Combination of experimental and numerical approaches to determine the main characteristics of skimming flow in stepped spillways

Tassinari, Lucas Camargo da Silva; Sanagiotto, Daniela Guzzon; Marques, Marcelo Giulian; Lauffer, Luísa Lüdtke; Trierweiler Neto, Edgar Fernando

doi:10.1590/2318-0331.252020190070

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Scientific/Technical Article • RBRH 25 • 2020 • https://doi.org/10.1590/2318-0331.252020190070 copy

Combination of experimental and numerical approaches to determine the main characteristics of skimming flow in stepped spillways

Combinação de abordagens experimental e numérica para determinar as principais características do escoamento sobre turbilhões em vertedouros em degraus

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The traditional approach for the hydrodynamic characterization of the flow down stepped spillways is through physical modeling, which is susceptible to scale effects and has limitations related to experimental apparatus, laboratory space and the spatial discretization of data collection. Computational fluid dynamics (CFD) is an important tool for hydrodynamic analysis because, if used properly, it presents great potential for application in hydraulics. In this work, CFD was used to model the skimming flow down a stepped spillway to investigate the effects of possible pressure measurement errors due to uncertainties in the position of the sensors within the steps. The numerical model was validated through literature velocity profiles and pressure experimental data. The results showed that the best values of water fraction (α) to define free surface are α = 0.30 in the nonaerated region and α = 0.10 in the aerated region. Statistical parameters were calculated using experimental data to estimate extreme pressures. These parameters and the simulation results were used to determine that the extreme maximum and minimum pressures occur, respectively, in the region of 0.81 < x/l < 0.98, in the horizontal faces, and in the region of 0.93 < y/h < 0.98, in the vertical faces.

Keywords:
Stepped spillways; CFD; Free surface; Turbulence; Pressure

Vertical face relative position (y/h)	N_0.1%	Horizontal face relative position (x/l)	N_99.9%
92%	4.1	92%	3.6
64%	3.8	64%	4.0
37%	3.5	36%	3.7

Author ^{^} [a] Amador et al. (2009); [b] Sánchez-Juny et al. (2007); [c] Sanagiotto (2003); , analyzed region ^{^} VFAR = vertical face in the aerated region; VFNAR = vertical face in the nonaerated region.	Mean pressure (mH₂O)	$σ_{d}$ (mH₂O)	N_0.1%	P_0.1% (mH₂O)	Relative position ( $y / h$ )	Correction at mean pressure (Figure 12)	Corrected mean pressure [2]/[7] (mH₂O)	Corrected P_0.1% (mH₂O)	Ratio [9]/[5]
[1]	[2]	[3]	[4]	[5]	[6]	[7]	[8]	[9]	[10]
[a], VFAR	-0.07	0.893	4.1	-3.73	93.2%	0.59	-0.12	-3.78	1.01
[b], VFAR	-0.10	0.893	4.1	-3.76	95.0%	0.99	-0.10	-3.76	1.00
[c], VFNAR	-0.23	2.455	4.1	-4.80	91.7%	0.22	-1.05	-5.62	1.17
[c], VFAR	-0.41	0.893	4.1	-4.07	91.7%	0.22	-1.86	-5.52	1.36

Author ^{^} [a] Amador et al. (2009); [b] Sánchez-Juny et al. (2007); [c] Sanagiotto (2003); , analyzed region ^{^} HFAR = horizontal face in the aerated region; HFNAR = horizontal face in the nonaerated region.	Mean pressure (mH₂O)	$σ_{d}$ (mH₂O)	N_99.9%	P_99.9% (mH₂O)	Relative position ( $x / l$ )	Correction at mean pressure (Figure 11)	Corrected mean pressure [2]/[7] (mH₂O)	Corrected P_99.9% (mH₂O)	Ratio [9]/[5]
[1]	[2]	[3]	[4]	[5]	[6]	[7]	[8]	[9]	[10]
[a], HFAR	2.49	3.124	3.6	13.73	86.3%	0.98	2.54	13.78	1.00
[b], HFAR	2.90	3.124	3.6	14.15	93.8%	0.93	3.12	14.37	1.02
[c], HFNAR	2.75	2.455	3.6	11.59	91.7%	0.98	2.81	11.64	1.00
[c], HFAR	2.59	3.124	3.6	13.84	91.7%	0.98	2.64	13.89	1.00

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[1] E-mails: lucascstassinari@gmail.com (LCST), dsanagiotto@ufrgs.br (DGS), mmarques@iph.ufrgs.br (MGM), luisalauffer@gmail.com (LLL), edtrier@furnas.com.br (EFTN)