Hafez, A. M., A. I. Abd El-Rahman, and H. A. Khater, "Curvature-Sensitive Transition Model Application to Flow Around a Smooth Circular Cylinder", Journal of Fluids Engineering, vol. 144, no. 11, pp. 114501, 07, 2022. AbstractWebsite

{Transition modeling in complex flow situations including adverse pressure gradient, streamline curvature, and massive flow separation represents one of the key challenges in computational fluid dynamics that greatly affects the flow characteristics in many thermal and fluid sciences applications. Here, we report a comparative study that helps investigate the capability of the curvature-sensitive kT−kL−ω−v2 transition model against the original kT−kL−ω algorithm in predicting the flow behavior surrounding a smooth circular cylinder subjected to Reynolds numbers in the range from 3.9×103 to 3.6×106. A C-program that fully accounts for the model's four transport equations is particularly developed and coupled with the transient solver of ansysfluent. The present simulation enables accurate prediction of the distributions of skin-friction and pressure coefficients along with careful specification of the corresponding drag coefficients and angles of separation and transition. The simulation reveals insignificant variations in the bulk flow behaviors using either model in both sub- and critical flow regimes while a remarkable improvement in the supercritical drag result is achieved using the curvature-sensitive model.}

Hafez, A. M., A. I. Abd El-Rahman, and H. A. Khater, "Field inversion for transitional flows using continuous adjoint methods", Physics of Fluids, vol. 34, no. 12, pp. 124110, 12, 2022. AbstractWebsite

{Transition modeling represents one of the key challenges in computational fluid dynamics. While numerical efforts were traditionally devoted to either improving Reynolds-averaged Navier–Stokes-based turbulence modeling or developing scale-resolving simulations, cautious attention has been recently given to field inversion and machine learning techniques. This paper discusses an updated development of field inversion model for transitional flows based on k–ω shear stress transport model using the continuous adjoint approach, instead of the typical discrete adjoint method. The original model is modified by multiplying the production term of the turbulent kinetic energy equation by a spatially varying discrepancy function η(x). The adjoint equations and the relevant boundary conditions are specifically derived and integrated in OpenFOAM. The present model is validated using two zero pressure-gradient and four non-zero pressure-gradient from flow-over-flat-plate T3-series test cases. The gradient descent method is employed in the optimization process to minimize the discrepancy in the calculated shear stress. The inferred solution indicates a smooth transition to turbulence at the reported critical Reynolds numbers. The optimized model significantly improves the predictions of skin-friction coefficients, originally incorporated in the objective function. To demonstrate the usefulness of the present approach, the investigation is further extended to determine both velocity and shear Reynolds-stress profiles, which to our knowledge has not been reported before. Furthermore, a reduction in the percentage error from 50.2\% to 7.3\% is well observed in the predicted boundary layer thickness considering the laminar regime in the T3C5 test case.}

Hafez, A. M., M. A. Kassem, and O. A. Huzayyin, "Smart adaptive model for dynamic simulation of horizontal thermally stratified storage tanks", Energy, vol. 142, pp. 782-792, 2018.
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