M.Sc Thesis

M.Sc StudentDanon Ron
SubjectCoanda-based Reciprocating Wind-Energy Generator
DepartmentDepartment of Energy
Supervisor PROF. David Greenblatt
Full Thesis textFull thesis text - English Version



Wind turbines are a major source of renewable energy with worldwide total installed capacity growing exponentially. Nevertheless, they are at a disadvantage when compared to conventional fossil-fuel power plants due to their high capital and maintenance costs. The current research presents a new patented concept of wind energy generation and investigates some of its fundamental aerodynamic phenomena. This concept utilizes active flow control in order to generate oscillatory loads that drive a large pendulum in reciprocating motion. Conceptually, the system comprises a sting-mounted circular cylinder on a pivot, with either one or two nominal degrees-of-freedom (DOF). The cylinder is counterbalanced by a concentrated mass, torsional springs and torsional loads. The cylinder is equipped with two blowing slots on opposite sides that are activated periodically. This results in a periodically varying and alternating direction Coandă effect that generates periodic lift and drag forces. These periodic forces can be exploited to drive the system at one or more of its resonance frequencies. A linear mathematical development concluded that the system can produce positive net output power.

Steady Coandă data are available in the literature, but there are virtually no transient or three-dimensional (tip effects) Coandă data; thus a wind tunnel experiment was designed and used to quantify these effects. Slot blowing was produced by means of an air flow controller and wind tunnel data comprised steady and transient pressure measurements, including three-dimensional effects. The unsteady pressure sensitive paint (PSP) technique, in conjunction with Nitrogen blown from the slot, was used for flow visualization. A simple dimensional analysis was adopted in the case of ambient surrounding and resulted in a first-order linear model that facilitated appropriate analysis of the problem. In addition, in the presence of a freestream, a dimensionless parameter depicting the rise time for the lift coefficient transient response was found to be consistent. Finally, the experiment indicated a reasonable two-dimensional flow in the absence of a free-stream, and strong three dimensional effects in the presence of a freestream.

The proposed system can potentially reduce manufacturing, installation and maintenance costs in terms of dollars per megawatt installed. A single relatively simple cylinder replaces typically three blades and maintenance is, in principle, much simpler with the drive-train and generator located close to the ground. Nevertheless, for a meaningful appraisal of the system, further research should consider efficiently converting reciprocation motion to useful energy; system control and optimization; and design and manufacturing.