Influence of Surface Roughness on the Aerodynamic Performances of a Transonic Axial Compressor under Varying Fighter Operational Altitudes

This study investigates the aerodynamic effects of blade surface roughness under varying altitude conditions relevant to high-altitude operation of military aircraft engines. To analyze the flow behavior and performance variations induced by surface roughness, a three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulation was conducted using NASA Rotor 67 as the base geometry. The commercial CFD software ANSYS CFX was employed, and grid independence was ensured through the Grid Convergence Index (GCI) method. To capture the transition-sensitive boundary layer behavior, the Shear Stress Transport (SST) Gamma-Theta transition turbulence model was applied. In order to represent flight conditions at various altitudes, a Reynolds Number Index (RNI) ranging from 0.3 to 1.0 was introduced to define the inlet flow regime. Three blade configurations with different surface roughness levels were modeled and compared. The analysis focused on changes in boundary layer characteristics, pressure ratio, and surge margin, highlighting the role of surface roughness under varying RNI conditions. Specifically, the boundary layer thickness, flow separation and reattachment locations, and the structure of shock waves were found to change depending on the surface roughness and RNI. Consequently, these changes led to variations in the aerodynamic performance and flow stability of the compressor.