Contractions and expansions are commonly found in various piping systems including flow control in the oil and gas industry. They impose complex flow characteristics such as flow recirculation, boundary layer separation and unsteady re-attachment. Computational Fluid Dynamics (CFD) using RANS simulations can offer general information about the time-averaged flow properties in expansion and contraction geometries including the pressure drop across the fitting. However, they generally fail to provide details of turbulent flow such as shedding of vortices and high turbulent intensities which are observed in experimental data at the expansion and contraction regions. Large Eddy Simulations (LES) can resolve a turbulence spectrum by filtering Navir-Stokes equations over the computational cells. In this study, LES is utilized to examine a sudden-contraction and expansion pipe flow. Furthermore, Stress-Blended Eddy Simulations (SBES) as a hybrid LES-RANS model is employed for comparison. All of these Scale-Resolving Simulations (SRS) are examined against the experimental data and compared to commonly used RANS simulations. Various flow parameters are examined at different locations for a 50.8 mm pipe which is suddenly reduced to a 25.4 mm pipe and then suddenly expands to the original size, and highlights of each model are presented. The details of the turbulent flow in these geometries are critical to many applications such as particle-laden flows and this investigation would provide insight into the appropriate flow modeling in the expansion and contraction geometries.

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