Provided is a trailing edge assembly of a wind turbine rotor blade, which includes a mounting portion; a flap portion flexibly connected to the mounting portion so that a flap angle subtended between the mounting portion and the flap portion can be altered; a volume adjustable chamber arranged between the mounting portion and the flap portion and realised to alter its volume between a minimum volume associated with a minimum flap angle and a maximum volume associated with a maximum flap angle; and at least one tube to face into an airflow passing over the airfoil region of the rotor blade, and an inner orifice arranged to face into the interior of the volume adjustable chamber such that an airflow between the outer orifice and the inner orifice alters the volume of the volume adjustable chamber. Embodiments of the invention further describe a wind turbine rotor blade.