Scale-by-scale energy budget in fractal element grid-generated turbulence

Measurements were conducted downstream of a square-fractal-element grid at , where L0 is the size of the largest element in the grid. The scale-by-scale energy budget for grid turbulence is used to investigate the phenomenological change in the turbulence between the inhomogeneous and homogeneous regions downstream of the grid, providing greater insight into the evolution of the turbulence in these two regions. It is shown that in the far field, x/L0 ? 20, where the flow is approximately homogeneous and isotropic, the scale-by-scale energy budget for grid turbulence is well balanced. In the near field, x/L0 < 20, the same energy budget is not satisfied, with the imbalance of the budget occurring at scales in the range ? ? r ? L0. It is proposed that the imbalance is caused by non-zero transverse transport of turbulent kinetic energy and production due to transverse mean velocity gradients. Approach of the spectra to k?5/3 behaviour with a decade long scaling range in the inhomogeneous region is attributed to forcing by these non-zero transverse terms

Influence of an extended non-equilibrium region on the far-field of grid turbulence

The turbulence produced by two regular square mesh grids is compared to that produced by a square-fractal-element grid composed of an array of small square fractals. All three grids have approximately the same blockage. One of the regular grids is designed to have the same mesh length, M, as the fractal element grid, while the other matches the maximum bar thickness of the fractal. The transition of the turbulence from a non-equilibrium to a near equilibrium regime is assessed through the scale-by-scale kinetic energy budget and the velocity derivative skewness. It is found that the turbulence produced by all three grids agrees with many of the predictions for equilibrium phenomenology after approximately 20 M, with the regular grids reaching quasi-equilibrium earlier than the fractal. In the far-field, the fractal grid produces comparable or lower Relambda than the regular grids in both dimensional and non-dimensional measurements of the streamwise position. This is attributed to an extended rapidly decaying non-equilibrium region in the wake of the fractal grid relative to the regular grids

Decay of turbulence generated by a square-fractal-element grid

A novel square-fractal-element grid was designed in order to increase the downstream measurement range of fractal grid experiments relative to the largest element of the grid. The grid consists of a series of square fractal elements mounted to a background mesh with spacing $L_0 = 100\, {\rm mm}$L0=100mm. Measurements were performed in the region $3.5 \le x/L_0 \le 48.5$3.5?x/L0?48.5, which represents a significant extension to the x/L_0 < 20x/L0&lt;20 of previously reported square fractal grid measurements. For the region $x/L_0 \gtrsim 24$x/L0?24 it was found that a power-law decay region following $\langle {q}^2 \rangle \sim (x - x_0)^m$?q2??(x?x0)m exists with decay exponents of $m = -1.39$m=?1.39 and $-1.37$?1.37 at $\mathit{Re}_{L_0} = 57\, 000$ReL0=57000 and $65\, 000$65000, respectively. This agrees with decay values previously measured for regular grids ($-1 \gtrsim m \gtrsim -1.4$?1?m??1.4). The turbulence in the near-grid region, x/L_0 < 20x/L0&lt;20, is shown to be inhomogeneous and anisotropic, in apparent contrast with previous fractal grid measurements. Nonetheless, power-law fits to the decay of turbulent kinetic energy in this region result in $m = -2.79$m=?2.79, similar to $m \approx -2.5$m??2.5 recently reported by Valente &amp; Vassilicos (J. Fluid Mech., vol. 687, 2011, pp. 300–340) for space-filling square fractals. It was also found that $C_\epsilon$C? is approximately constant for $x/L_0 \ge 25$x/L0?25, while it grows rapidly for x/L_0 < 20x/L0&lt;20. These results reconcile previous fractal-generated turbulence measurements with classical grid turbulence measurements

Multi Visualization and Dynamic Query for Effective Exploration of Semantic Data

Semantic formalisms represent content in a uniform way according to ontologies. This enables manipulation and reasoning via automated means (e.g. Semantic Web services), but limits the user’s ability to explore the semantic data from a point of view that originates from knowledge representation motivations. We show how, for user consumption, a visualization of semantic data according to some easily graspable dimensions (e.g. space and time) provides effective sense-making of data. In this paper, we look holistically at the interaction between users and semantic data, and propose multiple visualization strategies and dynamic filters to support the exploration of semantic-rich data. We discuss a user evaluation and how interaction challenges could be overcome to create an effective user-centred framework for the visualization and manipulation of semantic data. The approach has been implemented and evaluated on a real company archive

