LES Simulation of the Loop-Shaped Stator Core Duct of an Air-Cooled Turbogenerator

The development of an algorithm for numerical simulation of the loop-shaped stator core duct of the air-cooled turbogenerator has been undertaken for the purpose of studying the character of air flow in it, finding the places of recirculation and determining the aerodynamic characteristics. In the numerical algorithm, two methodologies for modelling turbulent flows are considered: firstly, stationary methods, namely RANS (Reynolds-averaged Navier-Stokes equations) using the Menter’s Shear Stress Transfer (SST) turbulence model; and secondly, non-stationary methods, namely large eddy simulation (LES) using the dynamic subgrid-scale Smagorinsky model (DSG). A comparison of these calculation methods with experimental results has been carried out. It is evident that, upon the attainment of the aerodynamic characteristics of the duct and the measurement of the pressure drop across the air coolers during the unit operation, the determination of the actual air flow rate through the stator core of the main packages will be possible. The present study demonstrates that the aerodynamic characteristics obtained by the LES and RANS methods yield close results in the area of the expected design air flow rate of 3.25 l/s at a rated speed 3000 rpm of the turbogenerator. The discrepancy between these results and the experimental value does not exceed 8%. Concurrently, the LES method offers a realistic depiction of the temporal progression of airflow, thereby enabling estimations of the vortices’ structure and pressure fluctuations. Conversely, RANS does not necessitate a protracted computation time and facilitates the acquisition of an averaged depiction of the flow with a satisfactory degree of accuracy. Moreover, it does not demand labour-intensive tuning of the solver to ensure the convergence of the problem. The validation of the computational algorithm was carried out on a full-scale experimental model of the duct. The experimental model was created using additive technologies, namely, it was created on a 3D printer from PLA plastic and describes the duct geometry and surface roughness with high accuracy.