Validation of ADCP Velocity Measurements in Open-Channel Flow Using PIV and CFD

Accurate experimental characterization of velocity profiles in open-channel flows is essential for hydraulic research and field-scale monitoring; however, the performance of Acoustic Doppler Current Profilers (ADCPs) near flow boundaries remains insufficiently constrained due to acoustic blind zones and instrument-induced biases. This contribution presents a comprehensive multi-method validation framework combining laboratory-scale Particle Image Velocimetry (PIV), ADCP measurements, and Computational Fluid Dynamics (CFD) simulations to quantify ADCP accuracy and limitations under controlled conditions.

Initial experiments were conducted in a straight rectangular flume under six steady flow conditions spanning Reynolds numbers from 6.5 × 10⁴ to 1.76 × 10⁵. High-resolution 2D2C-PIV provided near-wall velocity measurements with millimeter-scale spatial resolution and served as the primary experimental reference. ADCP measurements were obtained using a 3 MHz profiler (RS5). Validated CFD simulations reproduced the mean velocity profiles across the full flow depth and were used to complement regions inaccessible to acoustic measurements.

Results show that ADCP-derived mean velocities agree well with both PIV and CFD in the core flow region, with typical deviations within ±3–5%. Larger discrepancies occur in the lower and upper parts of the water column, where ADCP velocities exhibit depth-dependent measurement bias of up to 25–30% at low Reynolds numbers, associated with blanking distance, reduced signal correlation, and side-lobe interference. A tendency toward reduced velocity discrepancies with increasing Reynolds number is observed in the lower part of the water column, although the trend is not strictly monotonic across all flow cases. Consistent agreement between PIV and CFD confirms that the observed deviations primarily arise from instrumental limitations rather than flow physics. Building on these validated results, ongoing work focuses on optimizing ADCP configuration parameters, developing CFD- and PIV-assisted blind-zone reconstruction strategies, and extending the framework toward instrument-aware CFD and field-scale applications. The study establishes a reproducible benchmark for ADCP validation and provides practical guidance for interpreting acoustic velocity measurements in laboratory and natural open-channel flows.