Cetin Canpolat

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.

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

Observation of the Vortical Flow over a Yawed Delta Wing

AbstractThe development and formation of the leading-edge vortices due to the change in the angle of attack, α, and yaw angle, θ, for a unique cross-flow plane at a dimensionless distance of x/C=0.8 from the apex of the stationary delta wing with a sweep angle of Λ=40° were observed using stereoscopic particle-image velocimetry (stereo-PIV). In addition, the experiments were conducted on three different cross-flow planes such as x/C=0.6, 0.8, and 1 using dye visualization to reveal the development of leading-edge vortices over the delta wing. The angle of attack was varied within the range of 7≤α≤17° and the yaw angle was varied within the range of 0≤θ≤8°. The vortical flow structure and loadings toward the wing surface due to the fluctuations and unsteadiness in the flow structure near the delta wing are investigated using time-averaged parameters such as streamlines, contours of vorticity distributions, Reynolds stress correlations, distributions of turbulent kinetic energy, vertical velocity, and RMS o...

Induced-charge electro-osmotic flow around cylinders with various orientations:

Induced-charge electro-osmosis around multiple gold-coated stainless steel rods under various AC electric fields is investigated using the techniques of microparticle image velocimetry and numerical simulation. In this study, the results of interactions between induced electric double layers of two identical conductive cylinders on surrounding fluid are presented. The induced-charge electro-osmosis flow around multiple rods in touch and with one cylinder diameter gap reveals quadrupolar flow structures with four vortices. The induced-charge electro-osmotic flow structure and velocity magnitude also depend on the cylinder geometry and orientation. It is seen that four small vortices develop in the close region of cylinder surface for multiple rods with gap, while the other four large vortices are surrounding them. The distributions of vorticity patterns also strongly depend on cylinder orientation in the close region of cylinder surface.

ANN approaches for the prediction of bridge backwater using both field and experimental data

This paper presents the findings of laboratory model testing of arched bridge constrictions in a rectangular open-channel flume whose bed slope was fixed at zero. Four different types of arched bridge models, namely single-opening semi-circular arch, multiple-opening semi-circular arch, single-opening elliptic arch, and multiple-opening elliptic arch, were used in the testing program. The normal crossing (φ  =  0) and five different skew angles (φ  =  10°, 20°, 30°, 40°, and 50°) were tested for each type of arched bridge model. Recently, a major coverage of backwater field data obtained from the medieval arched bridge constrictions was published by the Hydraulic Research Wallingford in the UK (Brown, P.M., 1985. Hydraulics of bridge waterways: Interium report. Wallingford, UK: Hydraulic Research Wallingford, Report SR 60; Brown, P.M., 1987. Afflux at arch bridges: second interium report. Wallingford, UK: Hydraulic Research Wallingford, Report SR 115; Brown, P.M., 1988. Afflux at arch bridges. Wallingford, UK: Hydraulic Research Wallingford, Report SR 182). These data were also used in the analysis. The main aim of this study is to develop a suitable model for estimating backwater through arched bridge constrictions with normal and skewed crossings using both experimental and field data. Therefore, different artificial intelligence approaches, namely multi-layer perceptron (MLP), radial basis neural network (RBNN), generalized regression neural network (GRNN), and multi-linear and multi-nonlinear regression models, MLR and MNLR, respectively were used. The comparison between these developed models and one of the most commonly used traditional methods (Biery, P.F. and Delleur, J.W., 1962. Hydraulics of single span arch bridge constrictions. ASCE Journal of the Hydraulics Division, 88, 75–108) has been made. The test results showed that the MLP model gave highly accurate results than those of Biery and Delleur, MLR, MNLR, and GRNN and gave similar results with the RBNN model when applied to both field and experimental data.

MECHANICAL TESTING STRATEGIES FOR DENTAL IMPLANTS

Dental implants, which are utilized for substituting missing teeth are appealed in clinical applications for decades. Moreover, they also are used for supporting craniofacial reconstructions and for orthodontic appliances. Besides having esthetically similar view to natural tooth, dental prostheses have no harmful effect to neighboring teeth and non-disturbing nature for the patient during mastication. On the other hand, the dental implant can result in bone resorption, biocompatibility problems and high costs. There are four main types of dental implant designs, which are developed and employed in clinical dentistry entitled as subperiosteal form, blade form, ramus frame, and endosseous form. From the beginning of this technic, a great evolution not only on implant design and surgical technologies of dental implants, but also on the classification of clinical success, failure and different surface treatments of dental implants is done. The failures are generally influenced on the mechanical properties of dental implants. Therefore, it is critical to estimate possible failures in a specific design of dental implant, which could protect the patients’ health and comfort. For this purpose, the experimental methods for the dental implants provide precise data for clinicians and engineers. Maximum allowable stress and strain, resonance frequency and resistance to fracture are key parameters to determine long term durability of dental implants. In this study, current status of frequently utilized mechanical tests to measure these properties, such as tensile, resonance and fracture tests are summarized. Test procedures with related standards, their strength and weaknesses are briefly discussed. This review is prepared to inform the tester about mechanical testing methods of dental implants in the light of recent advancements.

Effects of Trailing-Edge Attachment on the Flow Structure over a Generic Delta Wing

AbstractThe objective of this work is to reveal the significance of a trailing-edge attachment on the flow structure over a generic nonslender delta wing using the dye visualization technique on th...