Person: Pinelli, Alfredo
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First Name
Alfredo
Last Name
Pinelli
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Matemáticas
Department
Area
Matemática Aplicada
Identifiers
19 results
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Now showing 1 - 10 of 19
Item The role of the forcing term in the large eddy simulation of equilibrium channel flow(Engineering Turbulence Modeling and Experiments, 1990) Benocci, C.; Pinelli, AlfredoItem A parallel spectral multi-domain solver suitable for DNS and LES numerical simulation of incompressible flows(Progress and Challenges in CFD Methods and Algorithms p(SEE N 96-36048 12-34), 1996) Pinelli, Alfredo; Vacca, A.Item Chebyshev collocation method and multidomain decomposition for the incompressible Navier‐Stokes equations(International journal for numerical methods in fluids, 1994) Pinelli, Alfredo; Vacca, A.The two-dimensional incompressible Navier-Stokes equations in primitive variables have been solved by a pseudospectral Chebyshev method using a semi-implicit fractional step scheme. The latter has been adapted to the particular features of spectral collocation methods to develop the monodomain algorithm. In particular, pressure and velocity collocated on the same nodes are sought in a polynomial space of the same order; the cascade of scalar elliptic problems arising after the spatial collocation is solved using finite difference preconditioning. With the present procedure spurious pressure modes do not pollute the pressure field. As a natural development of the present work a multidomain extent was devised and tested. The original domain is divided into a union of patching sub-rectangles. Each scalar problem obtained after spatial collocation is solved by iterating by subdomains. For steady problems a C1 solution is recovered at the interfaces upon convergence, ensuring a spectrally accurate solution. A number of test cases have been solved to validate the algorithm in both its single-block and multidomain configurations. The preliminary results achieved indicate that collocation methods in multidomain configurations might become a viable alternative to the spectral element technique for accurate flow prediction.Item The instability of streaks in near-wall turbulence(Center for Turbulence Research, Annual Research Briefs, 1998) Kawahara, Genta; Jiménez, Javier; Uhlmann, Markus; Pinelli, AlfredoItem A preconditioning technique for Chebyshev collocated advection diffusion operators(Computationa, Computational fluid dynamics' 92; Proceedings of the European Computational Fluid Dynamics Conference, 1st, Brussels, Belgium, Sep. 7-11, 1992, 1992) Pinelli, Alfredo; Benocci, C.; Deville, M.An original method for preconditioning Chebyshev collocated advection-diffusion operators is proposed. The preconditioner, based on an upwind finite difference approximation, is tested on one and two dimensional problems with both Neumann and Dirichlet boundary conditions.Item Chebyshev pseudospectral solution of advection-diffusion equations with mapped finite difference preconditioning(Journal of Computational Physics, 1994) Pinelli, Alfredo; Benocci, C.; Deville, M.A new Chebyshev pseudo-spectral algorithm with finite difference preconditioning is proposed for the solution of advection-diffusion equations, A mapping technique is introduced which allows good convergence for any Peclet number both for one-dimensional and two-dimensional problems. Numerical results show that first-order Lagrange polynomials are the optimal mapping procedure for the one-dimensional problem and second-order Lagrange polynomials, for the two-dimensional one.Item Wall turbulence: How it works and how to damp it(4th Shear Flow Control Conference, 1997) Jiménez, Javier; Pinelli, AlfredoItem Turbulent flow above a porous surface(American Physical Society, Division of Fluid Dynamics Meeting, November 21-23, 1999 New Orleans, LA, abstract #BF.08, 1999) Jiménez, J.; Uhlmann, Markus; Kawahara, Genta; Pinelli, AlfredoWe have investigated a fully turbulent, low-Reynolds number plane channel with one impermeable and one porous wall. The latter is assumed to obey Darcy's law and to be mass-neutral in the mean. Our DNS data show an enhancement of wall friction up to 40%, along with an increase in overall turbulence intensity. Most strikingly, a strong spanwise organization of the flow is observed due to the presence of large-scale, roller-like structures. Their effect is to alternatively energize and almost laminarize the buffer zone and the sublayer streaks. Linear analysis of the turbulent mean profile over a porous surface shows it to be unstable, with spanwise two-dimensional eigenfunctions whose shape and phase velocity are similar to those of the observed rollers. Finally, we show that the above effects of passive porosity can be duplicated by means of active two-dimensional wall transpiration, with the right shape and advection velocity. Interestingly, active injection with the wrong advection velocity has no effect on the average skin friction.Item The autonomous cycle of near-wall turbulence(Journal of fluid mechanics, 1999) Jiménez, Javier; Pinelli, AlfredoNumerical experiments on modified turbulent channels at moderate Reynolds numbers are used to differentiate between several possible regeneration cycles for the turbulent fluctuations in wall-bounded flows. It is shown that a cycle exists which is local to the near-wall region and does not depend on the outer flow. It involves the formation of velocity streaks from the advection of the mean profile by streamwise vortices, and the generation of the vortices from the instability of the streaks. Interrupting any of those processes leads to laminarization. The presence of the wall seems to be only necessary to maintain the mean shear. The generation of secondary vorticity at the wall is shown to be of little importance in turbulence generation under natural circumstances. Inhibiting its production increases turbulence intensity and drag.Item The autonomous near-wall turbulent region(American Physical Society, Division of Fluid Dynamics Meeting, November 22-24, 1998 Philadelphia, PA, abstract #AH.04, 1998) Jiménez, J.; Pinelli, AlfredoThe near-wall region is the only place in zero-pressure-gradient boundary layer where the production of turbulent energy exceeds dissipation. The excess energy helps maintain turbulence in the core region, where the opposite is true. It is shown that it is possible to maintain turbulence in the region below y^+≈ 60 without any input from the outer flow. In the numerical experiment all the fluctuations in a plane channel are artificially damped by increasing viscosity with height, and the outer flow is laminar above that level. The near-wall region nevertheless survives indefinitely, suggesting that wall turbulence can be studied in terms of modular units, with the near-wall and the logarithmic and outer layers as interacting but distinct phenomena. The cycle responsible for maintaining near-wall turbulence is shown to involve low-velocity streaks and streamwise vortices, but essentially no hairpins. The intensity of the near-wall longitudinal velocity fluctuations agrees well with those in fully developed flows, but the wall-normal fluctuations are weaker, in agreement with the Reynolds number behaviour found experimentally for those quantities. The reason is explored using higher Reynolds number simulations.