Aerospace Science and Technology
Jafar Jafari; Hamid Parhizkar; Sajad Ghasemlooy
Abstract
This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve ...
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This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve and optimized to increase the average torque of the wind turbine. We used a novel, simple way for remeshing new design points in the optimization process. The Nelder-Mead simplex method was used for optimization, which enhanced the Turbine's performance by 33.7 percent. Results show that optimization of the blade cross-section is effective for increasing the performance of a VAWT (Vertical Axis Wind Turbine), and Nelder-Mead simplex is a proper and fast optimization method to be used in this case. Finally, the optimized airfoil was analyzed and compared with the initial one to understand optimization effects. It was concluded that optimization was more effective in azimuth positions of 90 to 160 degrees. And it decreased the performance in some regions according to changing nature of flow around each blade because of rotational motion. Analyzes show that optimization increased the Turbine's performance by increasing lift force of airfoil in some positions or affecting interaction flow -even accompanied by decreasing lift force of airfoil- in other positions, and it decreased performance in some other azimuth points.
Aerospace Science and Technology
Hossein Shadmehr; Sajad Ghasemloo; Hamid Parhizkar
Abstract
In this article, the idea of building a supersonic wind tunnel has been provided that uses a high-pressure steam flow of a combined cycle power plant. This has been investigated by CFD method. Using the plant's output steam as a high-pressure source can be used in the ejector to create supersonic airflow ...
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In this article, the idea of building a supersonic wind tunnel has been provided that uses a high-pressure steam flow of a combined cycle power plant. This has been investigated by CFD method. Using the plant's output steam as a high-pressure source can be used in the ejector to create supersonic airflow in the test chamber. For this purpose, first, the numerical model has been validated in comparison with the previous numerical and experimental results. The numerical model used is the viscous compressible flow, which is performed by the k-ω-SST turbulent modeling of the turbulence model. All calculations are performed in ANSYS-FLUENT software. After validating the numerical process, various geometries have been proposed to achieve the ultrasonic secondary flow and each structure is examined numerically separately in a range of functional conditions. Through trial and error method and looking at the achievements of previous research, in a very long process and by testing several different structures, a suitable structure has been obtained to achieve the supersonic testing chamber. This structure has been studied parametrically under different functional conditions. It has been shown that the proposed structure can generate an ultrasonic flow in an acceptable range of power plant steam flow and pressure. This structure has been proposed for the first time in the literature in this field, and in no previous research has such a structure been proposed. Access to the ultrasonic secondary flow is also a major innovation of this research.
Aerospace Science and Technology
Sajad Ghasemlooy; mahsa dehnamaki; Hamid Parhizkar
Abstract
The calculation of aerodynamic heating is one of the most important steps in designing high speed flying bodies, especially reentry bodies. Because ignoring that, it can damage the thermal protection system and cut off the radar connections to the reentry capsule. Due to the high speed of the capsule ...
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The calculation of aerodynamic heating is one of the most important steps in designing high speed flying bodies, especially reentry bodies. Because ignoring that, it can damage the thermal protection system and cut off the radar connections to the reentry capsule. Due to the high speed of the capsule and the lack of a material medium, the radiation heat transfer rate is important in comparison to the convection heat transfer rate of the displacement in determining the total thermal flux, and ignoring it in the calculations caused many errors in the determination of the total heat flux . In this paper, various parameters affecting the heat transfer rate of the nose of the reentry capsule have been investigated. To calculate the capsule nose radiation, a theoretical method is presented which is compared with the reference simulation results to confirm its correctness. In this simulation, the heat transfer rate of the Apollo4 capsule has been investigated. Due to the low optical thickness of the model, the DO radiation model is used to simulate CFD. This simulation was carried out using Fluent software version 16 and solved with a laminar flow of gray gas and non-gray gas. The results show that the radiation heat transfer rate in non-gray gas mode is lower error than the gray gas state, and it is also observed that at high altitudes, the radiation transfer rate is 80% of the total heat transfer rate.
Aerospace Science and Technology
Hamid Reza Talesh Bahrami; Sajad Ghasemlooy; hamid Parhizkar
Volume 12, Issue 1 , March 2019, , Pages 65-74
Abstract
Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, ...
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Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, the large eddy simulation technique is used to simulate the flow field over a three-dimensional cylinder. In the following, the Ffowcs Williams and Hawkings equation is used to estimate the noise at the specified locations using the oscillating pressure components on the cylinder wall. The acoustic behavior of both stationary and rotating cylinders are studied. Results show that the acoustic behaviors of cylinders rotating with smaller frequencies (up to f=16f0, where f0 is the dominant detaching frequency of vortices on a stationary cylinder) are nearly the same. However, at higher rotational frequencies (24f0) where vortices are omitted, OASPL of the generated noise is reduced considerably (about 20 dB at different angles with constant radial positions, r=26D, at mid-span plane). On the other hand, when the rotational frequency is increased over this limit, the pressure oscillation on the wall becomes significant and the OASPL approaches higher values.
