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large-eddy simulation models for complex fluids

Modelos para simulação das grandes escalas de fluidos complexos

Reference
2023.15779.PEX
Project Start Date
2025-01-01
Project End Date
2026-12-31
Principal Investigator
Scientific Area
Engineering and technology
Funding Program
Concurso de Projetos Exploratórios em Todos os Domínios Científicos 2023

Abstract

The efficient use of thermal and mechanical energy is one of the cornerstones of sustainable development and by implication of the actions required to mitigate the effects of climate change. The increasing use of synthetic fluids in engineering processes, obtained by the addition of macromolecules, surfactants, particles or chemicals into Newtonian fluids, allow process optimization and the reduction of energy needs and of energy waste. Theresulting complex fluids exhibit non-linear behavior that is usually viscoelastic and is known to lead to the reduction of momentum and energy transfer under certain conditions. Examples can be found in the food and process industries [1], and also as thermal fluids in district heating and cooling systems [2], among others [3]. The full benefit of energy savings requires those flows to be turbulent or transitional and engineering design needs adequate simulation strategies and accurate turbulence models for the simulations. Such endeavor is very challenging because of the complex interactions between the non-linear rheology and the multiscale turbulent fluctuations. Presently, the numerical simulation of turbulent flows of complex fluids is almost exclusively based on Reynolds-averaged Navier-Stokes equations (RANS) [4]. These models have inherent limitations and oen result in substantial deviations from the actual flow statistics [5], therefore large-eddy simulations (LES) have been increasingly employed in engineering. In LES the largest scales of motion (GS – grid scales) are explicitly simulated and the effects of the smallest scales (SGS – subgrid-scales) are modelled using an SGS model. LES is the most advanced and accurate method for the simulation of turbulent flows [6], but LES of fluids with complex rheology remains elusive, as attested by the small number of LES studies devoted to these flows [7]: virtually no SGS models are available today for routine engineering LES of viscoelastic fluids. The goal of this proposal is to develop SGS models for LES of a large class of complex viscoelastic fluids. The investigation starts with the FENE-P model [8], which has been extensively used in turbulent flow investigations using direct numerical simulations (DNS) [A], and is extended to constitutive equations like the FENE-CR, Phan-Thien-Tanner and Giesekus models [9,10,B], to widen the range of complex fluids available for future LES. The work is based on massive DNS of complex fluids in isotropic turbulence (HIT) [A,11] and turbulent channel flows (CHAN) [D], which allow a detailed investigation of the turbulence dynamics for fluids with complex rheology, and the investigation of GS/SGS interactions in the governing equations, including their coupling, in three different situations: without solid walls and mean shear (HIT), with the presence of mean shear (PJET) and with the presence of solid walls (CHAN). In DNS all the scales of motion are explicitly simulated, from the large energy containing scales, to the smallest scales associated with the dissipation of kinetic energy. Whenever feasible DNS is virtually unsurpassed by any other technique and is equivalent to an experiment, since it allows the access to the full unsteady, three-dimensional, multiscale complexity of the turbulent fields, including the non-linear rheology [5,14,15,A,B]. DNS is a crucial ingredient of the present proposal and has been used in previous works from the authors, including DNS of fluids of complex rheology described by the FENE-P model [A,C,D,E,16]. DNS will be used to conduct classical a-priori tests in the governing equations, and to develop new SGS closures arising from these equations [E,16]. Finally, the DNS will also be used as reference data for the subsequent assessment of the results obtained by LES of the same flows, using the new models developed in the course of this project. The starting point in terms of the SGS closure is the distortion similarity SGS model (DSIM) [E], recently developed by the authors, with excellent and good performances in HIT [E], and PJET [16], respectively, while CHAN remains to be studied. The investigation will also assess if DSIM can be improved and applied to wakes and whether its modeling assumptions remain valid for other complex fluids.

Institutions

Main Institutions

  • Instituto de Engenharia Mecânica (IDMEC)

Other Institutions

  • Universidade do Porto Centro de Estudos de Fenómenos de Transporte (CEFT)

Funding 49.055,75 €

Fundação para a Ciência e a Tecnologia (FCT) - Portugal

49.055,75 €