Analysis on Internal Flow Characteristics of Tubular Turbine Draft Tube

The internal flow characteristics of the tubular turbine draft tube have a great influence on the operation of the turbine. By the numerical simulation, the unsteady internal flow field in a Tubular Turbine of a plant was carried out The internal flow characteristics of the tubular turbine draft tube under different working conditions were also analyzed. The simulation results show that under the rated operating condition,the pressure fluctuation amplitude that from the runner inlet to the draft tube increases at first then decreases, and the overall pressure pulsation amplitude is small. Under the off design operations, along the flow direction of the water flow, the amplitude of the low-frequency pressure pulsation increases,and the dominant effect of the low-frequency on the pressure pulsation becomes more and more obvious.Under the low flow conditions, the rotating direction of the vortex rope in the draft tube is consistent with the rotating direction of the runner. Under the large flow conditions, the rotational direction of the vortex rope in the draft tube is opposite to the rotational direction of the turbine runner. These changes are consistent with the trend of the calculated pressure pulsation at the outlet of the turbine runner chamber. These rules provide evidence for the design of the draft tube.