This thesis investigates fluid flow near solid surfaces, focusing on the invisible boundaries between smooth and turbulent regions. Using high-precision laser-based measurement tools developed during the study, it captures small-scale flow details and introduces a new method to identify these boundaries. The research examines flow in two scenarios: between parallel flat walls and along a single flat surface. By enhancing understanding of how flow transitions across these boundaries, the work improves turbulence prediction, with practical applications in aircraft design, transportation, and environmental modelling.