Imprint of Vortical Structures on the Near-Field Pressure of a Turbulent Jet

Abstract

The distributions of turbulent scales in a Mach 0.9 isothermal round jet are investigated for the purpose of developing linear surface-based models for the noise source that can be informed by a Reynolds-averaged Navier Stokes (RANS) solution of the flow field. The jet is calculated by large-eddy simulation (LES) which enables the computation of two-point space-time correlations throughout the jet and its near acoustic field. Time, length, and convective-velocity scales are examined on the surface of peak Reynolds stress (SPS), representing the location of the most energetic eddies, and on a "radiator surface" at the boundary between the rotational and irrotational fields. The nature of the space-time correlations is different for axial velocity fluctuations and pressure fluctuations. Velocity-based correlations appear to capture localized turbulent events, while pressure-based correlations appear dominated by the interaction of large eddies with the surrounding potential flow. The correlation length scales are larger on the radiator surface than on the SPS thus indicating that small-scale eddies do not make a significant imprint on the radiator surface. The scales associated with an emulated RANS solution of the flow are compared to the LES-based scales. Simple relationships are inferred that may aid the development of rapid predictive models.

Noise predictions of a Mach 0.9 round jet using tailored adjoint Green’s functions

“…for instance. More details and results of the jet LES can be found in previous 115 studies [1,14,17].…”

“…(1) 11 is the longitudinal integral length scale computed from R u ′ z u ′ z as defined in [28], then l s ≈ L 11 has been computed along the jet lip-line from the large-eddy simulation [1], and serves as a reference for the calibration of equation (23). Two evaluations of formula (23) along the jet lipline are presented in figure 1 for which proportionality constants of 1.0 and 2.0 are used respectively.…”

Intermittency and Stochastic Modeling of Low- and High-Reynolds-Number Compressible Jets

“…Signals are recorded at a sampling frequency allowing spectra to be computed up to = 6. 4. More details about the numerical simulations are reported in [22][23][24].…”

“…There is a large body of literature that seeks to clarify the nature of pressure events that dominate both fields. The pressure fluctuations in the near field are influenced by vortical structures generated in the jet shear layer (see [2,3] and the recent paper by Andres, Papmoschou and Bogey [4]) and, according to the typical statistics of vorticity in turbulence, they exhibit a non Gaussian intermittent behaviour. In a statistical sense, intermittency is intended as a sequence of quiescent phases interrupted by active events inducing a non-stationary distribution of energy in time.…”

Effects of the upstream-propagating guided jet waves on the mixing layers of Mach number 0.9 free jets

“…Results obtained for the four jets, including their nozzle-exit mean and r.m.s. velocity profiles, can be found in several previous papers [1,20,28,29].…”