Heat Transfer Analysis in an Engine-Realistic Turbine Rear Structure

Paper i proceeding, 2026

Rising turbine inlet temperatures and pressure ratios in modern aircraft engines increase the challenges of thermal management. This makes detailed heat transfer analysis essential for predicting material stresses and reducing engine maintenance costs. In this context, the turbine rear structure (TRS) is exposed to the hot, swirling flow leaving the low-pressure turbine (LPT), where residual swirl, hot streaks, and temperature gradients induce complex and non-uniform heat transfer. Cooling of TRS relies primarily on hub-located cooling provided by bypassed purge flow from engine compressor stage. As a consequence of a broad operational envelope, the TRS is subjected to substantial thermal loading and cyclic temperature variations, which promote fatigue and reduce component durability. Therefore, the accurate knowledge of the heat transfer on the TRS hub and vanes is essential.      

The heat transfer in a state-of-the-art TRS was investigated for the first time in a low-speed, large-scale 1.5-stage facility at Chalmers University of Technology. The investigated TRS was equipped with twelve engine-realistic outlet guide vanes (OGVs). Tests were conducted at on- and off-design conditions provided by an upstream shrouded LPT stage. The experimental setup was realized in two complementary configurations. In the first configuration, the focus was on the heat transfer measurements on the OGV, hub and shroud surfaces. The temperature difference between the flow and the walls was imposed by internal water circulation in a specially designed TRS sector. In the second configuration, the facility was equipped with a purge flow system delivering pre-heated purge flow at 1% of the core mass flow. This allowed adiabatic wall measurements on the TRS hub and the evaluation of the film cooling effectiveness in the near-hub passage between the turbine stage and the TRS. In both configurations the detailed surface temperature maps were acquired by an accurate IR camera.

The paper results include novel heat transfer and film cooling measurements in an engine-realistic TRS, covering the OGV and endwall surfaces, including the midspan leading edge region and the inter-passage region between the LPT and TRS. The heat transfer measurements revealed strong dependence of the laminar-turbulent transition on operating conditions, which influenced the transition location and the heat transfer within the transition region. Under idle conditions, the high-incidence inflow led to a fundamentally different flow and heat transfer in the TRS. For the first time, film cooling effectiveness distributions were obtained in a realistic TRS geometry with purge flow, providing detailed information in the hub-vane leading edge region for both on-design and idle conditions. In addition, state-of-the-art industrial CFD simulations were performed at the same operating conditions. The numerical simulations well reproduced the transition shift and heat transfer variation but somewhat underpredicted the heat transfer magnitudes, which may be explained by the unsteady flow effects absent in the steady calculations. A thorough analysis of the novel experimental data is provided in the paper.