Navegando por Assunto "Difusor"

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Acesso aberto (Open Access)
Uma abordagem matemática aplicada ao projeto de turbinas hidrocinéticas e eólicas com difusor utilizando a teoria do elemento de pá
(Universidade Federal do Pará, 2019-04-30) VAZ, Déborah Aline Tavares Dias do Rio; VAZ, Jerson Rogério Pinheiro; http://lattes.cnpq.br/1623983294183975
It is known surrounding a turbine with 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, as well as the use of minimum pressure coefficient criterion to avoid cavitation during the optimization of the hydrokinetic chord along the blade. Hence, this work 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. In addition, both efficiency and load generated on a diffuser are considered to the extension of existing formulation to determine power coefficient in cases where diffuser losses are taken into account through efficiency (ηd) and area ratio (β). To assess the proposed model, a comparative evaluation of two different diffusers (flanged conical diffuser and flanged lens diffuser) is performed. Numerical and theoretical results are compared for a shrouded turbine equipped with 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. The optimization model of hydrokinetic chord shows relevant results in relation to the prevention of cavitation.
Acesso aberto (Open Access)
An Investigation of a Mathematical Model for the Internal Velocity Profile of Conical Diffusers Applied to DAWTs
(Universidade Federal do Pará, 2015-06) BARBOSA, Disterfano Lima Martins; VAZ, Jerson Rogério Pinheiro; FIGUEIREDO, Sávio W.O. ; SILVA, Marcelo de Oliveira e; LINS, Erb Ferreira; MESQUITA, André Luiz Amarante
The Diffuser Augmented Wind Turbines (DAWTs) have been widely studied, since the diffusers improve the power coefficient of the wind turbine, particularly of small systems. The diffuser is a device which has the function of causing an increase on the flow velocity through the wind rotor plane due to pressure drop downstream, therefore resulting in an increase of the rotor power coefficient. This technology aids the turbine to exceed the Betz limit, which states that the maximum kinetic energy extracted from the flow is 59.26%. Thus, the present study proposes a mathematical model describing the behavior of the internal velocity for three conical diffusers, taking into account the characteristics of flow around them. The proposed model is based on the Biot-Savart's Law, in which the vortex filament induces a velocity field at an arbitrary point on the axis of symmetry of the diffusers. The results are compared with experimental data obtained for the three diffusers, and present good agreement.
Acesso aberto (Open Access)
Avaliação de modelo de elemento de pá aplicado a turbinas eólicas com difusores através de análise CFD
(Universidade Federal do Pará, 2023-05-30) BEZERRA, Waldson Melo; MESQUITA, André Luiz Amarante; http://lattes.cnpq.br/1331279630816662
The diffuser effect on free flow turbines shows a possibility of reaching a power coefficient greater than that of a classic turbine, exceeding the Betz limit. The present work evaluated the effect of an Eppler 423 profile diffuser coupled in a horizontal axis wind turbine with a 4-bladed rotor NACA 65(3) 618 profile. Using computational fluid mechanics (CFD, Computational Fluid Dynamics), numerical simulations were performed allowing to obtains more information about the fluid flow and the increase in extracted power for configurations with and without diffuser for the velocity of 7 m/s. Considering the dimensions of the test section, the results obtained in the CFD analyses were validated through experimental results, in which the rotor and diffuser assembly were confined in a wind tunnel. It was observed that coupling the diffuser to the turbine considerably increased the fluid velocity, providing a 37% increase in the initial velocity of the flow. Showed an increase in the power coefficient in the order of 45,45% with the use of the diffuser, for the same flow velocity, 7 m/s. Thus, through the results obtained numerically in this work, it was possible to obtain reliable data for the evaluation of a specified Blade Element Momentum (BEM) model applied to diffuser-augmented wind turbines, which is employed to analyze the same turbine rotor and diffuser designs. Despite the good results of the BEM model, the present study indicates possible improvements for the consistency of the modeling.
Acesso aberto (Open Access)
Estudo da eficiência de uma turbina hidrocinética com difusor projetada para o aproveitamento da energia remanescente da barragem de Tucuruí
(Universidade Federal do Pará, 2023-05-15) LIMA, Adry Kleber Ferreira de; LINS, Erb Ferreira; http://lattes.cnpq.br/5272283698536321; https://orcid.org/0000-0002-6643-5889; VAZ, Jerson Rogério Pinheiro; http://lattes.cnpq.br/1623983294183975; https://orcid.org/0000-0001-6440-4811
Harnessing the remaining energy downstream of dams has recently attained great attention as the kinetic energy transported by the water current is indeed considerable. This work develops a study on the performance of a horizontal-axis hydro turbine under di!user e!ect, in order to quantify the energy gain by comparing both turbines with and without di!user. A 3-bladed hydro turbine with 10 m diameter shrouded by a flanged conical di!user is employed. A numerical modeling using computational fluid dynamics is carried out based on the Reynolds Averaged Navier-Stokes formulation, using the Ÿ – Ê – SST (Shear Stress Transport) turbulence model. The results yield good agreement with experimental and theorical data available in literature.
Acesso aberto (Open Access)
Otimização geométrica de pás de turbinas hidrocinéticas cavitantes sob efeito difusor
(Universidade Federal do Pará, 2022-11-22) PICANÇO, Hamilton Pessoa; VAZ, Jerson Rogério Pinheiro; http://lattes.cnpq.br/1623983294183975; https://orcid.org/0000-0001-6440-4811; LINS, Erb Ferreira; http://lattes.cnpq.br/5272283698536321; https://orcid.org/0000-0002-6643-5889
Diffuser technology placed around hydrokinetic rotors may improve the conversion of the fluid’s kinetic energy into shaft power. However, rotor blades are susceptible to the phenomenon of cavitation, which can impact the overall power efficiency. This paper presents the development of a new optimization model applied to hydrokinetic blades shrouded by a diffuser. The proposed geometry optimization takes into account the effect of cavitation inception on the rotor blades surface. The main contribution of this work to the state-of-the-art is the development of an optimization procedure that takes into account the effects of diffuser efficiency, ηd, and thrust, CT d. The model uses the Blade Element Momentum Theory to seek optimized blade geometry in order to minimize or even avoid the occurrence of cavitation. The minimum pressure coefficient is used as a criterion to avoid cavitation inception. Also, a Computational Fluid Dynamics investigation was carried out to validate the model based on the Reynolds Averaged Navier-Stokes formulation, using the κ-ω Shear-Stress Transport turbulence and Rayleigh-Plesset models, to estimate cavitation by means of water vapor production. The methodology is applied to the design of a 10 m diameter hydrokinetic rotor, rated at 250 kW of output power at a flow velocity of 2.5 m/s. An analysis of the proposed model with and without a diffuser is carried out to evaluate the changes in the optimized geometry in terms of chord and twist angle distribution. It is found that the flow around a diffused-augmented hydrokinetic blade doubles the cavitation inception relative to the unshrouded case. Additionally, the proposed optimization model can completely remove the cavitation occurrence, making it a good alternative for the design of diffuser-augmented hydrokinetic blades free of cavitation.