Blade Design Overview

Once the airfoil polars have been created or imported (see Airfoil Analysis Overview and Polar Extrapolation Overview), they can be used in an aerodynamic blade design. To access the aerodynamic blade design module in QBlade, click on the blade symbol in the main toolbar, as shown in Fig. 74.

Blade design module in QBlade.

Fig. 74 The aerodynamic blade design module is represented by the blade symbol in the QBlade main tool bar.

An overview of the blade design module is shown in Fig. 75. The module is split into three main parts. On the left side, the controls dock allows the user to define the blade sections and to control the 3D view section. The latter is located in the middle of the module and allows the user have a interactive 3D representation of the current blade design. The right side of the module presents a graphical representation of the aerodynamic quantities along the blade. The user can interact with these graphs in the same manner as with all the other graphs within QBlade (see GUI Overview).

Overview of the Blade Design Module in QBlade

Fig. 75 Overview of the blade design module in QBlade. The control dock is located on the left, the interactive 3D view in the center and the graphs on the right.

In QBlade, the aerodynamics of a blade are defined by splitting the blade into several stations. This is shown in Fig. 76. The aerodynamic parameters are defined by the user at each station and QBlade interpolates these values between stations (i.e. over a blade element).

Aerodynamic Blade Definition in QBlade is done in stations.

Fig. 76 Aerodynamic blade definition in QBlade is done in stations. Values are linearly interpolated along the elements between the stations.

HAWT Blade Design

Each blade station is defined by a series of aerodynamic properties. The global blade/rotor parameters are the number of blades and the hub radius. The distributed blade properties are split into basic and advanced aerodynamic blade properties. The columns of the basic blade properties are:

  • Pos [m] is the position of the station along the blade pitch axes (in m). It can be given in blade root coordinates or in hub coordinates.

  • Chord [m] is the local chord length of the blade station (in m).

  • Twist [deg] the local twist of the blade station (in deg).

  • Foil is the airfoil object used for that station (see Airfoil Generation Overview).

  • Polar is the particular polar used for this station (linked to the airfoil object).

In addition to the manual blade definition option, QBlade allows for some automated setups to speed up the blade design. It has the option to automatically set the thread axis at the position of maximum thickness of the airfoil. It also offers the option to do a blade shape optimization so that the twist angle is optimal for a given tip speed ratio. In addition the chord distribution can be optimized according to the theories of Betz and Schmitz (see Gasch and Twele1 for details). Finally, the blade design can also be scaled to another size using different scaling methods. These include position scaling, chord scaling and twist scaling.

The HAWT blade design module

Fig. 77 The HAWT blade design module

Advanced HAWT Blade Design

The advanced blade design table can be accessed through the Advanced Blade Design Table, as shown in Fig. 78.

The columns of the advanced blade property table are:

  • Position [m] is the position of the station along the blade pitch axis (in m). It should match the position given in the basic blade properties.

  • X (IP) Offset [m] is an additional offset of the blade station in the global y-direction. This is the in-plane direction.

  • Y (OOP) Offset [m] is an additional offset of the blade station in the global x-direction. This is the out-of-plane direction.

  • P Axis [%c] is the position of the pitch axis as a percentage of the local chord. It is used to define the axis at which the station is rotated and also to define the position of the structural beam (see Cross Sectional Coordinate Systems).

The Advanced Blade Design tab

Fig. 78 The Advanced Blade Design tab

VAWT Blade Design

The VAWT blade design is analogous to the HAWT blade design module in QBlade, with the exception of the different geometrical properties the user has to define to construct a VAWT blade. These properties are:

  • Height [m] is the height position of the station (in m).

  • Chord [m] is the local chord length of the blade station (in m).

  • Radius [m] is the local radial distance from the axis of rotation (in m).

  • TOffset [m] is the local tangential offset at the blade station (in m).

  • Twist [deg] the local twist of the blade station (in deg).

  • Circ [deg] the local circumferential angle of the blade station, to be used for helical rotor designs (in m).

  • P Axis [%c] is the position of the pitch axis as a percentage of the local chord. It is used to define the axis at which the station is rotated and also to define the position of the structural beam (see Cross Sectional Coordinate Systems).

  • Foil is the airfoil object used for that station (see Airfoil Generation Overview).

  • Polar is the particular polar used for this station (linked to the airfoil object).

The VAWT blade design module

Fig. 79 The VAWT blade design module

Multi Polar Blade Definition

The extrapolated airfoil polar data used in the blade definition is always linked to an airfoil object. Several different airfoil polars can be linked to one airfoil object (e.g. for different Reynolds numbers). A blade station can also contain multiple polars for one airfoil object e.g. for different Reynolds numbers. If the blade shall have a multi-polar definition, then these need to be previously created and assigned to an airfoil object and the corresponding option has to be enabled in the blade design dock (see Fig. 80).

The multi Reynolds number polar option in the blade designer dock.

Fig. 80 The multi Reynolds number polar option in the blade designer dock.

