Nappe Oscillations on Free-Overfall Structures: Size Scale Effects

• Published in: Journal of hydraulic engineering (New York, N.Y.) Vol. 145; no. 6
• Main Authors: Lodomez, M, Tullis, B. P, Dewals, B, Archambeau, P, Pirotton, M, Erpicum, S
• Format: Journal Article Web Resource
• Language: English
• Published: New York American Society of Civil Engineers 01-06-2019; American Society of Civil Engineers (ASCE)
• Subjects: Civil engineering; Engineering, computing & technology; Evaluation; Experimental facilities; Free overfall; Height; Hydraulic structures; Hydraulics; Ingénierie civile; Ingénierie, informatique & technologie; Instability; Mathematical models; Modelling; Nappe oscillation; Oscillation characteristics; Oscillation frequency; Oscillation phenomenon; Oscillations; Physical model; Physical modeling; Prototypes; Scale models; Secondary influences; Size scale effect; Structural stability; Technical Papers; Weirs
• ISSN: 0733-9429; 1943-7900
• DOI: 10.1061/(ASCE)HY.1943-7900.0001615

AbstractNappe oscillation and its potentially undesirable impact associated with significant noise production can be an issue for free-overfall hydraulic structures. Although nappe oscillation has been observed on various prototype free-overfall structures, this instability behavior may not be evident during the design process in which experimental and/or numerical modeling may be utilized. In addition, previous studies regarding nappe oscillation scalability using similitude or other relationships has received very limited attention in the literature. An experimental study aimed at investigating the possible size scale effects on nappe oscillations was undertaken utilizing two experimental facilities: a prototype-scale linear weir (3-m fall height) and a geometrically similar 1:3-scale model (1-m fall height). The nappe oscillation occurrence assessment and oscillation frequency evaluation were performed using sound and image analyses. Experiments on both models showed that the nappe oscillation phenomenon generally occurs over a fixed range of unit discharge and is independent of size scale. Nappe oscillation can therefore not be reproduced at different model scales according to standard similarity laws. This study also highlights the secondary influences of the crest profile and the fall height on the oscillation characteristics.