both exhibit significantly enhanced fluctuations.This study not only reveals the impact of flapwise vibration on wind turbine blade performance,including the reduction of torque and axial thrust and increased operational fluctuations,but also clarifies the radial distribution patterns of blade aerodynamic characteristics,which is of great significance for optimizing wind turbine blade design and reducing fatigue risks.

Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

For the quad tilt rotor aircraft, a computational fluid dynamics method based on multiple reference frames (MRF) was used to analyze the influence of aerodynamic layout parameters on the aerodynamic characteristics of the quad tilt rotor aircraft. Firstly, a numerical simulation method for the interference flow field of the quad tilt rotor aircraft is established. Based on this method, the aerodynamic characteristics of isolated rotors, rotor combinations at different lateral positions on the wing, and rotor rotation directions under different inflow velocities were calculated and analyzed, in order to grasp their aerodynamic interference laws and provide reference for the design and control theory research of such aircraft.

Train-induced aerodynamic characteristics of vertical sound barriers influenced by several factors

Investigations into the aerodynamic properties of vertical sound barriers exposed to high-speed operations employ computational fluid dynamics.The primary focus of this research is to evaluate the influence of train speed and the distance(D)from the track centerline under various operating conditions.The findings elucidate a marked elevation in the aerodynamic effect amplitude on sound barriers as train speeds increase.In single-train passages,the aerodynamic effect amplitude manifests a direct relationship with the square of the train speed.When two trains pass each other,the aerodynamic amplitude intensifies due to an additional aerodynamic increment on the sound barrier.This increment exhibits an approximate quadratic correlation with the retrograde train speed.Notably,the impact of high-speed trains on sound barrier aerodynamics surpasses that of low-speed trains,and this discrepancy amplifies with larger speed differentials between trains.Moreover,the train-induced aerodynamic effect diminishes significantly with greater distance(D),with occurrences of pressure coefficient(CP)exceeding the standard thresholds during dual-train passages.This study culminates in the formulation of universal equations for quantifying the influence of train speed and distance(D)on sound barrier aerodynamic characteristics across various operational scenarios.

Research on the Aerodynamic Characteristics of Leading Edge and Bulge of Ram-Air Parafoil Based on CFD

This study focuses on the aerodynamic characteristics and flow mechanism of three different configurations of ram-air parafoil with open/closed air inlet and bulges. Firstly, we designed a special parafoil configuration for this study. Then we used numerical simulation to obtain the aerodynamic data of three parafoils at different angles of attack, and studied the influence of the bulge and the leading edge open/closed inlet on the aerodynamic performance of the ram-air parafoil. Finally, we study the flow mechanism of the ram-air parafoil through the pressure distribution and flow field. The results of the study show that compared with the aerodynamic parameters of the parafoil without bulges, the optimal angle of attack of the two parafoils with bulges is increased by 4?, the maximum lift to drag ratio of the parafoil with closed leading edge is reduced by about 4.3% and the optimal angle of attack is reduced by about 2?. The maximum lift to drag ratio of the parafoil with open leading edge is reduced by about 23.6% and the stalling angle of attack is reduced by about 4?. The pressure on the surface of a ram-air parafoil with open leading edge inlet is the highest. .

Experimental study on aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds

In this study, experiments were carried out to investigate aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds using a 1:25 scaled sectional model wind-tunnel testing. Pressure measurements of two typical sections, one train-head section and one train-body section, at the windward and leeward tracks were conducted under the smooth and turbulence flows with wind attack angles between-6° and 6°, and the corresponding aerodynamic force coefficients were also calculated using the integral method. The experimental results indicate that the track position affects the mean aerodynamic characteristics of the vehicle, especially for the train-body section. The fluctuating pressure coefficients at the leeward track are more significantly affected by the bridge interference compared to those at the windward track. The effect of turbulence on the train-head section is less than that on the train-body section. Additionally, the mean aerodynamic force coefficients are almost negatively correlated to wind attack angles, which is more prominent for vehicles at the leeward track. Moreover, the lateral force plays a critical role in determining the corresponding overturning moment, especially on the train-body section.

Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains

To study the influence of the pantograph fixing position on aerodynamic characteristics of high-speed trains, the aerodynamic models of high-speed trains with eight cars were established based on the theory of com- putational fluid dynamics, and eight cases with pantographs fixed on different positions and in different operational orientations were considered. The pantographs were fixed on the front or the rear end of the first middle car or fixed on the front or the rear end of the last middle car. The external flow fields of the high-speed trains were numeri- cally simulated using the software STAR-CCM＋. The results show that the pantograph fixing position has little effect on the aerodynamic drag force of the head car and has a large effect on the aerodynamic drag force of the tail car. The influences of the pantograph fixing position on the aerodynamic lift forces of the head car, tail car and pan- tographs are obvious. Among the eight cases, considering the total aerodynamic drag force of the train and the aerodynamic lift force of the lifted pantograph, when the pantographs are fixed on the rear end of the last middle car and the lifted pantograph is in the knuckle-upstream ori- entation, the aerodynamic performance of the high-speed train is the best.

Numerical simulation of subsonic and transonic flow flieds and aerodynamic characteristics of anti-tank intelligent mine

Anti-tank intelligent mine is a kind of new intelligent anti-tank bomb relying on high precision detector.It can effectively capture and damage targets with wind resistance coefficient and other factors affecting its flight characteristics under consideration.This article is based on the three-dimensional model of intelligent mine.To analyze its subsonic and transonic flow fields and the change law of aerodynamic force factor with the growth of the angle of attack,computational fluid dynamics software is used for intelligent mine flow field numerical calculation and the change law of pressure center.The results show that the large drag coefficient is conducive to the stability of scanning.Drastic changes of the flow field near the intelligent mine will disable its scanning movement.The simulation results can provide a reference for scanning stability analysis,overall performance optimization and appearance improvement.

Aerodynamic Characteristics,Power Requirements and Camber Effects of the Pitching-Down Flapping Hovering

The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studies on the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention is to improve the aerodynamic characteristics of flapping Micro Air Vehicles(MAVs).In this paper the pitching-down flapping is briefly introduced.The major works include:(1)Computing the power requirements of pitching-down flapping in three modes(advanced,symmetrical, delayed),which were compared with those of pitching-up flapping;(2)Investigating the effects of translational acceleration time,Δτ_t,and rotational time,Δτ_r,at the end of a stroke,and the angle of attack,α,in the middle of a stroke on the aerodynamic characteristics in symmetrical mode;(3)Investigating the effect of camber on pitching-down flapping.From the above works, conclusions can be drawn that:(1)Compared with the pitching-up flapping,the pitching-down flapping can greatly reduce the time-averaged power requirements;(2)The increase in Δτt and the decrease in Δτ_r can increase both the lift and drag coefficients, but the time-averaged ratio of lift to drag changes a little.And α has significant effect on the aerodynamic characteristics of the pitching-down flapping;(3)The positive camber can effectively increase the lift coefficient and the ratio of lift to drag.

Experimental Study of Effects of Tail Wings on Submunition Aerodynamic Characteristics

Aimed at the needs of deceleration of submunitions dispensed from the ballistic missile, wind tunnel tests were performed on the submunitions with different tail wing sizes at the Mach number range from 0.7 to 3.0 and the angle of attack range from 0° to 14°. Experimental data about the variance of aerodynamic coefficients with the Mach number and angle of attack were obtained systemically. The effects of the tail wing sizes on the drag coefficients and the center of pressure coefficients were discussed. Analyzed results show the arc tail wings designed are beneficial to both the deceleration effect and static stability. These results are significant to the tail wing design and its applications to the submunitions deceleration..

Wind Tunnel Experimental Investigation on the Aerodynamic Characteristics of the Multifin Rockets and Missiles

The transonic-supersonic wind tunnel experiment on the aerodynamics of the rockets and missiles that have four, six, eight flat or wrap-around fins is introduced. The experimental results show, while M∞〈2.0, with the increase of the fins＇number, the derivative of lift coefficient is increasing, the pressure center is shifting backwards, and the longitudinal static stability is augmenting. On the contrary, while the Mach number exceeds a certain supersonic value, the aerodynamic effectiveness of the eight-fin missiles would be lower than that of the six-fin missiles. For the low speed short-range missiles, by adopting six, eight or ten flat fins configuration, the lift effectiveness can be greatly increased, the pressure center can be shifted backwards, the static and dynamic stability can be obviously enhanced. For the high speed long-range large rockets and missiles launched from multi-tube launcher, the configuration adopting more than six fins can not be useful for increasing the stability but would make the rolling rate instable during the flight.

Numerical Study on Aerodynamic Characteristics of Ducted Fan Aircraft

Based on investigations into the flow field of ducted fan aircrafts,structural parameters of duct are quantified.A three-dimensional model is established for numerical simulation,and adaptive Cartesian grid is used to mesh the model in order to improve calculation speed and solution accuracy.Three-dimensional Navier-Stokes equations are brought in to analyze different duct styles.Generalization of simulation results leads to several conclusions in duct aerodynamics to help design ducted fan aircrafts.

