Characterization of hydraulic behavior of orifices in conduits

Surge tanks in high-head power plants ensure safe and flexible transient operation of the hydraulic machinery. Orifices or throttles in surge tanks are often critical structural elements in view of the good performance of surge tanks and the stability of the whole waterway system combined with hydraulic-mechanical equipment. The design and the dimensioning of orifices ore throttles placed at surge tanks has to be carried out with great care since a non-functioning of this critical structural elements can endanger the safe operation of the whole hydropower scheme. Orifices or throttles have to produce a distinct head loss for flow entering and leaving the surge tank. In the design, the best geometry has to be found which produces the desired head losses. The search of the most adapted geometry of the orifice or throttle is often challenging and has frequently to be complemented by systematic hydraulicmodel tests. In order to allow a preliminary design of orifices, Dr. Nicolas Adam studied for the first time systematically with laboratory experiments and numerical simulations a large number of different geometries of throttles, i.e. orifices. Based on the extensive catalogue of the orifice geometries tested and the developed empirical relationships, he could give efficient design guidelines based on empirical formulae and on a useful expert sheet in order to find efficiently the appropriate orifice geometry for a wished head loss. Dr. Adam studied also for the first time systematically the transient head losses through orifices. The systematical experiments and numerical simulations allowed also a better understanding of the hydraulic behavior of orifices in view of the influence length of the orifice i.e. the reattachment length of the jet leaving the orifice and associated risk of cavitation. Finally, Dr. Adam gives helpful practical recommendation for an efficient and safe design of orifices in surge tanks.