Impact of Turbulator Design on the Heat Transfer in a High Aspect Ratio Passage of a Turbine Blade

The trailing edge region of gas turbine blades is generally subjected to extremely high external heat loads due to the combined effects of high mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfils both the part mechanical integrity and turbine performance, highly efficient and reliable cooling of the trailing edges is required without increasing the coolant consumption. In this paper, the heat transfer and pressure drop characteristic of three different turbulator designs in a very high aspect ratio passage have been investigated. The turbulator designs included angled and tapered ribs, broken discrete ribs and V-shaped small chevrons ribs. The heat transfer and pressure drop characteristics of all the turbulator configurations was initially investigated via numerical predictions and subsequently in a scaled experimental perspex model. The experimental study was conducted for a range of operational Reynolds numbers and the TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients on all surfaces of the passage. Pressure taps were located at several locations within the perspex model and both the local and average heat transfer coefficients and pressure loss coefficients were determined. The measured and predicted results show, that for all cases investigated, the local internal heat transfer coefficient, which is driven by the highly three dimensional passage flows, is highly non-uniformly within the passage. The highest overall average heat transfer was obtained for the angled and tapered turbulator. Although the average heat transfer coefficient of the discrete broken turbulator and the small chevron turbulator were slightly lower than the baseline case, they had much higher pressure losses. In terms of the overall non-dimensional performance index, which incorporates both the heat transfer and the pressure drop, it was found that the angled and tapered turbulator gave the best overall performance.