Direct numerical simulation of a turbulent bubbly flow in a vertical channel: Towards an improved second-order reynolds stress model

Two-phase turbulence has been studied using a Direct Numerical Simulation (DNS) of an upward turbulent bubbly flow in a so-called plane channel. Fully deformable monodispersed bubbles are tracked by a Front-Tracking algorithm implemented in TrioCFD code on the TRUST platform. Realistic fluid properties are used to represent saturated steam and water in pressurised water reactor (PWR) conditions. The large number of bubbles creates a void fraction of 10%. The Reynolds friction number is 180. Time- and space-averaging is used to compute the main variables of the averaged scale description (e.g. void fraction, liquid and vapour velocities…) along with the Reynolds stresses and the turbulent dissipation rate tensor. Altogether, they provide reference profiles to assess and further improve Reynolds Stress models. A low-Reynolds version of the SSG model (Speziale et al., 1991) called EBRSM (Manceau and Hanjalić, 2002; Manceau, 2005) is applied in the context of two-phase flows with additional interfacial production terms. The model has been implemented and tested in the two-fluid Euler-Euler model of NEPTUNE_CFD code. The comparison with DNS demonstrates that the interfacial momentum closure plays a dominant role over the turbulent closure hypothesis in the present physical conditions.