Person: Pinelli, Alfredo
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 14
PublicationComparison between large-eddy simulation and Reynolds-averaged Navier–Stokes computations for the MUST field experiment. Part I: Study of the flow for an incident wind directed perpendicularly to the front array of containers(Springer, 2010) Santiago, J. L.; Dejoan, A.; Martilli, A.; Martin, F.; Pinelli, AlfredoThe large-eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) methodologies are used to simulate the air flow inside the container's array geometry of the Mock Urban Setting Test (MUST) field experiment. Both tools are assessed and compared in a configuration for which the incident wind direction is perpendicular to the front array. The assessment is carried out against available wind-tunnel data. Effects of including small geometrical irregularities present in the experiments are analysed by considering LES and RANS calculations on two geometries: an idealized one with a perfect alignment and an identical shape of the containers, and a second one including the small irregularities considered in the experiment. These effects are assessed in terms of the local time-mean average and as well in terms of spatial average properties (relevant in atmospheric modelling) given for the velocity and turbulent fields. The structural flow properties obtained using LES and RANS are also compared. The inclusion of geometrical irregularities is found significant on the local time-mean flow properties, in particular the repeated flow patterns encountered in a perfect regular geometry is broken. LES and RANS provide close results for the local mean streamwise velocity profiles and shear-stress profiles, however the LES predictions are closer to the experimental values for the local vertical mean velocity. When considering the spatial average flow properties, the effects of geometrical irregularities are found insignificant and LES and RANS provide similar results. PublicationReynolds number dependence of mean flow structure in square duct turbulence - CORRIGENDUM(Cambridge University Press, 2010) Pinelli, Alfredo; Uhlmann, Markus; Sekimoto, Atshushi; Kawahara, Genta PublicationImmersed boundary method for generalised finite volume and finite difference Navier-Stokes solvers(American Society of Mechanical Engineers, 2010) Pinelli, Alfredo; Naqavi, I.Z.; Piomelli, U.In Immersed Boundary Methods (IBM) the effect of complex geometries is introduced through the forces added in the Navier-Stokes solver at the grid points in the vicinity of the immersed boundaries. Most of the methods in the literature have been used with Cartesian grids. Moreover many of the methods developed in the literature do not satisfy some basic conservation properties (the conservation of torque, for instance) on non-uniform meshes. In this paper we will follow the RKPM method originated by Liu et al.  to build locally regularized functions that verify a number of integral conditions. These local approximants will be used both for interpolating the velocity field and for spreading the singular force field in the framework of a pressure correction scheme for the incompressible Navier-Stokes equations. We will also demonstrate the robustness and effectiveness of the scheme through various examples. PublicationReynolds number dependence of mean flow structure in square duct turbulence(Cambridge University Press, 2010) Pinelli, Alfredo; Uhlmann, Markus; Sekimoto, Atshushi; Kawahara, GentaWe have performed direct numerical simulations of turbulent flows in a square duct considering a range of Reynolds numbers spanning from a marginal state up to fully developed turbulent states at low Reynolds numbers. The main motivation stems from the relatively poor knowledge about the basic physical mechanisms that are responsible for one of the most outstanding features of this class of turbulent flows: Prandtl's secondary motion of the second kind. In particular, the focus is upon the role of flow structures in its generation and characterization when increasing the Reynolds number. We present a two-fold scenario. On the one hand, buffer layer structures determine the distribution of mean streamwise vorticity. On the other hand, the shape and the quantitative character of the mean secondary flow, defined through the mean cross-stream function, are influenced by motions taking place at larger scales. It is shown that high velocity streaks are preferentially located in the corner region (e.g. less than 50 wall units apart from a sidewall), flanked by low velocity ones. These locations are determined by the positioning of quasi-streamwise vortices with a preferential sign of rotation in agreement with the above described velocity streaks' positions. This preferential arrangement of the classical buffer layer