Wake flow analysis of a vortex shedder situated downstream of double elbows out-of-plane

Experiments were made in a 50 mm pipe system, with a vortex flowmeter situated downstream of double elbows out-of-plane. A Micro-Electro-Mechanical-System (MEMS) sensor was installed on the vortex shedder for sensing the flow motions associated with vortex shedding. Analysis of the MEMS sensor signals was carried out to obtain the quantitative information concerning the vortex shedding frequency, its uncertainty and the signal quality defined. As found, the lowest measurement uncertainty reduced was 0.319%, due to the case of the vortex shedder situated 18 D downstream of the double elbows for Re_D = 6.25 × 10⁴. On the other hand, the best signal quality in terms of the signal to noise ratio defined was 9.645, for the vortex shedder situated at 16 D downstream of the double elbows at Re_D = 6.25 × 10⁴. Further, under this flow condition, an X-type hotwire probe was positioned at 3 D and 1 D, respectively, downstream of the vortex shedder for surveying the velocity distributions in these cross-sectional planes. By applying a conditional sampling technique referring to the MEMS sensor signals obtained simultaneously, the hot-wire signals were analyzed and reduced for the ensemble-averaged flow structures in these two cross-sectional planes. The results indicate that the vortex shedding structures could be clearly identified at 1 D downstream of the vortex shedder, but had diffused greatly at 3 D downstream.