Abstract
An experimental study of active control of the vortex shedding narrowband tonal noise radiated near the blunt trailing edge of a flat plate with elliptical leading edge was performed using three different configurations of the single dielectric barrier discharge (DBD) plasma actuators. These devices can produce electric winds in the tangential, downward and spanwise directions, respectively, near the blunt trailing edge. Acoustics and flow measurements were carried out simultaneously at Reynolds numbers between 0.75 × 105 and 4 × 105, based on the flat plate chord length, inside an aeroacoustic facility. The range of alternating-current (AC) input voltages to these plasma actuators was relatively low at < 5 kV. The “tangential” plasma actuator is not very effective in the suppression of vortex shedding tonal noise (maximum 1–2 dB reduction), although the spatial distribution of the wake coherent modes calculated from the proper orthogonal decomposition becomes more compact than that produced by the baseline plasma off case, resulting in a shift of the tone frequency to a higher value. The “downward” plasma actuator can suppress the vortex shedding noise almost completely at the tone frequency (about 15 dB reduction at input voltage of 4.2 kV). The mechanism is related to the induced plasma jet acting as a virtual barrier to inhibit the interaction between the upper and lower separating shear layers, and to delay the formation of the vortex shedding. The “spanwise” plasma actuator, which can project array of streamwise vortices into the wake and compartmentalise the vortex shedding across the span, demonstrated a more superior tonal noise reduction capability at low input voltage (about 12 dB reduction at 3.0 kV). It is found that the plasma-induced jet magnitudes between 9 and 10% and 7% of the freestream velocity for the downward and spanwise plasma actuators, respectively, are already sufficient to achieve an effective reduction of the vortex shedding tonal noise.
Highlights
The unsteady flow structure behind a bluff body or blunt trailing edge has been studied extensively due to its importance in many engineering applications
This paper attempts to fill this gap by performing a simultaneous flow and acoustic study on the application of plasma actuators and their reduction of the high amplitude, narrowband vortex shedding tonal noise generated by a flat plate with blunt trailing edge
This paper investigates three dielectric barrier discharge (DBD) plasma actuator configurations, namely the tangential actuation (PA1), downward actuation (PA2) and spanwise actuation (PA3), and their effectiveness in the suppression of vortex shedding and tonal noise radiation from a flat plate with blunt trailing edge
Summary
The unsteady flow structure behind a bluff body or blunt trailing edge has been studied extensively due to its importance in many engineering applications. The separation of the free shear layer from the sharp corners of the blunt trailing edge, for example, can lead to formation of vortices that shed alternately from each side of the body These coherent vortices along with the unsteady velocity field will produce a force loading that increases the aerodynamic drag. CD drag coefficient that includes the mean CD(mean), and the fluctuating CD(rms) components f frequency, Hz f(input) H input frequency to the plasma actuators, kHz flat plate thickness, the bluntness, m l U u,v,w eigenvectors of the covariance matrix Cij mean flow velocity of the nozzle jet, msÀ1 velocity components in the streamwise, wall-normal and spanwise directions, respectively, msÀ1 x,y,z streamwise direction measuring from the blunt trailing edge, wall-normal direction and spanwise direction, respectively, m û, ṽ plasma-induced jet velocity in the x-direction and y-direction, respectively, msÀ1 urms, vrms root-mean-square of the velocity fluctuation in the streamwise and vertical directions, respectively, msÀ1 u∞.
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