Unsteady CFD simulations of moving flow-control valves by an unstructured overset grid method.

摘要

In this research, a Computational Fluid Dynamics (CFD) algorithm for simulation of complex unsteady flows around moving bodies using an unstructured overset or Chimera grid method is presented. A highly automated three-dimensional tetrahedral unstructured overset grid method is developed to model moving parts of arbitrary geometries. Internal flows in industrial flow-control moving valves, such as butterfly valves, moving piston (regarded as a kind of flow-control valve) of internal combustion engine, etc., are targeted as the main applications of the research. "Choked" flows, complex system of expansion and shock waves developed downstream of valves and transonic, supersonic flows in the vicinity of the valve-disk and downstream, turbulent and jet flows in an internal combustion (IC) engine with piston movement have been predicted. Unsteady simulations of the nature of the fluid motion within the cylinder of a piston engine have been performed and compared with experiments. The developed overset-grid method, which has been validated with numerical examples such as a supersonic ramp of oblique shock, a transonic converging-diverging duct and an unsteady case of NACA0012 quasi-3D airfoil with pitching oscillations, can equally be applicable to other types of flows with relative motions, for instance, store-separation problem. The newly developed overset grid algorithm has been integrated into a computer program named SunFlo3D, developed at the IUPUI Computational Fluid Dynamics Laboratory, which is a general-purpose three-dimensional CFD code for compressible internal and external flows with features such as finite volume method, implicit-time scheme, Sparlat-Allmaras one-equation turbulence model, and viscous and inviscid flow options. The automated overset grid movements are performed for unsteady flow simulations for continuously moving body parts in the flow domains, which may be rotating or moving back and forth regularly. We have demonstrated the automated mesh cutting and donor cell searching capabilities of the overset grid method. Mesh refinement and conservation studies performed showed the accuracy and efficiency of the developed method. Validations with experimental data for steady and unsteady flows around rigid bodies with relative motions are conducted.