Effects of meshing and RANS turbulence modelling on the numerical prediction of a flow through a square-edged orifice in a round pipe.

Sofiane Benhamadouche, Wadih Malouf, Mario Arenas

Thursday 2 july 2015

15:05 - 15:20h at South America (level 0)

Themes: (T) Water engineering, (ST) Hydraulic machinery and industrial flows

Parallel session: 12C. Engineering - Industrial

The orifice plate is a pressure differential device commonly used for flow measurements in numerous industries. The instrument benefits from a large and well-understood pressure difference between the upstream and downstream tapings, which results in a relatively small measurement uncertainty. The present study demonstrates the quality one can obtain with CFD (here Code_Saturne [1], [4]) to predict the pressure loss and discharge coefficient for a flow through a square-edged orifice in a round pipe (see Figure 1) at a Reynolds number equal to 25000. The computations correspond to the experiment of Shan et al. [9]. Sensitivity studies are carried out using different mesh refinements and RANS turbulence models. The results show that both spatial discretisation and turbulence modelling significantly influence the RANS solutions (see Figure 2 which shows the pressure loss coefficient). First and second moment closure approaches with near-wall modelling such as the standard k-_ [6] and the Reynolds Stress Model SSG [10] show a significant sensitivity to the mesh refinement with standard two velocity scales wall functions. However, the second moment closure turbulence model with near-wall resolution (EB-RSM, [7]) exhibits less sensitivity to the mesh refinement. The pressure loss and discharge coefficients are compared to the ISO 5167-2 standards [5]. The final article will compare local quantities such as the velocity and the Reynolds stresses to experimental data from [9] and fine LES results [3]. Finally, two variations of the Grid Convergence Index (GCI) [2], [8] are used to estimate the spatial discretisation error on global quantities.