M.Sc Thesis

M.Sc StudentGarzozi Anan
SubjectExploitation of the Coanda effect for wind energy generation
DepartmentDepartment of Energy
Supervisor PROF. David Greenblatt
Full Thesis textFull thesis text - English Version


Greenhouse-gases (GHG) emissions, as a result of energy supply and use, is unsustainable economically, environmentally and socially. Sustainable and low-carbon energy technologies must be on the agenda because of the pressing need to accelerate the development of clean energy technologies.

Exploiting wind energy is not a new technique. Mainly, wind energy is generated by wind turbines, which have experienced a high annual growth rate during the last three decades. Small wind turbines, defined as those with less than a 100kW rating, are experiencing a significant increase in demand. Nevertheless, they are at disadvantage when compared to other renewable energy sources due to their low efficiency at low wind speeds, as well as acquisition and maintenance costs. The current research investigated the viability of a new patented concept for wind energy generation in small-scale. The specific objectives were to build a prototype and, directly measure its performance and validate a mathematical model.

The proposed concept is a radically new concept for wind-energy generation by means of active flow control induced oscillations. The active flow control is activated periodically to produce periodic lift and drag forces that drive an inverted pendulum system. Conceptually, the system comprises a sting-mounted cylinder on a pivot that gives the system on degree of freedom motion. The cylinder is equipped with two blowing slots on opposite sides. Blowing an air jet from the slots periodically results in a periodic varying direction Coandă effect that generates periodic lift and drag forces. The cylinder is counterbalanced by tension springs and they are connected so that the cylinder is maintained vertically upright. A mechanism connected directly to the pivot converts the kinetic energy of the system (reciprocating motion) to electricity or another form of mechanical energy.

A linear mathematical model was developed for the system, and expression for the output power coefficient was derived. This expression includes the lift force developed on the system as a result of the Coandă effect. This lift force cannot be calculated theoretically, therefore, it was measured experimentally, compared with the literature and then substituted in the theoretical expression, resulting in a semi-theoretical model. In addition, the net power extracted from the wind was measured directly. The influence of different parameters on the output and input power were evaluated, mainly the mass flow rate, natural frequency of the system and the load applied to the system. These laboratory experiments served to isolate the most efficient operation regimes. Lastly, the theoretical and experimental output power results were compared in order to validate the semi-theoretical model of the system.

The major objective of this research, namely validation of the theory, was achieved. Based on the mathematical model, predictions were made for systems with different parameters. Predictions show that a two meter high system with natural frequency of 1.3Hz, at 4.8m/s wind speed can achieve a net power efficiency of 17%.

In conclusion, the proposed concept is potentially more efficient than small wind turbines. Moreover, this new approach can potentially reduce manufacturing, installation and maintenance costs.