Large eddy simulation of flow around two side-by-side spheres

Rahim Hassanzadeh,Besir Sahin,Muammer Ozgoren 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.7

Large eddy simulation, using a dynamic Smagorinsky sub-grid scale, is used for the prediction of flow structures around two identical spheres fixed side-by-side at a subcritical flow regime with the Reynolds number equal to 5,000. The QUICK discretization method is applied to discretize the convection terms of the Navier-Stokes equation by means of the finite volume approach. This work focuses mainly on the wake structures downstream of the two interactive spheres located at three various dimensionless separation distances between spheres such as G/D = 1.50, 2.00, and 3.00. The obtained results revealed that the interaction between wakes affects the flow structures downstream of spheres. The rate of this interaction is strongly altered as a function of separation distance. On the other hand,some flow data such as mean drag and mean lift coefficients are affected due to the wake interactions. Finally, examination of the Reynolds stress variation along the different lateral axis, L/D, revealed that the nozzle effect does not play a significant role on the turbulence characteristics beyond the G/D = 3.00.

Experimental and numerical studies of the flow around the Ahmed body

Tural Tunay,Besir Sahin,Huseyin Akilli 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

The present study aims to investigate characteristics of the flow structures around the Ahmed body by using both experimental and numerical methods. Therefore, ¼ scale Ahmed body having 25o slant angle was employed. The Reynolds number based on the body height, H and the free stream velocity, U was ReH=1.48x104. Investigations were conducted in two parts. In the first part of the study, Large Eddy Simulation (LES) method was used to resolve the flow structures around the Ahmed body, numerically. In the second part of the study the particle image velocimetry (PIV) technique was used to measure instantaneous velocity fields around the Ahmed body. Time-averaged and instantaneous velocity vectors maps, streamline topology and vorticity contours of the flow fields were presented and discussed in details. Comparison of the mean and turbulent quantities of the LES results and the PIV results with the results of Lienhart et al. (2000) at different locations over the slanted surface and in the wake region of the Ahmed body were also given. Flow features such as critical points and recirculation zones in the wake region downstream of the Ahmed body were well captured. The spectra of numerically and experimentally obtained stream-wise and vertical velocity fluctuations were presented and they show good consistency with the numerical result of Minguez et al. (2008).

Analysis of aerodynamic characteristics of 2 MW horizontal axis large wind turbine

Akin Ilhan,Mehmet Bilgili,Besir Sahin 한국풍공학회 2018 Wind and Structures, An International Journal (WAS Vol.27 No.3

In this study, aerodynamic characteristics of a horizontal axis wind turbine (HAWT) were evaluated and discussed in terms of measured data in existing onshore wind farm. Five wind turbines (T1, T2, T3, T4 and T5) were selected, and hub-height wind speed, UD, wind turbine power output, P and turbine rotational speed, Ω data measured from these turbines were used for evaluation. In order to obtain characteristics of axial flow induction factor, a, power coefficient, Cp, thrust force coefficient, CT, thrust force, T and tangential flow induction factor, a', Blade Element Momentum (BEM) theory was used. According to the results obtained, during a year, probability density of turbines at a rotational speed of 16.1 rpm was determined as approximately 45%. Optimum tip speed ratio was calculated to be 7.12 for most efficient wind turbine. Maximum Cp was found to be 30% corresponding to this tip speed ratio.

Serum Ghrelin and Leptin Levels in Patients with Depression and the Effects of Treatment

Saliha Ozsoy,Aslı Besirli,Ummuhan Abdulrezzak,Mustafa Basturk 대한신경정신의학회 2014 PSYCHIATRY INVESTIGATION Vol.11 No.2

Objective Ghrelin and leptin, appetite-regulating hormones, play a role in mood regulation. Current data about the relation between leptin/ghrelin and depression are still controversial. This study aimed to investigate serum leptin and ghrelin levels in patients with depression and the effects of treatment on these levels. Methods Serum ghrelin and leptin levels were measured before and after treatment with antidepressant drugs and/or electroconvulsive therapy in 28 patients with depression and once in 21 healthy controls. Results Serum ghrelin levels of the patients were high in the pre-treatment. After the treatment, ghrelin levels were not different from those of the controls. We found no difference in serum levels of leptin between the patients and controls and no change with treatment. body mass index of the patients increased after the treatment especially in the drug-treated group. Conclusion The present study found increased serum ghrelin levels in depressive patients and normalization with improving of depression but no alteration in leptin levels.

Serum Ghrelin and Leptin Levels in Patients with Depression and the Effects of Treatment

Saliha Ozsoy,Aslı Besirli,Ummuhan Abdulrezzak,Mustafa Basturk 대한신경정신의학회 2004 PSYCHIATRY INVESTIGATION Vol.1 No.2

Objective-Ghrelin and leptin, appetite-regulating hormones, play a role in mood regulation. Current data about the relation between leptin/ghrelin and depression are still controversial. This study aimed to investigate serum leptin and ghrelin levels in patients with depression and the effects of treatment on these levels. Methods-Serum ghrelin and leptin levels were measured before and after treatment with antidepressant drugs and/or electroconvulsive therapy in 28 patients with depression and once in 21 healthy controls. Results-Serum ghrelin levels of the patients were high in the pre-treatment. After the treatment, ghrelin levels were not different from those of the controls. We found no difference in serum levels of leptin between the patients and controls and no change with treatment. body mass index of the patients increased after the treatment especially in the drug-treated group. Conclusion-The present study found increased serum ghrelin levels in depressive patients and normalization with improving of depression but no alteration in leptin levels.

