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Mashhad, Iran

Karbasian H.R.,Pusan National University | Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Renewable Energy | Year: 2016

In the present study the power extraction capability by flapping foil hydrokinetic turbine is investigated. The heaving motion of the foil is considered in two different motion patterns including the simple linear translational motion and the rotation of swing arm on which the foil is mounted. The laminar and incompressible flow around a NACA0012 foil is conducted using Computational Fluid Dynamics (CFD) method. It is shown that the power extraction is possible and more desirable in the lower reduced frequencies. Additionally, the swing arm mode may increase the amount of extracted power and improve the performance of hydrokinetic turbine. Changes in kinematics of flapping foil alter the angle of attack profile and the local Reynolds number on the surface of the foil. These two sensitive changes influence on the sub-layer flow near to surface of the foil and make the vortex structure to be complex during flapping cycle. In the other words, in swing arm mode the vortex creation, growth, separation and shedding occur with an alternative pattern compared to simple mode. Finally, it is shown that the importance of the swing arm mode is in a certain range of swing arm lengths. © 2015 Elsevier Ltd.

Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University | Karbasian H.R.,Ferdowsi University of Mashhad
Computers and Fluids | Year: 2015

In the present study, the effect of elliptical motion trajectory on the aerodynamic characteristics and propulsive performance of a flapping airfoil is evaluated. A periodic horizontal motion (forward/backward) is combined with vertical motion (upward/downward) of the airfoil to introduce a new kinematic parameter, and of course, an elliptical motion trajectory for flapping airfoil. Similar kinematics is also observed in the flying of birds and swimming of the penguins or turtles. For this modeling, the Navier-Stokes equations are used to simulate the unsteady flow field over a two dimensional NACA0012 airfoil. The Navier-Stokes equations are discretized based on the finite volume method and are solved with a pressure-based algorithm. The flow is assumed to be laminar and incompressible and transient terms are conducted using a second order Euler implicit scheme. It is shown that the combination of horizontal and vertical motions for the flapping airfoil changes the kinematics, motion trajectory and hence the effective angle of attack profile during the flapping cycle. The elliptical motion trajectory will also influence on the fluid structures and change the vortex shedding pattern and wake zone behind the airfoil. Additionally, the introduced kinematics may influence significantly on the aerodynamics and propulsive performance of either pure plunging or pitching/plunging airfoil. © 2014 Elsevier Ltd.

Karbasian H.R.,Ferdowsi University of Mashhad | Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Renewable Energy | Year: 2015

In the present study the power extraction possibility by a number of flapping hydrofoils in tandem formation is investigated. A code is developed to predict power extraction capacity for the various number of flapping hydrofoils based on the kinematic and hydrodynamic models. The selected hydrodynamic model follows two dimensional quasi-steady hydrodynamic instability formulation. It is shown that the power extraction is also possible from water stream with the low Reynolds number. As a result of power extraction at low speed flows, the predicted maximum power efficiency is also in lower flapping frequencies. Furthermore, it is found that there are limited number of required flapping hydrofoils in tandem formation, in which the power influence rate drops notably after the second flapping hydrofoil. The flapping hydrofoils at downstream also experience higher hydrodynamic forces, while the flapping hydrofoil kinematics is the key parameter to harness extracted power. As a result of this investigation, the introduced model and code can be used as one of initial tools to predict power capacity for obtaining vast concept regarding tidal sites with the flapping foil hydrokinetic turbines. © 2015 Elsevier Ltd.

Esfahani J.A.,Ferdowsi University of Mashhad | Pishbin I.,Khayyam University | Modarres Razavi S.M.R.,Ferdowsi University of Mashhad
Applied Thermal Engineering | Year: 2015

The present experimental study aims to evaluate the stability, thermal and environmental behavior of the natural gas premixed combustion of a 55 kW Low Swirl Burner (LSB). The main focus of this investigation is to clarify the significance of recess length as a controlling factor of combustion performance. The results depicts that by varying the recess length, different flame regimes are distinguished. In terms of heat transfer efficiency and stack losses of the combustion, the lifted stable flame regime has superiority over the attached flames thanks to the more extended flame brush and proper temperature uniformity ratio. The attempt is also made to make an analogy between the effect of recess length and the effect of swirl number on the flame characteristics. The results revealed that the influence of reducing swirl number is proportional to the increase of recess length due to the decaying nature of swirl flow. © 2015 Elsevier Ltd. All rights reserved.

Esfahani J.A.,Ferdowsi University of Mashhad | Vahidhosseini S.M.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Applied Thermal Engineering | Year: 2015

A three-dimensional analytical solution of transport problem of convection-drying is accomplished using Green's function method (GFM). Mass conservation, momentum and energy equations must be solved to obtain convective heat and mass transfer coefficients. In most papers, these equations are solved using numerical methods alike. The mass transfer coefficients are calculated using analogy between the thermal and concentration boundary layers. The results of previous studies are used for these coefficients values. Green's function method has been used as a new simple method to solve equations of transport problem. The heat and mass transfer equations are solved using Green's function method and taking diffusion equation-related adjoint differential operator equal to Delta function. Of course, these equations are coupled with thermal diffusivity, because this parameter is a function of temperature and is used in mass transfer equation. These two coupled equations were solved with a good approximation which is a definition of a weighted function for moisture distribution. Thus, temperature and moisture distributions within the body obtained as functions of x, y, z and an independent time variable t. After these steps it is seen that there is a good consistency between the results and the existing solutions. The prominent advantages of the proposed solution are techniques which are less time and money consuming compared to numerical and experimental methods. © 2015 Elsevier Ltd.

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