Numerical modeling of the formation and transport of condensed moisture in the lower pool of a hydroproject during the operation of spring-board spillways

Abstract

A model of three-dimensional forced convection and transport of condensed moisture in the lower pools of hydroprojects is developed.The existence of special spillway structures for passage of seasonal flood flows is probably one of the basic characteristic features of large-scale hydroprojects, which distinguish them from other industrial entities with operating conditions that are relatively uniform throughout the year. For a number of large-scale HPP, the pools, which are separated by a spillway dam with a height of the order of 100 m and more, are connected by surface spillways with specially designed lips/spring boards, which ensure rigorous splitting of the discharge flow; this is required to reduce scouring of the channel beyond the structure. Here, however, water dust (condensed moisture), which for unfavorable orography of the lower pool, will complicate both construction work, and also the operation of individual zones at the site of the powerhouse, forms, as a rule, in the fall-out region of the spillway jets. Figure 1 shows a photograph of the Kapanda hydroproject (Angola) on which is apparent a water-air cloud that is formed in the narrow rocky canyon in the fall-out area of the spillway jets, and which spreads throughout the lower pool of the HPP. Under certain meteorological conditions and a vigorous discharge, this cloud may penetrate into the zone of the powerhouse. Here, the intensity of the precipitation may reach 10,000 mm/day greater.The situation in question is characteristic of the incomplete construction of the hydroproject, where with two generating sets of the HPP operating (phase I), their number will be increased to four (4´130 = 520 MW) on completion of phase II in 2007, and the duration of the effect of the air cloud at the site will be sharply curtailed, and will amount to less than 30 days per year during the passage of a 100-year flood.In our study, we are apparently the first to develop and implement a spatial numerical model of the forced circulation of air masses and transport of condensed moisture in the lower pool of a large-scale hydroproject with its spillway structures operating at near-full capacity. Data derived from field observations obtained at the Kapanda HPP during the spring-flood period of 2004, are being used to calibrate and test the model. In creating the model in question, we attempted to ascertain the principal physical mechanisms determining the phenomenon under investigation, and as a result, simplify the mathematical description of the process to the maximum extent possible, while retaining relationships (possibly empirical) on specific engineering characteristic features of the entity. The study was initiated by the Center for Hydraulic Studies affiliated with the JSC "NIIÉS," and the work is being performed through the efforts of the fol-

Numerical investigations for solution of hydraulic problems

“…Based on data obtained in 2005 -2006, a unique computerized model of three-dimensional forced convection and transport of droplet moisture in the area of a large hydroproject [23] in which the head and tail races are connected by the release of jets providing for vigorous breakdown of the descending flow to prevent scouring of the bottom in the trail race, was developed, calibrated, and tested with the participation of employees from the A. A. Dorodnitsyn Computer Center.…”