A new mixed subgrid-scale model for large eddy simulation of turbulent drag-reducing flows of viscoelastic fluids

Abstract

A mixed subgrid-scale (SGS) model based on coherent structures and temporal approximate deconvolution (MCT) is proposed for turbulent drag-reducing flows of viscoelastic fluids. The main idea of the MCT SGS model is to perform spatial filtering for the momentum equation and temporal filtering for the conformation tensor transport equation of turbulent flow of viscoelastic fluid, respectively. The MCT model is suitable for large eddy simulation (LES) of turbulent drag-reducing flows of viscoelastic fluids in engineering applications since the model parameters can be easily obtained. The LES of forced homogeneous isotropic turbulence (FHIT) with polymer additives and turbulent channel flow with surfactant additives based on MCT SGS model shows excellent agreements with direct numerical simulation (DNS) results. Compared with the LES results using the temporal approximate deconvolution model (TADM) for FHIT with polymer additives, this mixed SGS model MCT behaves better, regarding the enhancement of calculating parameters such as the Reynolds number. For scientific and engineering research, turbulent flows at high Reynolds numbers are expected, so the MCT model can be a more suitable model for the LES of turbulent drag-reducing flows of viscoelastic fluid with polymer or surfactant additives.

Drag reduction characteristics of heated spheres falling into water

“…There are many methods to reduce drag, such as by using polymeric additives, [1][2][3] microbubble injection, [4,5] exploiting supercavitation or partial cavitation, [6,7] and hydrophobic coating. [8][9][10] These methods reduce drag mainly by changing the surface characteristics of the object or by changing the viscosity of the fluid near the object.…”

LES Investigation of Drag-Reducing Mechanism of Turbulent Channel Flow with Surfactant Additives

“…The N-parallel FENE-P model is capable to characterize the anisotropy of the relaxation-deformation of microstructures in non-Newtonian fluid and has been demonstrated a good prediction accuracy benefiting from the multiple relaxation timescales. Furthermore, for convenience of results discussion and to widen the application scope of our finding, here only the dimensionless form of governing equations are presented as follows, interested readers can refer to [24] for more details on the non-dimensionalization process, which are beyond the scope of present work.…”

“…1. In the simulation, a 32 × 64 × 32 mesh system is applied and the grid independence test can refer to [18,24,25]. For the hybrid SGS model used in LES, the width for spatial filter is set as 0.0634, and the width for temporal filter of both velocity and conformation tensor is set as 10Δt * .…”

“…One reason for the drag reduction in turbulent flow is that the surfactant additives in turbulence change the balance of shear stress and lead to the redistribution of shear stress. Therefore, it is essential to analyze different shear stresses in turbulent flow, as shown in formula (24),…”

“…Li et al [24] developed a mixed SGS model coupling a coherent-structure Smagorinsky model (CSM) and TADM, which was named as the mixed CSM and TADM (MCT) model. The cornerstone of MCT is to filter the continuity and momentum equations using the spatial CSM and filter the constitutive equation using the TADM, respectively.…”