Experimental and numerical analysis of decelerated swirling flow from the discharge cone of hydraulic turbines using pulsating jet technique

It is well known that the spiral vortex (or vortex rope) is developed in the conical diffuser of hydraulic turbines with fixed pitch blades (e.g. Francis and propeller) when operating conditions are far away from best efficiency point. The paper will present a new technique in order to mitigate, even eliminate the bad behave associated to this phenomenon. By injecting a pulsating water jet, along the cone axis, the unsteady pressure fluctuations given by the vortex rope are mitigated. Our investigations are performed on the test rig from Politehnica University. In order to assess the velocity profiles given by the swirling flow with and without pulsating water jet, an extensive 3D numerical simulations were performed. Second, the experimental data of pressure fluctuations was analysed. This technique, shows that the pressure recovery is improved and the hydraulic losses decreases along the conical diffuser. Also, it is shown that the stagnant region associated to the spiral vortex is mitigated since the pulsating jet is introduced. Also, the pressure fluctuations are mitigated.