Coupled oscillations of flow along a perforated plate

Abstract

Turbulent shear flow past a perforated plate bounded by a closed cavity can give rise to highly coherent oscillations, which have a wavelength of the order of the plate length. The present investigation focuses on the coupling between unsteady events on either side of the plate when the oscillations are self-sustaining. A cinema technique of high-image-density particle image velocimetry, which provides a space-time representation of the unsteadiness at a large number of locations over entire planes, is employed to characterize the distinctively different patterns of flow structure on the back ͑low-speed͒ side of the plate relative to those on the front ͑high-speed͒ side. Global cross-spectral analysis leads to patterns of spectral peaks and phase variations, along and across the plate. This approach, along with complementary types of image evaluation, delineates the physics of the oscillations, which include downstream propagating disturbances along either side of the plate and a coherent region of unsteadiness at its trailing-edge. On the backside of the plate, a sequence of upstream-oriented, pulsatile jets are formed, and the time-averaged flow pattern is a counterflow wall jet.

Hydrodynamic instability and sound amplification over a perforated plate backed by a cavity

“…The amplitude and phase of v approximately remain the same across the plate, as shown in Fig. 4(c,d), which are in agreement with experimental results of [22]. It can also be found in Fig.…”

“…A second type large-scale instability over a perforated plate backed by a single cavity, where the instability wavelength is of the order of the total plate length, has also been reported. It was first observed in experiments in water channels that long-wavelength instability along perforated and slotted plates can occur without acoustic or gravity wave resonance [21][22][23]. The coupling of this large-scale instability with the acoustic [24] and gravity wave [25] resonance of the bounding cavities was also investigated.…”

Flow–acoustic resonance in a cavity covered by a perforated plate

“…A spatially growing wave appears along the perforated plate. The amplitude and phase of v approximately remain the same across the plate, as shown in figure 3(c,d), which is in agreement with the previous experiment where the phase variations on both sides of the perforated plate have been measured (Celik & Rockwell 2004). It can also be found in figure 3(c) that the growth always happens in the small holes, suggesting that the large-scale spatially growing wave is linked to the small-scale KH instability of the shear flow over the holes.…”

Effect of transverse perforations on fluid loading on a long, slender plate at zero incidence

“…Turbulent flow over a perforated plate can generate substantial levels of radiated acoustic noise and vibrations (Howe, 1990(Howe, , 1997aCelik and Rockwell, 2004) where sources corresponding to the individual perforations can be modeled as either monopoles (Ffowcs Williams, 1972) or linearly distributed vortex sheets, depending on the relative dimensions of the perforations relative to the displacement thickness of the boundary layer (Howe, 1997a). Coupling of the flow oscillations with acoustic pressure pulsations has received significant attention (Howe, 1986(Howe, , 1997bMalavasi and Bossi, 2012;Oshkai and Velikorodny, 2013;Parker, 1966;Parker and Welsh, 1983;Welsh et al, 1984).…”