Wind Turbine Enables modeling of wind turbines. The links from within the Wind Turbine editor can be used to build an example setup (scaffolding) for either a mono pile or a floating wind turbine. Alternatively, examples can be found for RIFLEX, SIMO, and RIFLEX-Coupled. 1. Wind turbine components 1.1. RIFLEX or RIFLEX-Coupled Wind Turbine A wind turbine model in RIFLEX includes lines which represent the outer parts of the blades (Blade Lines), lines which represent the inner part of the blades (Eccentricity Lines), a shaft (including a flex joint where the generator torque is applied to the system), and (optionally) a tower line. If the tower line is defined, the effect of the tower on the incoming wind is accounted for (tower effect) when computing the loads on the blades. A shared supernode at the hub should connect the blades and the shaft. Each blade must consist of two lines. The inner line represents eccentricity and the outer line the actual foil blade. A rigid supernode connection is used to represent connection between the two lines. The constant term, c0, in the linear constraint equation is subsequently used for blade pitch control. One and only one flex-joint has to be specified within the shaft line (line type). The flex-joint has to be fixed in the bending degrees of freedom and be given a specified stiffness in the torsional degree of freedom. The specified torsion stiffness will be used during static analysis. During dynamic analysis, the torsion will be controlled be the regulator. Figure 1. Outline of a wind turbine model In a RIFLEX-Coupled analysis, a SIMO body with wind coefficients must be defined as a part of the turbine. This body is used to ensure that the wind data is read correctly in the simulation. 1.2. SIMO Wind Turbine A SIMO wind turbine is connected to a rotating body, which must be coupled to a reference body as described in the SIMO user manual. The generator torque is applied at the moment coupling between the two bodies. The SIMO turbine geometry is described by the turbine radius and cone angle, while the tilt angle can be defined based on the orientation of the bodies. Aerodynamic input data is given in a table with reference to the airfoils for different sections along the blade. All of the turbine blades are identical. Note that the local twist angle is given with opposite sign compared to RIFLEX. 2. Aerodynamic loads The wind loads on the blades are computed based on the load coefficient description in the air foil library file and together with a blade element momentum (BEM) method. The applied BEM code includes dynamic inflow, i.e. a time delay on changes of induced velocity related to the time it takes to convect vorticity in the wake downstream away from the rotor. With dynamic inflow, the BEM method will give correct time series of rotor and blade loads under conditions of changing blade pitch angle, wind speed and direction, and tower motion. The main features of the BEM theory are: Induced velocity is calculated assuming momentum balance for a ring-shaped control volume. Blade sections are treated as independent. Aerodynamic coefficients from wind tunnel tests are used for the blades. Empirical corrections are used for tip-vortices and cascade effects / lift amplification. The BEM theory is a proven, simple and CPU efficient method to simulate rotor aerodynamics and the method represents the industry standard. In the Wind Turbine editor for RIFLEX, several options for modifying the aerodynamic load calculation are given. 2.1. Turbine Orientation The turbine can be defined as upwind or downwind. The definition of turbine orientation is needed in order to select the correct tower shadow model and to set the correct coordinate system for the generator. 2.2. Tower Line and tower influence options If the tower line is defined, the influence of the tower on the wind will be included. For an upwind turbine, a potential flow tower effect is used. For a downwind turbine, a cosine-squared type of wake is applied. 2.3. Wind Load Option One can choose to include or ignore the wind moment around longitudinal axis of the blades. If the wind moment is excluded, the aerodynamic moment (Cm in the airfoil tables) is set to zero, and the offset between the aerodynamic center and structural center is ignored. 3. Controller The generator torque and blade pitch controller options are identical for SIMO and RIFLEX wind turbines. The controller actions can be defined by user-defined input to a generic internal controller. The internal control system will be suitable in many situations. For some analyses it is however desirable to use a specialized control system. A typical example of this could be if the wind turbine manufacturer can provide a black-box control system for use in simulations. Using such a control system could yield more realistic results compared to the generic control system. In this situation, the external control system option must be used. There are two external controller interfaces: A Java based interface and a Bladed style controller interface. The Java based interface has more flexibility and more input signals available than the Bladed style controller interface. In some situations a controller might however already be available with a Bladed style interface in which the latter option could be useful. An external controller will typically return the commanded blade pitch angles, generator torque, and nacelle yaw rate to SIMA. It is important to note that drivetrain losses are not taken into account by SIMA, so the torque to be applied on the rotor should correspond to the torque "before losses". In other words, if the wind turbine has for example a nominal power of 10 MW and an efficiency of 94%, the torque such be such that, when multiplied by the rotor speed, results in a power of 10/0.94 MW. 4. Turbine and blade results An additional output file is created for analyses which include a wind turbine. Several wind-turbine-specific coordinate systems are defined in order to present the results. Shaft system (XS,YS,ZS): Follows the non-rotating shaft element. Wind output, azimuth, and out-of-plane (OoP) tip deflection follow this system. Rotor system (XR,YR,ZR): Follows the rotating shaft element and 1st blade. The