Analysis of the Contribution of Large Scale Motions to the Skin Friction of a Zero-Pressure-Gradient Turbulent Boundary Layer Using the Renard-Deck Decomposition

Coherent flow structures in turbulent boundary layers have been an active field of research for many decades, as they might be the key to reveal the mechanics of turbulence production and transport in turbulent shear flows. Renard and Deck (2016) proposed a theoretical decomposition for the mean skin-friction coefficient based on the mean kinetic energy budget in the streamwise direction. This decomposition, referred to as the Renard-Deck (RD) decomposition, decomposes the mean skin friction generation into three physical mechanisms in an absolute reference frame, namely, direct viscous dissipation, turbulent kinetic energy production, and spatial growth. In this study, the large scale motions (LSMs) are extracted using a proper orthogonal decomposition (POD) of the velocity field based on high-spatial-resolution two-dimensional – two-component particle image velocimetry (HSR 2C-2D PIV) of a zero-pressure-gradient turbulent boundary layer (ZPG-TBL), and their effect on the skin friction via RD decomposition.

Binder Jetting Additive Manufacturing: Effect of Particle Size Distribution on Density

This paper reports a study on the effects of particle size distribution (tuned by mixing different-sized powders) on density of a densely packed powder, powder bed density, and sintered density in binder jetting additive manufacturing. An analytical model was used first to study the mixture packing density. Analytical results showed that multimodal (bimodal or trimodal) mixtures could achieve a higher packing density than their component powders and there existed an optimal mixing fraction to achieve the maximum mixture packing density. Both a lower component particle size ratio (fine to coarse) and a larger component packing density ratio (fine to coarse) led to a larger maximum mixture packing density. A threshold existed for the component packing density ratio, below which the mixing method was not effective for density improvement. Its relationship to the component particle size ratio was calculated and plotted. In addition, the dependence of the optimal mixing fraction and maximum mixture packing density on the component particle size ratio and component packing density ratio was calculated and plotted. These plots can be used as theoretical tools to select parameters for the mixing method. Experimental results of tap density were consistent with the above-mentioned analytical predictions. Also, experimental measurements showed that powders with multimodal particle size distributions achieved a higher tap density, powder bed density, and sintered density in most cases.

Discreteness of Space and Its Consequences

Based on the general principle of the unity of the nature of interacting entities and the principle of the relativity of motion, as well as following the requirement of an indissoluble and conditioning connection of space and time, the model of a discrete space-time consisting of identical interacting particles is proposed as the most acceptable one. We consider the consequences of the discreteness of space, such as: the occurrence of time quanta, the limiting speed of signal propa­gation, and the constancy of this speed, regardless of the motion of the reference frame. Regularly performed acts of particles of space-time (PST) interaction en­sure the connectivity of space, set the quantum of time and the maximum speed – the speed of light. In the process of PST communication, their mixing occurs, which ensures the relativity of inertial motion, and can also underlie quantum uncertainty. In this case, elementary particles are spatial configurations of an excited “lattice” of PST, and particles with mass must contain loop struc­tures in their configuration. A new interpretation of quantum mechanics is pro­posed, according to which the wave function determines the probability of de­struction of a spatial configuration (representing a quantum object) in its corresponding region, which leads to the contraction of the entire structure to a given, detectable component. Particle entanglement is explained by the appear­ance of additional links between the PST – the appearance of a local coordinate along which the distance between entangled objects does not increase. It is shown that the movement of a body should lead to an asymmetry of the tension of the bonds between the PST – to the asymmetry of its effective gravity, the es­tablishment of which is one of the possibilities for experimental verification of the proposed model. It is shown that the constancy of the speed of light in a vac­uum and the appearance of relativistic effects are based on ensuring the connec­tivity of space-time, i.e. striving to prevent its rupture.

The influence of particle size and density of pelleted samples of forest fuel on thermokinetic characteristics of pyrolysis and oxidation

This paper presents the results of experimental studies of thermokinetic characteristics of pyrolysis and oxidation of pine needles, taking into account the influence of particle size and density of forest fuel in pelleted samples. The sample densities range within 206-955 kgm-3 (i.e. from typical sample densities to average ones for pressed pelleted samples), and the component particle sizes amount to 60-140 ?m. The range of studied temperatures is 20-1000 o?. The particle size and density of the material are found to be important parameters that significantly affect the kinetics of pyrolysis. According to the results of measurements, the activation energy of needles pyrolysis is within the range of 22.8-113.8 kJmol-1, and that of oxidation corresponds to 134.7-211 kJmol-1. Three intervals with significantly different values of activation energy and pre-exponential factor are distinguished in the studied temperature range. Approximation expressions are formulated for the activation energies of pyrolysis and oxidation as functions of forest fuel particle sizes, sample density and temperature.

