It is projected that, in the following years, the wind-energy industry will maintain its rapid growth over the last few decades. Such growth in the industry has been accompanied by the desirability and demand for larger wind turbines aimed at harnessing more power. However, the fact that massive turbine blades inherently experience increased fatigue and ultimate loads is no secret, which compromise their structural lifecycle. Accordingly, this demands higher overhaul-and-maintenance (O&M) costs, leading to higher cost of energy (COE). Introduction of flow-control devices on the wind turbine is a plausible solution to this issue. Flow-control mechanisms feature the ability to effectively enhance/suppress turbulence, advance/delay flow transition, and prevent/promote separation, leading to enhancement in aerodynamic and aeroacoustics performance, load alleviation and fluctuation suppression, and eventually wind turbine power augmentation. These flow-control devices are operated primarily under two schemes: passive and active control. Development and optimization of flow-control devices present the potential for reduction in the COE, which is a major challenge against traditional power sources. This review performs a comprehensive and up-to-date literature survey of selected flow-control devices, from their time of development up to the present. It contains a discussion on the current prospects and challenges faced by these devices, along with a comparative analysis centered on their aerodynamic controllability. General considerations and conclusive remarks are presented after the discussion.

In this work, a new composition based on Paraffin wax and HTPB fuel, loaded with nanoparticles has been proposed for hybrid propulsion system. Lithium aluminium hydride (LiAlH₄) and Magnesium hydride (MgH₂) nanoparticles have been used as additives. A detailed rheological, thermal and ballistic characterisation has been carried out. The Magnesium hydride doped hybrid fuel exhibits lower viscosity as compared to the Lithium aluminium hydride doped one, leading to comparatively enhanced entrainment-aided combustion. LiAlH₄ doped hybrid fuels also exhibit solid-like behaviour and thus greater stability in the solid phase in contrast to the MgH₂ doped fuel. LiAlH₄ doped fuel is thermally more stable and produces relatively greater residual-mass. The loading of nanoparticles significantly improves the fuel regression performance during ballistic firing. This can be attributed to the release of nascent hydrogen and metal nanoparticles during dehydrogenation of metal hydrides. Regression rate enhancement in the range of 350%–475% is observed in comparison to the conventional HTPB hybrid fuels. A power law governing regression rate has been proposed for the tested hybrid fuels.

Hybrid propulsion offers safe, reliable and environment friendly alternative to conventional systems. There is a wide range of propellants and additives reported for hybrid propulsion. In this paper some energetic particles comprising metals, and light metal hydrides and their advantages in terms of regression behavior are discussed. Additive particles like aluminium, boron, boron carbide, tungsten, iron, carbon, magnesium, magnesium hydride, aluminium hydride, lithium aluminium hydride, ammonium perchlorate and ammonia borane are discussed. Regression rate enhancement of 20%-150% has been reported and found to be dependent on additive percentage. Metals have high density and heat of oxidation which helps in regression rate augmentation. Metal hydrides are good source of hydrogen varying from 7.6% for Magnesium hydride to 19.6% for Ammonia borane. These hydrides release nascent hydrogen during combustion and improve regression rate thereby boosting specific impulse and characteristic velocity of the rocket. Energetic particle laden hybrid rocket fuel has potential to make chemical propulsion safer, economical and sustainable.