This paper presents a finite-volume method for solving the compressible, two-dimensional Euler equations using unstructured triangular meshes. The integration in time, to a steady-state solution, is performed using an explicit, multistage Runge-Kutta algorithm. A special treatment of the artificial viscosity along the boundaries reduces the production of numerical losses. Convergence acceleration is achieved by employing local time-stepping, implicit residual smoothing and a multigrid technique.
The use of unstructured meshes, based on Delaunay triangulation, automatically adapted to the solution, allows arbitrary geometries and complex flow features to be treated easily. The employed refinement criterion does not only detect strong shocks, but also weak flow features.
Solutions are presented for several subsonic and transonic standard test cases and cascade flows that illustrate the capability of the algorithm.
The flow in exhaust diffusers along with the channel geometry strongly depends on the inflow conditions, including Mach number level, total pressure distribution, flow angle, and turbulence. In the first part of this paper, the impact of these parameters is analyzed using computational fluid dynamics, experimental data from the test rig, and field measurements. A widespread opinion is that the optimal condition for the diffuser is an axial uniform inflow. However, it is shown in this paper that nonuniform pressure distribution compared with a uniform one can lead to better diffuser performance and that a moderate residual swirl can improve the performance as well. In the second part of this paper, the minimization of exhaust losses in heavy-duty gas turbines is discussed and illustrated by two practical examples.
The key aspects for the reliable CFD modelling of exhaust diffusers are addressed in this paper. In order to identify adequate turbulence models a number of 2D diffuser configurations have been simulated using different turbulence models and results have been compared with measurements. An automated procedure for a time- and resource-efficient and accurate prediction of complex diffuser configuration is presented. The adequate definitions of boundary conditions for the diffuser simulation using this procedure are discussed. In the second part of this paper, the CFD procedure is being applied to investigate the role of secondary flow on axial diffusers. Prediction results are discussed and compared with available measurement data.
This paper describes the application of an unstructured mesh, solution-adaptive, 2D Navier-Stokes solver to the numerical simulation of the flow through film-cooled turbine cascades. The Navier-Stokes equations are solved using a cell-vertex explicit finite-volume method. Integration in time, to a steady-state solution, is performed by a five-stage Runge-Kutta algorithm. Turbulence effects are accounted for by a k-ε model.
The use of unstructured meshes, based on Delaunay triangulation, allows to mesh the entire flow domain, including internal coolant passages, without any geometrical limitations. In combination with a solution-dependent mesh-adaption technique, the strong interactions between coolant and outer flow, leading to complex flow features, can be simulated in a realistic and efficient way.
Solutions are presented for several test cases with and without film-cooling and are compared with experimental data, illustrating the capabilities of the presented flow solver.
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