Measurement of Turbulence Properties at the Time of Flow Reversal Under High Wave Conditions in Hujeong Beach

摘要

The temporal distribution of the turbulence kinetic energy (TKE) and the vertical component of Reynolds stresses ( −u′w′¯¯¯¯¯¯−u′w′¯mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1" display="inline"mml:mrowmml:mo−/mml:momml:mover accent="true"mml:mrowmml:msupmml:miu/mml:mimml:mo′/mml:mo/mml:msupmml:msupmml:miw/mml:mimml:mo′/mml:mo/mml:msup/mml:mrowmml:mo¯/mml:mo/mml:mover/mml:mrow/mml:math) was measured during one wave period under high wave energy conditions.The wave data were obtained at Hujeong Beach in the east coast of Korea at January 14~18 of 2017 when an extratropical cyclone was developed in the East Sea.Among the whole thousands of waves measured during the period,hundreds of regular waves that had with similar pattern were selected for the analysis in order to give three representing mean wave patterns using the ensemble average technique.The turbulence properties were then estimated based on the selected wave data.It is interesting to find out that −u′w′¯¯¯¯¯¯−u′w′¯mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m35" display="inline"mml:mrowmml:mo−/mml:momml:mover accent="true"mml:mrowmml:msupmml:miu/mml:mimml:mo′/mml:mo/mml:msupmml:msupmml:miw/mml:mimml:mo′/mml:mo/mml:msup/mml:mrowmml:mo¯/mml:mo/mml:mover/mml:mrow/mml:math has one clear peak near the time of flow reversal while TKE has two peaks at the corresponding times of maximum cross-shore velocity magnitudes.The distinguished pattern of Reynolds stress indicates that vertical fluxes of such properties as suspended sediments may be enhanced at the time when the horizontal flow direction is reversed to disturb the flows,supporting the turbulence convection process proposed by Nielsen (1992).The characteristic patterns of turbulence properties are examined using the CADMAS-SURF Reynolds-Averaged Navier-Stokes (RANS) model.Although the model can reasonably simulate the distribution of TKE pattern,it fails to produce the −u′w′¯¯¯¯¯¯−u′w′¯mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m36" display="inline"mml:mrowmml:mo−/mml:momml:mover accent="true"mml:mrowmml:msupmml:miu/mml:mimml:mo′/mml:mo/mml:msupmml:msupmml:miw/mml:mimml:mo′/mml:mo/mml:msup/mml:mrowmml:mo¯/mml:mo/mml:mover/mml:mrow/mml:math peak at the time of flow reversal,which indicates that the application of RANS model is limited in the prediction of some turbulence properties such as Reynolds stresses.