Patent Publication Number: US-2023138124-A1

Title: Aerodynamic load reduction during blade installation and service in a wind turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No.PCT/EP2021/055356, having a filing date of Mar. 3, 2021, which claims priority to EP Application No. 20165448.0, having a filing date of Mar. 25, 2020, the entire contents both of which are hereby incorporated by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to a method for reducing the aerodynamic load during blade installation and service in a wind turbine. 
     BACKGROUND 
     During blade installation and service cases there is no control on the aerodynamic loads of the blades, because pitch control and rotor speed control are not active. These loads can drive the design of the wind turbine components like hub and blade bolts and of the installation and service tools, e.g. cranes. Blade loads during installation may drive requirement on the number of blade bolts needed before removing the crane. Blade loads during service may drive requirement on rotor components, such as rotor lock and pitch lock. 
     Methods are known, which may be used for reducing such loads. For example, the blade may be installed with an alignment to the wind trying to minimize the aerodynamic load, or the rotor may be oriented such that aerodynamic blade loads are reduced. Further, temporary add-on like stall strips may be installed on the blade during installation. EP 2 708 734 A1, for example, discloses a wind turbine blade comprising one or more flow disturbing devices for provoking air flow separation arranged on the suction side of the blade, wherein the flow disturbing device is removable. EP 3 225 834 A1 describe a method which comprises the steps of attaching a temporary cover on the rotor blade for covering at least a part of the aerodynamic device before lifting the rotor blade to the top of the tower of the wind turbine, and detaching the cover subsequently. 
     Such methods are not yet considered optimal. Therefore, an aspect relates to efficiently reducing loads during blade installation and service in a wind turbine. In particular, it would be desirable to achieve such scope without using additional temporary elements on the blades, in order to reduce time of intervention and costs. 
     SUMMARY 
     According to embodiments of the present invention, it is provided a method for installing or servicing a wind turbine including at least a rotor blade having a plurality of aerodynamic devices for influencing the airflow flowing from the leading edge of the rotor blade of the wind turbine to the trailing edge of the rotor blade. The method comprising the steps of:
         activating the aerodynamic devices,   installing the rotor blade or performing a service on the wind turbine,   deactivating the aerodynamic devices.       

     The phase of activating the aerodynamic devices is performed before or during the phase of installing the rotor blade or performing a service on the wind turbine. The phase of deactivating the aerodynamic devices is performed during or after the phase of installing the rotor blade or performing a service on the wind turbine. 
     The method of embodiments of the present invention allows activation of the aerodynamic devices to change the blade shape during installing or servicing a wind turbine. The change in the blade shape reduces the aerodynamic forces developed by the wind flowing on the blade. Lower aerodynamic forces lead to lower blade oscillation and lower blade loads, that the installation tools (e.g. cranes) or the wind turbine have to compensate or carry. Such aerodynamic devices are integrated in the rotor blades, not a temporary add-on like stall strips. Therefore, it is not needed to add it before the installation/service and remove it after installation/service. The above method is, with respect to the prior art installation and service:
         more flexible because blades are made more less sensitive to the wind direction and speed and more stable;   faster due to more flexibility, also depending on the fact that removable add-ons are not needed;   cheaper because it requires less time and the tools can be smaller, due to lower loads.       

     Lower blade loads during installation reduces requirement on the number of blade bolts needed before removing the crane. Lower blade loads during service reduce requirement on rotor components, such as rotor lock and pitch lock. 
     The aerodynamic devices are flaps, i.e. aerodynamic devices installed at the trailing edge of the rotor blade. Alternatively, the aerodynamic devices are spoilers, i.e. an aerodynamic device installed at the leading edge or in a position intermediate between the leading edge and the trailing edge of the rotor blade. Flaps and spoilers may be together provided on the rotor blade. 
     The aerodynamic devices may be activated before the phase of installing the rotor blade or performing a service, for example before the lifting phase of the rotor blade. Alternatively, the aerodynamic devices may be activated during the installation of the rotor blade or performing a service, for example during the lifting phase of the rotor blade. 
     According to embodiments of the present invention, each aerodynamic device is movable by an actuator between a first protruded configuration and a second retracted configuration, the aerodynamic devices being in the first protruded configuration when activated and in the second retracted configuration when deactivated. 