Research on Aerodynamic Characteristics of Hovering Rotor Based on Leading Edge Droop

In view of the reduction of hovering efficiency near high tension when a helicopter rotor hovers,a numerical simulation method of lifting rotor hovering aerodynamic characteristics based on leading edge droop is established in this paper. It is dominated by Reynolds average N-S equation in integral form. Firstly,VR-12 airfoil is taken as the research object,and the influence of leading edge droop angle on the aerodynamic characteristics of two-dimensional airfoil is studied. Secondly,the modified 7 A rotor is taken as the research object,and the effects of different leading edge droop angles at the position of blade r/R=0.75—1 on the aerodynamic characteristics in hover are explored. It is found that the leading edge droop can significantly improve the aerodynamic characteristics of two-dimensional airfoil and three-dimensional hovering rotor near high angle of attack,and can effectively inhibit the generation of stall vortex.

Calculation of Aerodynamic Characteristics of Hypersonic Vehicles Based on the Surface Element Method

A program for calculating the aerodynamic properties of hypersonic vehicles based on the surface element method was developed using the general-purpose programming language C++. The calculated values of lift coefficients, drag coefficients, and surface pressure coefficients are discussed with the results of wind tunnel experiments using the HL-20 lift body and the NASA hypersonic aircraft STS Columbia OV-102 as research subjects. Finally, the results of the experimental and wind tunnel studies of the aerodynamic characteristics of the HL-20 lift body at an altitude of 65 km and Mach numbers of 6 and 10 Ma are discussed. The maximum error in the aerodynamic characteristics at 6 Ma does not exceed 3%, consistent with the results. The maximum error at 10 Ma occurs in the 11° - 14° angle of attack and does not exceed 10%, which is still within the error tolerance. The STS results for NASA’s hypersonic aircraft were also tested using this procedure. Experimental aerodynamic data for the Colombian OV-102 aircraft. The results show that the program takes only 10 minutes to calculate the results, with no more than 2% error from the wind tunnel experimental results.

Wind tunnel tests on aerodynamic characteristics of vehicles on same-storey highway and rail bridge under crosswind

In recent years,the safety and comfort of road vehicles driving on bridges under crosswinds have attracted more attention due to frequent occurrences of wind-induced disasters.This study focuses on a container truck and CRH2 high-speed train as research targets.Wind tunnel experiments are performed to investigate shielding effects of trains on aerodynamic characteristics of trucks.The results show that aerodynamic interference between trains and trucks varies with positions of trains(upstream,downstream)and trucks(upwind,downwind)and numbers of trains.To summarize,whether the train is upstream or downstream of tracks has basically no effect on aerodynamic forces,other than moments,of a truck driving on windward sides of bridges(upwind).In contrast,the presence of trains on the bridge deck has a significant impact on aerodynamic characteristics of a truck driving on leeward sides(downwind)at the same time.The best shielding effect on lateral forces of trucks occurs when the train is located downstream of tracks.Finally,the pressure measuring system shows that only lift forces on trains are affected by trucks,while other forces and moments are primarily affected by adjacent trains.

Aerodynamic characteristics of moving vehicles of two trains passing each other on bridge under crosswinds

Two trains passing each other is controlling factor for the wind-vehicle-bridge systems.To test the aerodynamic characteristics of moving vehicles under crosswinds when two trains are passing each other,a wind tunnel test device,which has two moving tracks,was developed.The rationality of the test result was discussed,the effects of intersection mode,yaw angle and lane spacing on the aerodynamic coefficients of the leeward train were analyzed,and the difference of aerodynamic coefficients between the head vehicle and the tail vehicle was discussed.The results show that the proposed test device has good repeatability.The intersection modes have a certain effect on the aerodynamic force of the leeward train when two trains are passing each other,and the results should be more reasonable during the two trains dynamic passing each other.With the decrease of yaw angle,the sudden change of train aerodynamic coefficients is more obvious.The decrease of lane spacing will increase the sudden change of leeward vehicles.In the process of two trains passing each other,the aerodynamic coefficients of the head vehicle and tail vehicle are significantly different,so the coupling vibration analysis of wind-vehicle-bridge system should be considered separately.

