Detailed Local Heat Transfer Measurements in a Model of a Dendritic Gas Turbine Blade Cooling Design

Abstract

A novel form of gas turbine blade or vane cooling in which passages repeatedly branch within the wall of the cooled component is introduced in this paper. These so called dendritic cooling geometries offer particular performance improvements compared to traditional cooling holes where the external cross flow is low, and conventional films have a tendency to lift off the surface. In these regions improved internal cooling efficiency is achieved, while the coolant film is ejected at a low momentum ratio resulting in reduced aerodynamic losses between the film and hot gases, and a more effective surface film. By varying the number of branches of the systems at a particular location it is possible to tune the flow and heat transfer to the requirements at that location whilst maintaining the pressure margin. The additional loss introduced using the internal branching structure allows a full film-coverage arrangement of holes at the external blade surface. In this paper the results of transient heat transfer experiments characterising the internal heat transfer coefficient distribution in large scale models of dendritic passages are reported. Experiments were conducted with 1, 2 and 3 internal flow branches at a range of engine representative Reynolds numbers and exit momentum ratios. CFD models are used to help explain the flow field in the cooling passages. Furthermore the sensitivity of the pressure loss to the blowing ratio at the exit of the cooling holes is characterised and found to be inversely proportional to the number of branches in the dendritic system. Surprisingly the highly branched systems generally do not exhibit the highest pressure losses.

Quantifying ageing effects in thermochromic liquid crystal thermography as applied to transient convective heat transfer experiments

“…Today, these challenges are leading to the development of increasingly complex internal cooling schemes characterised by long intersecting passages that include either roughness elements or impinging jets to maximise convective efficiency. A novel example is provided by Batstone [2], who considered so-called dendritic cooling systems comprised of multiple interconnected, bifurcated passages. The application of such geometries has been facilitated by recent advances in manufacturing technologies, which have expanded the available design space by permitting intricate features to be employed cost effectively [3].…”