Validation of a Navier-Stokes Solver for CFD Computations of Transonic Compressors

The progress of numerical methods and computing facilities has led to using Computational Fluid Dynamics (CFD) as a current tool for designing components of gas turbine engines. It is known, however, that a sophisticated numerical model is required to well reproduce the many complex flow phenomena which characterize compression systems, such as shock waves and their interactions with boundary layers and tip clearance flows. In this work, the flow field inside the NASA Rotor 37, a well known test case representative of complex three-dimensional viscous flow structures in transonic bladings, was simulated using a commercial CFD code based on the 3-D Reynolds-averaged Navier-Stokes equations. In order to improve the accuracy of predictions, different aspects of the numerical model were analyzed; in particular, an attempt was made to understand the influence of grid topology, number of nodes and their distribution, turbulence model, and discretization scheme of numerical solution on the accuracy of computed results. Existing experimental data were used to assess the quality of the solutions. The obtainment of a good agreement between computed and measured performance maps and downstream profiles was clearly shown. Also, detailed comparison with experimental results indicated that the overall features of the three-dimensional shock structure, the shock-boundary layer interaction, and the wake development can be calculated very well in the numerical approach for all the operating conditions. The possibility of a numerical model as a valid tool to better understand the aerodynamic behaviour of existing transonic compressors and to design new ones was demonstrated. It was also pointed out that the development of an accurate model requires the knowledge of both the physical phenomena involving the flow field and the features of the code which model them.