Besir Sahin

Gas-solid flow behavior in a horizontal pipe after a 90° vertical-to-horizontal elbow

Abstract The characteristics of the particle flow in a horizontal pipe following a 90° vertical-to-horizontal elbow were investigated both numerically and experimentally. Laboratory experiments were conducted in a 0.154 m ID test section. The effects of air velocity, the ratio of air-to-solids mass flow rate, geometry of the elbow and inlet conditions on gas–solid flow patterns were investigated experimentally. Pulverized coal with a mean particle diameter of 50 μm was used as the solid material. Experiments were performed with conveying air velocities ranging from 15 to 30 m/s and air-to-solids mass flow rate ratios of 1 and 3, with elbows having bend radius to pipe diameter ratios of 1.5 and 3. Measurements of particle concentration and particle velocity were performed at various locations along the horizontal pipe using a fiber-optic probe which was traversed over the pipe cross-section of the pipe. It was observed that the strong rope created by the elbow disintegrates within an axial distance of 10 pipe diameters. Fully developed concentration and velocity profiles were obtained within approximately 30 pipe diameters from the elbow exit plane. The rope behavior was different for the two elbows studied ( R / D =1.5 and 3). The shapes of the fully developed profiles were found to be independent of inlet conditions. CFD simulations of gas–solid flow through 90° circular elbows were performed using the Lagrangian approach. The simulations were used to predict the location of the rope and its dispersion rate along the horizontal pipe after the elbow exit plane.

Estimation of global solar radiation using ANN over Turkey

The main objective of the present study is to develop an artificial neural network (ANN) model based on multi-nonlinear regression (MNLR) method for estimating the monthly mean daily sum global solar radiation at any place of Turkey. For this purpose, the meteorological data of 31 stations spread over Turkey along the years 2000-2006 were used as training (27 stations) and testing (4 stations) data. Firstly, all independent variables (latitude, longitude, altitude, month, monthly minimum atmospheric temperature, maximum atmospheric temperature, mean atmospheric temperature, soil temperature, relative humidity, wind speed, rainfall, atmospheric pressure, vapor pressure, cloudiness and sunshine duration) were added to the Enter regression model. Then, the Stepwise MNLR method was applied to determine the most suitable independent (input) variables. With the use of these input variables, the results obtained by the ANN model were compared with the actual data, and error values were found within acceptable limits. The mean absolute percentage error (MAPE) was found to be 5.34% and correlation coefficient (R) value was obtained to be about 0.9936 for the testing data set.

Wind Characteristics and Energy Potential in Belen-Hatay, Turkey

In this study, wind characteristics in the Belen-Hatay province situated in southern Turkey were investigated by using the Wind Atlas Analysis and Application Program (WAsP) for future wind power generation projects. Hourly wind speeds and directions between the years 2004 and 2005 were collected by the General Directorate of Electrical Power Resources Survey Administration (EIEI). Before the construction of the wind turbine generator in Belen-Hatay province, several fundamental properties of the site such as wind behavior, availability, continuity, and probability were carried out in order to provide the necessary information to the potential investors about cost and economical aspects of the planning wind energy project. The dominant wind directions, probability distributions, Weibull parameters, mean wind speeds, and power potentials were determined according to the wind directions, years, seasons, months, and hours of day, separately. Finally, at a 10 m height above ground level, mean wind speed and power potential of the site were found to be 7.0 m/s and 378 W/m2, respectively.

Control of Vortex Shedding of Circular Cylinder in Shallow Water Flow Using an Attached Splitter Plate

In the present work, passive control of vortex shedding behind a circular cylinder by splitter plates of various lengths attached on the cylinder base is experimentally investigated in shallow water flow. Detailed measurements of instantaneous and time-averaged flow data of wake flow region at a Reynolds number of Re=6300 were obtained by particle image velocimetry technique. The length of the splitter plate was varied from L∕D=0.2 to L∕D=2.4 in order to see the effect of the splitter plate length on the flow characteristics. Instantaneous and time-averaged flow data clearly indicate that the length of the splitter plate has a substantial effect on the flow characteristics. The flow characteristics in the wake region of the circular cylinder sharply change up to the splitter plate length of L∕D=1.0. Above this plate length, small changes occur in the flow characteristics.

Vortex Structure on a Delta Wing at High Angle of Attack

The structure of the leading-edge vortex from a delta wing at high angle of attack is addressed using a scanning laserversion of high-image-density particleimagevelocimetry.Emphasisis ontheglobal patterns of instantaneous vorticity.Thesepatternsarerelated to distributions ofaveraged and e uctuating velocity and vorticity. At low angle ofattack,intheabsenceofvortex breakdown,itispossibleto detecta totalofe vedistinctlayersofvorticity;theyall exhibit small-scale concentrations of azimuthal vorticity. Immediately downstream of thetrailing edgeof the wing, larger-scale vorticity concentrations appear in the outermost vorticity layers. At sufe ciently high angle of attack, vortex breakdown evolves from the innermost two vorticity layers. For all of these classes of vortical structures, the values of dimensionless wavelength and circulation are assessed. Moreover, the onset of vortex breakdown is interpreted in terms of both instantaneous and averaged patterns of velocity and vorticity. These considerations lead to a direct comparison of vorticity-based and stagnation criteria for breakdown. In turn, these criteria are linked to the onset of regions of e uctuating vorticity in the initial region of breakdown.

