Challenges in maintaining a favourable flow regime over turbine blades
Friday April 8, 2016 08:08
As wind turbine rotors grow in size, maintaining a favourable flow regime over turbine blades is increasingly challenging. Rotational effects, thick airfoil sections and turbulence in the atmosphere give rise to an altogether complex flow regime over the blades. However, in order to deliver the optimum torque for power production whilst mitigating fatigue loads, air flow around the blades needs to be optimal.
One way to ensure this is by mounting vortex generators along the span of the rotor blades. Flow impinging on the vanes gives rise to streamwise vortices which (passively) enhance mixing of the outer energetic flow with the slow-moving boundary layer, as visualised. If designed properly, this can prevent or even delay flow separation.
An integrated blade design considering vortex generators requires proper understanding of the influence of such devices on boundary layer properties. To this end, vortices behind an experimental set of vortex generators in a boundary layer wind tunnel have been measured. Such a set up ‘magnifies’ the boundary layer and allows for a more detailed assessment of the vortex behaviour and in-turn, their influence on the encompassing boundary layer. The insights from such measurements can lead to the development engineering tools which consider these passive devices in a robust, inexpensive manner suitable for iterative design.
Passive vortex generator pairs and (right) visualised vortical motion in the boundary layer