blade tip in-plane (IP) deflection follows this system. Foil system (XAF,YAF,ZAF): Follows the blade airfoil, with XAF aligned with the chord axis. Aerodynamic results on element level follows this system. Figure 2. Rotor and shaft coordinate systems Figure 3. Out-of-plane deflection Figure 4. In-plane deflection Figure 5. Aerodynamic axis 4.1. Wind turbine results Result storage can be specified for the wind turbine and for individual blades. If wind turbine storage is specified, the following results are stored: Result Unit Interpretation Rotor speed [degrees/s] Rotational speed of the rotor and low-speed shaft (LSS) Rotor speed (rpm) [rpm] Rotational speed of the rotor and LSS Generator speed (LP-filtered) [rpm] Rotational speed of the generator and high-speed shaft, equal to \(N_{gb}*\Omega_{LSS}\) Mechanical generator torque on LSS [Nm] Torque applied from the generator on the low-speed shaft, equal to \(N_{gb}*Q_G\). Gearbox losses are not considered. Electrical generator output [W] Electrical power produced by the generator. Equal to \(Q_G*N_{gb}*\Omega_{LSS}*\eta_{gen}\) Azimuth angle blade 1 [deg] The azimuth angle of blade 1, with azimuth angle of 0 deg defined as the blade pointing upwards Incoming wind speed X-dir in shaft system [m/s] Undisturbed wind velocity in X-direction in the shaft coordinate system. Incoming wind speed Y-dir in shaft system [m/s] Undisturbed wind velocity in Y-direction in the shaft coordinate system. Incoming wind speed Z-dir in shaft system [m/s] Undisturbed wind velocity in Z-direction in the shaft coordinate system. Aero force X-dir in shaft system [N] Aerodynamic force acting in \(X_s\). Calculated from integrating the aerodynamic load over all blades. Aero force Y-dir in shaft system [N] Aerodynamic force acting \(Y_s\). Calculated from integrating the aerodynamic load over all blades. Aero force Z-dir in shaft system [N] Aerodynamic force acting \(Z_s\). Calculated from integrating the aerodynamic load over all blades. Aero moment around X-axis in shaft system [N] Aerodynamic moment acting around \(X_s\), corresponding to the aerodynamic torque. Calculated from integrating the aerodynamic load over all blades. Aero moment around Y-axis in shaft system [N] Aerodynamic moment acting around \(Y_s\). Calculated from integrating the aerodynamic load over all blades. Aero moment around Z-axis in shaft system [N] Aerodynamic moment acting around \(Z_s\). Calculated from integrating the aerodynamic load over all blades. Pitch angle blade N, Line: line name [deg] Pitch angle of blade N. Equal to the pitch command sent from the controller and the actual applied pitch angle Tip In-Plane deflection blade N, Line: line name [m] In-plane deflection of the blade tip of blade N. Deflection is calculated relative to the blade tip ghost node. Tip Out-of-Plane deflection blade N, Line: line name [m] Out-of-plane deflection of the blade tip of blade N. Deflection is calculated relative to the blade tip ghost node. \(N_{gb}\): Gearbox ratio. \(\Omega_{LSS}\): Rotor speed \(Q_G\): Generator torque \(\eta_{gen}\): Generator efficiency 4.2. Blade results The following results are given if turbine blade response is stored. Results are stored for the specified blades, segments and elements. 4.2.1. Minimum storage Result Unit Interpretation Lift force intensity in foil system [N/m] Lift force per unit length, calculated as \(1/2*\rho_{air}*C_l(\alpha)*U^2*c\) Drag force intensity in foil system [N/m] Drag force per unit length, calculated as \(1/2*\rho_{air}*C_d(\alpha)*U^2*c\) Moment intensity in foil system [N/m] Aerodynamic moment around blade X-axis per unit length, calculated as \(1/2*\rho_{air}*C_m(\alpha)*U^2*c^2\) Relative wind velocity in foil system [m/s] Relative wind velocity seen by the airfoil, including incoming wind, rotation velocity, and induced velocities. \(\rho_{air}\): Air density. \(\alpha\): Angle of attack. \(U\): Wind velocity over the airfoil, including induced velocities. \(c\): Chord length. \(C_l\): Lift coefficient. \(C_d\): Drag coefficient. \(C_m\): Moment coefficient. 4.2.2. Medium storage Minimum storage and: Result Unit Interpretation Angle of attach in foil system [deg] Angle of attack (\(\alpha\)) of airfoil at the relative wind velocity Lift force coefficient in foil system [-] \(C_l(\alpha)\) Drag force coefficient in foil system [-] \(C_d(\alpha)\) Moment coefficient in foil system [-] \(C_m(\alpha)\) Induced wind speed x-dir in foil system [m/s] Induced velocity along the foil x-axis Induced wind speed y-dir in foil system [m/s] Induced velocity along the foil y-axis Induced wind speed z-dir in foil system [m/s] Induced velocity along the foil z-axis Incoming wind speed x-dir in foil system [m/s] Incoming velocity along the foil x-axis Incoming wind speed y-dir in foil system [m/s] Incoming velocity along the foil y-axis Incoming wind speed z-dir in foil system [m/s] Incoming velocity along the foil z-axis Separation point, fraction of chord [-] The calculated separation point for the airflow over the foil. 0 corresponds to separation at the leading edge, 1 is no flow separation (separation at the trailing edge) Axial induction factor in rotor system [-] Axial induction factor \(a\). Tangential induction factor in rotor system [-] Tangential induction factor \(a'\). Annulus average axial induced wind in rotor system [m/s] Induced axial wind velocity (parallel to the shaft axis), averaged over all blades in the annulus defined by the element. Annulus average tangential induced wind in rotor system [m/s] Induced tangential wind velocity, averaged over all blades in the annulus defined by the element. Annulus average axial force in rotor system [N] Axial aerodynamic force (parallel to the shaft axis), averaged over all blades in the annulus defined by the element. Annulus average tangential force in rotor system [N] Tangential aerodynamic force, averaged over all blades in the annulus defined by the element. 4.2.3. Maximum storage Medium storage and: Result Unit Interpretation Transformation matrix rotor to foil I=i J=j [-] Element i,j of the transformation matrix describing the transformation between the rotor coordinate system and local foil coordinate system. External Wrapping Generic Internal Controller