Abstract: A roof 201 has an apex 200. A wind turbine 202 is positioned above the apex 200. Air flows through the gap 204 between the apex 200 and the turbine 202. A flow optimizer 203 diverts a section of airflow close to the apex 200 into the region 205, downstream of the apex. This section of diverted airflow is turned away from the local airflow direction towards the surface of the roof 201, downstream of the apex. This reduces the boundary layer separation and turbulence downstream of the apex 200, which reduces energy loss associated with sub-optimal static pressure recovery downstream of the apex 200, and thus increases the discharge coefficient of the system.

Abstract: A turbine assembly comprising, a rotor having a plurality of blades, and a shroud at least partially enclosing the rotor and adapted to expose a portion of the rotor. At least two shroud portions extend axially along the rotor and around the rotor to at least partially enclose the rotor. At least two shroud portions are rotationally adjustable. In use, the shroud defines a variable inlet and a variable outlet. The inlet area and outlet area are variable independently of each other. Adjustment of the area of the inlet area does not result in the same magnitude of adjustment in area of the outlet area. Adjustment of the position of the inlet area does not result in the same magnitude of adjustment of the position of the outlet area.