Resolvent analysis of subsonic jets: trapped modes and resonance mechanisms

Trapped acoustic waves in the potential core of compressible jets have been shown to participate in a variety of resonance phenomena. To further investigate these, a global resolvent-based approach is considered and applied to a subsonic jet flow at Ma = 0.9. Compressible Reynolds-averaged Navier-Stokes equations, are coupled with a Spalart-Allmaras turbulence model. Nozzle geometry is explicitly taken into account through the use of an in-house finiteelement solver. Both modal and resolvent analyses confirm the existence of resonances for several frequencies. Trapped waves appear in the optimal forcing patterns for resonance frequencies and are further explored with a spatial Fourier transform, allowing the identification of the wavenumber of the resonating waves.