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Acoustic Doppler Velocimeters (ADV) have been widely used in measuring three dimensional turbulent velocities. A new development of ADV, MicroADV from SonTek, is used to measure the flow in free hydraulic jumps with Froude numbers of 2.0, 2.5 and 3.32. The effects of air bubbles and boundary on the measurements of MicroADV are evaluated. Measurements of the mean air concentration and mean velocity were obtained using a fiber optic probe and a Prandtl tube respectively. It was found that the error of mean velocity measured by MicroADV is increased linearly with the air concentration at very low concentration. The boundary effect on the measurements of MicroADV starts when the distance from the measurement point to the boundary is less than about 3 cm. The relative error of MicroADV measurements increases when the distance reduces, and at a distance of 0.5 cm the relative error is estimated to be 12 ∼ 25%. The relative error is within 6% for the situations without the effects of air bubble and boundary.
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Liu et al. (2002) studied this question.