Fault linkage and its controls on fault growth and basin evolution: Insights from analogue experiments

<p>The evolution of fault-bounded basins and the concomitant migration of hydrocarbons and fluids are strongly influenced by fault activity and, in the case of an extensional tectonic setting, by the interaction of fault planes in relay zones. Fault linkage is a process that develops at relays between sufficiently closely spaced fault planes during their propagation. Fault interaction depends on several factors, such as the degree of under- or overlapping fault arrays, the similar or opposed polarity of fault planes and a separation that should not exceed a critical distance.</p><p>Motivated by observations at a km-scale fault relay of a major normal fault in the Magdalena Valley, Northern Andes of Colombia, we designed an analogous sandbox model, in which we simulated the linkage of rift zones separated at distances equivalent to two to four times the dimension of the height of a uniform sand layer. Fault nucleation took place at pre-designed seeds or at the velocity discontinuity of a moving sheet along the base of the sandbox and gave rise to two offset graben structures. Early fault linkage took place by means of two sub-vertical faults, which formed a shortcut between an inner and an adjacent outer border fault of the offset graben structures, enclosing a small horst in between.</p><p>The kinematic meaning of these short-cut faults became evident by the subsequent growth pattern of the faults opposite to the linked strands. On approaching the relay zone, these faults turned into an attitude almost perpendicular to their imposed trend. According to the displacement senses set up parallel to the axes of the offset graben structures, the displacement transfer on the two short-cut faults accommodated a strike-slip component. Particle analysis by means of the MATLAB’s PIVlab © tool and photogrammetric processes corroborated these findings. Displacement transfer on the short-cut faults set in at the very onset of the formation of the two graben structures. During successive deformation stages two distinct velocity fields parallel to the graben axes became established, each one pointing away from the structural high of the relay zone.</p><p>Although our boundary conditions are restricted to a uniform layer and orthogonal extension, this experimental scenario may form a starting point for testing new questions about the propagation of bounding faults at the termination of graben structures, such as those found at the East Africa Rift. Here, rifting evolved within a lithospheric high, impeding the accumulation of fine-grained or “soft” sedimentary sequences in precursor basins.</p>

Arrangement Effects of 30 deg Inclined Teardrop-Shaped Dimples on Film Cooling Flow Over Dimpled Cutback Surface at Airfoil Trailing Edge Investigated by 2D3C-PTV

The objective of this study is to determine the differences in flow fields between the 30 deg in-line and staggered arrangements of teardrop-shaped dimples, and to explain why the surface-averaged Nusselt number with the 30 deg in-line arrangement was 28.7% higher than that with the 30 deg staggered arrangement in our previous study. Measurements of the instantaneous velocity fields over the dimpled cutback surfaces in the two arrangements were performed at five spanwise cross sections using two-dimensional three-component particle tracking velocimetry (2D3C-PTV). Recirculation flows were observed only inside the dimples in the in-line arrangement, and the region above the recirculation flows exhibited a higher Reynolds shear stress. In this region, turbulent mixing between the high-speed cooling-flow and the low-speed recirculation-flow can be promoted. Streamlines of the time-averaged velocities showed that approximately half the fluid flowing out of a teardrop-shaped dimple in the in-line arrangement hardly flowed into the ones downstream. The remainder of the fluid mostly flowed into the dimple immediately downstream, and the inflow of the fluid into further downstream dimples decreased gradually. From the PTV results, we can deduce that the fluid motions in the in-line arrangement leads to a larger temperature-difference between the dimple wall and the fluid because the inflow of fluid heated inside upstream dimples into the downstream ones is less than in the staggered arrangement. Consequently, the Nusselt number in the in-line arrangement was higher.

An all white magnet by combination of electronic properties of a white light emitting MOF with strong magnetic particle systems

A multi-component particle system was developed that combines the properties of white color, white light emission and strong magnetism on the macroscopic and microscopic scale.