Person: Pinelli, Alfredo
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 22
PublicationMarginally turbulent flow in a square duct(Cambridge University Press, 2007) Uhlmann, Markus; Pinelli, Alfredo; Kawahara, Genta; Sekimoto, AtshushiA direct numerical simulation of turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain is around 190 wall units, roughly independently of the Reynolds number. We present a characterization of the flow state at marginal Reynolds numbers which substantially differs from the fully turbulent one: the marginal state exhibits a four-vortex secondary flow structure alternating in time whereas the fully turbulent one presents the usual eight-vortex pattern. It is shown that in the regime of marginal Reynolds numbers buffer-layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind. PublicationLES and RANS simulations of the MUST experiment. Study of incident wind direction effects on the flow and plume dispersion(2007) Santiago, J. L.; Dejoan, A.; Martilli, A.; Martín , F.; Pinelli, AlfredoIn this study, we propose to assess and compare the performance of LES and RANS methodologies for the simulation of pollutant dispersion in an urban environment by making use of field and wind tunnel measurements of the MUST experiment configuration. First, the proposed analysis addresses the relevance of taking into account the small geometrical irregularities of the obstacle array in the computations. For this, local and spatial averaged time mean flow properties are compared for two geometries, one with a perfect alignment of the containers and another one including the irregularities present in the experiment. In both geometries the incident flow is orthogonal to the front array of obstacles. The second part of this study presents simulations with different approaching wind directions to analyse the effect of small changes in the incident wind direction on the flow and on the plume dispersion. In this second part, the mean concentration field is compared with the experimental data and an analysis that relates the channelling effects with the plume deflection is provided. PublicationTurbulent shear flow over active and passive porous surfaces(Cambridge University Press, 2001) Jiménez, J.; Uhlmann, Markus; Pinelli, Alfredo; Kawahara, GentaThe behaviour of turbulent shear flow over a mass-neutral permeable wall is studied numerically. The transpiration is assumed to be proportional to the local pressure fluctuations. It is first shown that the friction coefficient increases by up to 40% over passively porous walls, even for relatively small porosities. This is associated with the presence of large spanwise rollers, originating from a linear instability which is related both to the Kelvin–Helmholtz instability of shear layers, and to the neutral inviscid shear waves of the mean turbulent profile. It is shown that the rollers can be forced by patterned active transpiration through the wall, also leading to a large increase in friction when the phase velocity of the forcing resonates with the linear eigenfunctions mentioned above. Phase-lock averaging of the forced solutions is used to further clarify the flow mechanism. This study is motivated by the control of separation in boundary layers. PublicationCoherent structures in marginally turbulent square duct flow(Springer, 2008) Uhlmann, Markus; Pinelli, Alfredo; Sekimoto, Atshushi; Kawahara, Genta; Kaneda, YukioDirect numerical simulation of fully developed turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain measures around 190 wall units, roughly independently of the Reynolds number. Furthermore, we present a characterization of the marginal state, where coherent structures are found to have significant relevance to the appearance of secondary flow of Prandtl’s second kind. PublicationThe eﬀect of coherent structures on the secondary ﬂow in a square duct(Springer, 2009) Sekimoto, Atshushi; Pinelli, Alfredo; Uhlmann, Markus; Kawahara, Genta; Eckhardt, BrunoThe appearance of secondary flow of Prandtl’s second kind is a well-known phenomenon in fully developed turbulent rectangular duct flow. The intensity of the secondary flow is two orders of magnitude smaller than that of the mean streamwise velocity; however, it plays an important role in the crossstreamwise momentum, heat and mass transfer. Our recent study  revealed that the mean secondary flow is a statistical footprint of the turbulent flow structures, i.e. streamwise vortices and streaks which are observed in the nearwall region, whose cross-sectional positions are constrained by the presence of the side walls at marginal Reynolds number (approximately 1100, based on the bulk velocity and the duct half width, corresponding to a friction Reynolds number of about 80). In this marginal case, one low-speed streak associated with a pair of counter-rotating streamwise vortices can exist over each wall and they are self-sustained . When considering the higher Reynolds numbers, the increment of duct width in wall unit allows the simultaneous presence of multiple low velocity streaks and pairs of streamwise vortices upon the wall. PublicationDistribution and deposition of low stokes number particles in turbulent channel flow(Elsevier, 2004) García Ybarra, P. L.; Pinelli, Alfredo PublicationThermophoretic sampling of combustion particles from a fluidized bed combustor(Elsevier, 2001) Sanz, D.; Muñoz, R.; Armesto, L.; Hontañón, E.; Pinelli, Alfredo; Espigares, M. M. PublicationComparison between LES and RANS computations for the study of contaminant dispersion in the MUST field experiment(AMS, 2007) Dejoan, A.; Santiago, J. L.; Pinelli, Alfredo; Martilli, A. PublicationDNS of non-isothermal turbulent flows carrying low Stokes number particles(Elsevier, 2003) Pinelli, Alfredo; García Ybarra, P. L. PublicationTravelling waves in a straight square duct(Springer, 2009) Uhlmann, Markus; Kawahara, Genta; Pinelli, AlfredoIsothermal, incompressible flow in a straight duct with square cross-section is known to be linearly stable . Direct numerical simulation, on the other hand, has revealed that turbulence in this geometry is self-sustained above a Reynolds number value of approximately 1100, based on the bulk velocity and the duct half-width . Numerous non-linear equilibrium solutions have already been identified in plane Couette, plane Poiseuille and pipe flows [3, 4, 5], and their role in the transition process as well as their relevance to the statistics of turbulent flow have been investigated [6, 7, 8]. No non-linear travelling-wave solutions for the flow through a square duct have been published to date.