Experimental setup for measuring roll waves on laminar open channel flows G.H. Fiorot a,b,n , G.F. Maciel a,c , E.F. Cunha a,b , C. Kitano a,d a Faculdade de Engenharia de Ilha Solteira - UNESP, Ilha Solteira, São Paulo, Brazil b Departamento de Engenharia Mecânica, Av. Brasil Sul, 55, 15385-000, Ilha Solteira, São Paulo, Brazil c Departamento de Engenharia Civil, Alameda Bahia, 550, 15385-000, Ilha Solteira, São Paulo, Brazil d Departamento de Engenharia Elétrica, Campus III, 15385-000, Ilha Solteira, São Paulo, Brazil article info Article history: Received 23 September 2013 Received in revised form 27 September 2014 Accepted 23 October 2014 Available online 25 December 2014 Keywords: Open channel flow Free surface Light absorption technique Roll waves abstract Experimental studies on open channel flows are explored mostly because of their importance in validating analytical and numerical models. Although steady flows are usually measured and explored, difficulties arise in the precise execution of this task when the free surface becomes oscillatory. This paper presents a methodology for measuring a particular non-stationary phenomenon that occurs under specific conditions, namely, roll waves. Limited data exists in literature on roll waves. The objective of this work is to contribute to this database and to describe a useful experimental method for measuring roll waves. Based on some well-known literature experiments, an experimental setup was designed to achieve the free surface flow of a viscous fluid in a steady and uniform configuration. The flow was set to generate roll waves and controlled disturbances were applied at the inlet to develop roll waves. These waves were then measured using a photometric device based on a light absorption technique. The wave profiles for different flow configurations are presented. Experimental results were compared with numerical simulations to assess the validity of the measurements taken. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Free surface flows can occur in many forms in industrial and environmental processes and they have therefore been a subject of much interest in fluid mechanics studies. Rivers, seas, sewers, channels, and drainage systems are a few examples of situations where this particular hydraulic model can be used. The char- acterization of flow properties using physical and mathematical models is necessary in many applications, such as for designing structures, better predicting flow behavior, and applying safety policies. The precise study of free surface flows based on experimental results is of significant importance for understanding transitional flow. The occurrence of non-stationary phenomena on free sur- faces implies that infrastructure projects should take additional considerations into account to guarantee their safe functioning. Among the possible phenomena that could affect free surface flow, roll wave instabilities are of interest, as discussed in this paper. These instabilities can usually be seen on artificial channels (such as spillways) where turbulence occurs. They are configured as periodic fronts, and present hydraulic jump characteristics that propagate downstream at constant velocity. Roll waves are differ- ent from normal gravity waves as they result from the amplification of flow disturbances. In laminar flow, especially for non-Newtonian fluids, they are more visible and present higher amplitudes (of the same order of magnitude as the flow) [1–3]. Because of this oscillatory configuration, measuring their free surface inclination and elevation is rather difficult. The inherent difficulty of this task has resulted in a lack of data for the calibration and/or validation of numerous roll wave models and has therefore raised the interest of researchers in the scientific community. The work of Kapitza [4] is among the first in this area where this task was executed successfully. Kapitza [4] conducted impor- tant experimental work by collecting free surface information from film flows using the shadowgraph technique. This technique, which is still used by some researchers, has great advantages in terms of flow visualization, despite the fact that it is less precise than some other techniques [5,6]. Many techniques rely on the Beer–Lambert law to detect the surface elevation, once the light properties of a fluid are known. As shown by Barter et al. [7], it is possible to acquire both the inclination and elevation of the free surface, if necessary, by Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ flowmeasinst Flow Measurement and Instrumentation http://dx.doi.org/10.1016/j.flowmeasinst.2014.10.020 0955-5986/& 2014 Elsevier Ltd. All rights reserved. n Correspondence to: Institut National des Sciences Appliquées de Rennes, France. E-mail addresses: gfiorot@insa-rennes.fr (G.H. Fiorot), maciel@dec.feis.unesp.br (G.F. Maciel), evandrofernandesc@gmail.com (E.F. Cunha), kitano@dee.feis.unesp.br (C. Kitano). Flow Measurement and Instrumentation 41 (2015) 149–157