Wind turbine blade, wind turbine generator including wind turbine blade, and method for designing wind turbine blade

A method for designing a wind turbine blade comprising:

• defining a blade back shape from a maximum blade thickness position toward a rear edge so that
• when a distance from a front edge along a blade chord line is represented by X and a distance from the blade chord line to a blade back side is represented by Y,
• the blade back shape includes
• a first region that extends from the maximum blade thickness position toward the rear edge on the blade back side with dY/dX as a primary derivative amount of the Y to the X decreasing by a first amount of change,
• a second region that is located on a side of the rear edge of the first region and extends toward the rear edge with the dY/dX having a second amount of change smaller than the first amount of change, and
• a third region that is located on the side of the rear edge of the second region and is connected to the rear edge with the dY/dX decreasing by a third amount of change larger than the second amount of change.