     The aerodynamic devices may be deactivated after the phase of installing the rotor blade or performing a service on the wind turbine is terminated, for example after the rotor blade has been connected to the hub of the wind turbine. Alternatively, the aerodynamic devices may be deactivated during the installation of the rotor blade, for example during the lifting phase of the rotor blade. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
         FIG.  1    shows a wind turbine; 
         FIG.  2    shows a rotor blade of a wind turbine with an aerodynamic device, which is operatable for performing embodiments of the present invention; 
         FIG.  3    shows a first radial section of the rotor blade of  FIG.  2   ; 
         FIG.  4    shows a second radial section of the rotor blade of  FIG.  2   ; 
         FIG.  5    shows a block diagram of a method according to embodiments of the present invention; and 
         FIG.  6    shows a block diagram of another embodiment of a method according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The drawings are in schematic form. Similar or identical elements are referenced by the same or different reference signs. 
       FIG.  1    shows a conventional wind turbine  10  for generating electricity. The wind turbine  10  comprises a tower  11  which is mounted on the ground  16  at one end. At the opposite end of the tower  11  there is mounted a nacelle  12 . The nacelle  12  is usually mounted rotatable with regard to the tower  11 , which is referred to as comprising a yaw axis substantially perpendicular to the ground  16 . The nacelle  12  usually accommodates the generator of the wind turbine and the gear box (if the wind turbine is a geared wind turbine). Furthermore, the wind turbine  10  comprises a hub  13  which is rotatable about a rotor axis Y. When not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotor axis Y. 
     The hub  13  is often described as being a part of a wind turbine rotor, wherein the wind turbine rotor is capable to rotate about the rotor axis Y and to transfer the rotational energy to an electrical generator (not shown). 
     The wind turbine  1  further comprises at least one blade  20  (in the embodiment of  FIG.  1   , the wind rotor comprises three blades  20 , of which only two blades  20  are visible) mounted on the hub  13 . The blades  4  extend substantially radially with respect to the rotational axis Y. Each rotor blade  20  is usually mounted pivotable to the hub  13 , in order to be pitched about respective pitch axes X. This improves the control of the wind turbine and in particular of the rotor blades by the possibility of modifying the direction at which the wind is hitting the rotor blades  20 . Each rotor blade  20  is mounted to the hub  13  at its root section  21 . The root section  21  is opposed to the tip section  22  of the rotor blade. 
       FIG.  2    illustrates the rotor blade  20  comprising an aerodynamic device  30  in the form of an actuated spoiler. Between the root section  21  and the tip section  22  the rotor blade  20  furthermore comprises a plurality of aerofoil sections for generating lift. Each aerofoil section comprises a suction side  25  and a pressure side  26 . The aerofoil shape of the aerofoil portion is symbolized by one aerofoil profile which is shown in  FIG.  2    and which illustrates the cross-sectional shape of the rotor blade at this spanwise position. Also note that the suction side  25  is divided or separated from the pressure side  26  by a chord line  27  which connects a leading edge  41  with a trailing edge  31  of the rotor blade  20 . The aerodynamic device  30  in  FIG.  2    is movable by means of a pressure line  53  connected to a pneumatic actuator  34 . According to the embodiment of the attached figures, the pneumatic actuator  34  is realized as a hose. The hose  34  comprises an elastic outer skin, such that it can inflate and deflate reversibly and during many cycles when operated by means of the pressure line  53 . The pressure line  53  is comprised in a pressure supply system  52  and controlled by a control unit  51 . The pressure supply system  52  provides pressurized air or other pressurized gas, to the pneumatic actuator  34 . In this context, the term “pressurized fluid” not only implies positive pressure but also negative pressure, wherein fluid is sucked (or “drawn”) out of the pneumatic actuator  34 . The pressure line  53  could be in practice realized as tubes or pipes which do not significantly change their volume. The control unit  51  is responsible for setting a specific pressure at the pressure supply system  52  which subsequently leads to a certain predetermined pressure at the pneumatic actuator  34 . By controlling the pressure of the pressurized air, the pneumatic actuator  34  is operated between an inflated and a deflated configuration. Any of the control unit  51  and the pressure supply system  52  may be located in the root section  21  of the rotor blade  20  or placed elsewhere in the wind turbine, such as e.g. in the hub  13  of the wind turbine  10  or in the nacelle  12  or in the tower  11 . The rotor blade  20  additionally comprises a flow regulating unit  40  comprising multiple pairs of vortex generators. The flow regulating unit  40  are arranged on the suction side  25  of the blade  20  between the aerodynamic device  30  and the trailing edge  31 . The flow regulating unit  40  may be arranged on the suction side  25  of the blade  20  between the leading edge  41  and the aerodynamic device  30 . The flow regulating unit  40  may be not present and only the aerodynamic device  30  may be used to regulate the flow on the surface of the blade  20 . The blade  20  may comprise a plurality of aerodynamic devices  30 . The aerodynamic device  30  may be configured as a trailing edge flap. The blade  20  may comprise a plurality of aerodynamic devices  30  including flaps and spoilers. 
