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Research Papers: Techniques and Procedures

Unsteady Wall Shear Stress in Transient Flow Using Electrochemical Method

[+] Author and Article Information
H. Zidouh, M. William-Louis

 Université Lille Nord de France, F-59000 Lille, France; UVHC, LME, 59313 Valenciennes, France

L. Labraga1

 Université Lille Nord de France, F-59000 Lille, France; UVHC, LME, 59313 Valenciennes, Francellabraga@univ-valenciennes.fr

1

Corresponding author.

J. Fluids Eng 131(5), 051403 (Apr 15, 2009) (8 pages) doi:10.1115/1.3112387 History: Received August 18, 2008; Revised February 24, 2009; Published April 15, 2009

Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Concentration fields and velocity profile over a single probe

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Figure 2

Pulsed ultrasonic Doppler velocimetry technique: measurement setup

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Figure 3

Experimental setup

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Figure 4

Synoptic of the acquisition system

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Figure 5

Experimental results showing pressure time history and associated velocity profiles

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Figure 6

Mean velocity during deceleration

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Figure 7

Instantaneous deceleration

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Figure 8

Comparison between wall shear stress obtained with different methods

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Figure 9

Wall shear stress and pressure distributions during deceleration

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Figure 10

Unsteady wall shear stress component and acceleration

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Figure 11

Dependence of the ratio between unsteady and steady wall shear stresses on the acceleration parameter

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Figure 12

Dependence of k on the acceleration parameter

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