Two-phase gas-liquid flows occur in a wide variety of situations, e.g. , in chemical processes, power generation, water supply systems, and petroleum industry This type of flow typically occurs in pressurized flow tunnels, culverts, siphons, bends and pipelines in which the air bubbles are trapped in water flow and are released while the pressure reduces. To identify the hydraulic specifications of two-phase air-water flows, former experimental studies were performed by injection of pressurized air under controlled conditions into the water flow. Therefore, natural air suction into the pipeline due to the generation of swirling flow over the pipe inlet has not been considered yet. It seems that flow measurements under the realized conditions would be applicable in practical purposes. In the present experimental study, natural air suction due to the establishment of the air-core vortices at the pipe inlet were modeled and the hydraulic parameters of the air-water two-phase flow inside the pipeline were examined simultaneously. The study was aimed to achieve a logical relationships between the hydraulic characteristics of two-phase air-water flow inside the pipeline and the specifications of the swirling flow over the pipe inlet. To investigate the most sever flow conditions, experiments were conducted under the condition of forced swirling flow over the entrance of the vertical pipe intake. Applying the dimensional analysis, the influential hydraulic and geometrical dimensionless parameters of both swirling flow and two-phase flow were recognized. Tests were performed in the Hydraulic Laboratory of department of Civil Engineering, Isfahan University of Technology, Isfahan. The hydraulic model involves a cylindrical main reservoir 2 m in diameter and 1 m high. Three different vertical pipe intakes of (D=10.16 cm, h=30 cm) (D=7.62 cm, h=30 cm) and (D=7.62 CM, h=50 cm) (where D is the pipe inner diameter and h is the pipe intake height) were installed at the center over the floor of the main reservoir. Experiments were conducted for different floe discharges under the establishment of different vortex types e.g. Types 1 to 6. Two meter long of the bottom outlet was made of traarent Plexiglas to observe the two-phase flow hydraulic behavior for different swirling flow situations and to detect the two-phase flow regimes in the outlet pipe. The results including tangential velocity profiles inside the main reservoir, discharge-head relationships, pressure fluctuations in the outlet pipe and the relation between swirling flow over the pipe inlet and two-phase flow inside the bottom outlet were presented by applying the most prevailing dimensionless parameters. According to the results, for the vertical intakes with D=10.16 cm, h=30 cm and D=7.62 cm, h=30 cm, different types of swirling flow including types 2 to 6 were observed. Although, in the outlet pipe for swirls of types 2, 3 and 6 just the stratified two-phase flow was observed, for the swirls of types 4 and 5 slug flow was the dominant two-phase flow regime inside the bottom outlet. For the shaft with geometrical specifications of D=7.62 and h=50 cm, swirling flows of type 2 to 6 were established, however for all of these swirling flow situations the only two-phase flow observed in the outlet pipe was stratified flow and slug flow was not formed inside the bottom outlet. By increasing the flow discharge, the swirling flow strength is increased, thereby the slug flow frequency, wave length and wave height are increased. The pressure fluctuations as well as the maximum recorded pressure inside the outlet pipe are also increased. Results inferred that the two-phase flow void fraction decreases if the type of the swirling flow changes from type 2 to types 6, 3, 4 and 5, respectively. Keywords: Bottom outlet, model experimentation, slug flow regime, swirling flow, vertical pipe intake.