Numerical Study on Influence of Key Parameters of Aerodynamic Characteristics of Shaftless Ducted Rotor

Shaftless ducted rotor(SDR)is a new type of ducted rotor system designed with ducted-rotor-motor integration,which is quite different from traditional ducted rotor(DR)in aerodynamic characteristics.The sliding mesh based on unstructured grid is used to simulate the aerodynamic characteristics of SDR and DR.Then,the effects of five key parameters,namely,the rotor disk height,the number of blades,the spread angle of the duct,the central hole radius and the ducted lip radius on the aerodynamic characteristics of the SDR are investigated.It is found that the same-sized SDR produces a larger total lift than the DR in hovering,but the lift proportion of its duct is reduced.In the forward flight,a large low-speed region is generated behind the SDR duct,and the reflux vortex in blade root above the advancing blade has the trend for inward diffusion.The rotor disk height has similar effects on SDR and DR.Increasing the number of blades can effectively increase the total lift of SDR,which also increases the lift proportion of duct.Increasing the spread angle of the duct will lead to the rotor lift coefficient decrease,reducing the central hole radius can increase the total lift,but the component lift coefficient decreases.Appropriately increasing the ducted lip radius can increase the total lift,which begins to decrease after reaching a certain value.

Tests and numerical simulation of aerodynamic characteristics of airfoils for general aviation applications

This paper was to validate the effects of airfoil thickness ratio on the characteristics of a family of airfoils. Research was carried out in different ways. First,tests were conducted in the wind tunnel. And numerical simulation was performed on the basis of tests. Results from calculation were consistent with tests,indicating that numerical method could help evaluate characteristics of airfoils. Then the results were confirmed by compared with empirical data. The study also showed that the determining factor of lift is not only the thickness ratio,but the angle of attack,the relative camber and the camber line. The thickness ratio appears to have little effect on lift coefficient at zero angle of attack,since the angle of zero lift is largely determined by the airfoil camber. According to the research,numerical simulation can be used to determine the aerodynamic characteristics of airfoils in different environment such as in the dusty or humid air.

Development of Airfoils Based on Their Aerodynamic Characteristics Using Artificial Neural Networks

One of the main concerns in Engineering nowadays is the development of aircrafts of low consumption and high performance. For this purpose, airfoils are studied and designed to have an elevated lift coefficient and a low drag coefficient, thus generating a highly efficient airfoil. The higher the efficiency value is, the lower the aircraft fuel consumption will be; thus improving its performance. In this sense, this work aims to develop a tool for airfoil creation from some desired characteristics, such as the lift and drag coefficients and maximum efficiency rate, using an algorithm based on an ANN （artificial neural network）. In order to do so, a database of aerodynamic characteristics with a total of 300 airfoils was initially collected from the XFoil software. Then, through a routine implemented in the MATLAB software, network architectures of one, two, three and four modules were trained, using the back propagation algorithm and momentum. The cross-validation technique was applied to analyze the results, evaluating which network possesses the lowest value in RMS （root-mean-square） error. In this case, the best result obtained was from the two-module architecture with two hidden neuron layers. The airfoils developed by this network, in the regions with the lowest RMS, were compared to the same airfoils imported to XFoil. The presented work offers as a contribution, in relation to other works involving ANN applied to fluid mechanics, the development of airfoils from their aerodynamic characteristics.

Longitudinal Aerodynamic Characteristics of the Novel Wing-Body

The Longitudinal Aerodynamic Characteristics （LACs）of a wing-body without tail unit is computed and tested in wind tunnel. The empirical formulas of Datcom and some other authors are applied to estimate the basic Aerodynamic Coefficients. Two wing options are covered as analysis space, namely, the double-delta wing and streak wing, getting two analysis groups respectively. Good agreement between the computation results and the wind tunnel tests shows that the methodology presented is a simple and reliable way to calculate this kind of novel wing-body configurations.

Effect of Fuselage Cross Section on Aerodynamic Characteristics of Reusable Launch Vehicles

An experimental study on examining aerodynamic characteristics of fuselage cross sections for RLVs (Reusable Launch Vehicles) was conducted at Mach number 0.3, 0.9 and 4.0 in the wind tunnel of ISAS (Institute of Space and Astronautical Science), JAXA (Japan Aerospace Exploration Agency). Three bodies, having the same projected area and length, with and without a set of fins, were tested. Their cross sections are a circle, a square and a triangle with rounded corners. The results showed that the fuselage cross sections had large effects on aerodynamic characteristics in subsonic and transonic flow. The lift coefficient of the model having the triangular cross section with a set of the fins was larger than that of the others in high angles of attack region due to contributions of the separation vortices generated from the fuselage expanding to the wing surface.