Swirling flow through a curved diffuser (flow properties and vibration in pipeline)

A swirling flow through a curved diffuser of circular cross-section was examined experimentally. First, the experiment was performed for airflow at a bulk mean velocity where the inlet of the diffuser of W_a1 ≈ 8.7 m/s, corresponding to the Reynolds number of 60000. The distribution of the wall pressure was measured and three components of mean velocity were obtained over the pipe crosssection by means of the technique of rotating a probe with an inclined hot wire. Secondly, the waveform of pipe vibration and axial velocity was measured in the range of Reynolds number from 20 000 to 80 000 and of dimensionless angular momentum of swirling flow from 0.13 to 1.01 and the measured results were analyzed by FFT. Based on the results obtained, physical explanations were given to the phenomena obtained in the diffuser.