Comparison of SST and γ-Re_θ transition model for prediction of aerothermal performances in a highly accelerated turbine nozzle guide vane

On turbine nozzle guide vane (NGV), boundary layer will undergo forward transition (laminar to turbulent) as well as reverse transition (relaminarization). In this paper, the effect of boundary layer transition on the aerothermal performances of a highly accelerated NGV was numerically examined, with the simulations conducted with the standard SST model and γ-Re_θ transition model. A comparison of the predicted velocity profiles, skin friction coefficients, and heat transfer coefficients from the two models was conducted to quantify the impact of boundary layer transition. It is found that under the intense favorable pressure gradient along pressure side (PS), γ-Re_θ transition model suppresses the production of turbulent kinetic energy, which in turn allows boundary layer to maintain laminar pattern. On the suction side (SS) with dual adverse pressure gradient, the boundary layer undergoes a complicated evolution, as predicted by γ-Re_θ transition model: initial forward transition, followed by relaminarization, and then a subsequent forward transition. Regarding skin friction, owing to the direct influence of pressure gradient, skin friction exhibits little sensitivity to boundary layer transition. Consequently, the predicted skin friction coefficients from the two models show good agreement over most regions of NGV. The lower skin friction from γ-Re_θ transition model results from the boundary layer relaminarization due to the favorable pressure gradient. In contrast, heat transfer is highly sensitive to the boundary layer state. As such, the standard SST model, with its fully turbulent assumption, tends to overestimate heat transfer, especially in laminar regions. In contrast, the γ-Re_θ transition model is capable of identifying the boundary layer state and consequently yields a heat transfer trend that mirrors boundary layer evolution.