Flow control device

An aerofoil comprising a low pressure surface and a spoiler arranged on the low pressure surface, the spoiler having a rest position where it is substantially flush with the low pressure surface and an activated position where it protrudes from the low pressure surface and modifies the airflow over that surface;

• wherein the spoiler is a device having a stable state in the rest position and a stable or quasi-stable state in the activated position;
• the spoiler bends to move from the rest position to the activated position;
• and
• the coupling of the spoiler to the aerofoil transfers at least some strain from the aerofoil to the spoiler and the movement of the spoiler is triggered by the strain in the aerofoil crossing a threshold,
• wherein in the activated position the low pressure surface is depressed below the surrounding surface to define a recessed channel transverse to an oncoming airflow configured so that the oncoming airflow can flow into the recessed channel.

A flow control device with a device aerodynamic surface arranged on a structure with a structure aerodynamic surface such that strain in the structure is at least partially transferred to the flow control device, the flow control device having a first state corresponding to a first shape of the device aerodynamic surface, and a second state corresponding to a second shape of the device aerodynamic surface,

• wherein the first state is a stable state of the flow control device and the second state is either a steady state or a second stable state of the flow control device,
• wherein the flow control device is arranged to rapidly transition from the first state to the second state when strain in the structure exceeds an activation threshold of the flow control device,
• wherein the strain in the structure which is at least partially transferred to the flow control device and exceeds an activation threshold of the flow control device is in a direction transverse to an oncoming airflow direction, and
• wherein the flow control device has attached lateral sides and unattached fore and aft edges with respect to the airflow direction.