Assessment of Transition Modeling and Compressibility Effects in a Linear Cascade of Turbine Nozzle Guide Vanes

The flow field in a linear cascade of highly loaded turbine nozzle guide vanes (NGVs) has been numerically investigated at low and high-subsonic regime, i.e., exit isentropic Mach number of M_2is = 0.2 and 0.6, respectively. Extensive experimental data are available for an accurate assessment of the numerical procedure. Aerodynamic measurements include not only vane loading and pressure drop in the wake but also local flow features such as boundary layer behavior along both pressure and suction sides of the vane, as well as secondary flow structures downstream of the trailing edge (TE). Simulations were performed by using two computational fluid dynamics (CFD) codes, a commercial one and an open-source based in-house code. Besides computations with the well-established shear-stress transport (SST) k–ω turbulence model assuming fully turbulent flow, transition models were taken into account in the present study. The original version of the γ–Re_θ model of Menter was employed. Suluksna–Juntasaro correlations for transition length (F_lenght) and transition onset (F_onset) were also tested. The main goal was to establish essential ingredients for reasonable computational predictions of the cascade aerodynamic behavior, under both incompressible and compressible regime. This study showed that transition modeling should be coupled with accurate profiles of inlet velocity and turbulence intensity to get a chance to properly quantify aerodynamic losses via CFD method. However, additional weaknesses of the transition modeling have been put forward when increasing the outlet Mach number.