Improved Eddy-Viscosity Modelling of Turbulent Flow around Porous–Fluid Interface Regions

Abstract

The RANS modelling of turbulence across fluid-porous interface regions within ribbed channels has been investigated by applying double (both volume and Reynolds) averaging to the Navier-Stokes equations. In this study turbulence is represented by using the Launder and Sharma (1974) low-Reynolds number k − ε turbulence model, modified via proposals by either Nakayama and Kuwahara (2008) or Pedras and de Lemos (2000), for extra source terms in turbulent transport equations to account for the porous structure. One important region of the flow, for modelling purposes, is the interface region between the porous medium and clear fluid regions. Here, corrections have been proposed to the above porous drag/source terms in the k and ε transport equations that are designed to account for the effective increase in porosity across a thin near-interface region of the porous medium, and which bring about significant improvements in predictive accuracy. These terms are based on proposals put forward by Kuwata and Suga (2013), for second-moment closures. Two types of porous channel flows have been considered. The first case is a fully developed turbulent porous channel flow, where the results are compared with DNS predictions obtained by Breugem et al. (2006) and experimental data produced by Suga et al. (2010). The second case is a turbulent solid/porous rib channel flow to examine the behaviour of flow through and around the solid/porous rib, which is validated against experimental work carried out by Suga et al. (2013). Cases are simulated covering a range of porous properties, such as permeability and porosity. Through the comparisons with the available data, it is demonstrated that the extended model proposed here shows generally satisfactory accuracy, except for some predictive weaknesses in regions of either impingement or adverse pressure gradients, associated with the underlying eddy-viscosity turbulence model formulation.

Flow leakage and Kelvin–Helmholtz instability of turbulent flow over porous media

“…The key reason that the current LES calculations include these three Re numbers is that the onset and evolution of K-H instabilities can be clearly captured and discussed in this range of Re numbers since it presents a wide range of different flow structures. Moreover, not only the current study, but also the previous studies about the flow physics over and inside the porous block used this range of Re numbers in their work [19,20,24,[60][61][62]. At Re=3600, the formation of K-H instabilities is retarded downstream, starting approximately at "Point A" with 𝑋/𝐷~4.6, as marked in Figure 12(a).…”

Effect of porous blocks on flow development through a serpentine cooling passage under stationary and rotating conditions

“…It was also found that as the permeability increased much of the fluid passes through the baffles the recirculation bubbles become weaker and are shifted downstream. As also confirmed by a recent numerical study from the authors' group, Al-Aabidy et al [17], the development of reliable RANS models for turbulent flow through passages with porous regions, depends on the availability of reliable local flow data. This means that to extend the effective use of RANS models to the prediction of cooling flows through rotating passages with porous regions, there is a need for local flow experimental data.…”

Numerical simulation of hyporheic exchange driven by an emergent vegetation patch

“…The sediment layer was divided into two zones by porosity, namely, a porous medium region with uniform porosity $$$ {\phi}_0 $$$ and a transition region. According to Al‐Aabidy et al (2020), the transition layer's thickness was set to 2 D p , and the porosity of the transition region $$$ {\phi}^{\prime } $$$ was computed using Equation (). The turbulence level near the SWI will be overstated if the thin transition layer between the overlying water and homogenous porous medium area is not taken into account (Kuwata & Suga, 2013).…”