       FIG.  3    shows the aerodynamic device  30  in a first protruded configuration, corresponding to an inflated configuration of the pneumatic actuator  34 . In the first configuration the aerodynamic device  30  deviates the airflow  71  which is flowing from the leading edge  41  to the trailing edge  31  of the rotor blade. The aerodynamic device  30  in the first protruded configuration induces stall. This is visualized with relatively large vortices  63  downstream of the aerodynamic device  30 . A consequence of the induced stall is a decrease in lift of the rotor blade and, consequently, a reduced loading of the rotor blade and related components of the wind turbine. 
       FIG.  4    shows the aerodynamic device  30  in a second retracted configuration, i.e. moved downwards towards the surface of the rotor blade  20 , corresponding to a deflated configuration of the pneumatic actuator  34 . In this second configuration, the airflow  71  flowing across the aerodynamic device  30  remains attached to the surface of the rotor blade  20 , thus that no flow separation, i.e. stall, occurs. As a consequence, the lift of the rotor blade increases. Re-energizing vortices  64  are generated in the boundary layer by the vortex generators  40 , which have the effect of helping to increase the lift. As a result, the highest lift values can be achieved. 
     By operating the pneumatic actuator  34  of the aerodynamic device  30  through the pressure line  53 , the aerodynamic device  30  can be moved between the first protruded configuration and the second retracted configuration in order to vary the aerodynamic properties of the blade as desired and requested when installing or servicing the wind turbine  10 . 
     As shown in  FIG.  5   , when installing the wind turbine  10 , the method  100  comprises a first step  110  of activating the aerodynamic device  30  at the beginning or during the lift and installation of the rotor blade  20 . In the first step  110  the aerodynamic device  30  is activated to reach the first protruded configuration. The activation of the aerodynamic device  30  changes the blade shape. The change in the blade shape reduces the aerodynamic forces developed by the wind flowing on the rotor blade  20 . In a second step  120  of the method the rotor blade  20  is installed on the hub  13 . In a third step  130  of the method, after the installation has completed, the aerodynamic device  30  is deactivated, i.e. the aerodynamic device  30  is brought to the second retracted configuration. 
     Alternatively, when servicing the wind turbine  10 , the method  100  comprises a first step  110  of activating the aerodynamic device  30  at the beginning or during the service procedure. In the first step  110  the aerodynamic device  30  is activated to reach the first protruded configuration. The activation of the aerodynamic device  30  changes the blade shape. The change in the blade shape reduces the aerodynamic forces developed by the wind flowing on the rotor blade  20 . In a second step  120  of the method the service is performed. In a third step  130  of the method, after the service has been completed, the aerodynamic device  30  is deactivated, i.e. the aerodynamic device  30  is brought to the second retracted configuration. 
     In another embodiment, as shown in  FIG.  6   , the first phase of activating  110  the aerodynamic devices  30  and/or the third phase of deactivating  130  the aerodynamic devices  30  are performed during the phase of installing  120  the rotor blade  20  or performing a service on the wind turbine. For example, the aerodynamic devices  30  may be activated and/or deactivated during a phase of lifting a rotor blade  20  towards the hub  13 , depending on the conditions (intensity and direction) of the wind. 
     Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.