Increasing Wind Velocity Research Articles

Investigation on the Nonlinear Vibration Characteristics of Current-Carrying Crescent Iced Conductors under Aerodynamic Forces, Ampere’s Forces, and Forced Excitation Conditions

Aiming at the problem of nonlinear vibration of current-carrying iced conductors, the aerodynamic forces are introduced into the previous vibration equation of current-carrying conductors that only considered Ampere’s forces. At the same time, on this basis, a forced excitation load is further introduced to study the influence of dynamic wind on the nonlinear vibration characteristics of current-carrying iced conductors, and a new current-carrying iced conductors system under the combined action of Ampere’s forces, forced excitation, and aerodynamic forces has been established, and the improved theoretical modeling of current-carrying iced transmission lines made the model more in line with practical engineering. Firstly, the model of current-carrying iced conductors was established, and then the vibration equation of the model was derived. And the vibration equation was transformed into a finite dimensional ordinary differential equation by using the Galerkin method. The amplitude-frequency response functions of the nonlinear forced primary resonances and super-harmonic and subharmonic resonances of the system are derived by using the multiscale method. Through numerical calculation, the influence of current-carrying, spacing, wind velocity, tension, and excitation amplitude on the response amplitude when the primary resonance of the system appears is analyzed, and the difference between the two working conditions (considering the aerodynamic forces and without considering aerodynamic forces) is compared. The influence of the variation of current-carrying i on the response amplitude of super-harmonic and subharmonic resonances and the stability of the steady-state solution of forced primary resonance was analyzed. The results show that the response amplitude and the nonlinearilty of system under the action of aerodynamic forces are smaller and weaker than without the action of aerodynamic forces; the variation of line parameters has a certain influence on the response amplitude of conductor and the nonlinearity of system; the response amplitudes of the primary resonance, super-harmonic resonance, and subharmonic resonance increase with the increase in the excitation amplitudes, and the resonance peak is offset towards the negative value of the tuning parameter σ, showing the characteristics of soft spring, and the response amplitudes are accompanied by complex nonlinear dynamic behaviors such as the multivalue and jump phenomenon. The change of current-carrying i has an obvious effect on the nonlinearity of the system. The nonlinear and response amplitudes of the system are also enhanced with the increase in wind velocity. The stability of the system is judged when the primary resonance occurs, and it is found that the response amplitude shows synchronization and the out-of-step phenomenon with the change of tuning parameters. The research results obtained in this paper would help to further improve the theoretical modeling about current-carrying iced lines, and the research of line parameters can give a certain reference value to practical engineering, and it will have a positive effect on the safe operation of high-voltage transmission lines.

THE EFFECT OF NUMBER OF BLADES EXPERIMENTALLY ON THE HORIZONTAL WIND TURBINE SPEED

The aim of this research is to find the effect of the number of blades on the wind turbine speed and to find which number of blades is suitable for low wind areas and high wind areas. In wind turbine design; the number of blades, tip speed ratio, and the rotational speed of the rotor are the most important factors. At first, the tip speed ratio and the number of blades must be selected. The power of a wind turbine generator depends on the rotational speed of the rotor. The increase in wind velocity leads to an increase in the rotor speed. At wind velocity 2.36m/s, the rotational speed of 6 blades, 4 blades and 3 blades was 288, 54, and 34 rpm respectively. And, at wind velocity 13.85m/s, the rotational speed of 6 blades, 4 blades, and 3 blades are 1856, 2220, and 2103 rpm respectively. So, when the number of blades decreases, the rotational speed will increase at high wind velocity. But, at low wind velocity, the rotational speed is more effective when the number of blades increases. So, 6 rotor blades were found as suitable for low wind velocity areas as in Iraq.

Flight Trajectory Optimization of Sailplane After Rope Break

A study was performed to characterize an optimum return trajectory for a sailplane after a rope-break failure during an aerotow launch procedure. The performance of an SGS 1-26E sailplane was simulated using the equations of motion for quasi-steady flight in a time-stepping routine and published aerodynamic polar data. A gradient-based optimization algorithm was implemented using the simulated trajectory considering the glide velocity, bank angles, and runway offset angle to determine the minimum rope-break altitude from which a successful return could be theoretically produced. The SGS 1-26E sailplane was used in a flight-test campaign for empirical turn modeling and validation of the performance simulation. The minimum altitude where a return trajectory and downwind runway landing could be successfully completed after a rope-break event was observed to be 76.4 ft above ground level. A headwind and crosswind presence was observed to decrease the minimum rope-break altitude with increasing wind velocity up to a critical value, after which rope-break altitudes began to increase. These minimum rope-break altitudes serve as a theoretical indication that safe trajectories can be performed at lower failure altitudes than the commonly practiced decision altitude of 200 ft for certain wind conditions.

