The main objective of this experimental investigation was to measure the convective heat transfer coefficient of impingement for different target wall roughness geometries of an airfoil leading edge, for jet to wall spacings and exit flow schemes. Available data in open literature are mostly for impingement on flat or curved smooth surfaces. This investigation covered two relatively new features in blade leading-edge cooling concepts namely the curved as well as roughened target surfaces. Experimental results are presented for four test sections representing the leading-edge cooling cavity with cross-over jets impinging on 1) a smooth wall, 2) a wall with high surface roughness, 3) a wall roughened with conical bumps, and 4) a wall roughened with tapered radial ribs. The tests were run for two supply and three exit flow arrangements and a range of jet Reynolds numbers. The major conclusions of this study were: a) there is a heat transfer enhancement benefit in roughening the target surface, b) while the surface roughness increases the impingement heat transfer coefficient, the driving factor in heat transfer enhancement is the increase in surface area, c) amongst the four tested surface geometries the conical bumps produced the highest heat transfer enhancement.
Influence of surface roughness and porosity of inclusion in water droplet on heat transfer enhancement