The swirling inlet flow effects on the pressure recovery of a low head water turbine draft tube

In this paper, the experimental results concerning the swirling inlet now effects on the pressure recovery of a divergent passage whose cross-section changes from annular to rectangular were discussed. A developed turbulent flow having a swirling flow component was introduced into the diffuser and the alterations of the flow patterns both in the velocity and pressure distributions in each test cross-sections were carefully examined. The influence of swirling flow component on the axial velocity profile as well as on the streamwise wall pressure distributions was identified for different inlet swirl conditions. To give a detail explanation to the now behavior and pressure recovery, a now visualization technique using a tuft grid and surface tuft methods was adopted. Furthermore, based on the measured velocity and pressure, the approximated energy profiles at the best efficiency point of the unit were presented.