Robust and accurate open boundary conditions for incompressible turbulent jets and plumes

• Published in: Computers & fluids Vol. 86; pp. 284 - 297
• Main Authors: Craske, John, van Reeuwijk, Maarten
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 05-11-2013
• Subjects: Axisymmetric; Boundary conditions; Computational fluid dynamics; Computer simulation; Direct numerical simulation; Fluid flow; Inflow boundary condition; Large eddy simulation; Outflow boundary condition; Plumes; Turbulence; Turbulent flow; Large eddy simulation; Direct numerical simulation; Inflow boundary condition; Outflow boundary condition
• ISSN: 0045-7930; 1879-0747
• DOI: 10.1016/j.compfluid.2013.06.026

•We describe new open boundary conditions (OBCs) for simulations of jets and plumes.•We show that a popular convective OBC is unsuitable for such simulations.•The new OBCs are robust and independent of the size and shape of a domain.•The new OBCs adjust to a given flow dynamically without relying on input parameters.•They can be applied to many problems involving unsteady, localised turbulence.
We show that a popular convective open boundary condition (OBC) is unsuitable in the direct simulation of incompressible turbulent jets and plumes, because (1) the boundary condition modifies their spreading rate; (2) the results are domain dependent; and (3) the boundary condition is liable to cause instability and therefore requires domains that are much larger than the area of interest. We demonstrate the accuracy of new axisymmetric OBCs compared to the standard OBC by conducting direct numerical simulation (DNS) of a turbulent plume and a turbulent jet. The new OBCs conform to the fundamental features of statistically axisymmetric turbulent flows, regardless of the computational domains on which they are imposed. They do not contain tunable parameters and are dynamical, accounting for the strength and extent of a flow at a given time, which eliminates the need for calibration to particular cases. The implementation presented herein is computationally efficient and robust in the vicinity of turbulent flows.