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COBEM 2021
26th International Congress of Mechanical Engineering
EXPERIMENTAL STUDY OF THE TRANSIENT RESPONSE OF A LAMINAR SEPARATION BUBBLE
Submission Author:
omar elias horna pinedo , RJ , Peru
Co-Authors:
omar elias horna pinedo, Pedro Bruno Pereira Panisset, Igor Braga de Paula
Presenter: omar elias horna pinedo
doi://10.26678/ABCM.COBEM2021.COB2021-2265
Abstract
This work investigates the transient response of a laminar separation bubble (LSB) subjected to controlled periodic disturbances under different adverse pressure gradients, the periodic wake-LSB interaction is usually found in cascades of turbine blades that operate at low Reynolds numbers, which are present in aircraft engines and gas turbines. The wake-LSB interaction is associated with the generation of aero acoustic noise, mechanical vibrations, increased drag and consequently performance loss. Given the complexity of the involved phenomena many features of wake-LSB interaction are not yet well understood. In addition, such a problem is difficult to be reproduced accurately by using turbulence models in numerical simulations. To shed some light onto the description of the wake-LSB interaction, a series of experiments were performed in a low turbulence intensity water channel. The laminar separation bubble was formed on a flat plate and an adverse pressure gradient was induced by a false wall. This wall created a convergent-divergent channel, and the bubble was formed on the region of adverse pressure gradient. Tollmien-Schlichting waves were excited in the boundary layer with a vibrating ribbon. The disturbance source was located upstream of the LSB formation region. Velocity fields were acquired using the time-resolved two-dimensional particle image velocimetry technique. The data analysis was carried out in the light of hydrodynamic stability theory. Results suggest that separation of the boundary layer is weakly dependent of flow dynamics downstream from the separation location. Seemingly, the instability mechanism which governs the evolution of the LSB does not change significantly during the transitory regeneration process. The results contribute to characterize the dynamics of the LSB in transitory regime and offer original information about the phenomenon.
Keywords
Laminar separation bubble, Instability Hydrodynamics, Particle image velocimetry