Getting jammed in all directions: Dynamic shear jamming around a cylinder towed through a dense suspension

Experimental results of towing a cylinder through a dense suspension of cornstarch and sucrose-water are presented. Focus is placed on the jamming fronts that exist in such systems. The literature has concentrated on the propagation of the jammed region under pushing, pulling or shearing conditions independently. How the different fronts interact and if the fronts are symmetric when generated simultaneously has remained unexplored. Investigating this is our main goal. With the current setup, we are able to view a continuous, quasi-2D field around the cylinder. As such, a new way of generating jamming fronts is presented whereby pushing, pulling and shearing can be examined simultaneously. In agreement with previous studies, the front propagates roughly twice as fast in the longitudinal direction compared to the transverse direction, which is attributed to a single underlying onset strain, regardless of orientation from the cylinder. Although the jamming front shows nearly perfect transverse symmetry, there is clear longitudinal asymmetry. This is evident in the velocity and strain fields, and is also detectable in the front propagation velocity and onset strain

Global hydrodynamic analysis of the molecular flexibility of galactomannans

In the past, intrinsic viscosity and sedimentation velocity analyses have been used separately to assess the conformation and flexibility of guar and locust bean gum galactomannans based on worm-like chain and semi-flexible coil models. Publication of a new global method combining data sets of both intrinsic viscosity and sedimentation coefficient with molecular weight, and minimising a target (error) function now permits a more robust analysis. Using this approach, values for the persistence length of (10 ± 2) nm for guar and (7 ± 1) nm for locust bean gum are returned if the mass per unit length ML is floated as a variable. Using a fixed mass per unit length based on the known compositional data of each galactomannan yields a similar value for Lp in both cases, (8 ± 1) nm for guar and (9 ± 1) nm for locust bean gum, with combined set of data yielding (9 ± 1) nm: within experimental error the flexibilities of both galactomannans are very similar. © 2007 Elsevier Ltd. All rights reserved

Technical concept for rock mechanics tests, Climax Granite, NTS

If we are to believe our predictions of the thermomechanical behavior of the material surrounding a nuclear waste repository in granite, we must test the computational methods used in making the predictions. If thermal loadings appropriate to a real repository are used, thermally induced displacements and strains are quite small, and available geotechnical instrumentation is only marginally able to measure these effects to the accuracy desired to make thorough tests of the predictions. We outline a three-step program to address these issues. (1) Conduct experiments in which the thermal loading is large compared to that induced by a real repository. This will permit us to make accurate measurements with available instrumentation. (2) Simultaneously, develop improved instrumentation that will enable us to make accurate measurements of motions induced by thermal loadings appropriate to a real repository. (3) Finally, conduct a second set of experiments, with the improved instrumentation and thermal loading similar to that of a real repository in granite. If we can predict the effects of this thermal loading to a few percent over distances of tens of meters for time periods of a few years, and demonstrate that these predictions are correct, we can have reasonable confidence that, using the same methods, we can predict the behavior over thousands of meters for hundreds of years to an order of magnitude. That accuracy should be satisfactory for those distances and times

Technical concept for rock mechanics tests, Climax Granite, NTS

If we are to believe our predictions of the thermomechanical behavior of the material surrounding a nuclear waste repository in granite, we must test the computational methods used in making the predictions. If thermal loadings appropriate to a real repository are used, thermally induced displacements and strains are quite small, and available geotechnical instrumentation is only marginally able to measure these effects to the accuracy desired to make thorough tests of the predictions. We outline a three-step program to address these issues. (1) Conduct experiments in which the thermal loading is large compared to that induced by a real repository. This will permit us to make accurate measurements with available instrumentation. (2) Simultaneously, develop improved instrumentation that will enable us to make accurate measurements of motions induced by thermal loadings appropriate to a real repository. (3) Finally, conduct a second set of experiments, with the improved instrumentation and thermal loading similar to that of a real repository in granite. If we can predict the effects of this thermal loading to a few percent over distances of tens of meters for time periods of a few years, and demonstrate that these predictions are correct, we can have reasonable confidence that, using the same methods, we can predict the behavior over thousands of meters for hundreds of years to an order of magnitude. That accuracy should be satisfactory for those distances and times