No abstract

No abstract

The acoustic analogy provides a general framework for predicting broadband jet noise. The accuracy of the noise predictions are strongly dependent on the second-and fourth-order integral time and length scales of the turbulence quantities in the jet. Two low-order models for the second-and fourth-order integral length scales are examined. The low-order models are defined by locally isotropic scales estimated from 2D particle image velocimetry measurements. These measurements are of screeching underexpanded unheated round jets issuing from a purely converging nozzle at conditions, which corresponds to ideally expanded Mach numbers of 1.45 and 1.59. The jets are dominated by the helical C instability screech mode, which is associated with large-scale coherent periodic fluctuations. These fluctuations are filtered using a proper orthogonal decomposition method to assess low-order models that approximate the length scales associated with the broadband noise mechanisms. The length scale model parameters are shown to be insensitive for the two Mach numbers considered. The root-mean-square error associated with the low-order models indicates that either is sufficient for approximating the integral length scales required to model equivalent sources of broadband jet noise.

No abstract

This paper investigates the broadband shock-associated noise (BBSAN) radiated from supersonic jets at the root source level. The sources are modelled according to an acoustic analogy. The acoustic analogy model is informed by high spatial resolution 2D-2C particle image velocimetry (PIV) data and solutions to the Reynolds-Averaged Navier-Stokes (RANS) equations for the reconstruction of the equivalent BBSAN sources. The measurements are of screeching underexpanded jets issuing from a purely converging nozzle at ideally expanded Mach numbers of 1.45 and 1.59. The jet conditions are simulated using a RANS solver with a k − ω shear stress transport turbulence model. The RANS scales are modelled using formulations of a two-time scale model based on the turbulence dissipation and large eddy convection time. The large eddy convection based scale is recommended as a replacement for the standard turbulence dissipation scale in low-order BBSAN models. The equivalent BBSAN sources are reconstructed from the PIV measurements and RANS solutions at the peak Strouhal number. The equivalent BBSAN sources extracted from the PIV and RANS data are shown to have favourable agreement.