No abstract

To decrease NOx emissions from combustion systems, lean premixed combustion is used. A disadvantage is the higher sensitivity to combustion instabilities, leading to increased sound pressure levels in the combustor and resulting in an increased excitation of the surrounding structure: the liner. This causes fatigue, which limits the lifetime of the combustor. This paper presents a joint experimental and numerical investigation of this acoustoelastic interaction problem for frequencies up to 1kHz. To study this problem experimentally, a test setup has been built consisting of a single burner, 500kW, 5bar combustion system. The thin structure (liner) is contained in a thick pressure vessel with optical access for a traversing laser vibrometer system to measure the vibration levels of the liner. The acoustic excitation of the liner is measured using pressure sensors measuring the acoustic pressures inside the combustion chamber. For the numerical model, the finite element method with full coupling between structural vibration and acoustics is used. The flame is modeled as an acoustic volume source corresponding to a heat release rate that is frequency independent. The temperature distribution is taken from a Reynolds averaged Navier Stokes (RaNS) computational fluid dynamics (CFD) simulation. Results show very good agreement between predicted and measured acoustic pressure levels. The predicted and measured vibration levels also match fairly well.

No abstract

No abstract

A numerical case study on a HPT-shroud of a medium-sized commercial engine has been carried out to investigate the heat loading and the possible redistribution (number of channels, position and exit angle) of shroud cooling channels facing the turbine blade tip. A combination of modeling vehicles was used to quantify the aerodynamics, the thermodynamics and resulting heat loads on the shroud. This includes a 1-D gas turbine performance simulation model, engineering models for cooling flow distributions and heat loads, CFD modeling of the HPT flow including some tip flow effects and the finite element modeling to calculate the temperature and stress distribution in the solid shroud. Regions with high temperatures and/or maximum thermal stresses and the potential for reduction by relocating the cooling channels at equal amounts of cooling flow were identified. Although the physics involved in the processes is much more complicated than modeled, the parametric studies gave valuable insight and quantitative results in terms of differences in shroud temperatures and thermal stresses. A complementary experimental study on shroud maintenance and service experiences (not published yet) has delivered data for model input support and comparison with the numerical results.