Esmaeel Fatahian

Bio: Esmaeel Fatahian is an academic researcher from Islamic Azad University. The author has contributed to research in topics: Turbulence & Turbine. The author has an hindex of 6, co-authored 22 publications receiving 119 citations. Previous affiliations of Esmaeel Fatahian include Universiti Sains Malaysia.

Performance improvement of a Savonius vertical axis wind turbine using a porous deflector

Abstract: The present study proposed a novel porous deflector in front of the Savonius wind turbine to improve the performance. This new deflector was specifically proposed to minimize the severe effects of the complex wake zone created behind the conventional solid deflector that had not been investigated yet. This caused a deeper investigation into the effect of severe negative effects on the turbine performance to achieve an appropriate design configuration. Therefore, different configuration parameters were taken into account during the numerical process. The unsteady Reynolds-averaged Navier-Stokes equation in conjunction with the SST k-ω turbulence model was numerically solved. Comprehensive comparisons of torque, power, and flow structures between deflector configurations and the standard Savonius turbine were performed to illustrate the mechanism of how the porous deflector improved the turbine performance. Using a porous deflector caused the wind flow passed through the porous zone resulted in a breakdown of the wake zone behind the deflector. Thereby, the flow structures became more regular with fewer fluctuations. The results demonstrated that there is an appropriate porosity value to obtain the highest torque and power coefficients. The maximum value of the power coefficient increased by approximately 10% using the favorable configuration of porous deflector at a tip speed ratio of 1. The notable observation was that the appropriate configuration increased the static torque coefficient approximately 2 times in the rotation angles between 0° and 30° which proved the self-starting ability besides power coefficient enhancement.

Improving efficiency of conventional and square cyclones using different configurations of the laminarizer

Abstract: In the present study, effects of different configurations of the laminarizer including inlet, vortex finder and both inlet and vortex finder on the separation efficiency, pressure drop, tangential velocity, and 50% cut size are analyzed. The computational fluid dynamics (CFD) method is applied to predict and demonstrate the flow field inside both conventional cylindrical style and square cyclones. The Reynolds stress model (RSM) is used to simulate the turbulent flow field. Particle trajectories are calculated via discrete phase model (DPM). The discrete random walk (DRW) model is used to model the turbulent dispersion of particles. The results show that installing both inlet and vortex finder laminarizers has the most effect on increasing separation efficiency compared to other configurations of the laminarizer. The cyclone with both inlet and vortex finder laminarizers has the smallest 50% cut size in both conventional and square cyclones. Installing the laminarizer caused a minor increase in the pressure drop for all cases. By installing the laminarizer at inlet and vortex finder simultaneously, a minor increase of about 4.6% and 6.4% is obtained for conventional and square cyclones at the inlet velocity of 18 m/s, respectively. Also, installing the laminarizer at both inlet section and vortex finder of conventional and square cyclones reduced the 50% cut size at inlet gas velocity of 18 m/s about 8% and 27%, respectively. This reduction proved that using the laminarizer in the square cyclone was more effective than the conventional cyclone.

CFD simulation of a novel design of square cyclone with dual-inverse cone

Abstract: The objective of the present study is to propose a novel design to improve the separation efficiency of the conventional square cyclone. For this purpose, the conical section of the conventional square cyclone with single-cone is modified to dual inverse-cone. In addition, the effect of second-cone length on the performance of cyclone is considered. A three-dimensional numerical simulation is done by solving the Reynolds averaged Navier-Stokes equations with the Reynolds Stress Model (RSM) turbulence model and applying the Eulerian-Lagrangian two-phase method. The turbulent dispersion of particles is predicted by the application of the Discrete Random Walk (DRW) model. The numerical results demonstrate that dual inverse-cone square cyclone although produces higher pressure drop but its separation efficiency is higher than the square cyclone with single-cone. This is due to a smaller separation zone and shorter path of particle movements which force the particles exit from the outlet section of the cyclone. Finally, using dual-inverse cone square cyclone reduces the 50% cut size about 10% and 30% for inlet velocities of 12 m/s and 28 m/s, respectively.

An innovative deflector system for drag-type Savonius turbine using a rotating cylinder for performance improvement

Abstract: The present study mainly focused on a new design of deflector by utilizing a rotating cylinder to augment the overall performance of the drag-type Savonius turbine since the negative torque generated by the returning blade is the primary cause of its poor efficiency. This has never been studied previously. The influence of distance, angular velocity, and cylinder deflector diameter on torque and power coefficients, as well as the wake zone on Savonius rotor performance, were numerically evaluated using the Computational Fluid Dynamics (CFD) method. The performance of the Savonius rotor was improved the most via the rotating cylinder deflector for almost all Tip Speed Ratios (TSRs). At a high angular velocity (ω = 40 rad/s), it performed better at redirecting incoming wind flow with high-velocity magnitude toward the concave surface of the advancing blade to increase positive pressure while reducing pressure on the convex side of the returning blade. On the other hand, at low angular velocity (ω = 3 rad/s) it required less energy to rotate in terms of energy consumption with a net torque up to 14% improvement compared to without the deflector case. Overall, there is a huge efficiency gain using the rotating cylinder deflector for all TSR ranges with about 50% more than the stationary deflector improvement at TSR = 0.6.

