Origin of the synchronous pressure fluctuations in the draft tube of Francis turbines operating at part load conditions

A Review on Remedial Attempts to Counteract the Power Generation Compromise from Draft Tubes of Hydropower plants

The unsteady pressure at the wall of the conical diffuser without and with a 74° heel elbow is examined. The self-induced instability is experimentally investigated on the swirl generator test rig. As a result, the asynchronous (rotating) pressure pulsation associated with the vortex rope and it second harmonic are discriminated. The discriminated Fourier spectra with plunging and rotating components of the unsteady pressure signals are analyzed for several geometrical configurations in order to identify the frequency associated to the heel elbow. It is shown that a plunging component of 8 Hz corresponds to a 74° heel elbow in the Fourier spectra.

Experimental Investigation of the Unsteady Pressure Field in Decelerated Swirling Flow with 74° Sharp Heel Elbow

The paper focuses on the influence of the reshaped elbow geometry of the draft tube on the unsteady pressure field under different operating conditions. The experimental investigations are conducted considering two simplified geometrical configurations of the draft tubes with sharp heel elbow and modified/reshaped elbow, respectively. The discriminated power spectra (rotating and plunging components) of the acquired pressure signals on the wall are determined on five levels for seven operating conditions to quantify the influence of the reshaped elbow. The influence of the reshaped elbow on the fundamental frequencies of both rotating and plunging components and on the amplitude of the rotating component is negligible. In contrast, the equivalent amplitude associated with the root mean square of the plunging power spectrum that propagates along the hydraulic passage is mitigated up to 25% by the reshaped geometry of the elbow. The equivalent amplitude on the narrow band around the fundamental frequency of the plunging component is diminished with 40–50% by reshaping the elbow geometry of the simplified draft tube.

https://www.mdpi.com/1996-1073/14/5/1393/pdf

D. C. Moş

Papers

Investigation of the Plunging Pressure Pulsation in a Swirling Flow with Precessing Vortex Rope in a Straight Diffuser

Experimental Investigation of the Unsteady Pressure Field in Decelerated Swirling Flow with 74° Sharp Heel Elbow

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