Numerical study on the bearing response trend of perforated sheet-type sand fences

• The displacement and stress of the sand fence had three stages with time. • The stress on the sand fence was mainly distributed at the bottom of the column. • The maximum stress on the sand fence increases with the increase of wind speed. • The stress on the sand fence increases with the decrease of pore sizes. Based on the 3D fluid–solid coupling numerical calculation method, a systematic study was conducted on the bearing characteristics of a perforated sheet-type sand fence at a given penetration rate, opening size, and wind velocity. According to the results of this study, both the displacement and stress of the sand fence experienced an impact stage, a coupling stage, and a stabilization stage under different wind velocities and times. At the initial moment of the impact stage, both the displacement and stress of the sand fence reached their maximum, i.e., the maximum position of the sand fence displacement was at the top of the panel central line, whereas the maximum position of the stress was at the site of the column 4.5 cm away from the column bottom. The duration of the impact stage was 1.5 s and did not change with the opening size or wind velocity. In the coupling stage, the displacement and stress of the sand fence underwent intense fluctuations, and the amplitude of fluctuations decreased with time. The duration of the coupling stage did not change with opening size, but increased with the increase in wind velocity. In the stabilization stage, both the displacement and stress of the sand fence reached a stable state and did not significantly change with time. In each stage, both the displacement and stress of the sand fence are inversely proportional to the opening size and directly proportional to the wind velocity, i.e., the lower the opening size, the higher the wind velocity, and the greater the displacement and stress of the sand fence. However, when the hole diameter drops below 1.03 cm, it is no longer a main influencing factor of sand fence displacement or stress change. For the sand fence in each stage, the panel displacement was higher than the column displacement, whereas the column stress was higher than the panel stress. This paper provides a basis for the design and optimization of sand fence structures, lays the foundation for establishing a mechanics-physics model for the stress distribution of sand fence structures, and presents relatively high research values.

Two-wind interactions in binaries with two orbiting giant stars

ABSTRACT Some red giant envelopes present spiral structures (seen either in dust-scattered stellar continuum or in molecular line emission), the most striking example probably being AFGL 3068. This object has been modeled (both analytically and numerically) in terms of a wind ejected from a star in orbit around a binary companion. We revisit both analytical models and 3D simulations of a wind from an orbiting red giant star, and extend the numerical simulations to the case of a binary with two red giants with strong winds. We find that most two-wind models on the orbital plane show a ‘double spiral’ structure close to the binary source, and that these two arms merge into a single spiral structure at larger distances. However, for the case of a binary with two identical winds, the two spiral arms are still present at large distances from the binary source. We also find that for models of two (not identical) dynamically important winds, a region close to the orbital plane has material from both winds. Also, an approximately conical region centered on the orbital axis is filled exclusively by the wind with larger momentum rate. These two structures lead to morphologies reminiscent of the so-called ‘hour glass’ planetary nebulae. Finally, we find that increasing wind velocity disparities lead to the formation of clumpy structures along the spiral arms. Observations of ‘clumpy spirals’ are therefore likely to indicate the presence of two strong winds from the stars in the central binary system.

Characterization of Wind‐Blown Sand With Near‐Wall Motions and Turbulence: From Grain‐Scale Distributions to Sediment Transport

AbstractThe impact and lift‐off parameters of particles play a key role in the understanding of the saltation mechanisms in aeolian environment. However, limitations of experimental instruments and numerical simulation may result in unreliable motion parameters near the bed surface. Here, we report on the impact and lift‐off parameters of saltating particles in wind‐blown sand predicted with Reynolds‐averaged Navier–Stokes (RANS) or large eddy simulation (LES) and the three‐dimensional stochastic particle‐bed collision model. Simulation results showed new phenomena, including: (a) a reduced mean impact velocity and an increased probability of lift‐off velocities distribution at left extreme with increasing free stream velocity, and (b) two peaks of the impact angle distribution. These phenomena disappear when the statistical height is increased to five times the particle diameter, suggesting that the near‐wall motions are not negligible. In addition, when turbulence is considered and wind velocity increases, the extreme value of velocity distribution increases, impact angle distribution shows a longer tail, and mean impact and lift‐off parameters increase (except impact velocity). We conclude that new velocity distribution with near‐wall motions and turbulence will significantly improve the prediction of aeolian transport flux.

