RESEARCH ARTICLE Application of a high-speed laser-induced fluorescence technique for studying the three-dimensional structure of annular gas–liquid flow Sergey Alekseenko • Andrey Cherdantsev • Mikhail Cherdantsev • Sergey Isaenkov • Sergey Kharlamov • Dmitry Markovich Received: 24 October 2010 / Revised: 20 August 2011 / Accepted: 12 September 2011 / Published online: 2 October 2011 Ó Springer-Verlag 2011 Abstract The wavy structure of liquid film in annular gas–liquid flow was studied using a high-speed modifica- tion of the laser-induced fluorescence (LIF) technique, which was adapted for three-dimensional measurements. The three-dimensional structure of different types of waves in regimes with and without liquid entrainment was investi- gated. A comparison of the circumferential size of different types of waves was performed. Disturbance waves at high liquid Reynolds numbers were shown to be circumferentially non-uniform, and it was shown that this non-uniformity affects the generation of ripples. 1 Introduction The combined flow of liquid film and a high-velocity gas stream is usually termed annular gas–liquid flow. At high enough gas and liquid flow rates, entrainment of liquid from the film surface into the core of the gas stream occurs. It is generally accepted that, in such cases, the film surface is covered by a complicated pattern of waves of different scales, including fast long-lived disturbance waves and slow short-lived ripples (see, e.g., the review by Azzopardi 2006). It has been suggested that entrainment occurs due to a disruption of the ripples at the crests of disturbance waves by gas shear (Woodmansee and Hanratty 1969). The investigation of such interactions between disturbance waves and ripples requires a measuring technique that would allow the tracking of both the spatial and temporal evolution of each wave. This includes field measurements of local film thickness with high spatial resolution. The latter implies a small area, over which the measuring technique averages the signal, and small distances between neighboring measurement points. The temporal resolution should also be high enough because the investigated pro- cesses are characterized by short time scales. Many experiments have been performed without such a system. In most cases, measurements of local film thick- nesses at several downstream points (usually with con- ductivity probes) were performed. This approach is adequate for measuring the average characteristics of dis- turbance waves and/or ripples, such as amplitude, velocity, passing frequency, spacing, etc. It was found that, when the gas stream velocity is increased, the disturbance wave velocity and passing frequency increase, amplitude decreases, and longitudinal length remains nearly constant. An increase in the liquid flow rate leads to slight increases in all of the aforementioned characteristics (e.g., Chu and Dukler 1975; Azzopardi 1986; Han et al. 2006; Sawant et al. 2008). Properties of disturbance waves evolve with distance below the inlet; in particular, their amplitude and velocity increase and their frequency decreases down- stream (Hall Taylor and Nedderman 1968; Wolf et al. 2001). All of these changes are hypothesized to occur because of the coalescence of disturbance waves. Larger amplitude, velocity, length, and lifetime values of disturbance waves, as compared to those of ripples, were observed. Ripples are less studied: their properties were investigated in several works (e.g., Chu and Dukler 1974) independently of disturbance waves. S. Alekseenko  A. Cherdantsev  M. Cherdantsev  S. Kharlamov  D. Markovich Institute of Thermophysics, 1 Lavrentiev ave., Novosibirsk 630090, Russia S. Alekseenko  A. Cherdantsev (&)  S. Isaenkov  D. Markovich Novosibirsk State University, Pirogov str. 2, Novosibirsk 630090, Russia e-mail: cherdantsev@itp.nsc.ru 123 Exp Fluids (2012) 53:77–89 DOI 10.1007/s00348-011-1200-5