Abstract
This paper describes a systematic and comprehensive hot-wire investigation into the turbulent statistics of low-, moderate- and high-speed subsonic jets. Experiments were performed to obtain the one-point and two-point statistics of a single-stream, unheated jet turbulence field over a broad region of the jet plume. Results show that hot-wires can be used to measure both the one-point and two-point statistics of the high turbulence intensity, noise-producing regions of unheated, compressible, subsonic jets. For the two-point measurements, probe pairings are performed over the three orthogonal axes. Analysis of the experimental data reveals four main conclusions: (1) both the statistical and joint moments of the turbulence scale well with the local jet shear layer half-width; (2) a simple relationship exists between the statistics of the velocity fluctuations and the square of the velocity fluctuations; (3) a simple relationship exists between the longitudinal and transverse length-scales, and (4) a semi-empirical model has been developed to predict the cross-correlation coefficients, power spectral density, frequency-dependent length-scales and coherence decay of the turbulent velocity field. From the second and third conclusions, it is shown that, in the locations near an eddy’s centre of rotation (i.e. the midpoint of the jet shear layer), the turbulence statistics can be described as quasi-homogeneous and quasi-frozen. The joint statistical moments, therefore, can be inferred simply from single-point tests. These results will help to develop models for predicting jet mixing noise, highlighting the situations in which the simplifying assumptions are inadequate.Graphical abstract
Highlights
Aircraft noise has been recognised as an issue since commercial airliners were powered by turbojet engines in the late 1940s
Note that the spreading rate, is constant throughout the jet. This leads to the conclusion that two different shear layer growth rates exist: one ranging from the nozzle exit to the end of the jet potential core, and another from the end of the potential
The fact that the shear layer half-width does not grow at the same rate in the initial and transitional regions suggests that the characteristic large scales of the jet have different growth rates
Summary
Aircraft noise has been recognised as an issue since commercial airliners were powered by turbojet engines in the late 1940s. The RANS solutions can be supplemented with model-scale experimental data to provide the stationary statistics of the jet noise source region. These data can be used to validate and develop new LES and DNS methods. Approximate scaling laws for the properties used to model the jet mixing noise source are presented These models extend other databases in the literature (Harper-Bourne 2003; Kerhervé et al 2006; Morris and Zaman 2010b) by showing the effects of jet exit velocity and axial location, the non-evenness of the joint moment functions, and coherence decay for different probe separation directions.
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