Investigation of Coherence behind a Single Foamed Tube

Abstract

In this paper the flow structures downstream of a foamed tube are compared to those of a bare tube with the same frontal areaand length. Experiments were conducted in a wind tunnel at Reynolds numbers 4000 and 16000. Particle image velocimetry (PIV) was used to obtain velocity vector field in two different perpendicular planes. To measure the effect of flow three-dimensionality, field of divergence on both planes was obtained and compared with each other. Moreover, to characterize the size of the flow structures downstream of the tube, for each of the aforementioned cases, two-point correlation functions were used as the statistical analysis tool. Analysis showed that, compared to the bare tube, the foamed one, in the X-Z plane (stream-wise, span-wise) increases the threedimensionality of the flow which is set forward in the perpendicular plane despite being less pronounced. Moreover, the structures downstream of a foamed tube are elongated in the stream-wise direction and are linearly independent of the inlet velocity, however, in span-wise and normal direction no significant change in the size of the structures between bare and foamed tube has been observed.