structures determines the pattern of the mean streamwise vorticity that approaches the corners with increasing Reynolds number. On the other hand, the centre of the mean secondary flow, defined as the position of the extrema of the mean cross-stream function (computed using the mean streamwise vorticity), remains at a constant location departing from the mean streamwise vorticity field for larger Reynolds numbers, i.e. it scales in outer units. This paper also presents a detailed validation of the numerical technique including a comparison of the numerical results with data obtained from a companion experiment. PublicationTurbulent puffs in a horizontal square duct under stable temperature stratification(Begell House, 2012) Otsuki, T.; Kawahara, Genta; Uhlmann, Markus; Pinelli, AlfredoDirect numerical simulations of streamwise-localized turbulent flow (turbulent puff) in a horizontal square duct heated from above are performed at Richardson numbers 0 ≤ Ri ≤ 0.58 to characterize differences between isothermal and non-isothermal puffs. It is found that the structure of the non-isothermal puff exhibits significantly different properties from that of the isothermal puff. In particular, differences are observed in wall shear stresses. In the upstream part of the non-isothermal puff, higher shear appears on the horizontal walls than the vertical ones. In the downstream part, meanwhile, higher shear appears on the vertical walls than the horizontal ones. The higher shear on the horizontal walls in the upstream part is interpreted in terms of coherent streamwise vortices induced by buoyancy in the corner regions. The higher shear on the vertical walls in the downstream part is considered to be a consequence of higher wall-normal (horizontal) turbulence intensity on the vertical walls under the weaker constraint of the stable stratification. PublicationComparison between large-eddy simulation and Reynolds-averaged Navier–Stokes computations for the MUST field experiment. Part II: effects of incident wind angle deviation on the mean flow and plume dispersion(Springer, 2010) Dejoan, A.; Santiago, J. L.; Martilli, A.; Martin, F.; Pinelli, AlfredoLarge-eddy simulations (LES) and Reynolds-averaged Navier-Stokes (RANS) computations of pollutant dispersion are reported for the Mock Urban Setting Test (MUST) field experiment flow. In particular we address the effects of incident wind angle deviation on the mean velocity and on the mean concentration fields. Both computational fluid dynamical methods are assessed by comparing the simulation results with experimental field data. The comparative analysis proposes to relate the plume deflection with the flow channelling effects. The results show that the plume deflection angle varies with the altitude. As the ground is approached the plume is shown to be almost aligned with the street canyon direction and independent of the incident wind directions considered. At higher altitudes well above the obstacles, the plume direction is aligned with the mean wind direction as in dispersion over flat terrain. The near-ground plume deflection is the consequence of a strong channelling effect in the region near the ground. The mean concentration profiles predicted by LES and RANS are both in good qualitative agreement with experimental data but exhibit discrepancies that can be partly explained by the influence of small incident wind angle deviation effects. Compared to RANS, LES predicts a higher channelling and thus a higher deflection of the plume. Results on the fluctuating intensity of the concentration obtained from LES show a satisfactory agreement with experiments. This information is not available from RANS for which only the mean concentration modelling is considered. PublicationBlock tridiagonal solvers on heterogeneous architectures(IEEE, 2012) Valero Lara, P.; Pinelli, Alfredo; Favier, J.; Matías, M.P.Modern multi-core and many-core systems offer a very impressive cost/performance ratio. In this paper a set of new parallel implementations for the solution of linear systems with block-tridiagonal coefficient matrix on current parallel architectures is proposed and evaluated: one of them on multi-core, others on many-core and finally, a new heterogeneous implementation on both architectures. The results show a speedup higher than 6 on certain parts of the problem, being the heterogeneous implementation the fastest. PublicationTurbulence-and buoyancy-driven secondary flow in a horizontal square duct heated from below(American Institute of Physics, 2011) Sekimoto, Atshushi; Kawahara, Genta; Sekiyama, K.; Uhlmann, Markus; Pinelli, AlfredoDirect numerical simulations of fully developed turbulent flows in a horizontal square duct heated from below are performed at bulk Reynolds numbers Re(b) = 3000 and 4400 (based on duct