Investigation of the instability of stratified flow in a horizontal pipe subjected to periodic perturbations on the liquid level

Paula S. C. Farias¹; Igor B. de Paula¹; Luis Fernando A. Azevedo¹

¹ PUC-Rio

doi:10.20906/CPS/COB-2015-0874

Resumo

The evolution of interfacial waves in a stratified flow is investigated experimentally for a horizontal pipe. The waves are introduced artificially in the flow using an oscillating plate, located close to the gas-liquid interface. Amplitude and frequency of oscillation are controlled during the experiments with a power amplifier and a waveform generator. The evolution of the excited waves is captured using high speed cameras placed at different distances from the disturbance source. The interface contour is extracted from the images by applying digital image processing techniques. The acquisitions are synchronized with the disturbance generation, enabling the application of ensemble average techniques. Therefore, averaged properties such as wave celerity, wavelength, skewness, and spectral content of the fluctuations are obtained for different mixture velocities. The work focused in a region close to the disturbance source, where the amplitude of the waves is below 5% of the pipe diameter. At this region a linear behavior is expected. The results obtained are compared with a linear stability calculations based on Kelvin Helmholtz linear theory. Some degree of agreement is observed for wave speeds and wavelengths. However, discrepancies are found for amplification rates. The investigation suggests simple models based on one dimensional linear stability calculations might be not suitable to describe accurately the evolution of interfacial waves.

Palavras-chave: stratified flow; instability; slug initiation