Ultrasound image velocimetry (UIV) allows for the non-intrusive measurement of a wide range of flows without the need for optical transparency. In this study, we used UIV to measure the local velocity field of a model drilling fluid that exhibits yield stress flow behavior. The radial velocity profile was used to determine the yield stress and the Herschel-Bulkley model flow index n and the consistency index k. Reference data were obtained using the conventional offline Couette rheometry. A comparison showed reasonable agreement between the two methods. The discrepancy in model parameters could be attributed to inherent differences between the methods, which cannot be captured by the three-parameter model used. Overall, with a whole flow field measurement technique such as UIV, we were able to quantify the complex rheology of a model drilling fluid. These preliminary results show that UIV can be used as a non-intrusive diagnostic for in situ, real-time measurement of complex opaque flow rheology.

Ultrasound imaging velocimetry (UIV) has received considerable interest as a tool to measure in non-transparent flows. So far, studies have only reported statistics for steady flows or used a qualitative approach. In this study, we demonstrate that UIV has matured to a level where accurate turbulence statistics can be obtained. The technique is first validated in laminar and fully developed turbulent pipe flow (single-phase, with water as fluid) at a Reynolds number of 5300. The flow statistics agree with the literature data. Subsequently, we obtain similar statistics in turbulent two-phase flows at the same Reynolds number, by adding solid particles up to volume fraction of 3 %. In these cases, the medium is completely opaque, yet UIV provides useable data. The error in the measurements is estimated using an ad hoc approach at a volume load up to 10 %. For this case, the errors are approximately 1.9 and 0.3 % of the centerline velocity for the streamwise and radial velocity components, respectively. Additionally, it is demonstrated that it is possible to estimate the local concentration in stratified flows.