Flow structures around a three-dimensional rectangular body with ground effect

Gurlek, Cahit,Sahin, Besir,Ozalp, Coskun,Akilli, Huseyin Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.5

An experimental investigation of the flow over the rectangular body located in close proximity to a ground board was reported using the particle image velocimetry (PIV) technique. The present experiments were conducted in a closed-loop open surface water channel with the Reynolds number, $Re_H=1.2{\times}10^4$ based on the model height. In addition to the PIV measurements, flow visualization studies were also carried out. The PIV technique provided instantaneous and time-averaged velocity vectors map, vorticity contours, streamline topology and turbulent quantities at various locations in the near wake. In the vertical symmetry plane, the upperbody flow is separated from the sharp top leading edge of the model and formed a large reverse flow region on the upper surface of the model. The flow structure downstream of the model has asymmetric double vortices. In the horizontal symmetry plane, identical separated flow regions occur on both vertical side walls and a pair of primary recirculatory bubbles dominates the wake region.

Experimental and numerical studies of the flow around the Ahmed body

Tunay, Tural,Sahin, Besir,Akilli, Huseyin Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

The present study aims to investigate characteristics of the flow structures around the Ahmed body by using both experimental and numerical methods. Therefore, 1/4 scale Ahmed body having $25^{\circ}$ slant angle was employed. The Reynolds number based on the body height, H and the free stream velocity, U was $Re_H=1.48{\times}10^4$. Investigations were conducted in two parts. In the first part of the study, Large Eddy Simulation (LES) method was used to resolve the flow structures around the Ahmed body, numerically. In the second part of the study the particle image velocimetry (PIV) technique was used to measure instantaneous velocity fields around the Ahmed body. Time-averaged and instantaneous velocity vectors maps, streamline topology and vorticity contours of the flow fields were presented and discussed in details. Comparison of the mean and turbulent quantities of the LES results and the PIV results with the results of Lienhart et al. (2000) at different locations over the slanted surface and in the wake region of the Ahmed body were also given. Flow features such as critical points and recirculation zones in the wake region downstream of the Ahmed body were well captured. The spectra of numerically and experimentally obtained stream-wise and vertical velocity fluctuations were presented and they show good consistency with the numerical result of Minguez et al. (2008).

Robust Control of Current Controlled PWM Rectifiers Using Type-2 Fuzzy Neural Networks for Unity Power Factor Operation

Acikgoz, Hakan,Coteli, Resul,Ustundag, Mehmet,Dandil, Besir The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.2

AC-DC conversion is a necessary for the systems that require DC source. This conversion has been done via rectifiers based on controlled or uncontrolled semiconductor switches. Advances in the power electronics and microprocessor technologies allowed the use of Pulse Width Modulation (PWM) rectifiers. In this paper, dq-axis current and DC link voltage of three-phase PWM rectifier are controlled by using type-2 fuzzy neural network (T2FNN) controller. For this aim, a simulation model is built by MATLAB/Simulink software. The model is tested under three different operating conditions. The parameters of T2FNN is updated online by using back-propagation algorithm. The results obtained from both T2FNN and Proportional + Integral + Derivate (PID) controller are given for three operating conditions. The results show that three-phase PWM rectifier using T2FNN provides a superior performance under all operating conditions when compared with PID controller.

Investigation of crossflow features of a slender delta wing

Mehmet O. Tasci,Ilyas Karasu,Besir Sahin,Huseyin Akilli 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.31 No.3

In the present work, the main features of primary vortices and the vorticity concentrations downstream of vortex bursting in crossflow plane of a delta wing with a sweep angle of Λ=70° were investigated under the variation of the sideslip angles, β. For the pre-review of flow structures, dye visualization was conducted. In connection with a qualitative observation, a quantitative flow analysis was performed by employing Particle Image Velocimetry (PIV). The sideslip angles, β were varied with four different angles, such as 0°, 4°, 12°, and 20° while angles of attack, α were altered between 25° and 35°. This study mainly focused on the instantaneous flow features sequentially located at different crossflow planes such as x/C=0.6, 0.8 and 1.0. As a summary, time-averaged and instantaneous non-uniformity of turbulent flow structures are altered considerably resulting in non-homogeneous delta wing surface loading as a function of the sideslip angle. The vortex bursting location on the windward side of the delta wing advances towards the leading-edge point of the delta wing. The trajectory of the primary vortex on the leeward side slides towards sideways along the span of the delta wing. Besides, the uniformity of the lift coefficient, CL over the delta wing plane was severely affected due to unbalanced distribution of buffet loading over the same plane caused by the variation of the sideslip angle, β. Consequently, dissimilarities of the leading-edge vortices result in deterioration of the mean value of the lift coefficient, CL.

Analysis of aerodynamic characteristics of 2 MW horizontal axis large wind turbine

Ilhan, Akin,Bilgili, Mehmet,Sahin, Besir Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.27 No.3

In this study, aerodynamic characteristics of a horizontal axis wind turbine (HAWT) were evaluated and discussed in terms of measured data in existing onshore wind farm. Five wind turbines (T1, T2, T3, T4 and T5) were selected, and hub-height wind speed, $U_D$, wind turbine power output, P and turbine rotational speed, ${\Omega}$ data measured from these turbines were used for evaluation. In order to obtain characteristics of axial flow induction factor, a, power coefficient, $C_p$, thrust force coefficient, $C_T$, thrust force, T and tangential flow induction factor, a', Blade Element Momentum (BEM) theory was used. According to the results obtained, during a year, probability density of turbines at a rotational speed of 16.1 rpm was determined as approximately 45%. Optimum tip speed ratio was calculated to be 7.12 for most efficient wind turbine. Maximum $C_p$ was found to be 30% corresponding to this tip speed ratio.