Laminar separation bubble dynamics and its effects on thin airfoil performance during pitching-up motion

This article reports an investigation into dynamic characteristics of the laminar separation bubbles (LSBs) associated with aerodynamic loads unsteadiness of a cambered thin airfoil in pitching-up motions at low Reynolds number flows. Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations were conducted for a 4%c cambered thin airfoil at Reynolds number of 30,000 and 60,000. The airfoil pitches up from 0 degrees to 25 degrees angles of attack at dimensionless pitch rate alpha of 0.0398 and 0.0199. The k - omega SST gamma - (R) over tildee(theta t) turbulence transition model was used to account for the effect of transition on LSBs' development. The LSBs are shown to evolve in their shape and size during the pitching motion. The influence of the LSBs on the airfoil upper surface during pitching motion continues to a higher incidence in comparison with that under static conditions before developing into a fully detached flow. Vortex merging is observed in the rear part of the LSBs in the turbulent portion for a Reynolds number of 30,000. At Reynolds number 60,000, the changing of the LSB length during pitching-up motion is similar to that of steady cases, except a delayed transition is observed as incidence increases. The results show further insight into the dynamic characteristics of the LSBs and their relation to the aerodynamic performance of the airfoil.

Automated summary

This article investigates the dynamic characteristics of laminar separation bubbles associated with aerodynamic loads unsteadiness of a cambered thin airfoil during pitching-up motions at low Reynolds number flows. The study reveals that the shape and size of the separation bubbles evolve during pitching motion, affecting the airfoil's upper surface and eventually leading to a fully detached flow. Vortex merging is observed in the rear part of the turbulent separation bubbles at Reynolds number 30,000, with a delayed transition observed as incidence increases at Reynolds number 60,000.