Mitigation of Draft Tube Pressure Pulsations by Radial Protrusion of Solid Bodies into the Flow Field: An Experimental Investigation

Abstract

An experimental investigation of frequential protrusion of four solid rods into the draft tube of a propeller turbine operating under partial discharge has been undertaken. The effectiveness of mitigating the pressure fluctuations associated with the rotating vortex rope (RVR) has been quantified using pressure measurements on the wall of the draft tube cone. Three azimuthal configurations of the phase difference between the rods, and four protrusion lengths were investigated. It is shown that the rotating component of the RVR decreases, irrespective of the azimuthal configuration and protrusion length, with imposed phase differences in the same direction as the runner rotation being the most effective, reducing the amplitude of the rotating component by a maximum of 62%. However, for each azimuthal configuration, the plunging mode of the RVR is amplified for large protrusion lengths, with the smallest amplification occurring for the case of 180 degrees phase difference between protrusions. Therefore, to quantify the most efficient configuration in mitigating the harmful effects of the RVR, an overall assessment of its effects on the entire turbine must be made before a conclusion can be drawn.

An experimental investigation on the effects of cylindrical rods in a draft tube at part load operation in down-scale turbine

“…As can be seen, the frequency of the RVR increases for both modes with the increase of protrusion length. The only exception to this is 𝐿 * = 0.6 where the RVR frequency reaches its minimum, possibly due to the rods meeting the RVR as Shiraghaee et al [18] previously explained, which falls in line with the decrease of the RVR frequency. This length is where significant mitigation of the rotating component also happens in addition to what seems to be only the effects of swirl deceleration.…”

“…They also managed to improve the pressure recovery and change the structure of the RVR from a helical vortex shape into a bubble shape. Shiraghaee et al [18] studied the effect of oscillating rod protrusions inside the draft tube. Their results displayed significant mitigation of the rotating component along with an increase of the plunging component.…”

Experimental Investigation of Part Load Vortex Rope Mitigation With Rod Protrusion in an Axial Turbine

“…The present authors have previously introduced a new method that can combine the effects mentioned in the sense that it can be both directed toward the tangential flow region and stagnant region. Oscillating and stationary protrusion of rods into the draft tube flow field were investigated, and a maximum RVR mitigation of 77% was obtained on a reduced turbine model with a runner diameter of 100 mm [41,42]. In these investigations, four cylindrical rods that could be traversed in the radial direction were installed in the draft tube.…”

Experimental Investigation of a Free Runner Concept Downstream of Francis Turbines

“…One of the earlier passive techniques was proposed back in 80`s by Thicke [15]. Later, many other passive technics as J-grooves mounted on the cone wall [16], fins [17], runner cone extensions [18], diaphragm mounted downstream the conical diffuser [19], radial protrusion of solid bodies [20], flow-feedback method [21] and stator mounted downstream the runner [22] were investigated. Active control technics as air or water injections thru various zones of the hydraulic turbine [23][24][25][26][27] and magneto-rheological control technique [28,29] were also investigated.…”