On the influence of longitudinal mean flow over Langmuir circulations

The Craik-Leibovich equations including vortex forcing terms and a pressure gradient force in x-momentum are integrated numerically. Some typical envi ronmental problems with strong longitudinal currents are analysed. Results are compared with Leibovich & Paolucci's stability analysis which a llows to identify situations where Langmuir cells exist, An establishing ch aracteristic time for the setting of cells has the same order of magnitude as in field observations. Its variation with Langmuir number (La) and nondi mensional depth is pointed out. A scaling analysis of the momentum equations is made for vanishing La. Infl uence of the longitudinal current intensities over Langmuir circulations st ructure is showed and confirmed by numerical results : more energetic conve ctive cells are verified for situations where stronger longitudinal velocit ies are present. Results indicate how the redistribution of the shear stres s induced by secondary flows is important for mixing in the water column an d for coastal sediment transport.