Effects of wall vibrations on channel flows

The effect of surface vibrations on the pressure-gradient-driven flows in channels has been studied. analysis considered monochromatic waves and laminar flows. effectiveness was gauged by determining pressure gradient correction required to maintain same flow rate as without vibrations. Waves propagating upstream always increase losses. Flow response downstream is more complex changes a function Reynolds number. Such reduce losses if number $Re <\ \sim\!\!100$ , but these must be sufficiently fast for larger Re values. In general, supercritical waves, i.e. faster than reference flow, with magnitude reduction increasing monotonically wave phase speed wavenumber. need an external eliminated short are used. Generally, subcritical velocities similar This somewhat irregularly wavenumber forming local maxima minima. These can only becomes large enough. It shown that very small amplitudes matching natural frequencies produce significant