Applicability of linear type revised k-ε models to flow over topographic features

Accurate prediction of the wind energy distribution over terrains is essential for the appropriate selection of a suitable site for a wind power plant. This paper presents two-dimensional numerical simulations of flow over three common types of topographic features, i.e., a hill and two types of slopes (up-slope and down-slope). In a previous investigation by the present authors [Lun, Y.F., Mochida, A., Murakami, S., Yoshino, H., Shirasawa, T., 2003. Numerical simulation of flow over topographic features by revised k-ε models. J. Wind Eng. Ind. Aerodyn. 91(1-2), 231-245], the revised k-ε model proposed by P.A. Durbin [1996. Technical note: on the k-ε stagnation point anomaly. Int. J. Heat Fluid Flow 17, 89-90] was applied to flow prediction over a hill. Although, this model works well for flow around bluff bodies, a limitation was revealed in the area downstream of the hill. In this study, two new revised k-ε models proposed by Y. Nagano, H. Hattori and T. Irikado [2001. Prediction of flow over a complex terrain using turbulence model. In: Proceedings of the TED-Conference'01, JSME, in Japanese] and by Y. Nagano and H. Hattori [2003. A new low-Reynolds-number turbulence model with hybrid time-scales of mean flow and turbulence for complex wall flows. In: Proceedings of the Fourth International Symposium on Turbulence, Heat and Mass Transfer, Antalya, Turkey, October 12-17, 2003], i.e., the Ω and S-Ω models, were employed. These models are based on a mixed-time-scale concept. Their performance in predicting flow over various topographic features, namely a hill, up-slope and down-slope, was investigated. The problem of the Durbin model was corrected by the Ω model. However, a drawback of the Ω model was found in the upstream region. A new model, the S-Ω model, was introduced and was found to correct this problem. The S-Ω model showed best agreement with experiments for the hill case and the slope cases.