CFD investigations of interference effects of building groups with flat roofs on snow load

To investigate the interference effects of building groups with flat roofs on snow load, a modified Eulerian-Eulerian model was proposed and verified by three typical cases. Based on the verified model, the impact of wind velocity on snow distribution on an isolated building with a flat roof was discussed first, and then a series of CFD simulations were carried out to investigate the snow distribution on building groups with the regular and staggered arrangement. The results showed that the amount of snow on the isolated building decreases significantly with the increase of wind velocity. The critical building density of the building group with the regular and staggered arrangement is about 0.25, above which the interference effects of the building groups on snow load are not significant. The interference effects of the building groups with the staggered arrangement on snow load are weaker than that of the building group with the regular arrangement.

Numerical simulation of wind veering effects on square-section super high-rise buildings under various wind directions

In wind resistance research involving super high-rise buildings, most studies have focused on increases in wind velocity with height. However, Ekman layer effects, which induce wind veering, have rarely been considered. The main objective of this study is to investigate the wind veering effects on square-section super high-rise buildings under various wind directions based on computational fluid dynamics (CFD). After a validation for the reliability of the numerical simulation method, large eddy simulations (LESs) are systematically performed on a 3D square cylinder with an aspect ratio of approximately 9:1. Simulated wind loads with and without wind veering under wind directions of 0°–75° are compared, and the flow mechanisms are discussed in depth. The results reveal that when wind veering is considered, the wind loads on square-section super high-rise buildings under certain wind directions (particularly in the range of 60°–75°) may be greater than those when wind veering is not considered under a 0° wind direction. More importantly, if the city in which the building will be located has a non-zero prevailing wind direction, the wind loads within the range of this non-zero wind direction may become controlling loads, which should be given sufficient attention by structural designers.

Numerical study on crosswind stability of spherical structures

Karman Vortex Street will be formed when steady incoming flow flows around square cylinder under a certain Reynolds number. The alternate shedding of Karman Vortex Street will affect the structure of the object which will cause structural vibration, and may even cause structural damage in severe cases. The “world’s largest artificial moon” located in Hongguo, Panzhou City, Guizhou Province was selected as the research object in this paper, the flow around characteristics under different crosswind velocity of which are numerically studied by computational fluid dynamics, and then the crosswind stability of the structure is analyzed. Results shows that the vortex shedding mainly occurs in the cylindrical structure, while there is no obvious vortex shedding in the spherical structure and the natural frequency of the artificial moon is much higher than the vortex shedding frequency. There are 3 low-speed regions at different heights on the central section. The lowest velocity appears at the lower part of the leeward side of the spherical structure, and there is even a backflow phenomenon, resultsing in a local vortex. Under the same Reynolds number, Karman vortex street is more likely to appear in cylindrical structure than in spherical structure. In addition, as the Reynolds number increases from 8.1×105 to 1.6×107, except to the increase in overall wind velocity, the characteristics of flow around structure at the rear of the building change little under steady-state condition. The natural frequency of the artificial moon is much higher than the vortex shedding frequency. It means that the crosswind stability of the artificial moon investigated is satisfactory.

Experimental study of the effect of wind above irregular waves on the wave-induced load statistics

The design load from waves on offshore structures are often estimated by aid of experimental studies in wave flumes and basins. When going from open sea to laboratorial conditions a number of factors are either added or omitted such as wind above waves. The paddle-generated waves are based on a spectrum taking the indirect effect of wind into account, whereas the direct effect of wind is left out. Previous studies have focused on the direct effect of wind on waves themselves, but no investigations on the load have been made. The question is whether or not airflow separation, vortexes etc. in the wind field alter physical properties such as steepness of waves, the number of breaking waves and hereby the force; especially the in-line force. To investigate the matter, an experimental study of depth-integrated force on a circular cylinder from irregular waves both with and without wind above, was conducted. An objective, when conducting the tests, was to achieve the same significant wave height whether wind was present or not. Exceedance probability curves for wave crest height, depth-integrated force and pressure were obtained. Moreover, a more descriptive assessment of the phenomena was done by studying the average force shape of the hundred largest force events. In addition, there was applied a phase-based harmonic separation method to explore the wind's effect on the harmonic force components of higher order. The front steepness of the waves was clearly increased with the introduction of wind and further increased, when increasing the wind velocity. The introduction of wind consistently increased the number of breaking waves detected with a breaking criterion. The wave-induced load in the tail of the exceedance probability curve was only increased for some of the sea states, when wind was present. This was very dependent on the size of the crest height of the largest breaking waves. The maximum wave-induced pressure in the tail of the exceedance probability curve was on the contrary increased for all sea states, when wind was present, and it kept increasing with increasing wind velocity. For one of the sea states with increased force extrema, the averaged force shape for the hundred largest events of a case with wind revealed a shape with a spiky peak consistent with that generated from breaking waves. This was not present for the case without wind. The separated harmonic contents of the force up to fourth order also showed a tendency towards more energy at harmonic components of higher order for the case with wind.

