A flexible experimental apparatus for investigating water hammer and column separation in an unsteady friction-dominated pipelines has been developed and designed. The apparatus has been tested for steady and unsteady flow conditions. Transient cavitation and column separation phenomena have been observed in a number of experimental runs. Water hammer has been triggered by both the closing and opening of electro-pneumatic (EV) and hand-operated (HV) valves. The experimental data have been compared with results given from in-house numerical code written in Visual Fortran based on the method of the characteristics (MOC) with a convolution-based unsteady friction model (CBM) included. The column separation and transient cavitation phenomena are modelled via a discrete gas cavity model (DGCM). There is good agreement between the experimental and numerical results; the model is robust and, therefore, it is recommended for engineering practice. In addition, the influence of variations of the pressure wave speed and the uncertainty in flow rate measured by the electromagnetic flow meter are also investigated.
COBISS.SI-ID: 13773595
The research refers to the experimental study of cavitation phenomena when water was passing through the slot orifice. The contribution brought up by this article is the detailed time and space dependent analysis of bubbly structures identified using high speed video, microresistivity probes, optical fibre pressure probe, and hot film probe. Two principle experiments were carried out to study cavitation in a confined geometry. The first one was designed to study an induced single bubble cavitation when the water pressure was reduced below the atmospheric pressure, but was still high enough so that there was not any saturated pressure in the slot region. The second experiment was undertaken at a reference pressure which was sufficient to produce a massive cavitation in the slot region. The following flow regimes were identified and analyzed in detail: the so-called detachment regime where bubble breakup was observed in the case of the individual bubble cavitation; and in the case of the large scale cavitation, the regime of macroscopic bubbles clustering into bubble cloud and the regime of collapsing bubbles. The reserarch contributes to better understaning of cavitating transient flow phenomena in general (cavitational regimes, possible dissipation mechanisms).
COBISS.SI-ID: 13255963