The use of perforated plates to control the flow emerging from a wide-angle diffuser, with application to electrostatic precipitator design

Abstract The flow through a wide-angle, pyramidal diffuser of area ratio 6.8, in which two perforated plates are used to control the emergent velocity distribution was investigated. (Wide-angle diffusers combined with perforated plates find application in electrostatic precipitator flow systems. The efficacy of these systems depends critically on the uniformity of the gas flow within the collection chamber downstream of the diffuser outlet plane.) The main results of the study are (i) the establishment of the main factor influencing the flow at the diffuser exit plane, (ii) the determination of plate characteristics which produce a uniform velocity profile in the collection chamber, and (iii) the establishment of the corresponding pressure drop characteristics of the plate—diffuser combinations. The results also extend the range of diffuser geometries for which two perforated plates provide uniform velocity profiles at exit.

Prediction of long-term monthly temperature and rainfall in Turkey.

Abstract In this study, artificial neural networks were applied to predict the long-term monthly temperature and rainfall at any target point of Turkey based on the use of the neighboring measuring stations data. For this purpose, meteorological data measured by the Turkish State Meteorological Service between the years 1975 and 2006 from 76 measuring stations were used as training (59 stations) and testing (17 stations) data. Four neurons which receive input signals of latitude, longitude, altitude, and month were used in the input layer of the network. Two neurons, which produce corresponding output signals of the long-term monthly temperature and rainfall, were utilized in the output layer of the network. Finally, the values determined by the artificial neural network model were compared with the actual data. Errors obtained in this model are well within acceptable limits.

Dye Visualization of the Flow Structure over a Yawed Nonslender Delta Wing

S TUDIES of aerodynamic structures and behaviors of the nonslender delta wings are invariably essential to develop a method to control the development of the vortex breakdown as well as the development of vortices. Unsteady aerodynamics of nonslender delta wings, consisting of shear layer instabilities, the structure of vortices, the occurrence of breakdown, and fluid/structure interactions were extensively reviewed by Gursul et al. [1]. They emphasized the sensitivity of the vortical flow structures varying the angle of attack of the deltawing.Yavuz et al. [2] studied thevortical flow structure on a plane immediately adjacent to the surface of nonslender delta wing, 38:7 deg. Yaniktepe and Rockwell [3] performed experimental investigations on the flow structures at trailing-edge regions of diamondand lambda-type wings. In both wings, vortical flow structures in the crossflowplanes of trailing edge vary rapidly with the angles of attack . Sohn et al. [4] visually investigated the development and interaction of vortices in crossflow planes at various locations on the delta wing with leading edge extension (LEX) using micro water droplets and a laser beam sheet. The range of angle of attack was taken as 12 24 deg at yaw angles of 0, 5, and 10 deg. It was indicated that, by introducing yaw angle , the coiling, merging, and diffusion of thewing and LEX vortices increased on the windward side, whereas they became delayed significantly on the leeward side. Their study confirmed that the yaw angle had a profound effect on the vortex structures. Taylor and Gursul [5] visualized leading-edge vortices of a 50 deg sweep angle, having angles of attack as low as 2:5 deg. Gursul et al. [6] report that combat air vehicles (UCAVs) and micro air vehicles have particularly dominant vortical flows having low sweep angles (25–55 deg), and future UCAVs are expected to be highly maneuverable and highly flexible. Yaniktepe and Rockwell [7] aimed at investigating the unresolved concepts, which included averaged structure of shear layer from the leading edge of the wing, unsteady features of separated layer adjacent to the surface of the wing, and control of flow structure by leading-edge perturbations. Elkhoury and Rockwell [8] have investigated to provide various measurements of the visualized dye patterns, including the degree of interaction of vortices, the onset of vortex breakdown, and effective sweep angle of the wing root vortex, as a function of both Reynolds number and angle of attack . Elkhoury et al. [9] had investigated the Reynolds number dependence of the near-surface flow structure and topology on a representative UCAV planform. The present investigation focuses on the formation and development of leading-edge vortices, vortex breakdown, and threedimensional separationandstallof thecomplexanddisorganizedflow structure over the delta wing. The leading-edge sweep angle was 40 deg. The angle of attack was varied within the range of 7 17 deg and the yaw angle was varied within the range of 0 15 deg.

