An efficient Two-Layer wall model for accurate numerical simulations of aeronautical applications

Two-Layer wall models have been widely studied since they allow wall modeled Large Eddy Simulationsof general non-equilibrium flows. However, they are plagued by two persistent problems, the "log-layermismatch" and the resolved Reynolds stresses inflow. Several methodologies have been proposed so far todeal with these problems separately. In this work, a time-filtering methodology is used to tackle both issuesat once with a single and low-computational-cost step, easily applicable to complex three-dimensionalgeometries. Additionally, it is shown that the techniques intended to suppress the Reynolds stresses inflowproposed so far, were not sufficient to completely mitigate their detrimental effects.Peer ReviewedPostprint (published version

Direct numerical simulation of backward-facing step flow at Ret = 395 and expansion ratio 2

Backward-facing step (BFS) constitutes a canonical configuration to study wallbounded flows subject to massive expansions produced by abrupt changes in geometry. Recirculation flow regions are common in this type of flow, driving the separated flow to its downstream reattachment. Consequently, strong adverse pressure gradients arise through this process, feeding flow instabilities. Therefore, both phenomena are strongly correlated as the recirculation bubble shape defines how the flow is expanded, and how the pressure rises. In an incompressible flow, this shape depends on the Reynolds value and the expansion ratio. The influence of these two variables on the bubble length is widely studied, presenting an asymptotic behaviour when both parameters are beyond a certain threshold. This is the usual operating point of many practical applications, such as in aeronautical and environmental engineering. Several numerical and experimental studies have been carried out regarding this topic. The existing simulations considering cases beyond the above-mentioned threshold have only been achieved through turbulence modelling, whereas direct numerical simulations (DNS) have been performed only at low Reynolds numbers. Hence, despite the great importance of achieving this threshold, there is a lack of reliable numerical data to assess the accuracy of turbulence models. In this context, a DNS of an incompressible flow over a BFS is presented in this paper, considering a friction Reynolds number (Reτ) of 395 at the inflow and an expansion ratio 2. Finally, the elongation of the Kelvin–Helmholtz instabilities along the shear layer is also studied.Postprint (published version

Institutional reforms to integrate regulation and competition policy : economic analysis, international perspectives, and the case of the CNMC in Spain

We review the related academic literature and the international evidence on the institutions of regulation and competition policy, to analyze the creation in 2013 of the new macro regulator in Spain, the CNMC. The institutional reform merged the competition policy authority with virtually all sector regulators with the exception of the financial regulator. The aim of the paper is to assess the extent to which the Spanish reform follows international best practices as well as how it fits within the analysis found in the academic literature. Although there is not a universally superior approach, neither in practice nor in theory, important shortcomings remain with the model that was finally adopted in Spain. Some institutional diversity would facilitate an optimal level of regulatory independence and governmental coordination for each sector, and ultimately achieving better results in terms of consumer welfare

The Lorenz-maximal core allocations and the kernel in some classes of assignment games

En aquest treball demostrem que en la classe de jocs d'assignació amb diagonal dominant (Solymosi i Raghavan, 2001), el repartiment de Thompson (que coincideix amb el valor tau) és l'únic punt del core que és maximal respecte de la relació de dominància de Lorenz, i a més coincideix amb la solucié de Dutta i Ray (1989), també coneguda com solució igualitària. En segon lloc, mitjançant una condició més forta que la de diagonal dominant, introduïm una nova classe de jocs d'assignació on cada agent obté amb la seva parella òptima almenys el doble que amb qualsevol altra parella. Per aquests jocs d'assignació amb diagonal 2-dominant, el repartiment de Thompson és l'únic punt del kernel, i per tant el nucleolo

Generalized three-sided assignment markets: core consistency and competitive prices

A generalization of the classical three-sided assignment market is considered, where value is generated by pairs or triplets of agents belonging to different sectors, as well as by individuals. For these markets we represent the situation that arises when some agents leave the market with some payoff by means of a generalization of Owen (Ann Econ Stat 25-26:71-79, 1992) derived market. Consistency with respect to the derived market, together with singleness best and individual anti-monotonicity, axiomatically characterize the core for these generalized three-sided assignment markets. When one sector is formed by buyers and the other by two different type of sellers, we show that the core coincides with the set of competitive equilibrium payoff vectors

