Surface roughness effects on film-cooling effectiveness in a fan-shaped cooling hole

Ali Zamiri, Sung Jin You, Jin Taek Chung

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


Large eddy simulations (LES) were carried out to investigate the influence of surface roughness, which was applied to the inner walls of a cooling hole, on cooling performance and flow structures. The cooling hole was a 30-degree inclined, baseline 7-7-7 fan-shaped hole relative to a turbulent flat plate boundary layer of the mainstream. Numerical simulations were performed at two different blowing ratios (M=1.5 and 3.0) and at a constant density ratio (DR=1.5) for various configurations of surface roughness. In order to numerically consider the effects of surface roughness, the equivalent sand-grain roughness model was utilized. Different correlations between the equivalent sand-grain roughness height and arithmetic average roughness height were numerically tested to find an accurate correlation compared to the measurements. The time-averaged numerical results were validated by experiments looking at the velocity and thermal fields for the smooth and rough cooling holes. Results revealed that increasing the surface roughness applied to the cooling hole, increases the thickness of the boundary layers within the hole, especially at the higher blowing ratio. This leads to a higher jet core flow at the cooling hole exit and lower cooling effectiveness at the flat plate surface compared with a smooth cooling hole. The minimum area-averaged film-cooling performance showed a 58% reduction compared to a smooth hole in the case of the highest blowing ratio (M=3.0) and the largest surface roughness height. In addition, the time-space evaluation of the velocity fluctuations showed greater flow unsteadiness and increased wavy patterns within the cooling hole in the case of rough holes.

Original languageEnglish
Article number107082
JournalAerospace Science and Technology
Publication statusPublished - 2021 Dec


  • Gas turbine
  • Laidback fan-shaped hole
  • Large eddy simulation
  • Sand-grain roughness
  • Surface Roughness

ASJC Scopus subject areas

  • Aerospace Engineering


Dive into the research topics of 'Surface roughness effects on film-cooling effectiveness in a fan-shaped cooling hole'. Together they form a unique fingerprint.

Cite this