Experimentelle und numerische Untersuchung verschiedenerInnengeometrien konvektionsgekühlter Turbinenschaufeln

Abstract

Gas turbine manufacturers aspire to increasing power outlets and efficiencies. Those can be obtained by enhanced turbine inlet temperatures, which in return demand for an improved turbine cooling. Within industrial applications of medium power class, convection cooling systems are applied for a high cooling effectiveness at low maintenance costs.

In the present work a geometry variation is performed for the internal cooling passages of a gas turbine blade. Herein, the cooling flow and heat transfer inside the cooling channels, as well as the impact on the thermal load of the blade are investigated by experiments and numerical calculations.

First, a base configuration of the cooling channels is defined. It consists of a two-passage system with turbulators at the leading edge, a plenum in the blade root and a pin fin array at the trailing edge. From this starting point, four variations are carried out which contain changes to the turbulators in the leading edge channels on the one hand and different flow paths on the other hand. In contrast, the blade profile remains constant.

Within the experiments, dead water areas are localized in the first instance. The closed-loop test rig for flow visualization features paint injection into water and was build-up at the Institute of Jet Propulsion and Turbomachinery at the RWTH Aachen University specifically for this investigation. More detailed investigations of the internal flows are carried out by CFD simulations reproducing the experimental conditions. The impact on the convective heat transfer and the temperature distribution in the solid are determined by conjugate heat transfer calculations (CHT) that include also the turbine blade and the outer flow besides the internal flow. To the author’s knowledge, this complexity of the latter numerical simulations is a first time application.

Inside the gas turbine blade, longitudinal vortices in the leading edge channels and flow separations behind the turbulators are identified besides large recirculations. Horse shoe vortices form in front of the pin fins. Those secondary velocities have a major effect on the heat transfer. While separations and recirculations reduce the convective heat transfer at the wall, reattachment and impingement enhance it. By averaging the heat transfer performance in sections an improvement of up to 46 % is achieved through the variation.
With an advanced internal heat transfer the integral cooling effectiveness of the blade is increased by up to 3,7 %. Temperature differences inside the solid blade lead to distinct temperature gradients at exposed positions. However, the average values show only a marginal sensitivity to the geometry variation.