The Reynolds number for the flow through LPT at cruise conditions is much lower than that at the take-off conditions. This low-Re flow has a great tendency to undergo separation on the suction surface of the turbine blade when an adverse pressure gradient is encountered. This prevailing flow separation is detrimental to the performance of the LPT. Hence, low-pressure turbine (LPT) stage in aircraft engines undergo significant losses during cruise conditions. Therefore, accurate prediction of flow separation is crucial for an effective design of LPT blade, and is achieved in the present work using a high-order accurate numerical solution procedure. The accurate prediction of flow separation is necessary for implementing flow control techniques, passive or active, to possibly delay or prevent the occurrence of flow separation in the low-pressure turbine stage in an aircraft engine. A multi-block, periodic, structured grid of multiple topologies generated by the grid generation software, GRIDPRO, is used for the present numerical analysis. The three-dimensional, unsteady, full Navier-Stokes equations are solved to analyze the flow. A MPI-based higher-order, parallel, chimera Large-Eddy Simulation (LES), version of the FDL3DI flow solver, developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbo-machinery application. A sixth-order accurate compact-difference scheme is usual for the spatial discretization, coupled with tenth-order filtering to minimize the numerical oscillations in the flow solution and maintain numerical stability, along with second-order accurate temporal discretization. Also examined is the effect of grid density and the location of the upstream inflow boundary location on the flow solution. Four different grids were used in this study, and it was observed that, as the grid density and the location of the upstream inflow boundary are increased, the oscillations in the predicted Cp distribution reduced significantly. Also, the physical, simulation-turn around time was reduced significantly with the multi-block and parallelization approach used in the present study through the parallelized code. Along with the two-dimensional study, the effect of the third spatial dimension on the location of the onset of separation and the transition process was studied, using a coarse-grid three-dimensional simulation with an Implicit Large-Eddy Simulation (ILES) echnique. Finally, baseline simulation results were generated for a simplified geometry of flow over a circular cylinder at a ReD = 13,400 as a starting step to implement flow control for preventing or delaying the flow separation. Two different turbine blade geometries are considered during the course of this numerical study. A high-pressure (HPT) turbine blade geometry is considered as a test case, and a low-pressure turbine (LPT) blade is studied as the main application. For the HPT blade geometry, it was found necessary to account for upstream influence in implementing the inflow/outflow boundary conditions in order for the leading-edge stagnation point to occur at the appropriate location and, hence, for the correct location of the onset of separation on the suction side of the blade. The computed Cp distribution for the LPT flow shows good agreement with the available experimental data and with the LES simulation result. The 3-D simulation showed significant effect in the growth of spanwise instabilities which thereby weaken the coherent vortical structures and break down in spanwise direction, thereby predicting the separation process more realistically and accurately. Finally, the baseline simulation study of flow over a circular cylinder at ReD = 13,400 is performed as a starting step for the future study of implementation of flow control techniques for preventing or delaying the flow separation. The Reynolds number for the flow through LPT at cruise conditions is much lower than that at the take-off conditions. This low-Re flow has a great tendency to undergo separation on the suction surface of the turbine blade when an adverse pressure gradient is encountered. This prevailing flow separation is detrimental to the performance of the LPT. Hence, low-pressure turbine (LPT) stage in aircraft engines undergo significant losses during cruise conditions. Therefore, accurate prediction of flow separation is crucial for an effective design of LPT blade, and is achieved in the present work using a high-order accurate numerical solution procedure. The accurate prediction of flow separation is necessary for implementing flow control techniques, passive or active, to possibly delay or prevent the occurrence of flow separation in the low-pressure turbine stage in an aircraft engine. A multi-block, periodic, structured grid of multiple topologies generated by the grid generation software, GRIDPRO, is used for the present numerical analysis. The three-dimensional, unsteady, full Navier-Stokes equations are solved to analyze the flow. A MPI-based higher-order, parallel, chimera Large-Eddy Simulation (LES), version of the FDL3DI flow solver, developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbo-machinery application. A sixth-order accurate compact-difference scheme is usual for the spatial discretization, coupled with tenth-order filtering to minimize the numerical oscillations in the flow solution and maintain numerical stability, along with second-order accurate temporal discretization. Also examined is the effect of grid density and the location of the upstream inflow boundary location on the flow solution. Four different grids were used in this study, and it was observed that, as the grid density and the location of the upstream inflow boundary are increased, the oscillations in the predicted Cp distribution reduced significantly. Also, the physical, simulation-turn around time was reduced significantly with the multi-block and parallelization approach used in the present study through the parallelized code. Along with the two-dimensional study, the effect of the third spatial dimension on the location of the onset of separation and the transition process was studied, using a coarse-grid three-dimensional simulation with an Implicit Large-Eddy Simulation (ILES) echnique. Finally, baseline simulation results were generated for a simplified geometry of flow over a circular cylinder at a ReD = 13,400 as a starting step to implement flow control for preventing or delaying the flow separation. Two different turbine blade geometries are considered during the course of this numerical study. A high-pressure (HPT) turbine blade geometry is considered as a test case, and a low-pressure turbine (LPT) blade is studied as the main application. For the HPT blade geometry, it was found necessary to account for upstream influence in implementing the inflow/outflow boundary conditions in order for the leading-edge stagnation point to occur at the appropriate location and, hence, for the correct location of the onset of separation on the suction side of the blade. The computed Cp distribution for the LPT flow shows good agreement with the available experimental data and with the LES simulation result. The 3-D simulation showed significant effect in the growth of spanwise instabilities which thereby weaken the coherent vortical structures and break down in spanwise direction, thereby predicting the separation process more realistically and accurately. Finally, the baseline simulation study of flow over a circular cylinder at ReD = 13,400 is performed as a starting step for the future study of implementation of flow control techniques for preventing or delaying the flow separation. |