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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.

Extraction of kinetic energy from the chimney flue gases for power generation using ducted turbine system is an innovative idea. This paper presents a comprehensive study on the Energy Recovery Ducted Turbine System (ERDT) system for power generation. Computational Fluid Dynamics (CFD) based analysis has been carried out to study the effect of number of blades and diffuser angle on the performance of the system. The Reynolds Averaged Navier-Stokes (RANS) modeling approach and finite volume numerical method has been used to solve the governing equations. The numerical simulations have been attempted to investigate the flow through the ERDT system, using the ANSYS-CFX with the standard k − e turbulence model. Two airfoil shapes NACA4412 and NACA4416 have been considered for the turbine blades. Results show that the power output of the ERDT system improves with increase in the number of blades and the diffuser angle. The optimum simulated results that have obtained for both the types of airfoil correspond to diffuser angle, θ = 11° & 12° for the whole range of number of blades. The maximum power obtained for same setup is 12.05 kW and 18.01 kW for airfoil NACA4412 and NACA4416 respectively. Thus, the proposed ERDT system appears to be quite useful to recover the waste kinetic energy in the chimney flue gases. The system can have good market potential due to abundant chimneys and other unnatural exhaust wind resources available globally.

An innovative idea of extracting kinetic energy from man-made wind resources (chimney flue gases) with ducted horizontal axis turbine system for producing electricity is introduced in this paper. The turbine system is positioned beyond the chimney outlet, to avoid any negative impact on the chimney performance. The duct acts as a safety cover for the energy recovery system and also enhances the performance of the system. The effect of airfoils NACA4412 and NACA4416 on the power extraction by the energy recovery system using a 6-bladed ducted turbine has been studied using CFD simulation. It is observed that the average flue gas velocity in the duct section at the throat is approximately twice that of the inlet velocity, whereas maximum throat velocity achieved is 2.6 times the inlet velocity. The results from the CFD (Computational Fluid Dynamics) based simulations analysis indicate that a significant power can be harnessed from the chimney exhaust. The system may be retrofitted to existing chimneys of thermal power plants, refineries and other industries. The market potential for this energy recovery system appears to be very high due to abundant chimneys, cooling towers and other man-made air/gaseous exhaust system present globally.