Experimental and Numerical Analyses of Wind-Induced Noise in Two-Way Radios

The generation of wind noise of entrance microphone cavities owing to turbulent airflow is an inherent problem with radio telecommunication systems, such as two-way radios. It will lead to a pressure fluctuation which is highly unpleasant and would degrade a two-way radio communication. This research aims to understand the relationship between noise level and the flow structure of the different parameters to the occurrence of noise during communication using a two-way radio device. A noise measurement is conducted to analyse the sound pressure level (SPL) within a cavity, in which computational fluid dynamic(CFD) is used to investigate the flow behaviour on the various effects of cavity positions at P1, P2, P3, P4, and P5 and wind velocities of 0.75 m/s, 1.49 m/s, 2.24 m/s, 2.99 m/s and 3.75 m/s which corresponding to Reynolds number (Re) of 8694, 17389, 26083, 34777, and 43471 respectively. CFD result showed the presence of separation of the shear layer, the development of vortex shedding, the recirculation region and vorticity were present inside the edges of the cavity. SPL increased with an increase in wind velocity and, the cavity distance of P4. In the cavity position of P5, SPL is decreased due to the wind velocity exceeding the maximum level of a wind tunnel. Therefore, the cavity position of P5 is suitable for reducing wind noise. These parameters are significant for improving the design of two-way radio to reduce the noise during outdoor communication.

Ventilation pattern and heat dissipation characteristics of a vertical dry storage cask for spent nuclear fuel: Wind tunnel experiments and CFD simulations

In this study, wind tunnel experiments and computational fluid dynamics (CFD) simulations were conducted to observe the channel airflow patterns and heat dissipation characteristics of dry storage casks for spent nuclear fuel. The parameter ranges were as follows: model scale = 1/10, Grashof number (Gr) = 1.0 × 1011, approaching wind angle (θ) = 0° or 45°, and Reynolds number (Re) = 2.6×104-8.0×105. The results show that a wind velocity = 3 m/s (Re = 8 × 104) is a critical condition for the channel airflow pattern inside the cask for cases in which θ = 0°. When θ = 45°, different wind velocities result in similar channel airflow patterns. As the wind velocity increases, the overall average surface temperature of the canister decreases, and the decrease lessens as the wind velocity increases.

Comprehensive mathematical study on solar chimney powerplant

Electricity generation by means of renewable energy such as solar energy has paid great attention over recent decades. In this paper, a comprehensive study on the effect of geometric parameters such as collector roof angle (β), chimney divergent angle (α) and wind velocity on the performance of solar chimney power plant (SCPP) is carried out. A new mathematical model for airflow through all components of SCPP including collector, turbine and chimney is presented. In order to validate the present model, the geometry and operating conditions same as ones in SCPP prototype built in Manzanares are considered in the present model and comparing the obtained results with the measured data of SCPP prototype verifies the accuracy of the present model. The parametric study is carried out at various α and β. Results show that the power output of SCPP increases with decreasing β at a specified α. In addition, it is proposed that the ratio of turbine pressure drop to total pressure potential is chosen in the range of 0.7–0.85 to attain the optimum performance of SCPP. Furthermore, results demonstrate that an increase in wind velocity has a remarkable positive effect on power generation.

