Fluid-mechanism interactions occur in a wide range of flow meter categories including turbine and positive displacement systems as well as many flow control devices. This paper outlines computational methods for calculating the dynamic interaction between moving parts and the flow in a flow meter system. Coupling of phenomena is allowed without need for access to the source codes and is thus suitable for use with commercially available codes. Two methods are presented one with an explicit integration of the equations of motion of the mechanism and the other with implicit integration. Both methods rely on a Navier-Stokes equation solver for the fluid flow. The more computationally expensive implicit method is recommended for mathematically stiff mechanisms such as piston movement. Example industrial applications shown are for positive displacement machines and axial turbines. The advances in mesh technology including deforming meshes with non-conformal sliding interfaces opens up this new field of application for Computational Fluid Dynamics and mechanical analysis in flow meter design.