Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Numerical Simulation of the boundary layer laminar-turbulent transition caused by a small gap
Submission Author:
Felipe Oliveira Aguirre , SP
Co-Authors:
Felipe Oliveira Aguirre, Marlon Sproesser Mathias, Marcello Augusto Faraco de Medeiros
Presenter: Felipe Oliveira Aguirre
doi://10.26678/ABCM.COBEM2021.COB2021-0582
Abstract
Aerodynamic surfaces in aircraft often have imperfections that might influence the location of the transitionfrom a laminar to a turbulent flow and, therefore, impact the overall drag. Among such imperfections are small gaps,which have been observed to cause transition at an order of magnitude lower Reynolds number based on displacementthickness when compared to a smooth surface. The type of transition depends on the gap: more unstable gaps may causegreater oscillations and lead to a bypass transition; while more stable gaps may enhance Tollmien-Schlichting waves thatwill, then, lead to the transition. Previous studies by our group demonstrated that, contrary to smooth surfaces, gapsand cavities may become more unstable as the Mach number is increased due to Rossiter modes, causing the transitionto move further upstream at higher Mach numbers. In this work, we simulate a boundary layer on a flat plate with asmall rectangular gap. The free stream Mach number is 0.5 and the Reynolds number based on displacement thickness is 693 and 775 at the gap. The simulation is carried out by high fidelity 3D DNS. No artificial disturbance is used to forcethe transition, representing a quiet enviroment. At the time of this writing, the simulation is ongoing and is monitoredby several probes at different stream-wise positions. The amplitude of the span-wise velocity component at the probesdownstream to the gap is steadily growing, indicating an increasing tridimensionality of the flow. After the transientphase dissipates and a limit-cycle is reached, we intend to use the mean flow profiles to verify whether the flow hastransitioned to turbulence. A DNS that can be used to simulate the transition to turbulence caused by a gap is a powerfultool in gaining a better understanding of this complex phenomenon and can be used to better explain experimental results.
Keywords
Boundary Layer, Flow instability, transition to turbulence, open cavity, DNS
