G. Voulgaris et Jh. Trowbridge, EVALUATION OF THE ACOUSTIC DOPPLER-VELOCIMETER (ADV) FOR TURBULENCE MEASUREMENTS, Journal of atmospheric and oceanic technology, 15(1), 1998, pp. 272-289
Accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in thi
s paper. Simultaneous measurements of open-channel how were undertaken
in a 17-m flume using an ADV and a laser Doppler velocimeter. Flow ve
locity records obtained by both instruments are used for estimating th
e true (''ground truth'') flow characteristics and the noise variances
encountered during the experimental runs. The measured values are com
pared with estimates of the true how characteristics and values of var
iance ([u'(2)], [w'(2)]),, and,,,,,,,,, covariance ([u'w']) predicted
by semiempirical models for open-channel flow. The analysis showed tha
t the ADV sensor can measure mean velocity and Reynolds stress within
1% of the estimated true value. Mean velocities can be obtained at dis
tances less than 1 cm from the boundary, whereas Reynolds stress value
s obtained at elevations greater than 3 cm above the bottom exhibit a
variation that is in agreement with the predictions of the semiempiric
al models. Closer to the boundary, the measured Reynolds stresses devi
ate from those predicted by the model, probably due to the size of the
ADV sample volume. Turbulence spectra computed using the ADV records
agree with theoretical spectra after corrections are applied for the s
patial averaging due to the size of the sample volume and a noise floo
r The noise variance in ADV velocity records consists of two terms. On
e is related to the electronic circuitry of the sensor and its ability
to resolve phase differences, whereas the second is flow related. The
latter noise component dominates at rapid flows. The error in how mea
surements due to the former noise term depends on sensor velocity rang
e setting and ranges from +/-0.95 to +/-3.0 mm s(-1). Noise due to she
ar within the sample volume and to Doppler broadening is primarily a f
unction of the turbulence dissipation parameter. Noise variances calcu
lated using spectral analysis and the results of the ground truthing t
echnique are compared with theoretical estimates of noise.