Abstract
An experimental study of two efficient receptivity mechanisms of excitation of cross-flow (CF) instability modes is carried out in a boundary layer of a real airfoil section of a swept wing due to: (i) action of localized surface vibrations, and (ii) scattering of 2D freestream vortices on them. It is found that the two mechanisms lead to rather efficient excitation of CF-modes both at surface vibration frequency and at combination ‘vortex-vibration’ frequencies. First estimations of the corresponding localized receptivity coefficients are obtained. Direct comparison of the experimental amplification curves of the excited CF-modes with those calculated based on the linear stability theory (LST) has shown that the experimental data obtained at vibration frequency are in excellent agreement with the LST. At the same time, growth rates of the CF-modes excited at combination frequencies are found to be completely inconsistent with the LST. A possible explanation of this phenomenon via action of a new efficient distributed receptivity mechanism is suggested. This mechanism is associated with scattering of freestream vortices on rather high-amplitude CF-modes excited by surface vibrations.
Highlights
Direct comparison of the experimental amplification curves of the excited CFmodes with those calculated based on the linear stability theory (LST) has shown that the experimental data obtained at vibration frequency are in excellent agreement with the LST
The receptivity stage of excitation of boundary-layer instability modes by various external perturbations is the first stage of the laminar-turbulent transition process
This paper is devoted to the first quantitative experimental results of investigations of localized mechanisms of excitation of CF-instability modes in a boundary layer of a real swept airfoil
Summary
The receptivity stage of excitation of boundary-layer instability modes by various external perturbations is the first stage of the laminar-turbulent transition process. A number of experiments devoted to the investigation of various receptivity mechanisms has shown that excitation of cross-flow (CF) instability modes (stationary and nonstationary ones) due to: (i) action of localized surface nonuniformities (roughnesses and vibrations) [1] and (ii) scattering of freestream vortices on them [2, 3] are the most efficient ones.
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