Erosional jets, the ultimate challenge in coupled flow-particle dynamics: Application to industrial post operational clean out (POCO)

Impinging jets are used in a wide range of process engineering applications; such as tunnelling operations, paint spraying and cavitation drilling. Liquid jets are also used as a method to estimate sediment strength in natural environment studies, e.g. to predict attrition in reservoir outlets or measure long term bed-slip in estuaries. Related is the use of jets as mixers to mobilise and homogenise sediment beds. This is particularly important within the nuclear waste industry (such as the sponsor Sellafield Ltd.) for mixing of radioactive wastes, as they are preferred over mechanical impellers, due to the lack of moving parts.

Despite the wide relevance of multiphase jet mixing systems, quantitative studies of their flow-profiles, turbulence and recirculation in sediment beds are lacking, while current predictions of erosion thresholds are also empirical. Difficulties arise in characterisation, due to the complex impingement profiles and because traditional laser or image techniques cannot be used at high solids loads. As an alternative, this PhD seeks new research to investigate the application of acoustic Doppler and backscatter instruments to characterise these complex flows and their erosion profiles. Measurements will be coupled with multiphase CFD simulations of the jets, to specifically enable the prediction of impinging jet mixers used to mobilise nuclear wastes, as part of post operational clean out (POCO) operations at Sellafield Ltd. In addition to impinging jets, simple boundary layer flows will also be examined experimentally and numerically to elucidate the underlying mechanisms responsible for particle resuspension from solid beds.