A modelling of large eddies in an axisymmetric jet

Abstract

Crow & Champagne (1971), Bechert & Pfizenmaier (1975) and Moore (1977) have observed that the growth, mixing and noise production of jet flows are sensitive to harmonic forcing. This paper describes an attempt to model numerically certain features of these flows. The model flow is restricted to be axisymmetric and is consequently unrepresentative of the detailed structure in a real jet. Nonetheless, it is found that reasonable qualitative agreement exists between the results of the model and experiments as far as the large eddies are concerned. This suggests that a substantial part of the large-scale structure in a jet is essentially axisymmetric. Harmonic excitation is also applied to the model jet and the changes in frequency and amplitude of the excitation cause distinct changes in the wavelengths of the jet eddies. This resulting large-eddy behaviour is consistent with many features of the nonlinear behaviour observed experimentally in forced jets.