Trajectories and air flow features of ski jump-generated jets

Abstract

Ski jumps are frequently applied as spillways of high dams. The resulting jet impact location on the plunge pool surface is often distant from the dam toe so that the latter is protected from scouring. Furthermore, the jet disintegrates and disperses prior to its impact, thereby reducing the specific energy addition to the plunge pool. The present research addresses four aspects, based on three physical modelling campaigns: (1) geometry of upper and lower jet trajectories; (2) virtual jet take-off angles for the trajectory computations; (3) average and minimum cross-sectional air concentrations along the jet; and (4) general jet air concentration profiles. It is shown that the trajectory parabola may also be applied for negative jet take-off angles, and that these are smaller than the bucket angle. As for the air concentration distribution along the jet, tests indicate that the latter depends exclusively on the relative jet black-water core length.

Towards quantifying rate of scour using the erodibility index method: Case study

“…The erosive capacity of plunging jets depends on the characteristics of the free falling jet (quantified based on Bollaert 2002; Ervine & Falvey 1987;and Pfister et al 2014) and the characteristic energy dissipation within the plunge pool (quantified based on Castillo 2006Castillo , 2007Bollaert 2002). Jet trajectory and degree of breakup vary depending on the type of jet and spillway structure.…”

“…The plunging jet geometry is also dependent on the issuance velocity, issuance jet thickness, average issuance angle, and Froude Number at the terminal structure. Jet breakup lengths for the flip-bucket type spillways were best represented by Pfister's (2014) relationships for rectangular jets.…”

Far-field properties of aerated water jets in air

“…In dam spillways, high-speed water jets quickly become aerated by entraining the ambient air. After leaving spillways, the aerated jets eject into the air at certain angles and then impinge into the plunging pool (Vischer and Hager, 1995;Pfister et al, 2014). The breakup of the jets in air can directly impact on the level of total dissolved gases in the downstream rivers and fish-kill (Geldert et al, 1998;Orlins and Gulliver, 2000;Politano et al, 2009).…”

“…Liquid jets in air have been studied extensively as they have wide applications in hydraulic structures (Chanson, 2009;Pfister et al, 2014), sewer dropshafts Camino et al, 2015), fountains, irrigation, fire extinction, atmosphere cleaning, industrial painting or printing, chemical reactors, atomization and spray, among others (Lefebvre, 2000;Surma and Friedel, 2004;Dumouchel, 2008;Chanson, 2009;Gowing et al, 2010;Osta et al, 2012). Most of the studies concentrated on liquid-air multiphase flow properties near the injection nozzle (near-field) such as liquid jet breakup, instability analysis, drop or spray formation, and multiphase flow dynamics (e.g., Bogy, 1979;Hoyt et al, 1974;Faeth et al, 1995;Sallam et al, 2002;Birouk and Lekic, 2009;Portillo et al, 2011).…”

An analytical model for simulating air concentration in drop and deflector jets

“…Bombardelli and Chanson [2] achieved progress in the observation and modeling of turbulent multiphase flows. Pfister and Hager [23,24] achieved air concentration characteristics of generated jets by drop and deflector and they studied the effect of pre-aerated approach flow on generated jets by deflector [20] and also they achieved deflector jets affected by pre-aerated approach flow [21], and moreover, they studied trajectories and air flow features of ski jump generated jets [25]. Chanson [4] studied advective diffusion of air bubbles in turbulent water flows and the results reveal the turbulent nature of the complex two-phase flows and the complicated interactions between entrained air bubbles and turbulence.…”