Experimental study on sand bed excavation by impinging swirling jets

Abstract

The excavation performance of swirling jets impinging normally against a sand bed from several distances is described. A specially-designed nozzle with adjustable swirl vanes was used to generate swirling jets of various swirl intensities. Two sand beds of different grain size distributions were considered. The main scour patterns on the sand bed produced by the swirling jets were measured by image processing of photographs of the bed illuminated by a laser sheet. The velocity profiles of the swirling jets at the nozzle exit were measured using Laser Doppler Anemometry for various test conditions. The scour patterns were then analysed in relation to the details of the velocity profile of the swirling jets, their Reynolds numbers and the distances from the nozzle to the bed. The optimum jet features resulting from the different swirl nozzles and the best impinging distances for sea bed excavation are identified and discussed.

Keywords:

• Erodible bed
• scour
• sediment transport
• swirling jet
• velocity profile

Acknowledgement

This research was supported by the Ministerio de Educación y Ciencia of Spain, grant No. FIS2007-60161.