Film cooling effectiveness under conditions of contamination of discrete cooler blow holes

Abstract

Modern gas turbine units (GTUs) operate under extreme conditions, with inlet gas temperatures reaching up to 1750 °C, while the heat-resistant materials of turbine blades are limited to a thermal resistance of 1000–1100 °C. This discrepancy necessitates advanced cooling techniques to ensure blade durability and reliability. Film cooling, achieved by injecting coolant air through small holes to form a protective layer on the blade surface, is a widely adopted method. However, during GTU operation, particle deposition (e.g., CaO–MgO–Al₂O₃–SiO₂) can cause partial blockage of coolant supply holes, significantly impacting film cooling effectiveness and heat transfer intensification, which underscores the importance of studying this phenomenon.

The Purpose of the Work. This study aims to investigate the effect of partial blockage of coolant supply holes on film cooling effectiveness under varying blowing ratios, with a particular focus on the transverse distribution of cooling effectiveness. By modeling a system with four injection holes, the research seeks to analyze the spatial non-uniformity of coolant distribution and its impact on cooling performance at different blockage degrees.

Research Methods. The investigation was conducted using numerical simulations in ANSYS CFX 2019 R2. The blockage degree was characterized by the dimensionless ratio h/d

, where (h) is the transverse blockage size and (d) is the hole diameter (0.8 mm). Three configurations were modeled: a baseline without blockage (h/d = 0), and two with partial blockages (h/d = 0.5 and h/d = 1.0). A hybrid unstructured mesh with 434,000 nodes and 1.1 million elements was employed, using the Reynolds-Averaged Navier-Stokes (RANS) equations and the SST turbulence model for closure.

Results and Conclusions. The results reveal that increasing the blockage degree (h/d) significantly reduces film cooling effectiveness due to flow detachment caused by a larger coolant injection angle, which enhances mixing with the mainstream flow. Specifically, the average film cooling effectiveness decreases by 2.7% at h/d = 0.5 and by 7.9% at h/d = 1.0 compared to the unblocked configuration. Additionally, as the blowing ratio (m) increases from 0.4 to 1.0, the effectiveness drops further, with a maximum reduction of 22% for h/d = 0, 29% for h/d = 0.5, and 36% for h/d = 1.0. Transverse non-uniformity in coolant distribution persists across all blowing ratios, with local effectiveness maxima along the hole axes and minima in inter-hole regions, highlighting the role of hole geometry in cooling performance. These findings emphasize the critical impact of hole contamination on film cooling effectiveness in gas turbine blade systems, indicating the need for strategies to mitigate blockage effects, such as exploring alternative hole designs or materials resistant to particle deposition, to improve cooling uniformity and thermal protection.