Velocity measurements in a turbulent open-channel flow using a Nortek Vectrino velocity profiler

Velocity measurement using acoustic Doppler velocimetry (ADV) in multiphase flows faces the challenge of data dropouts due to the passage of dispersed phase through the instrument’s sampling volume. Missing data can also occur in single-phase flows when the instrument malfunctions or when it is only partially submerged. A data interpolation method has been developed to replace missing data so that reliable estimates of the auto-spectral density function of velocity fluctuations can be obtained. The dataset contained herein is used to evaluate the performance of the proposed method. Real data of open-channel turbulence have been obtained in a recirculating water flume located in the Fluid Dynamics Laboratory at Texas A&M University. The flume is 30 m-long, 0.9 m-wide and is filled to a water depth of h = 25.5 cm. A centrifugal pump drives the flow inside the flume. To create a reasonably uniform current, two arrays of straight PVC pipes were placed at the beginning section of the flume. Each pipe has a length of 0.75 m and a diameter of 3 cm, forming a 1.5 m-long flow-straightening region. A horsehair mat is also placed in front of the flow straighteners to further break down the flow structures at the flume inlet. The downstream end of the flume is a sloping beach lined with dissipative elements to damp out reflected surface waves. The painted steel bottom of the flume is estimated to have a roughness height of 1-3 mm. Three-dimensional velocity measurements have been made using a Norterk Vectrino II velocity profiler at mid-section of the flume. This profiler is capable of measuring velocity profiles over a stretch of 35 mm at a user-defined spatial resolution of 1-4 mm and at a temporal frequency up to 100 Hz. The probe was mounted on a motorized vertical traverse for making measurements at different elevations above the flume bottom. Six vertical profiles, with a 5 mm overlap, were made to cover the water depths from 0.7 to 20 cm.