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ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
An empirical assessment of roll waves evolution in mud-like fluids flowing down steep slopes
Submission Author:
Valdirene Rocho , SC , Brazil
Co-Authors:
Valdirene Rocho, Guilherme Henrique Fiorot, Sergio Viçosa Möller, João Batista Pereira, Evandro Fernandes Cunha, Geraldo Maciel
Presenter: Guilherme Henrique Fiorot
doi://10.26678/ABCM.ENCIT2022.CIT22-0675
Abstract
Free-surface flows are a recurrent phenomenon observed in a wide range of natural and industrial settings. They occur in inclined channels by the effect of gravity, with various fluids, Newtonian or non-Newtonian. The prediction of the behavior of these flows is conditioned to the appearance of hydrodynamic instabilities. When instabilities present sufficient conditions for development and stabilization, we have what is known as roll waves. The study of these waves aims to examine the necessary conditions and how such instabilities develop in time and space. In this sense, this paper presents an experimental work that was carried out to observe and quantify certain aspects of the development of these waves in a laminar free-surface flow of non-Newtonian fluid of the Herschel-Bulkley type, representing muddy materials. Experiments were carried out in a rectangular channel, 3.00 m long and 0.30 m wide, applying inclinations varying from 13$^\circ$ to 20$^\circ$ and discharge rate from 0.88 to 1.07 l/s. The experimental apparatus developed allowed the simulation of stabilized roll waves in many scenarios, thus constituting a highly useful approach for understanding and controlling these waves. The test fluid used was a carpobol-based gel, a fluid that exhibits behavior typical of a Herschel-Bulkley fluid. The variation of the free surface interface was then measured using an ultrasonic system at different points along the length of the channel. To study the problem, firstly it was desired to identify the steady and uniform flow regime. Then, a disturbance with a fixed frequency (1.5 Hz) was applied upstream of the channel, using a wave generator. From the measurements, it was observed that the stabilized waves present themselves as long waves, validating the mathematical assumptions that are normally used in shallow water type flows. Furthermore, it was noted that the spatial evolution of roll waves follows an asymptotic behavior as a function of the distance traveled, presenting stabilization after traveling a few wavelengths. Also, it was noted that the amplitude of these waves depends on the Froude number and that the higher the Froude number, the higher the roll wave amplitude will be.
Keywords
Free-surface flow, Non-Newtonian flow, Herschel-Bulkley, Roll Waves
