Assessment of subgrid-scale stress statistics in non-premixed turbulent wall-jet flames

Abstract

We investigate the heat-release effects on the characteristics of the subgrid-scale (SGS) stress tensor and SGS dissipation of kinetic energy and enstrophy. Direct numerical simulation (DNS) data of a non-premixed reacting turbulent wall-jet flow with and without substantial heat release is employed for the analysis. This study comprises, among others, an analysis of the eigenvalues of the resolved strain rate and SGS stress tensors, to identify the heatrelease effects on their topology. An assessment of the alignment between the eigenvectors corresponding to the largest eigenvalues of these two tensors is also given to provide further information for modelling of the SGS stress tensor. To find out the heat-release effects on the dynamics of the turbulent kinetic energy and enstrophy dissipation, probability density functions (PDFs) and mean values are analyzed.The mean SGS shear stress and turbulent kinetic energy both slightly increase in the buffer layer and substantially decrease further away from the wall, due to the heat-release effects. Contrary to the kinetic energy, heat release decreases the mean SGS dissipation of enstrophy in the near-wall region. Moreover, differences in the shapes of the PDFs between the isothermal and exothermic cases indicate changes in the intermittency level of both SGS dissipations. Heat release also increases the SGS stress anisotropy in the near-wall region. Although, the structure of the mean resolved strain-rate tensor only marginally differs between the isothermal and exothermic cases in the near-wall region, substantial differences are observed in the jet area, where compressibility effects are important and heat-release effects are found to promote compression states. The differences in the relative alignment between the SGS stress and resolved strain-rate tensors in the isothermal and exothermic cases are discussed in connection with the differences in the SGS dissipation of kinetic energy.

Large-eddy simulation of turbulent dispersed flows: a review of modelling approaches

“…Modelling capabilities are much less established in flows where these processes occur at the smallest scales (e.g. molecular mixing and chemical reactions in turbulent combustion at high Reynolds and Damkohler numbers [67,88,95,96,103,104], droplet break-up in liquid spray atomization at high Weber number [7,15] or momentum transfer in near-wall flows at high Reynolds number [58,96]). …”

Neural-network-based mixed subgrid-scale model for turbulent flow

“…The SGS anisotropy tensor is defined as (Rasam et al. 2016; Inagaki & Kobayashi 2020) where denotes averaging over the – plane and time. The anisotropy invariant maps are constructed based on the two invariants of the anisotropy tensor , where and are the second and third invariants of , respectively.…”

“…The right curved edgy is the axisymmetric turbulence in which the streamwise component is larger than the other two components (Rasam et al. 2016). The origin corresponds to the isotropic turbulence state that occurs at the channel centreline.…”

“…In order to quantitatively compare the anisotropy of the predicted SGS stress by ANN-SGS models, the anisotropy invariant maps (Lumley & Newman 1977) of the SGS anisotropy tensor are examined in figure 32. The SGS anisotropy tensor is defined as (Rasam et al 2016;Inagaki & Kobayashi 2020) where II and III are the second and third invariants of a ij , respectively. The invariant map lies in the region bounded by the limits of the two-component turbulence state (II = 2/9 + 2III) and the axisymmetric turbulence state (II = 3/2(4/3|III|) 2/3 ).…”

“…In the invariant map, the two-component turbulence (II = 2/9 + 2III), which is the condition in which the wall-normal component is negligible relative to the other two components, occurs at the wall (Inagaki & Kobayashi 2020). The right curved edgy is the axisymmetric turbulence in which the streamwise component is larger than the other two components (Rasam et al 2016). The origin corresponds to the isotropic turbulence state that occurs at the channel centreline.…”