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 . 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.
Issue Section:
Techniques and Procedures
Keywords:
confined flow,
Doppler effect,
electrochemistry,
flow visualisation,
shear turbulence,
ultrasonic measurement
Topics:
Flow (Dynamics),
Shear stress,
Unsteady flow,
Pipes,
Pressure,
Transients (Dynamics),
Valves,
Probes
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.Copyright © 2009
by American Society of Mechanical Engineers
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