ADVANCES IN HYDRO-SCIENCE AND –ENGINEERING, VOLUME VI 1 NUMERICAL MODELING OF OSCILLATORY BOUNDARY LAYERS USING TWO- EQUATION TURBULENCE MODELS Ahmad Sana 1 and Hitoshi Tanaka 2 ABSTRACT Three versions of the low Reynolds number k-ε model and three versions of the k-ω model (one original model and two two-layer versions) are tested against the DNS data of one-dimensional sinusoidal and flat-crested oscillatory boundary layers, and experimental data of cnoidal wave boundary layer. A detailed comparison has been made for cross-stream velocities, turbulent kinetic energy (T.K.E.), ratio of Reynolds stress and turbulent kinetic energy and wall shear stress. It is observed that the newer versions of the k-ε model can predict the velocity and turbulent kinetic energy in a better way. The k-ω model and two-layer models underestimate the peak value of turbulent kinetic energy, which may be explained by the Reynolds stress to T.K.E ratio in the logarithmic zone. The bottom shear stress peak is predicted by the k-ω model in an excellent manner. The results of the present study may be useful for the practicing engineers and researchers for choosing appropriate turbulence models in a certain field condition. 1. INTRODUCTION An accurate prediction of sediment transport in coastal environments requires detailed analysis of coastal bottom boundary layers in changing field conditions with oscillatory motion. Nowadays, powerful computing facilities at affordable costs encourage the practicing engineers to use numerical models for this purpose. During the past three decades a large number of turbulence models have been proposed mainly to analyze steady boundary layers, k-ε model and k-ω model being the most popular types. The k-ε model was originally developed by Jones and Launder (1972) and the k-ω model by Saffman(1970) and then modified by Wilcox(1988) mainly for steady flow phenomena. Later these models were applied to a number of turbulent boundary layers including oscillatory ones and a number of modifications were proposed to improve their predictive abilities. Menter (1994) proposed a two-layer model in which both k-ε and k-ω models are utilized to obtain the best predictive abilities of these models. Although these models were mainly developed for steady boundary layers, their application to oscillatory boundary layers has been successful too. Sana and Tanaka (2000) and Sana and Shuy (2002) have provided brief reviews of the studies carried out in the past on the application of two 1 Assistant Professor, Department of Civil and Architectural Engineering, Sultan Qaboos University, PO Box 33, Al- Khod 123, Sultanate of Oman (sana@squ.edu.om) 2 Professor, Department of Civil Engineering, Tohoku University, Sendai 980-8579, Japan (tanaka@tsunami2.civil.tohoku.ac.jp)