A survey of the turbulence statistics of a model-scale installed jet at low and moderate mach numbers

Proenca, A. R., Lawrence, J. L.T. and Self, R. H. (2017) A survey of the turbulence statistics of a model-scale installed jet at low and moderate mach numbers. In 23rd AIAA/CEAS Aeroacoustics Conference, 2017. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2017-3705).

Abstract

In modern high-bypass ratio engine configurations, the exhausted jet is deflected and modified by the wing and high lift devices. The present paper reports a survey on a model-scale jet in the presence of a flat plate installed at two height (h) and two length (l) positions from the center of the nozzle. The aim of this work is to evaluate the one-point statistics of isolated and installed jets. Experimental data of the axial component of the velocity is acquired for a 1½” nozzle via hot-wire anemometry. The investigation is made for several jet velocities, ranging from acoustical Mach numbers 0.2 to 0.8. Mean velocity profile results show a slight acceleration of the jet in regions close to the plate. This effect is notorious for plate locations in which the jet wets the plate close to the nozzle exit. It also seems to have a weak velocity dependency. This acceleration of the jet is consistent with the conservation of mass and changes in the entrainment at that region. As a direct result of the local jet acceleration, locations close to the plate present lower levels of turbulence intensity. Other factor that may contribute to this effect is the break-down of the eddies at the rigid surface. Turbulence intensity profiles have also shown a spike immediately downstream of the trailing edge. This is possibly an effect of the boundary layer separation, or a wake-type of flow originated at the trailing edge. Results for low and higher-order statistics of the shear layer opposite to the plate are exactly the same as results measured for the isolated jet configuration. Boundary layer development along the plate in both streamwise and spanwise direction is presented. It is shown that, even though the present problem consists of a non-uniform flow interacting with a surface, boundary layer properties could be defined for close-coupled, long surfaces. Finally, the spectra information from hot-wire sensors are analysed and qualitatively compared to the spectra measured by near-field surface pressure transducers located streamwise along the plate. The power spectral density of the velocity signal has a -5/3 decay, which is not seen in the pressure spectra.

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Contributors

Author: A. R. Proenca

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