Home – Home – Jornals – Thermophysics and Aeromechanics 2002 number 3

The receptivity of a flat-plate boundary layer with a positive (adverse) pressure gradient with respect to 3D localized surface vibrations is investigated. The experiment was carried out under controlled disturbance conditions using two wave-train sources in the form of circular vibrators. The wave trains (consisting of Tollmien ( Schlichting waves) had been decomposed into oblique normal (harmonic in time and space) modes. The curves of growth of amplitudes and phases of the normal modes, obtained using the main source, were extrapolated to the position of its center by means of the corresponding curves obtained from the additional source located upstream. The shape and the amplitude of the surface vibrations were accurately measured by a noncontact optical system. After deep processing of the experimental data, the complex coefficients of the boundary layer receptivity to 3D surface vibrations were determined for four values of the disturbance frequency as functions of the spanwise wavenumber and the wave inclination angle to a flow direction. The calculations were performed within the framework of a linear receptivity theory for the experimental conditions under assumptions of a local flow parallelism. A good agreement between the experimental and theoretical receptivity coefficients is found. The flow under investigation is shown to be significantly more receptive to three-dimensional surface vibrations in comparison with two-dimensional ones. The receptivity amplitude increases with frequency, especially for the modes inclined at large angles to the flow direction. The positive pressure gradient is found to lead to a reduction of the vibration receptivity, especially for 3D modes.