Flow details of a circular cylinder mounted on a flat plate

The main purpose of this study is to investigate the flow structure up- and downstream of a circular cylinder mounted on a flat surface in the boundary layer region using a Particle ImageVelocimetry (PIV) technique for Reynolds numbers ranging from 750 to 9600. The interaction between the primary, incoming, and counter-clock-wise rotating vortices and the trail of the horseshoe vortices formed at the upstream base of the cylinder are quantitatively identified in terms of the instantaneous and time-averaged flow data. The entrainment is shown to be activated between the main and separated flow regions across the shear layer by interactions of opposite signed rotating vortices which are responsible for scour in the upstream region of the cylinder. The surface fluid bursts to create counter-clock-wise rotating vortices upstream of the cylinder to split the incoming clock-wise rotating vortex into an independent vortex. Since the counter-clock-wise rotating vortices are not fed continuously by the surface fluid, they gradually expand in size but lose the strength and later are swept away by the developing vortices

Yaw Angle Effect on Flow Structure over the Nonslender Diamond Wing

D ELTAwings have evolved over the years and are primarily used on many fighter aircraft. As these aircraft become more and more maneuverable, delta-wing vortex dynamics and the understanding of the physics of time-dependent unsteady flows have become substantially important [1]. Several variables affect the deltawing vortex dynamics. As indicated by Yaniktepe [2], some of these variables are angle of attack, leading-edge geometry, wing thickness, sweep angle, Reynolds number, and freestream conditions. Yaniktepe and Rockwell [3] investigated aerodynamics of the delta wing with a sweep angle of 38:7 for the value of Reynolds number based on the chord length C, which was maintained at Re 10. They reported that the nonslender delta wings exhibited more distinctive features than the slender delta wings, especially at a higher angle of attack as a result of the earlier onset of vortex breakdown, which are based on the time-averaged velocity and vorticity distributions in the crossflow plane. Canpolat et al. [4] observed the variation of flow structures on the delta-wing surface with a sweep angle of 40 as a function of the angle of attack and yaw angle , using the dye visualization technique. When the delta wing is under the effect of a yaw angle, the symmetrical flow structure deteriorates, and a vortex breakdown occurs earlier on the windward side of the delta wing, as compared with the leeward side. The main vortices in crossflow planes occur in the inner side close to the central axis of the delta wing. Many small-sized vortices are also evident next to themain rotating vortices. Yayla et al. [5] investigated the flow structure close to the surface of the nonslender diamond wing, both qualitatively and quantitatively, using the dye visualization and the stereoscopic particle image velocimetry (PIV) techniques. It was stated that, when the yaw angle is increased, the locations of vortex breakdowns approach thewing apex, but the other one moves toward the trailing edge. Goruney and Rockwell [6] investigated the near-surface flow structure and topology on a delta wing of low sweep angle having sinusoidal leading edges of varying amplitude and wavelength. Gursul et al. [7] reviewed unsteady aerodynamics of nonslender delta wings, covering topics of shear layer instabilities, structure of nonslender vortices, breakdown, maneuvering wings, and fluid/structure interactions. Yaniktepe and Rockwell [8] characterized the instantaneous and the time-averaged flow structure on the nonslender diamond and lambda planforms by using the PIV technique. Ozgoren et al. [9] investigated the structure of vortex breakdown and the effect in the surface of the wing of the separated flow region in the case of the high angle of attack over the slender delta wing. They declared that the high angle of attack rather affects the onset of vortex breakdown, spiral vortex structure, and separated flow region. Breitsamter [10] presented selected results from extensive experimental investigations on turbulent flowfields and unsteady surface pressures caused by leading-edge vortices, in particular, for vortex breakdown flow. Another important parameter for the delta wing is the yaw angle. The influence of sideslip on the flow about a sharp-edged biconvex delta wing of a unit aspect ratio was investigated by Verhaagen and Naarding [11] using flow visualization techniques as well as pressure and force balance measurements. It was observed that the yaw angle affects the structure of the leading-edge vortex, vortex breakdown, and formation of nonsteady flow structure substantially, which is generated after vortex breakdown. Sohn et al. [12] presented the development and interaction of vortices over a yawed delta wing with leading-edge extension (LEX) through offsurface flow visualization using microwater droplets and a laser beam sheet. By sideslip, the coiling, the merging, and the diffusion of the wing and LEX vortices increase on the windward side, whereas they are delayed significantly on the leeward side. Also, the migration behavior of vortices on the windward and leeward sides of the wing change considerably. A review of experimental data for delta wings under both steady and unsteady conditions was presented from a vortex dynamics point of view by Lee and Ho [13]. Conclusions were derived that vortices on the suction surface provide an important contribution to the lift of a delta wing, especially for the wings with large sweep-back angle. Delery [14] stated that, in three-dimensional flows, boundary-layer separation leads to the formation of vortices formed by the roll up of the viscous flow sheet, previously confined in a thin layer attached to the wall, which suddenly springs into the outer nondissipative flow. Comprehensive reviews of experimental and numerical works on vortex breakdown were reported by Leibovich [15,16], Escudier [17], and Visbal [18]. Sahin et al. [19] concluded that substantial retardation, or delay, in the onset of vortex breakdown, and thereby the development of largescale concentration of vorticity due to the helical mode of vortex breakdown, are attainable when the leading edge of the delta wing is perturbed at a natural frequency of vortex breakdown. They also found that upstream movement of the onset of vortex breakdown is attainable when the period of excitation frequency is sufficiently large. Akilli et al. [20] used the technique of PIV to characterize the alterations and structure of the leading-edge vortex formed from a