Film Cooling Modeling for Gas Turbine Nozzles and Blades: Validation and Application

Abstract

The design of modern gas turbines cooling systems cannot be separated from the use of computational fluid dynamics (CFD) and the accurate estimation of the effect of film cooling. Nevertheless, a complete modeling of film cooling holes within the computational domain requires an effort both from the point of view of the mesh creation and from computational time. It is here proposed a new way to model the film cooling (FCM), capable of representing the effect of the coolant at hole exit. This is possible due to the introduction of local source terms near the hole exit in a delimited portion of the domain, avoiding the meshing process of perforations. The goal is to provide a reliable and accurate tool to simulate film-cooled turbine blades and nozzles without having to explicitly mesh the holes. The model was subjected to an intensive validation campaign, composed of two phases. During the first one, FCM results are compared to experimental data and numerical results (obtained with complete cooling holes meshing) on a series of test cases reproducing flat plate cooling configurations for different coolant conditions (in terms of blowing and density ratio). In the second phase, a film-cooled vane test case has been studied, in order to consider a real injection system and flow conditions: FCM predictions are compared to an in-house developed correlative approach and full conjugate heat transfer (CHT) results. Finally, a comparison between FCM predictions and experimental data was performed on an actual nozzle of a GE Oil & Gas heavy-duty gas turbine, in order to prove the feasibility of the procedure. The presented film cooling model (FCM) proved to be a feasible and reliable tool, able to evaluate adiabatic effectiveness, simplifying the design phase avoiding the meshing process of perforations.

Numerical simulations and optimizations for turbine-related configurations

“…The injection source model in [10] is adopted to predict the influence of the tip injections on the aero-thermal performance of a linear turbine cascade in this paper. Since the jet fluid introduces extra energy into the flow field, source terms of Sma,jet, Smo,jet, and Sen,jet formulated in eq.…”

“…Definition of the Cpt is given in eq. (10) and process of calculating the grid convergence index (GCI) values can be referred to [19]. It is seen from tab.…”

“…The ΩS is discretized using nearly uniform meshes when seeing the surface grid in y-z plane. The grid cell width, WUM, is about one eighth of the Djet according to a grid independence study and the recommendation of Andrei et al [10]. Measured total pressure, Pt,in, and temperature, Tt,in, are set at the inlet, where a flow angle of 37.5° is also specified.…”

“…Moreover, an immersed mesh block (IMB) scheme, which reduced the cost of generating body-fitted meshes, was validated by Lad et al [9] for cooled turbine aero-thermal performance evaluation. Andrei et al [10] developed a film cooling model (FCM) for gas turbines. They declared that the FCM-based prediction has an excellent consistence in the adiabatic cooling effectiveness with measurements, and hence it can be utilized in turbine preliminary design systems.…”

“…The primary purpose of literature sources [6][7][8][9][10] is to avoid generating body-fitted meshes to facilitate numerical preprocessing and solution steps. Source terms are introduced to the governing equations to model multi-physical fields.…”