Exploratory study of the influence of the wake produced by acoustic Doppler velocimeter probes on the water velocities within control volume

ABAD J.; MUSALEM, R.; GARCÍA, C.M.; CANTERO, M.I.; GARCÍA M.H.

Salt Lake City, Utah, USA

Congreso; World Water and Environmental Resources Congress 2004; 2004

American Society of Civil Engineers (ASCE)

Acoustic doppler technique is widely used in both fields and laboratory facilities tocompute the mean water velocity and to characterize the turbulence of a flow. Ingeneral they provide the three dimensional components of flow velocity in ameasurement volume in the water body with fairly good spatial and temporalresolution for engineering applications. The most sophisticated devices can evengauge a velocity profile measuring the water velocity in several measurementvolumes along a line. However, these devices are semi intrusive which might have,depending on the experimental setup, substantial consequences in the measurementsobtained due the flow perturbation created by the probe. The goal of this paper is toexplore experimentally and numerically the wake effect of the probe on themeasurement volume in order to validate the measurements provided by this kind ofinstruments or incorporate some corrections if needed. A computational fluiddynamic (CFD) model is used to simulate an open channel flow where the model wasvalidated with previous experimental results. In the other hand, the laboratorymeasurements were conducted in an open channel flume located in the Ven Te ChowHydrosystems Laboratory of the University of Illinois. The measurements were doneusing particle image velocimetry technique (PIV) producing two dimensional velocityfields around the acoustic probe measurement volume with and without the presenceof the probe. The numerical and experimental ranges of Reynolds numbers (Re)tested were 3x10^6 to 1x10^7 and 1x10^4 to 5x10^4 respectively. Non dimensional contourplots showing the difference between the flow velocity and turbulent quantities withand without the probe are built. Both results show that the errors are less than 10percent around the probe. This methodology is still under development, however itprovides more insight for experimental setups and it could be applied to otheracoustic doppler instruments such as the ADV (Acoustic Doppler Velocimeter) andADCP (Acoustic Doppler Current Profiler) among others.