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A new approach for the design of diffuser-augmented hydro turbines using the blade element momentum
- Silva, Paulo A.S.F., Rio Vaz, Deborah A.T.D., Britto, Vinicius, de Oliveira, Taygoara F., Vaz, Jerson R.P., Brasil Junior, Antonio C.P.
- Energy conversion and management 2018 v.165 pp. 801-814
- diffusers, mass flow, mathematical models, momentum, shear stress, turbines, turbulent flow
- It is known surrounding a turbine with a diffuser may significantly increase its power. This effect has attained considerable attention as it shows theoretically the possibility of achieving a power coefficient about 2 times greater than an ordinary turbine. However, the effect of the diffuser efficiency has not been implemented into blade element momentum yet. Hence, this paper presents a novel approach to design diffuser-augmented hydro turbines considering the diffuser efficiency. Based on the blade element momentum, new expressions for the axial induction factor and thrust are obtained. To assess the proposed model, a comparative evaluation of two different diffusers (flanged conical diffuser and flanged lens diffuser) is performed. A numerical modeling investigation using computational fluid dynamics is carried out based on the Reynolds Averaged Navier-Stokes formulation, using the κ-ω shear-stress transport turbulence model. Evaluations for both turbine and diffuser are performed using experimental data available in the literature. Numerical and theoretical results are compared for a shrouded turbine equipped with a 83% efficiency diffuser. The relative difference observed for the maximum power coefficient between the proposed model and an actuator disk model with diffuser is about 5.3%. For the hydro turbine with flanged conical diffuser, the mass flow rate is about 20% higher than for a bare turbine, while for the turbine with flanged lens diffuser the increase is only 2.4% . Also, for the flanged conical diffuser the power is increased by 53%. Furthermore, it is observed that the proposed blade element momentum with diffuser achieved good agreement with the numerical model, providing improved results compared to other models available in the literature.