Abstract: A blade 20 for a horizontal-axis wind turbine rotor comprises a radially-outer, energy-extraction portion 32 and a radially-inner, ventilation portion 30. The radially-inner ventilation portion 30 is shaped to ventilate a central area 34 of a wake of the rotor during use such that it contains more kinetic energy compared to the wake from a conventional rotor design. The increased wind flow velocity at the centre 34 of the wake generates additional shear stresses, with corresponding turbulence development, which gives rise to increased wake diffusion.

Abstract: Formation testing which may involve circulating mud in a pipe string from a mud pit through a port in the pipe string to a downhole diverter sub, wherein the pipe string is suspended in a wellbore extending into a subterranean formation, operating a downhole pump to pump formation fluid from the formation, wherein the formation fluid comprises gas, and mixing the pumped formation fluid with circulated mud such that a proportion of the pumped formation gas in the circulated mud is maintained below a threshold value.