Twin-Rudder-System Configurations’ Impact on Ferry Ships’ Course-Keeping Ability under Windy Conditions

Ship course-keeping plays a vital role in navigation safety, especially when a ship is operating under windy conditions. A method to control ship movements through rudder-system configuration is necessary to stabilize a ship’s course. This paper describes the twin-rudder-system configuration design’s impact on a ship’s course-keeping ability under windy conditions. A time- domain simulation using the MATLAB-Simulink program was developed for this purpose. A proportional integral derivative (PID) controller was used to adjust the ship‘s heading angle according to the desired path. Several parameters—such as relative wind velocity and directions— were accounted for in the simulation. The result shows that, at a wind direction of 88o, the ship’s course-keeping speed decreased; however, increasing wind velocity caused a large deviation in the ship’s heading angle. Meanwhile, the ship‘s course-keeping speed increased with rising windspeed directions of 219o. The ship’s course-keeping time, at around 219o under the simulation’s wind direction, was 11.84% lower than during a previous sea-trial. A possible reason for this difference is that the simulation excluded waves and currents.

Natural ventilation measurements in a multi-room dwelling: Critical aspects and comparability of pressurization and tracer gas decay tests

Ventilation in built environments is essential to guarantee a good indoor air quality and a reduced probability of infection related to virus transmission. Measuring ventilation-related parameters is not easy and currently two methods can be adopted: pressurization and tracer gas decay. The pressurization test measures the airtightness of the building, whereas the tracer gas decay test measures the actual (site- and climate-specific) air exchange rate. Finding a relationship amongst the results provided by the two tests would be very useful in view of an exhaustive characterization of the building ventilation, but it still remains an open challenge for the scientific literature. The present paper aims at investigating the criticalities in correlating the two methods; thus, an experimental campaign was performed in a multi-room dwelling performing both air permeability and air exchange rate measurements in the entire dwelling and in parts of it. A detailed uncertainty budget of the two methods was also carried out in order to perform metrological compatibility analyses.The results of the campaign highlighted that the actual air exchange rates of the dwelling present a huge variability (from <0.2 to almost 1 h-1) due to the weather conditions. Consequently, the conversion factor between the air exchange rates at 50 Pa, provided by the blower door tests, and the actual air exchange rates, obtained through the tracer gas decay tests, ranged from <20 to >100, with an exponential decrease as the wind velocity increases. Thus, adopting constant conversion factors could significantly overestimate the actual ventilation of the building.

The impact of surface air leakage on coal spontaneous combustion hazardous zone in gob of shallow coal seams: A case study of Bulianta Mine, China

Determining the coal spontaneous combustion hazardous zone is of great significance to the fire prevention and extinguishing work of the gob. In this paper, considering the actual situation of the residual coal in the gob of the Bulianta Mine, a spontaneous combustion characteristics test of the water immersion coal (S180) and raw coal (S0) was carried out. According to the experimental results, and considering the air leakage from surface cracks, a three-dimensional model of coal spontaneous combustion in shallow coal seams gob is established, and the correctness of the model is verified by on-site measured data. Then, the model is used to study the effect of different surface air leakage conditions on the hazardous zone of coal spontaneous combustion in the gob of shallow coal seams. Surface air leakage volume increased from 0% to 12% of the working face air volume, and the maximum oxygen concentration in the overlying gob increase of nearly 30 times; the maximum wind velocity increase of 14 times. Even so, there is no coal spontaneous combustion hazardous zone that satisfies both wind velocity and the oxygen concentration in the overlying gob. In the gob of the lower coal seam, with the increase of surface air leakage, coal spontaneous combustion hazardous zone move to the air intake side and deep part of the gob, the maximum width gradually increases; and area increases first, then decreases, which has a quadratic functional relationship with the surface air leakage.

Numerical simulation of wind field and sand flux in crescentic sand dunes

Sand flux is the key factor to determine the migration of sand dunes and the erosion to the surrounding environment. There are crescent-shaped sand dunes of various scales in the desert, and there are significant differences in spatial wind field and sand flux among them. However, due to the difficulty of monitoring, it is difficult to continuously observe the spatial wind field and sand flux around the larger crescentic dunes. On the basis of the Reynolds-Average Navier–Stokes (RA-NS) equation and the stress and sand flux model, the distribution of wind field and sand flux of a circular dune with a height of 4.2 m and a length of about 100 m during the four evolutionary periods of the evolution into a crescentic dune was simulated in this study. By comparing with the measured results, we verified that the closer to the leeward side, the more the simulated values of the velocity in wind field and sand flux were in line with the measured results. In order to further analyze the influence of the height of dune and other relevant parameters on sand flux, we simulated the influence on wind field and sand flux by changing the air viscosity and wind velocity of upper boundary. We found that the air viscosity mainly affected the amount of deposited sand on the leeward side of sand dune, while the increase of wind velocity would undoubtedly increase the sand flux of the whole sand dune. In addition, the simulation results also showed that the influence of changes in height of dune on the turbulent intensity of leeward side was very significant, and the turbulent intensity increased with the height of dune. The height changes of tall dunes gradually affected the transport of sand caused by wind flow behind the leeward side because that the rotation of the wind flow would form new vortexes at the large pores behind the leeward side, which would increase the turbulent energy in space and thus would increase the distance of migration of the lifting sand. While the low sand dunes could not form extra small vortexes at the bottom of the leeward side, so the wind velocity was small and the eddy currents behind the leeward side were more stable. The simulation results indicated that wind velocity was not the only reason for increasing the amount of sand flux, and the fluctuation of wind flow caused by turbulence could also stimulate the movement of sand particles on the ground.

