The objective of the RANS group is to develop advanced solvers for the solution of the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and to use these solvers to provide insights into unsteady phenomena in turbomachinery components (compressors, turbines, and secondary flow systems.) In addition, these solvers are part of the integrated simulations efforts that our Center is carrying out and include interfaces to other RANS and Large Eddy Simulation (LES) solvers to describe the main flow path, secondary flow systems and cooling passages, and to structural analysis packages such as MSC/NASTRAN and FEAP for non-linear aeroelastic predictions.
The main URANS flow solver is TFLO (Turbomachinery FLOw solver): a three-dimensional, multiblock-structured, MPI-based, parallel solver with demonstrated scalability up to 1, 024 processors for reasonable problem sizes. TFLO solves the URANS equations using an implicit discretization and the dual-time stepping approach: an unsteady problem is solved as a sequence of pseudo-time steady-state solutions.
The inner pseudo-time steady-state iterations are carried out using a modified Runge-Kutta scheme, a full approximation storage multigrid algorithm, a number of convergence acceleration techniques such as local time stepping and implicit residual smoothing, and various formulations for artificial dissipation. The Reynolds stress is modeled with several options including one-, two-, and four-equation turbulence models which are solved segregated from the mean flow equations.
An example of application of TFLO to the high-pressure turbine and secondary flow system is illustrated in the figure.
Yao, J., Davis, R., Jameson, A., Alonso, J. J., Unsteady Flow Investigation in Axial Turbines Using the Massively Parallel Flow Solver TFLO, 39th AIAA Aerospace Sciences Meeting & Exhibit, AIAA Paper 2001-0529, Reno, NV, January 2001