APPLICATION OF A RANGE OF TURBULENCE ENERGY MODELS TO THE DETERMINATION OF M(4) TIDAL CURRENT PROFILES

A fully nonlinear, three-dimensional hydrodynamic model of the Irish S ea, using a range of turbulence energy sub-models, is used to examine the influence of the turbulence closure method upon the vertical varia tion of the current profile of the fundamental and higher harmonics of the tide in the region. Computed tidal current profiles are compared with previous calculations using a spectral model with eddy viscosity related to the flow field. The model has a sufficiently fine grid to r esolve the advection terms, in particular the advection of turbulence and momentum. Calculations show that the advection of turbulence energ y does not have a significant influence upon the current profile of ei ther the fundamental or higher harmonic of the tide, although the adve ction of momentum is important in the region of headlands. The simplif ication of the advective terms by only including them in their vertica lly integrated form does not appear to make a significant difference t o current profiles, but does reduce the computational effort by a sign ificant amount. Computed current profiles both for the fundamental and the higher harmonic determined with a prognostic equation for turbule nce and an algebraic mixing length formula, are as accurate as those d etermined with a two prognostic equation model (the so called q(2)-q(2 )l model), provided the mixing length is specified correctly. A simple , flow-dependent eddy viscosity with a parabolic variation of viscosit y also performs equally well.