Measurements in oscillatory flows with separation in support of stirling engine model development

This paper is a contribution to a larger program that seeks to improve computation of unsteady flows in Stirling engines. It presents flow visualization results from an experiment that replicates important features of oscillatory flows; such as large-scale separation and adverse and favorable, spatial and temporal acceleration. The geometry is a tube perpendicular to a space between two circular discs, one of which the tube penetrates such that the end of the tube is flush with the disc inner surface. The flow, driven by a piston in the tube, is oscillatory and acts on the exhaust stroke as a jet impinging on the center of a circular disc and on the intake stroke as a sink flow drawn into a tube from the space between the two discs. Time-varying recirculation zones and periodic appearances of highly turbulent flow are observed. In addition to a characterization of oscillatory, separating flow, this program provides code validation support for Stirling engine design models. The project goals are to identify the areas where 1-D modeling is especially weak and to provide support for developing more sophisticated design models that can be used with greater confidence. A complete description of the experiment and results is given. It is shown that a change in geometry can affect the flow in major way; i.e. whether a recirculation eddy survives an entire cycle or is eliminated upon flow reversal. Future work is outlined.