Numerical investigation of internal two-pass gas turbine cooling channels under the influence of rotation

Abstract

Numerical steady-state and transient conjugated simulations are applied to investigate a machine-like cooling channel configuration under the influence of rotation. Among other aspects, the comparison with the experimental data is given special consideration. With the transient thermochromic liquid crystal (TLC) measurement technique, local heat transfer coefficients can be determined. However, the evaluation method assumes that the values are constant over time. Together with the changing thermal conditions and the rotational motion this represents a contradiction, which is investigated in this thesis. As a basis, steady-state simulations are used. For validation, a test case from the literature has been selected to assess fundamental aspects such as turbulence modeling, rotational effects, and the influence of different inlet boundary conditions. This test case is further investigated to analyze the temporal development of heat transfer as it would occur in a transient TLC experiment. The isothermal walls are therefore replaced with a perspex solid body and transient conjugated simulations are performed. In the end, the dependency of heat transfer on the rotational buoyancy can be determined from the temporal development. Based on the preceding findings, the work concentrates on the ribbed channel configuration which has been experimentally investigated on the rotating test rig at ITLR. For an improved comparability with the transient TLC experiment, the color play of the TLCs is imitated from the numerical results. This enables the numerical data to be analyzed with the same evaluation software as the experiments. Although the heat transfer structures are remarkably similar, the heat transfer level of the experimental results is much higher than that of the numerical results. Of particular interest is the fact that the choice of the fluid reference temperature has a considerable influence on the local heat transfer distribution. Finally, the Nusselt numbers are illustrated as the ratio of the rotating case to the non-rotating case. Systematic influencing factors are thereby eliminated, and great similarities can be achieved between numerical simulation and experiment. The simulations not only provide a detailed analysis of the heat transfer characteristics of a machine-like cooling channel configuration, but also make a major contribution to a better understanding of the time-dependent processes in transient TLC experiments.