A numerical investigation of the effect of micro vortex generators on film cooling

Film cooling is a key technology for protecting turbine blades from high thermal loads, directly influencing component durability, efficiency, and operational safety. Micro vortex generators (MVGs) offer a passive approach to enhance near-wall mixing, suppress cooling jet lift-off, and stabilize the coolant film, enabling more uniform and effective surface cooling. Despite their widespread use, the detailed influence of MVG geometry, axial placement, and tip angle on aerodynamic and thermal performance remains insufficiently understood. This study examines MVG height (1.5 to 5.5 mm), axial location (- 7.5 to + 7.5 mm relative to the cooling hole), and tip angle (tested within ± 5° of the baseline design) on film cooling over a stator blade. Aerodynamic and thermal effects are evaluated using turbulence kinetic energy (TKE), surface pressure distributions, temperature, film cooling effectiveness, enthalpy, stagnation density, cfRe (friction Reynolds number), Nusselt number, adiabatic film cooling effectiveness, and pressure-loss measurements. Heights below 1.5 mm fail to generate coherent vortices, acting mainly as surface roughness, while heights above 5.5 mm induce local separation, vortex breakdown, and increased pressure loss, reducing overall cooling. Heights of 2.5-4.0 mm produce stable streamwise vortices that enhance near-wall mixing and extend the cooling film's effectiveness. Axial placement strongly influences vortex-jet interactions: upstream positions allow premature vortex dissipation, while positions too close to the jet disrupt the core flow and induce instabilities. Our study shows that the best cooling occurs for MVGs placed 5-7.5 mm upstream, where vortices remain coherent, jet lift-off is suppressed, and lateral spreading is promoted. Tip angle variations within the tested range have minimal impact. Compared to the baseline case, the best MVG configuration improves surface cooling by 33-46% along the blade, with maximum gains near the root and mid-chord (X/D ≈ 0.05-0.2), highlighting the importance of well-designed MVGs for sustaining effective film cooling across critical blade regions.