Active Blade Elements

QBlade can model and add active elements, such as active trailing edge flaps, to a blade definition. This is done in the advanced blade design tab, as shown in Fig. 78. To add an active element to the blade definition, one or more Dynamic Polar Sets must have been previously defined in the Polar Extrapolation Module (see: Polar Extrapolation Overview). Each active element is defined between two blade stations, where a dynamic polar set can be chosen at each blade station. Linear interpolation is used between the two Dynamic Polar Sets. An active element is always applied to each blade of the rotor.

The active element dialog.

Fig. 81 The active element dialog.

Blade Damage (Erosion)

A blade damage can be added to a blade definition. This feature is intended to model damaged blade elements (for instance leading edge erosion effects) through a modification of the underlying polar data at certain blade stations of individual blades. The airfoil polar for the damaged blade station must be created previously in the Polar Extrapolation Overview. Similar to an active element, the blade damage is defined between two stations. These can have different airfoils and polars, even multi-polar sets. QBlade will interpolate along the blade between the two stations with the different polars. Different to the active elements, a blade damage can be assigned to an individual blade and can thus be used to model an aerodynamic imbalance.

The blade damage dialog.

Fig. 82 The blade damage dialog.

Importing and Exporting Blade Definitions

Blade Definition Import Options

Fig. 83 Blade Definition Import Options

QBlade allows to import and export blade definitions in a series of formats. The import/export options are located in the menu item Blade Design, see Fig. 83. QBlade is currently capable of importing blade definitions in the following formats:

  • QBlade blade format (.bld),

  • Blade geometry in QBlade, AeroDyn and WT_perf format,

  • AeroDyn V15 full blade definition,

  • WindIO Yaml Definition

QBlade is currently capable of exporting blade definitions in the following formats:

  • QBlade blade definition ASCII format (.bld),

  • Full blade definition in AeroDyn V13 format,

  • 3D blade geometry in STL or .txt format.

Blade definition ASCII File

When a blade is exported into the .bld format, the associated 360 polar (.plr) and airfoil (.afl) files are automatically created. An exemplary .bld file is shown below:

----------------------------------------QBlade Blade Definition File------------------------------------------------
Generated with : QBlade IH v2.0.2_alpha windows
Archive Format: 310002
Time : 12:05:50
Date : 29.06.2022

----------------------------------------Object Name-----------------------------------------------------------------
NREL_5MW                                 OBJECTNAME         - the name of the blade object

----------------------------------------Parameters------------------------------------------------------------------
HAWT                                     ROTORTYPE          - the rotor type
3                                        NUMBLADES          - number of blades

----------------------------------------Blade Data------------------------------------------------------------------
POS [m]             CHORD [m]           TWIST [deg]         OFFSET_X [m]        OFFSET_Y [m]        TAXIS [-]           POLAR_FILE
1.5000              3.5420              0.0000              0.0000              0.0000              0.5000              t100.0_nre_5mw_Cylinder_1_section_with_a_Cd_of_0.50.plr
2.8674              3.5420              13.3080             0.0027              0.0006              0.5000              t100.0_nre_5mw_Cylinder_1_section_with_a_Cd_of_0.50.plr
5.5992              3.8540              13.3080             0.1057              0.0250              0.5000              t100.0_nre_5mw_Cylinder_1_section_with_a_Cd_of_0.50.plr
8.3289              4.1670              13.3080             0.2499              0.0591              0.5000              t90.0_nre_5mw_Cylinder_2_section_with_a_Cd_of_0.35.plr
11.7402             4.5570              13.3080             0.4586              0.1085              0.5000              t40.0_nre_5mw_DU40_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
15.8399             4.6520              11.4845             0.5696              0.1157              0.5000              t35.0_nre_5mw_DU35_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
19.9410             4.4580              10.1649             0.5485              0.0983              0.5000              t35.0_nre_5mw_DU35_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
24.0421             4.2490              9.0132              0.5246              0.0832              0.5000              t30.0_nre_5mw_DU30_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
28.1432             4.0070              7.7970              0.4962              0.0679              0.5000              t25.0_nre_5mw_DU25_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
32.2443             3.7480              6.5457              0.4654              0.0534              0.5000              t25.0_nre_5mw_DU25_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
36.3454             3.5020              5.3623              0.4358              0.0409              0.5000              t21.0_nre_5mw_DU21_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
40.4464             3.2560              4.1890              0.4059              0.0297              0.5000              t21.0_nre_5mw_DU21_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
44.5475             3.0100              3.1256              0.3757              0.0205              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
48.6486             2.7640              2.3193              0.3452              0.0140              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
52.7497             2.5180              1.5261              0.3146              0.0084              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
56.1676             2.3130              0.8629              0.2891              0.0044              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
58.9013             2.0860              0.3699              0.2607              0.0017              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
61.6338             1.4190              0.1059              0.1774              0.0003              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
63.0000             0.9610              0.0000              0.1201              0.0000              0.5000              t17.0_nre_5mw_NA64_A17_airfoil_with_an_aspect_ratio_of_17._Original_-180_to_180deg.plr
1

R. Gasch and J. Twele. Windkraftanlagen: Grundlagen, Entwurf, Planung und Betrieb. Vieweg+Teubner Verlag, 4th edtion edition, 2005. ISBN 978-3-322-99446-2.