| Offshore wind power has become an important direction of the renewable energy in the world.With the growing scale of wind turbine blade,the flexibility becomes higher.Therefore,the large wind turbines in practical engineering usually have tilt angels to prevent the collision of blade tip and tower during operation,which not only make the aerodynamic performance being more complicated,but also have important effects on the wake flow.Moreover,the typhoon has become an unavoidable problem for offshore wind farm,and it has no definite stipulations in design standards so far.To solve the above problems,taking the FX93-2500 wind turbine for research objects,this paper used the wind tunnel tests and CFD numerical method to analyze its aerodynamic characteristics and wake flow under operational states and typhoon states with full wind directions,the main contents and innovations are as follows.Based on the FX93-2500 wind turbine,using rigid model with a geometrical scale of 1/125,the wind tunnel tests are conducted under the prerequisite of guaranteeing the similar conditions of the kinematics and dynamics for the obvious limitations of wind tunnel test.The CFD method was used to simulate the flow field of the 1/125 wind turbine model with the same inflow conditions as wind tunnel test.The comparison of simulation results with experimental data implies that the CFD numerical method has high accuracy.Using the CFD method verified by the test results and taking the FX93-2500 wind turbine for research object,the numerical simulations were performed for wind rotors with different tilt angels in different inflow conditions.The results showed that the existence of shaft tilt angel could make the total aerodynamic load of wind rotor still display the 3p fluctuation as the wind shear,and it significantly influenced the inhomogeneity of wind load on rotor,producing opposite pitch moment to the wind shear and larger yawing moment,but it had little influence on the output power.With the combined impact of wind shear and shaft tilt angel,the average value of pitch moment was offset with being cut by 24.58%,but the fluctuation amplitude was increased by 24.38%;the average value of yawing moment was increased 2.59 times that of wind rotor without tilt,and the fluctuation amplitude was increased by 27.91%,which could influence the operation stability of wind turbine.Moreover,the shaft tilt angel can make the wake zone of wind rotor shifted to the upstream of rotor rotation,and the offset increased with increasing of downstream distance.It was verified that this influence of shaft tilt angel on wake flow was universal phenomena,and weakly correlated with inlet flow conditions.Based on numerical simulation results of single wind turbine,and considering the impact of shaft tilt angel,three dimensional numerical simulations of wind farm with two wind turbines in different layouts were performed to analyze the interactions among the wake flow of the two wind turbines.The results showed that the shift of wake flow field caused by shaft tilt angel could significantly affect the load distribution and output power of downstream wind turbine.The maximum of output loss did not appear in the tandem layout of the two wind turbines,but shifted the tandem layout 0.5D in the upstream direction of the rotating,which could reach 38.79%.It also could lead to the unbalance of the downstream wind rotor,the peak values of pitching moment and yawing moment of downstream wind rotor appeared in the tandem layout position or shifting 0.5D in the upstream direction of the rotating,and up to the 3.29 times and 15.88 times that of the upstream wind rotor.The downstream wind turbine will be away from the influence of the wake flow of upstream wind rotor when the vertical wind direction distance of the two wind turbines is 1.5D in the upstream direction of the rotating or 1D in the downstream direction of the rotating.Based on above analysis,we optimized the layout of wind turbines,which can provide references for the studies of wind farm layout.In this paper,3D simulation of the FX93-2500 offshore wind turbine was performed,based on the situation that the wind turbine was in braking-stop state and its yaw controls was inactive under typhoon with 360° full wind directions.The conclusions of this study are as follows,under the action of typhoon,it’s obvious that blades at different positions have different attack angles,among which the attack angle of blade in vertical position is the maximum,making the fluctuating wind loads greater than the other blades,and most risky under typhoon.In addition,there exist obvious interactions among the three blades of the same wind rotor,the downwind blades have an astringent effect on the trailing vortex of the upwind blades,making the fluctuating wind loads of upwind blades significantly decreased,the interactions among the three blades of wind rotor in θ=30° parking position are most significant.As the wind direction of typhoon changed from feathering position,the total aerodynamic forces acting on wind rotor approximately increased first and then decreased because of the special structural form of blade.The parking positions of wind rotor had small effect on the average total aerodynamic forces,but had great effect on the fluctuation characteristic of aerodynamic force.But,unlike the aerodynamic force,the average values and fluctuation characteristics of the total aerodynamic moments were all affected by the rotor parking positions significantly.As the wind rotor in θ=30°parking position had a better forcing performance,however,the yawing moment was far greater than that of the other parking positions,which surpassed 600kN·m at almost all wind directions,and also very sensitive to the wind direction changes.Therefore,it can be worthwhile to adopt the typhoon resistance without electrical power strategy to avoid the yaw control system inactive when the electric power network fails or wind direction device breaks down under typhoon,this study suggests to turn the wind rotor to θ=30° parking position,loosen the yaw brake,and make wind rotor as a tail vane in order to achieve free yawing,then the wind rotor will be eventually adjusted to the favorable wind direction under the function of great yawing moment. |
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