Acoustic and flow fields of an excited high Reynolds number axisymmetric supersonic jet

Abstract

An axisymmetric perfectly expanded Mach 1.3 jet, with a Reynolds number based on the nozzle exit diameter (ReD) of 1.1 × 106 and turbulent boundary layer at the nozzle exit, was excited using localized arc filament plasma actuators over a wide range of forcing Strouhal numbers (StDF). Eight actuators distributed azimuthally were used to excite azimuthal modes m = 0–3. Far-field acoustic, flow velocity and irrotational near-field pressure were probed with a three-fold objective: (i) to investigate the broadband far-field noise amplification reported in the literature at lower speeds and ReD using excitation of m = 0 at low StDF; (ii) to explore broadband far-field noise suppression using excitation of m = 3 at higher StDF; and (iii) to shed some light on the connection between the flow field and the far-field noise. The broadband far-field noise amplification observed is not as extensive in amplitude or frequency range, but still sufficiently large to be of concern in practical applications. Broadband far-field noise suppression of 4–5 dB at 30° polar angle peak frequency, resulting in approximately 2 dB attenuation in the overall sound pressure level, is achieved with excitation of m = 3 at StDF ~ 0.9. Some of the noteworthy observations and inferences are (a) there is a strong correlation between the far-field broadband noise amplification and the turbulence amplification; (b) far-field noise suppression is achieved when the jet is forced with the maximum jet initial growth rate frequency thus limiting significant dynamics of structures to a shorter region close to the nozzle exit; (c) structure breakdown and dynamic interaction seem to be the dominant source of noise; and (d) coherent structures dominate the forced jet over a wide range of StDF (up to ~ 1.31) with the largest and most organized structures observed around the jet preferred mode StDF.

Separation Control with Nanosecond-Pulse-Driven Dielectric Barrier Discharge Plasma Actuators

“…This work presents further evidence that the thermal mechanism observed in LAFPAs 13,15 and also presented by Roupassov et al 9 can be employed for separation control with a DBD load. This may permit the use of DBD plasma actuators for high speed flow control applications (Re>1x10 6 , U ∞ >100 m/s) although the freestream conditions presented here must be extended to verify this hypothesis.…”

“…In the case of LAFPAs, these waves propagate spherically as if generated by point source. 15 Similar, but substantially more complex behavior has been confirmed for NS-DBD plasma using phase-averaged schlieren imaging. approximately proportional to the density gradient in the positive y-direction.…”

“…Indeed, compression waves generated in quiescent air by localized heating of the near surface gas layer have been detected in both modeling and experiment. 9,12 This scenario is well-established for localized arc filament plasma actuators (LAFPAs) that are effective for controlling high Reynolds number and high-speed (subsonic/supersonic, cold/hot) jets in both experiments [13][14][15] and computations. 16 Like many flow control studies, the main idea of the LAFPA approach is to force the flow at a frequency approaching one of the flow instabilities, thereby triggering subsequent growth of seeded perturbation and their rollup into flow structures.…”

“…This is consistent with the high amplitude characteristics of LAFPAs. 13,15 The C L curve for the controlled cases is shown in Figure 26 40 but also employs the measured data away from the airfoil leading edge.…”

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

“…Figure 3(b) shows new results comparing computation with experimental farfield sound pressure levels (SPLs) (Samimy et al 2010), using the Ffowcs-Williams and Hawkings (FWH) method (Ffowcs-Williams & Hawkings 1969), at 30…”