Numerical study of the effect of suction at a compressible and high Reynolds number flow to control the flow separation over Naca 2415 airfoil

Abstract: This study focused on delaying and controlling the flow separation over Naca 2415 airfoil by finding the best slot location with the most effective suction velocity ratio and suction angle to apply suction at a compressible and high Reynolds number flow using computational fluid dynamics method. The results were obtained with two dimensional compressible Reynold-averaged Navier-Stokes equations, and the turbulence was simulated with k-e RNG turbulence model. The results indicated that the most effective slot locations for applying suction were between 0.3 to 0.6 of the airfoil chord length. Also, it was found that the maximum value of the lift coefficient was obtained at an angle of attack of 16° on 0.3 of airfoil chord length and suction velocity ratio of 1.5. This value is about 55% compared to the case without suction, and thus the stall angle increased from 10° to 16°.

Tubular solid oxide fuel cell/gas turbine hybrid cycle power systems - status

Abstract: The solid oxide fuel cell (SOFC) is a simple electrochemical device that operates at 1000°C, and is capable of converting the chemical energy in natural gas fuel to AC electric power at approximately 45% efficiency (net AC/LHV) when operating in a system at atmospheric pressure. Since the SOFC exhaust gas has a temperature of approximately 850°C, the SOFC generator can be synergistically integrated with a gas turbine (GT) engine generator by supplanting the turbine combustor and pressurizing the SOFC, thereby enabling the generation of electricity at efficiencies approaching 60% or more. Conceptual design studies have been performed for SOFC/GT power systems employing a number of the small recuperated gas turbine engines that are now entering the marketplace. The first hardware embodiment of a pressurized SOFC/GT power system has been built for Southern California Edison and is scheduled for factory acceptance tests beginning in Fall 1999 at the Siemens Westinghouse facilities in Pittsburgh, PA. The hybrid power cycle, the physical attributes of the hybrid systems, and their performance are presented and discussed.

Influence of the dipleg shape on the performance of gas cyclones

Abstract: The influence of dipleg shape on the flow pattern and performance of gas-solid cyclone was investigated. Different diplegs including cylindrical, inverted cone, conical, and diamond were studied. Due to the turbulent nature of the flow in the cyclone, the RSM turbulence model was used in the simulations. It was found that the mean tangential velocity in the cyclone for different dipleg geometries were about 1–1.2 times the inlet velocity, while the maximum tangential velocity was 1.7 times the inlet velocity. In addition, the tangential velocity in the cylindrical dipleg was greater than those of the other dipleg models. Changes in the dipleg shape significantly affect the axial velocity in the dustbin. The maximum axial velocity was observed in the vortex finder region and the entrance region of the dipleg for different models. It was also found that the dipleg geometry significantly affected the cyclone pressure drop. The cylindrical dipleg generated the highest pressure drop, whereas the lowest pressure drop was seen for the cyclone without dipleg. Among the studied geometries, the highest efficiency was found for the cyclone with conical dipleg and the diamond dipleg led to the lowest efficiency. Finally, the influence of constant parameter of the eddy lifetime model on the turbulent dispersion of particles and the corresponding cyclone performance was studied.

Experimental and numerical investigation on the performance of square cyclones with different vortex finder configurations

Abstract: The aim of this study was to analyse the effect of varying the vortex finder diameter and its insertion length on the flow field and overall performance in a square cyclone. A total of 15 different vortex finder configurations with 5 different diameters, each having 3 different insertion lengths, were analyzed. An in-depth analysis of flow field inside the separator was conducted by using stereoscopic particle image velocimetry (Stereo-PIV) and large eddy simulation (LES). The former makes use of two cameras that focused simultaneously over the region of interest to record the details of the flow field, whereas the latter approach directly resolves a large part of the flow and provides the three-dimensional time-dependent details of the turbulent flows. The results extracted from PIV and LES – viz. mean tangential, mean axial, and mean radial velocities – were compared, and good agreement was observed between the two. In addition, the separation efficiency and Euler number (Eu) were evaluated experimentally and by using LES. Conclusive results indicate that the geometric shapes of the vortex finder have a significant effect on the performance of square cyclone separators. Decreasing the diameter of the vortex finder resulted in a considerable increase in Eu compared to the base variant (maximal increase in Eu amounted to about 660%). However, increasing the diameter of the vortex finder decreased Eu by about 55%. An optimally configured geometry of the vortex finder increased overall separation efficiency by 16%.

Numerical investigation on the performance and flow pattern of two novel innovative designs of four-inlet cyclone separator

Abstract: In solid particle separation process, cyclone separators are commonly used due to their simplicity and low-cost manufacture. A reference design S1 and two novel designs C4, N4 of four-inlet cyclone separator have been investigated computationally using the Reynolds Stress Model for turbulent flow and the Discrete Phase Model for tracking the particles. The numerical model has been validated and confirmed to be a reasonable good candidate for the investigation. The results show that, the design S1 provides the lowest average Euler number (4.415) and the design C4 provides the smallest average cut-off diameter (1.399 μ m ). As comparing the performances using weighted sum method, both two novel designs provide the better performance than the reference design S1. The innovative design N4 delivers the best performance which is 1 % and 0.1 % better in performance than S1 and C4, respectively.