EXPERIMENTAL COMPARISON OF 2 LASER-BASED VELOCIMETERS FOR FLOWS WITH ALLUVIAL SAND

Nonintrusive measurements in a sediment-laden flow using two laser-bas ed techniques, Discriminator Laser-Doppler Velocimetry (DLDV) and Part icle Tracking Velocimetry (PTV), are compared. DLDV was previously dev eloped at the Iowa Institute of Hydraulic Research, while PTV was spec ially configured for this application. Mean and fluctuating velocity c omponents for both flow fractions were simultaneously measured in a la boratory-scale, submerged water jet loaded with alluvial sand. This in formation cannot be obtained using existing measurement techniques. Th e jet Reynolds number was 6120, and the sediment sieve diameter ranged from 0.5 to 0.6 mm. Small mass loadings of sand with inertial time co nstant tau(p) Of 0.6 ms were examined. The configuration, operation, a nd results obtained using the DLDV and PTV are presented. For each tec hnique, means to precisely distinguish between the light scattered by suspended sand and that originating from seed-particles following the water were implemented. The agreement in measurement for the two metho ds validates one another since they are based on completely different principles of operation. The capabilities of DLDV and PTV to reliably measure sand and water velocities in sediment-laden flows are further indicated by the agreement of the present findings with those obtained previously in similar studies. The comparison suggests that PTV, due to its whole field nature, could become a powerful tool for flow and p article-related diagnostics, yielding fundamental information in an ar ea with a long history of conflicting experimental evidence.