An experimental study was conducted to investigate surface heat transfer and boundary layer development associated with flow over a flat test surface covered with two roughness scales. Two-scale roughness was used because in-service aeroengines commonly display larger roughness concentrated at the leading edge with smaller roughness distributed downstream. The first scale, covering up to the first 5 cm of the test surface, was in the form of a sandpaper strip, an aluminum strip, or a cylinder. The second roughness scale covered the remainder of the test surface (2 m) in the form of sandpaper or a smooth surface. In part 1, the surface heat transfer results are examined. Even though the roughness scales were hydraulically smooth, they induced significantly earlier transition onset, with the two-dimensional roughness causing earlier transition than three-dimensional roughness. All of the rough/smooth cases unexpectedly triggered earlier transition than rough/rough cases. This indicated that the scale of the step-change at the joint between two roughness scales was predominant over the downstream roughness on inducing early transition. Reducing the overall height of the step change was shown to have a greater effect on transition than the specific geometry of the roughness scale.
- International Gas Turbine Institute
Effect of Two-Scale Roughness on Boundary Layer Transition Over a Heated Flat Plate: Part 1 — Surface Heat Transfer
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Pinson, MW, & Wang, T. "Effect of Two-Scale Roughness on Boundary Layer Transition Over a Heated Flat Plate: Part 1 — Surface Heat Transfer." Proceedings of the ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration. Indianapolis, Indiana, USA. June 7–10, 1999. V003T01A038. ASME. https://doi.org/10.1115/99-GT-158
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