Cavity Resonance Suppression Using Fluidic Spoilers

Abstract

This paper examines experimentally the use of a fluidic spoiler to suppress the resonance within a partially closed cylindrical cavity subject to a grazing flow. The relative movement of aircraft and high-speed land-based vehicles through air often results in structural cavities in these vehicles being subject to shear-layer-driven resonance. This can lead to high-amplitude pressure fluctuations within the cavity volume, causing damage to stores or equipment found within landing-gear wheel or weapon bays, for example, or else significant discomfort to the passengers of cars or trains. This large-scale buffeting can also cause vehicle stability problems and can increase drag. This work presents a novel method, in which passive flow control consisting of an upstream fluidic spoiler is used to redirect the upstream flow so that the cavity orifice is shielded. As a result, the grazing flow can no longer detach from the upstream leading edge of the cavity, and thus, vortex shedding is suppressed. The scope of the study includes an examination of higherorder azimuthal acoustic modes excited in the cylindrical cavity: modes which have received little attention in the literature, but which can be readily excited for many flow configurations for partially covered cavities.

Investigation on spatial distribution of acoustic resonance in annular cavity: Frequency and intensity

“…It can be stated that, in resonant cavity noise induced by the air flow, the depth mode is essential. That is different from the result from numerical simulation WEM, 23 in which the independent azimuthal/radial existed. The reason is that the oscillation in the cavity shear layer is a complex phenomenon and could not be simply simulated by a monopole noise source at the cavity opening.…”

“…21,35 j is the convection velocity of the cavity shear layer normalized by the freestream velocity and is typically valued as 0.5. 23 M is the order of Rossiter mode. The experimental PSD superimposed with the Rossiter formula (equation (37)) and the first-order depth mode (equation (34)) is shown in Figure 6.…”

“…Equation (34) is similar, but not exactly consistent with previously developed. Some literatures 20,23 take the open end as an antinode rather than pressure node. That means that the depth mode number j must be even rather than odd.…”

“…To diagnose whether coupling is possible between a given fluid dynamic instability and acoustic resonance, Rona 20 developed an analytical method from classical linear acoustic theory to determine the acoustic resonant frequencies and mode shapes of rectangular and cylindrical cavities. Bennett and co-workers [21][22][23] used the wave expansion method (WEM) to characterize the cavity resonance in the landing gear bay and a partially closed cylindrical cavity, respectively, in the absence of flow. By locating a numerical monopole volume source at the opening, the frequencies of their cavity modes were acquired, as well as the pressure field of each mode.…”

An Experimental Characterization on the Acoustic Performance of Forward/Rearward Retraction of a Nose Landing Gear

“…To predict frequencies or the Strouhal number of the oscillation, Rossiter [7] proposed a semiempirical equation based on the experimental data, which has been widely used in the subsequent cavity noise studies [8][9][10][11]. As for the noise reduction, a few ideas have been proposed either for the landing gear or for the bay, such as the fairings [12,13], plasma [14,15], mesh [16,17], air curtain [18][19][20][21], and upstream mass flow injection [22][23][24]. Regardless of their technology readiness level (TRL), all of them have been confirmed to be able to achieve noise suppression.…”