Spectral Characterization Of Wave Patterns In Stratified Concurrent Air–water Channel Flow Using LDV
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M. Fernandino & T. Ytrehus
Stratified flows have been widely studied during the last decades and it is now clear that the interface structure influences the pressure drop, interfacial shear and transport across the interface. An objective way of characterizing the wave pattern present in the interface is proposed. The method is based on spectral characterization, with spectra obtained from Laser Doppler (LDV) measurements of the vertical fluctuations of the water flow close to the air–sheared interface. For the air and water flow rate ranges used, four wave patterns are identified according to the peaks observed in each corresponding spectrum. Transitions are defined when some peaks disappear or new ones arise. Visual subjectivity in the determination of interfacial patterns is thus avoided. Keywords: stratified flow, channel flow, interfacial waves, flow pattern map, spectral characterization. 1 Introduction A stratified flow regime can be found in many industrial applications, such as flow of oil and natural gas in the petroleum industry or the flow of steam or water in emergency core cooling systems (ECC) in nuclear reactors, among others. It is known that the wave pattern occurring at the interface influences the pressure drop, liquid hold up, scalar transport across the interface and the interfacial shear . In addition, changes in the wave pattern may indicate a probable regime transition. Therefore, the prediction of the interfacial structure occurring in the system becomes important.