Stepped spillways with aerators: hydrodynamic pressures and air entrainment

Ferla, Rute; Novakoski, Carolina Kuhn; Priebe, Priscila dos Santos; Prá, Mauricio Dai; Marques, Marcelo Giulian; Teixeira, Eder Daniel

doi:10.1590/2318-0331.262120200110

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Scientific/Technical Article • RBRH 26 • 2021 • https://doi.org/10.1590/2318-0331.262120200110 copy

Stepped spillways with aerators: hydrodynamic pressures and air entrainment

Vertedouros em degraus com aeradores: pressões hidrodinâmicas e entrada de ar

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The possibility of damage due to the phenomenon of cavitation leads the design of stepped spillways considering maximum specific discharges of 15 to 30 m²/s, a limit considerably lower than that practiced on smooth chutes. Aerators promote the insertion of air in the flow, allowing for the increase of specific flow rates. This work analyzes the pressures on the vertical faces of the steps and the air entrainment coefficient in the flow, through an experimental study in a physical model with a stepped chute angle of 53.13^o, considering the installation of aerators in different places of the channel. Comparing the tested conditions with the natural aeration, it is concluded that the installation of the aerator does not change the magnitude of the minimum extreme hydrodynamic pressures, but anticipates the beginning of the flow aeration. A new equation is proposed to estimate the air entrainment coefficient, as well as a methodology for forecasting extreme pressures on the vertical faces of the steps, both valid in the range 3.0 ≤ Fr ≤ 6.0.

Keywords:
Hydraulic structures; Cavitation; Deflector

q (m²/s)	h_c (m)	h_{0 1} (m)	Fr₁	h_{0 10} (m)	Fr₁₀
0.054	0.067	0.020	6.10	-	-
0.082	0.088	0.029	5.30	-	-
0.108	0.106	0.039	4.48	-	-
0.150	0.132	0.050	4.28	-	-
0.200	0.160	0.064	3.94	0.053	5.23
0.300	0.209	0.091	3.49	0.073	4.86
0.400	0.254	0.117	3.19	0.091	4.65
0.500	0.294	0.140	3.05	0.108	4.50

		a	b	c	R²
S1	P_5%	-1.79x10^-2	2.62x10^-3	-9.25x10^-5	0.80
	P_1%	-3.07x10^-2	4.58x10^-3	-1.63x10^-4	0.86
	P_0.1%	-4.79x10^-2	7.11x10^-3	-2.53x10^-4	0.88
S10	P_5%	-9.35x10^-3	9.53x10^-4	-2.26x10^-5	0.90
	P_1%	-1.70x10^-2	1.96x10^-3	-5.80x10^-5	0.92
	P_0.1%	-2.86x10^-2	3.54x10^-3	-1.16x10^-4	0.91

		Superior envelope			Inferior envelope
		a	b	c	a	b	c
S1	P_5%	-1.37x10^-2	2.30x10^-3	-1.03x10^-4	-2.57x10^-2	3.84x10^-3	-1.33x10^-4
	P_1%	-2.64x10^-2	5.00x10^-3	-2.56x10^-4	-3.96x10^-2	5.85x10^-3	-2.01x10^-4
	P_0.1%	-4.39x10^-2	8.61x10^-3	-4.54x10^-4	-5.90x10^-2	8.64x10^-3	-2.95x10^-4

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[1] E-mails: ruteferla@hotmail.com (RF), carolkn04@gmail.com (CKN), priscilaspriebe@gmail.com (PSP), mauricio.daipra@ufrgs.br (MDP), mmarques@iph.ufrgs.br (MGM), eder.teixeira@ufrgs.br (EDT)