Characterization of linear interfacial waves in a turbulent gas-liquid pipe flow

Abstract

The evolution of interfacial waves on a stratified flow was investigated experimentally for air-water flow in a horizontal pipe. Waves were introduced in the liquid level of stratified flow near the pipe entrance using an oscillating plate. The mean height of liquid layer and the fluctuations superimposed on this mean level were captured using high speed cameras. Digital image processing techniques were used to detect instantaneous interfaces along the pipe. The driving signal of the oscillating plate was controlled by a D/A board that was synchronized with acquisitions. This enabled to perform phaselocked acquisitions and to use ensemble average procedures. Thereby, it was possible to measure the temporal and spatial evolution of the disturbances introduced in the flow. In addition, phaselocked measurements of the velocity field in the liquid layer were performed using standard planar Particle Image Velocimetry (PIV). The velocity fields were extracted at a fixed streamwise location, whereas the measurements of the liquid level were performed at several locations along the pipe. The assessment of the setup was important for validation of the methodology proposed in this work, since it aimed at providing results for further comparisons with theoretical models and numerical simulations. Therefore, the work focuses on validation and characterization of interfacial waves within the linear regime. Results show that under controlled conditions, the wave development can be well captured and reproduced. In addition, linear waves were observed for liquid level oscillations lower than about 1.5% of the pipe diameter. It was not possible to accurately define an amplitude threshold for the appearance of nonlinear effects because it strongly depended on the wave frequency. According to the experimental findings, longer waves display characteristics similar to linear waves, while short ones exhibit a more complex evolution, even for low amplitudes.

Statistical characterization of interfacial waves in turbulent stratified gas-liquid pipe flows

“…The main goal is to use this model to differentiate between linear and non-linear wave regimes in gas-liquid pipe flow. Note that the waves under investigation were purely wind-induced, i.e., they developed as result of gas-liquid interaction, as opposed to the mechanically induced waves described by Ayati et al (2017).…”

“…Nevertheless, the next generation of flow simulators are expected to include "regime-capturing" approaches which rely on finer grid resolution (Issa & Kempf, 2003;Carneiro et al, 2011;Danielson et al, 2012;Nieckele et al, 2011;Nieckele & Carneiro, 2017). Furthermore, recent developments in experimental investigation of this system (Birvalski et al, 2014(Birvalski et al, , 2015(Birvalski et al, , 2016Ayati et al, 2014Ayati et al, , 2015Ayati et al, , 2016Ayati et al, , 2017André & Bardet, 2017), have shown that the overall bulkflow is strongly coupled with wavy interface. To this end, detailed description of measured interfacial waves is expected to be of valuable use with respect to validation of models and CFD simulations.…”

Sub-Hinze scale bubble production in turbulent bubble break-up

“…The newly formed satellite interfaces increase drastically the exchange surface, enhancing the transfer between the two phases. Practical examples include oil spill mitigations (Gopalan & Katz 2010;Afshar-Mohajer et al 2018), oil and gas transportation from remote wells (Galinat et al 2005;Ayati et al 2017), air entrained by bow waves in naval applications (Baba 1969;Shakeri, Tavakolinejad & Duncan 2009), together with ocean-atmosphere interactions with breaking waves inducing bubble-mediated gas exchange (Deane & Stokes 2002;Deike, Lenain & Melville 2017;Deike & Melville 2018) and ejecting sea spray aerosols (Veron 2015).…”

Experimental investigation of airflow above waves in a horizontal pipe

“…However, they do not provide insight on the phase-dependency of the flow structure. This can only be achieved by conducting phase-locked measurements (Ayati et al, 2017) or by performing conditional-averaging techniques on statistically independent velocity fields. The latter is the scope of this paper.…”