Local Heat Transfer Characteristics of Blade Trailing Edge Internal Cooling Passage With Paired Pin

 Blade trailing edge is exposed to high thermal load due to the thin thickness profile. Also, sudden pressure field change induced by the shock wave and wake shedding makes this section vulnerable to structural load. As high-pressure turbine components of modern gas turbines operate above the materials' allowable temperature, these loads can cause severe damage to the trailing edge. Generally, cylindrical shape pin fin is applied to blade trailing edge for internal convective cooling and stiffness enhancement. However, continuous turbine inlet temperature rise requires an improved design.

 In this study, a new concept of pin fin array is suggested, so-called "paired pin." This geometry consists of a row of cylindrical pins, connected with a drop-shaped structure to accelerate the endwall flows and increase structural stiffness. The drop-shaped structure locates at the middle height of the pins. To investigate the effect of the paired pin on heat transfer performance, the naphthalene sublimation method performed for local heat transfer measurement. The simplified trailing edge internal cooling passage fabricated as a test section and naphthalene was coated on the two endwall regions (top and bottom surfaces). The test section has 5 rows of pin fin and converging flow passage in the streamwise direction.

 In the experiment, the Reynolds number based on pin diameter was 10,000. The geometrical variable was installing location of the paired pin; case 1 at 1st row, case 2 at 2nd row, case 3 at 1st and 2nd row. The heat transfer enhancement was observed in the paired pin installed region by impingement of highly accelerated flow with drop-shaped structure, followed by endwall reattachment flow. In other regions (not installed region), show similar heat transfer distribution in all cases.

 As a result of installing paired pin structure on trailing edge cooling passage, area averaged heat transfer and thermal performance increased up to 19% and 7%, respectively. Also, the spanwise heat transfer distribution became uniform.

(Acknowledgement: This work was supported by the Human Resources Development program (No.20174030201720) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry, and Energy. This work was partly supported by the Doosan Heavy Industries & Construction.)