Numerical study on sensibility of turbulence closure schemes at Oujiang River Estuary: Fid-Bau Portal

Numerical study on sensibility of turbulence closure schemes at Oujiang River Estuary

Liu, Jingui / Lu, Shasha / Li, Yichun

Abstract Oujiang River Estuary is characteristic of complex geometry, strong tide and short length. To elucidate the role of turbulent closures in applications, numerical studies are carried out to investigate the effects of the k- $ε$ and the q-ql with three typical wall proximity functions on hydrodynamics and salinity at Oujiang River Estuary. Therefore, four cases, based on the k- $ε$ scheme, three q-ql schemes with the original wall functions suggested by Mellor and Yamada (noted as MY), a modified wall function at open channel (noted as OC) and a symmetric linear shape used by Burchard (noted as Bur) are compared with in-situ data in tidal phases, velocity, salinity and so on. MY produces relatively better salinity structures than OC and Bur compared to in-situ data. The k- $ε$ scheme generates relatively higher water level and less bed stress compared to the q-ql schemes. The depth of the mixed layer may be over-predicted by more than 10%. The vertical eddy viscosity is almost twice as large in well-mixed or weakly stratified situations, therefore, a stronger mixing process can be produced. MY has anomalously high surface current at maximum ebb and low water level, and these findings are consistent with a previous conclusion. However, the anomalously high surface current disappears when strong stratification occurs in the upper water (<2 m in depth). Generally, MY simulates saltier water but contributes less length scale, which is due to the parabolic wall proximity function. OC and Bur calculate a roughly consistent vertical distribution of turbulent parameters, and they also simulate an identical distribution of stratification structure during both flood and ebb tide. MY based on the updated q-ql scheme shows relatively good results in a partially stratified situation.