Caracterització ambiental dels corotipus de plantes vasculars de Catalunya

Catalonia is a rich area in Biodiversity, its orography and geographic position produce a rich variability climatic area. In this paper, we determine environmental factors (climatic, geographic and geologic) that influence the regional corotypes of vascular plants. We use distance based redundancy analysis (dbRDA). Results show that environmental factors explain 83,77 % of the variance of the species distribution in corotypes, and the two first canonical axis explain 70,13 %. The first axis is related with altitude and the second axis with the soil reaction (basic/acid) and the coast distance (oceanity/continentality). The correlation of species distribution and environmental variables allow to study the behavior of the species to changes in environmental conditions

Consistency and the core of multi-sided assignment markets

[cat] En aquest treball es demostra que en el domini dels jocs d’assignació equilibrats multisectorials (Quint, 1991), el core és l’única solució no buida que satisfà derived consistency i projection consistency. També es caracteritza el core en tota la classe dels jocs d’assignació multisectorials amb els axiomes de singleness best, individual antimonotonicity i derived consistency. Com a casos particulars, s’obtenen dues noves axiomàtiques del core per als jocs d’assignació bilaterals (Shapley and Shubik, 1972).[eng] On the domain of balanced multi-sided assignment games (Quint, 1991), the core is characterized as the unique non-empty solution satisfying derived consistency and projection consistency. As a consequence, a new characterization of the core of two-sided assignment games (Shapley and Shubik, 1972) is provided by using simultaneously the aforementioned consistency axioms. We also characterize the core on the whole domain of multi-sided assignment games in terms of singleness best, individual anti-monotonicity and derived consistency. Again, as a particular case we obtain a new axiomatization for the bilateral case without making use of the non-emptiness axiom

An OpenCL-based parallel CFD code for simulations on hybrid systems with massively-parallel accelerators

A parallel finite-volume CFD algorithm for modeling of incompressible flows on hybrid supercomputers is presented. It is based on a symmetry-preserving high-order numerical scheme for structured meshes. A multilevel approach that combines di erent parallel models is used for large-scale simulations on computing systems with massively-parallel accelerators. MPI is used on the first level within the distributed memory model to couple computing nodes of a supercomputer. On the second level OpenMP is used to engage multiple CPU cores of a computing node. The third level exploits the computing potential of massively-parallel accelerators such as GPU (Graphics Processing Units) of AMD and NVIDIA, or Intel Xeon Phi accelerators of the MIC (Many Integrated Core) architecture. The hardware independent OpenCL standard is used to compute on accelerators of di erent architectures within a general model for a combination of a central processor and a math co-processor.Peer ReviewedPostprint (published version

Symmetry-preserving regularization of wall-bounded turbulent flows

The incompressible Navier-Stokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively low-Reynolds numbers because of the almost numberless small scales produced by the non-linear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the Navier-Stokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces an hyper-viscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a self-adjoint linear filter whose local filter length is determined from the requirement that vortex-stretching must stop at the smallest grid scale. To do so, a new criterion based on the invariants of the local strain tensor is proposed here. Altogether, the proposed method constitutes a parameter-free turbulence model.Peer ReviewedPostprint (published version

Contrary effects of flow intermittence and land uses on organic matter decomposition in a Mediterranean river basin

Flow interruption in intermittent rivers (IRs) generates a mosaic of terrestrial and aquatic habitats across the river network affecting ecosystem processes, as organic matter (OM) decomposition. Water use for farming in arid and semi-arid climates intensifies the dry conditions and affects local river characteristics. In that way, flow intermittence and the distribution of land uses may affect the OM processing along the river. To understand the role of IRs in global OM dynamics and how global change affecting water flow regimes determines these dynamics, it is important to estimate OM-processing rates at a basin scale. The aim of this study was to evaluate the effect of the intensity of flow intermittence on OM processing, and how this effect was modulated by local environmental factors related to land uses across a Mediterranean river basin. To do this, wood decomposition (mass loss and fungal biomass) was selected as a functional indicator. Drying duration and frequency were measured to characterize flow intermittence in different reaches along the river, as well as local environmental factors. Linear models stablished the role of factors on decomposition. The results showed that differences in decomposition rates across the river network were negatively related to the duration of flow interruption. Dissolved inorganic nitrogen associated with agriculture counteracted the negative effect of intermittence on mass loss (increasing by up to three times); but with a higher duration of dry conditions, its effect was insignificant. An increase of 20% of canopy (higher in natural areas) resulted in increases of up to 5% of mass loss. Overall, our study is relevant to understanding the interaction between flow intermittence and land uses on OM processing, especially considering the intensification of flow intermittence and its increased distribution to other regions, which is expected to be a consequence of climate warming and human activities