Low airborne tenacity and spread of ESBL-/AmpC-producing Escherichia coli from fertilized soil by wind erosion.

ESBL-/AmpC-producing Escherichia coli from organic fertilizers were previously detected on soil surfaces of arable land and might be emitted by wind erosion. To investigate this potential environmental transmission path, we exposed ESBL-/AmpC-positive chicken litter, incorporated in agricultural soils, to different wind velocities in a wind tunnel and took air samples for microbiological analysis. No data exist concerning the airborne tenacity of ESBL-/AmpC-producing E. coli. Therefore, we explored the tenacity of two ESBL/AmpC E. coli strains and E. coli K12 in aerosol chamber experiments at different environmental conditions. In the wind tunnel, ESBL/AmpC-producing E. coli were detected in none of the air samples (n= 66). Non-resistant E. coli were qualitatively detected in 40.7% of air samples taken at wind velocities exceeding 7.3m s-1 . Significantly increased emission of total viable bacteria with increasing wind velocity was observed. In the aerosol chamber trials, recovery rates of airborne E. coli ranged from 0.003% to 2.8%, indicating a low airborne tenacity. Concluding, an emission of ESBL/AmpC E. coli by wind erosion in relevant concentrations appears unlikely because of the low concentration in chicken litter compared with non-resistant E. coli and their low airborne tenacity, proven in the aerosol chamber trials.

Simulation and Analysis of Radial Temperature for Aluminum Conductor Steel Reinforced with 1250mm2 Large Cross-Section

In order to meet the growing demand for electricity, the construction of UHVDC project has vigorously carried out. With the improvement of voltage level, the cross-section of conductor also increases. For large cross-section conductor, the number of steel and aluminum single wires and layers of the conductor are large, and the internal structure is very complex. It has been proved that there is a temperature difference in the radial direction of the conductor due to the contact heat transfer between steel and aluminum based on previous studies. However, most studies are focused on normal conductors, not large cross-section conductors. Therefore, in this paper, the geometric model and temperature calculation model for 1250mm2 large cross-section ACSR conductor, which is widely used in UHVDC, were established. Simulation of conductor temperature distribution was carried out, and the influence of wind velocity, environment temperature and current on radial temperature difference was analyzed. The results show that, with the increase of wind velocity and the decrease of current, the radial temperature difference of conductor decreases gradually, while the environment temperature has little influence on the radial temperature difference.

Flutter study of flapwise bend-twist coupled composite wind turbine blades

Bending-twisting coupling induced in big composite wind turbine blades is one of the passive control mechanisms which is exploited to mitigate loads incurred due to deformation of the blades. In the present study, flutter characteristics of bend-twist coupled blades, designed for load alleviation in wind turbine systems, are investigated by time-domain analysis. For this purpose, a baseline full GFRP blade, a bend-twist coupled full GFRP blade, and a hybrid GFRP and CFRP bend-twist coupled blade is designed for load reduction purpose for a 5 MW wind turbine model that is set up in the wind turbine multi-body dynamic code PHATAS. For the study of flutter characteristics of the blades, an over-speed analysis of the wind turbine system is performed without using any blade control and applying slowly increasing wind velocity. A detailed procedure of obtaining the flutter wind and rotational speeds from the time responses of the rotational speed of the rotor, flapwise and torsional deformation of the blade tip, and angle of attack and lift coefficient of the tip section of the blade is explained. Results show that flutter wind and rotational speeds of bend-twist coupled blades are lower than the flutter wind and rotational speeds of the baseline blade mainly due to the kinematic coupling between the bending and torsional deformation in bend-twist coupled blades.