Numerical investigation of turbulent flow in a wavy channel partially filled with a porous layer

摘要

In this paper, the effect of inserting a porous layer inside a wavy channel on the mean flow and turbulent characteristics in both developing and repeated flow regions have been investigated numerically. The modified Launder-Sharma low-Reynolds number k - ε turbulence model, which was used in a previous study [1] with two extensions model, has been utilised to represent the turbulence in the porous region. For validation, the flow in a clear channel with wavy bottom wall has been considered. The results of clear channel have been compared with the experimental data produced by [2], where the results computed were in a good agreement with the experimental data. In the porous wavy channel flow case, the same dimensions of the clear wavy channel have been adopted but with covering the bottom wavy wall with a porous layer formed of an open-cell metal foam. Three values for the wave amplitude of the wavy bottom wall and porous layer thickness have been considered, which are (0, 0.1, 0.2) and (0, 0.15H, 0.3H), respectively. Three samples of metal foams have been tested along with the effect of the wave amplitude of the wavy surface and the thickness of the wavy porous layer on the turbulent flow. These types are (Φ = 0.9486 & ω = 10PPI), (Φ = 0.952 & ω = 40PPI) and (Φ = 0.81 & ω = 13PPI). For all calculations, a Reynolds number equals to 20,600 has been considered. In the near fluid-porous interface region, damping functions have been used. The results show that the repeated flow pattern tends to occur in earlier region towards upstream than the flow over solid wavy surface when the permeability of the porous layer is decreased. Moreover, the repeated flow pattern also tends to occur in early region of the wavy part of the channel when the wave amplitude and porous layer thickness are increased, compared to the lower wave amplitude and low porous layer thickness. Decreasing the permeability increases the size of the recirculation cell in the repeated flow region and also increases the turbulent energy in the clear region. Increasing porous layer thickness, on the other hand, reduces the size of circulation cell and the turbulent energy.