52,071 research outputs found
An old Syrian period stele from Avanos-Akarca, Anatolia
No full textIn 2014, a stele decorated with reliefs was found during an excavation undertaken by the villagers searching for water near the village of Akarca in the Avanos district which belongs to the province Nevşehir. The stele has a rounded top, four flat sides and belongs to the upper part of a larger (now missing) stele made from basalt. Figures were engraved in low relief technique on four sides of the stele and on the rounded top. The main theme the figures depict is religious; they reflect cultic/ritualistic and divine/mythological scenes. A presentation scene is depicted on the observe of the stele (a), a winged deity and a worshipper on the right side (b), a banquet scene with an offering table involving three participants on the reverse (c), a storm god standing on top of the mountains and holding the halter of a bull as well as a goddess/priestess on the left side (d) and a mountain chain on the top (e). The style and iconographic features of the figures depicted on the Avanos-Akarca stele are foreign to the Anatolian region and reflect the characteristics of Old Syrian figurative art. One of the figures that illuminates the origin and history of the stele is the royal figure with a peaked cap on the front side of the stele (a). Similar figures occur on Syro-Cappadocian/Old Syrian colony style cylinder seals and seal impressions that were found at Ktlltepe-Kanesh Karum level II, and at Hammam et-Turkman; unprovenanced examples are in the Louvre Museum collection. Such figures from the same era also occur on basalt cult basins from Tell Mardikh-Ebla and on the gold plaque from Byblos. There must be a close relationship between the Avanos-Akarca stele royal figure and the Ktiltepe, Ebla, Byblos and Hammam et-Turkman figures. The figures in question were defined as a king and a god on the Kültepe seals, on the Ebla cult basins, and on the Byblos gold plaque. These examples show that the roles assumed by the figure with a peaked cap, depicted both as a worshipper and worshipped can change. The divine role of the royal figure on the Avanos-Akarca stele was emphasized by two mortals in the act of giving offerings. The stele must have been dedicated to a deified king. The cultic/ritualistic and divine/mythological scenes engraved on all four sides of the stone shed light on a cultic act with a banquet, organized in the name of the deified king in which the continuity of the kingdom is ensured by divine beings. The stele is an example of the figurative artworks in relief reflecting the complex cultic actions of the Old Syrian period. The stele belongs to the Middle Bronze Age I and II around 1900-1750 BC due to the close similarity with the early/Classical Old Syrian period stone relief examples from Ebla in terms of subject matter and stylistic features. The Avanos-Akarca stele is one of the few stone relief pieces from the Middle Bronze Age discovered in Anatolia, like the Harput relief uncovered in recent years. In this study, while the stylistic and iconographic characteristics of the figures on the stele are examined, answers are sought to questions like who the stele belongs to or the reasons of the cult actions related to the themes formed by the figurative motifs. Some possibilities are discussed about where and how the stele came to central Anatolia. © 2019 Mersin University. All rights reserved
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Mean flow generation by Görtler Vortices in a rotating annulus with librating side walls
No full textLongitudinal libration of the cylinder side walls of a rotating annulus in the supercritical regime induces a centrifugally unstable Stokes boundary layer which generates Görtler vortices only in a portion of a libration cycle. We show for the first time that these vortices propagate into the fluid bulk and generate an azimuthal mean flow which is retrograde (prograde) over the outer (inner) cylinder side wall. Direct numerical simulations (DNS) are carried out and Reynolds-averaged equations and kinetic energy budget of mean and fluctuating flow are used as diagnostic equations to discuss the generation mechanism and scaling behavior of the azimuthal mean flow in the fluid bulk
Mean Flow generation due to longitudinal librations of side-walls of a rotating annulus
No full textLaboratory experiments with rotating annuli are reported that reveal a prograde jet, which is adjacent either to a (longitudinally) librating inner straight cylinder or to a librating inner truncated cone (frustum), whereas the outer cylindrical wall and bottom and top lids rotate with constant angular velocity. In the frustum case, the jet is located on a straight cylindrical surface which is circumscribed about the frustum and joins the bottom lid. These findings are supported by direct numerical simulations which show good agreement between experimental data and numerical results and, when the centrifugal instability of the Stokes boundary layer near the oscillating sidewall does not set in, highlight the important role of local dynamical processes in the corners, between the inner cylinder and the lids, in producing the prograde jet
DNS of inertial wave attractors in a librating annulus with height-dependent gap width
No full textDirect numerical simulations (DNS) of inertial wave attractors have been carried out in a librating Taylor-Couette system with broken mirror symmetry in the radial-axial cross-section. The inertial wave excitation mechanism and its localisation at the edges was clarified by applying boundary layer theory. Additional resonance peaks in the simulated response spectra were found to agree with low-order wave attractors obtained by geometric ray tracing. Numerics and theory are in qualitative agreement with recent lab experiments
Universal Statistical Properties of Inertial-particle Trajectories in Three-dimensional, Homogeneous, Isotropic, Fluid Turbulence
No full textWe obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(Φ), of the angle Φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(Φ) ∼Φ−, with a new universal exponent ≃ 4
Sweeping has no effect on renormalized turbulent viscosity
No full textWe perform renormalization group analysis (RG) of the Navier-Stokes equation in the presence of constant mean velocity field , and show that the renormalized viscosity is unaffected by , thus negating the ``sweeping effect", proposed by Kraichnan [Phys. Fluids {\bf 7}, 1723 (1964)] using random Galilean invariance. Using direct numerical simulation, we show that the correlation functions for and differ from each other, but the renormalized viscosity for the two cases are the same. Our numerical results are consistent with the RG calculations
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Reynolds number dependence of the dimensionless dissipation rate in stationary magnetohydrodynamic turbulence
No full textResults on the Reynolds number dependence of the dimensionless total dissipation rate C_ε are presented, obtained from medium to high resolution direct numerical simulations (DNSs) of mechanically forced stationary homogeneous magnetohydrodynamic (MHD) turbulence in the absence of a mean magnetic field, showing that C_ε -> const with increasing Reynolds number. Furthermore, a model equation for the Reynolds number dependence of the dimensionless dissipation rate is derived from the real-space energy balance equation by asymptotic expansion in terms of Reynolds number of the second- and third-order correlation functions of the Elsässer fields z± = u ± b. At large Reynolds numbers we find that a model of the form C_ε = C_ε,∞ + C/R describes the data well, while at lower Reynolds numbers the model needs to be extended to second order in 1/R in order to obtain a good fit to the data, where R is a generalised Reynolds number with respect to the Elsässer field z-
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