High pressure waterjets for oil containment in calm and wavy waters; a parametric study

Abstract

The use of high pressure waterjets (HPWJ) as oil barriers has been proposed and tesed. It has been shown that a series of waterjets directed horizontally above the free water surface provide an effective means of containing or deflecting oil slicks. The waterjets generate a high speed air flow capable of moving the surface layer of the liquid. A numerical model is implemented to study the chracteristics of the entrained turbulent air flow using the Spectral Element Method (SEM) and an algebraic turbulent model for the Reynolds stresses. A test of the code is done for turbulent Couette Flow to check the accuracy of the calculated shear stresses against published data. A parametric study is performed to evaluate the HPWJ system performance at various operating and design parameters which include manifold pressure, nozzle flow rate, nozzle characteristics, jet height and surface wave conditions. The total driving shear force and power required for effective containment are used as performance measures. Shear stress and the total driving shear force at the air-liquid interface are calculated over a reference waterjet distance. Performance is measured under calm and wavy sea conditions. It is found that the containment pressure required to generate a given shear force in wavy surface conditions are 30–50% less than those required in calm water. The driving shear force decreases as the jet height above the liquid surface increased. Shear forces also appear to decrease with the reduction of the entrained air flow. The latter is governed by nozzle type, spread angle and spacing. The results of the parametric study are consistent with the trends observed experimentally, and could be used in optimising the system design and performance as well as in setting appropriate operational conditions.