TStudy of residual swirl at the outlet of a water turbine

Water turbines operate most oflhe time away from their optimum operating point, either at part- or full-load capacity. The swirl at the outlet of the turbine plays a very important role in determining its efficient operation. When it exceeds a certain limit, in the case of part- or full-load operation, a surge is initiated in the system. The nature of the swirl is very complex. It does not obey any standard pattern. The swirl can be studied by making comprehensive traverses at the turbine exit and computing velocity and pressure distribution. The complex nature of the swirl is related to the angular momentum parameter (AMP) for various unit speeds. To study its behaviour downstream of the runner, the results are compared for the two cases: one axial chord downstream and the other three axial chords downstream of the runner. The effect of swirl is also noted on the draft tube oscillations.