width H) and bulk Richardson numbers 0 <= Ri <= 1.03. The primary objective of the numerical simulations concerns the characterization of the mean secondary flow that develops in this class of flows. On one hand, it is known that turbulent isothermal flow in a square duct presents secondary mean motions of Prandtl's second kind that finds its origin in the behavior of turbulence structures. On the other hand, thermal convection drives a mean secondary motion of Prandtl's first kind directly induced by buoyancy. As far as the mean structure of the cross-stream motion is concerned, it is found that different types of secondary flow regimes take place when increasing the value of the Richardson number. The mean secondary flow in the range 0.025 less than or similar to Ri less than or similar to 0.25 is characterized by a single large-scale thermal convection roll and four turbulence-driven corner vortices of the opposite sense of rotation to the roll, as contrasted with the classical scenario of the eight-vortex secondary flow pattern typical of isothermal turbulent square-duct flow. This remarkable structural difference in the corner regions can be interpreted in terms of combined effects, on instantaneous streamwise vortices, of the large-scale circulation and of the geometrical constraint by the duct corner. When further increasing the Richardson number, i.e., Ri greater than or similar to 0.25, the structure of the mean secondary flow is solely determined by the large-scale circulation induced by the buoyancy force. In this regime, the additional mean cross-stream motion is characterized by the presence of two distinct buoyancy-driven vortices of opposite sense of rotation to the circulation only in two of the four corner regions. With increasing Ri, the large-scale circulation is found to enhance the wall skin friction and heat transfer. In the significant-buoyancy regime Ri greater than or similar to 0.25, the mean cross-stream motion and its rms fluctuations are found to scale, respectively, with the buoyancy-induced velocity u(g)=root g beta Delta TH (g, beta, and Delta T being the gravity acceleration, the volumetric coefficient of thermal expansion, and the temperature difference across the duct, respectively) and with the mixed velocity scale root(nu/H)u(g) (nu being the kinematic viscosity). It is suggested that the probable scalings for the rms of streamwise velocity component and of temperature fluctuation are related with the friction velocity u(tau) and friction temperature T(tau) according to the magnitudes u(tau)(2)/ and T(tau)u(tau)/root(nu/H)u(g), respectively. PublicationTravelling-waves consistent with turbulence-driven secondary flow in a square duct(American Institute of Physics, 2010) Uhlmann, Markus; Kawahara, Genta; Pinelli, AlfredoWe present numerically determined travelling-wave solutions for pressure-driven flow through a straight duct with a square cross-section. This family of solutions represents typical coherent structures (a staggered array of counter-rotating streamwise vortices and an associated low-speed streak) on each wall. Their streamwise average flow in the cross-sectional plane corresponds to an eight vortex pattern much alike the secondary flow found in the turbulent regime. PublicationDirect numerical simulation of vertical particulate channel flow in the turbulent regime(Springer, 2010) Uhlmann, Markus; Pinelli, AlfredoWe have conducted a DNS study of dilute turbulent particulate flow in a vertical plane channel, considering up to 8192 finite-size rigid particles with numerically resolved phase interfaces. The particle diameter corresponds to approximately 9 wall units and their terminal Reynolds number is set to 136. The fluid flow with bulk Reynolds number 2700 is directed upward, which maintains the particles suspended upon average. Two different density ratios were simulated, varying by a factor of 4.5. The corresponding Stokes numbers of the two particles were O(10) in the near-wall region and O(1) in the outer flow. We have observed the formation of large-scale elongated streak-like structures with streamwise dimensions of the order of 8 channel half-widths and cross-stream dimensions of the order of one half-width. At the same time, we have found no evidence of significant formation of particle clusters, which suggests that the large structures are due to an mtxinsic instability of the flow, triggered by the presence of the particles. It was found that the mean flow velocity profile tends towards a concave shape, and the turbulence intensity as well as the normal stress anisotropy are strongly increased. The effect of varying the Stokes number while keeping the buoyancy, particle size and volume fraction constant was relatively weak. More details about part of this work can be found in (2008).