Fluctuating Characteristics of Two-Phase Air-Water Slug Flow in Pressurized Pipelines

Two-phase gas-liquid flows occur in a wide variety of situations, e.g., in chemical processing, power generation, water supply systems, and petroleum industry. The study of two-phase fluid flows is of great importance in hydraulic engineering. This type of flow typically occurs in pressurized flow tunnels, culverts, siphons, and bends in which the gas trapped in water pipelines releases from the water as the pressure reduces. The relative discharge rate of fluids and the pipe slope produce a wide variety of flow patterns including stratified, wavy, and slug flows. In this paper, the unstable two-phase air-water flow is experimentally investigated. The image processing technique is applied for estimating the fluctuations of such parameters as void fraction and length, period and celerity of slug waves. It is shown that the pipe inclination and air flow rate have significant effects on flow characteristics. Also, the relative wave length (L/D, D is the pipe diameter) in a slug flow varies from 10 to 85, while air bubble length varies from 1/3 to 1/2 of wave length

Improving Performance of Side Weirs Using Groups of Vane Plates or Piles

Weirs are among the most common hydraulic structures that have been used for centuries by hydraulic engineers for flow measurement, energy dissipation, flow diversion, regulation of flow depth, and flood passage. Side weirs, or lateral weirs, are essentially free overflow weirs installed along the side of the main channel to divert flow over them when the surface of flow in the channel rises above their crest. These weirs are often used in irrigation and flood regulation systems, urban drainage, and many other water resources and environmental projects. The flow over side weirs falls under the category of spatially varied flow. In this paper, methods are presented based on analytical and experimental models for improving side weir performance. For this purpose, groups of (one, two, and three) vane plates or piles were employed. Analytical models were developed based on momentum and continuity equations for determination of dynamic force on vane plates or piles, water surface profile and discharge coefficient of side weir. Measured data were used for calibrating the analytical models and for presenting expressions for the discharge coefficient. Results show that the diverted discharge coefficient can be increased by up to 30% compared to the simple side weir discharge coefficient