The present study is carried out to extend the applicability of the curvature correction model of Chung et al. to the case where the streamlines of a mean flow are unstably curved so that turbulence is augmented significantly by the centrifugal acceleration field. In the previous model of chung et al. the effect of such unstably curved stream-lines are neglected. But in unstably curved flows shch as the Cylinderical Couette Flow, the previous model under-predicts the momentum transfer and the mean velocity is over-predicted in the core region. Emphasis of the present study is placed on determining the lower limit of a curvature correction factor $A_{\tau}(=1+a(\tau_v/\tau_c)^n)$ of the third-order transport terms in k and ε equations after releasing the Heavyside step function which has been multiplied to the time scale ratio $\tau_v/\tau_c$ in the previous model. On the course of this study the lower limit of $A_{\tau}$ is tested down to 0.0. Given reasonable initial field values the lower limit of $A_{\tau}$ securing convergence runs down to about 0.3 and In comparision with experimental data of the Cylindrical Couette Flow the suitable lower limit is determined to be 0.7. A proper value of the power index n of the time scale ratio is also scrutinized among 0.5, 1.0 and 2.0 with two associated model constants a and b varying. Each optimum combination of n, a and b turns out to yield similar results. Considering the numerical convergence, however, the power n=1.0 is prefered. Then the correction factors and the constants determined through the above tests are applied to compute a Backward Facing Step Flow. As was expected, its results show better predictions compared to those by the previous model. But the agreement with experimental data is not yet fully satisfactory, and further study is needed to clarify the curvature effect on turbulence.
