Effect of number of blades in ducted turbine system on kinetic energy extraction from chimney flue gases – benchmarking with wind energy system

A multi-blade ducted wind turbine, also called the diffuser augmented wind turbine (DAWT) has a good wind energy conversion effect over the traditional wind turbine. The market potential for energy recovery from the chimney flue gases made it necessary to explore the possibility of extraction of the energy from flue gases using the DAWT. The duct is a converging-diverging nozzle with the turbineblades located at the throat. In general 3 or more number of blades is frequently used to maximize the energy conversion to the bladetorque. The effect of number of blades on the power extraction by the energy recovery ducted turbine has been studied in this paper. A CFD-based simulation study has been carried out. The results so obtained have been benchmarked with the published data for the results for the ducted turbines for wind power generation. The general airfoil NACA4420, NACA4416 and NACA4412 were adopted to produce various composite profiles for turbine-blade. The large number of blades appears to provide the sufficient blade areas for the conversion of energy of flue gases to the turbine-rotor torque. On other hand the more number of blades also increases the blockage to the flue gases, resulting in increased back-flow. This paper presents the variation of power coefficient (CP) and torque coefficient (CT) with respect to the tip speed ratio (λ) for different number of blades, and varying blade geometry.