Abstract
This work presents a detailed study of the turbulence flow statistics of a jet mounted with its axis parallel to a rigid flat plate. Hot-wire constant temperature anemometry has been used to measure the single-point and two-point statistics of the axial velocity component at several locations within the jet flow field. Results show that the jet mean flow near the plate surface is subjected to a local acceleration and redirection due to a Coandă-type effect. The propagation of these effects downstream of the plate trailing edge is strongly dependent on the plate position. Regarding the velocity fluctuations, the mean turbulence intensity levels are seen to decrease as the radial distance between the jet and surface decreases. Analysis of the single-point power spectral density data on the shear layer close to the plate shows that the reduction in magnitude of the low-frequency content of the energy spectrum is responsible for the decrease in turbulence intensity. Additionally, the characteristic time and length scales computed from two-point measurements reduce as the plate is mounted closer to the jet centre-line. The axial eddy convection velocity is seen to increase in the region of high turbulent kinetic energy in the shear layer adjacent to the surface. Empirical models for turbulence characteristic scales and eddy convection velocity are presented. These findings suggest that both the amplitude and distribution of the jet mixing noise sources are affected when closely installed next to a surface. This paper is a continuation of a recent investigation on the turbulence statistics of isolated jets presented in Proença (Exp Fluids 60(4):63, 2019).Graphic abstract
Highlights
Modern ultra-high-bypass ratio (UHBR) turbofans are expected to be installed in a close-coupled position underneath the wings of commercial aircraft
The cross power spectral density (CPSD) was computed except the averaged fast Fourier transform (FFT) calculated for the first probe was multiplied by the complex conjugate of the FFT obtained by the second probe
This paper has presented an experimental investigation into the turbulence statistics of both isolated and installed flatplate jets
Summary
Modern ultra-high-bypass ratio (UHBR) turbofans are expected to be installed in a close-coupled position underneath the wings of commercial aircraft. Jet installation effects for relatively simple flat plate surface geometries and single stream jet flows are reasonably well understood and various jet–surface interaction noise models have been successfully developed (Lyu et al 2017; Vera 2018; Bychkov and Faranosov 2018; Dawson et al 2020). These models incorporate three key assumptions: (1) the jet remains axisymmetric below the surface, (2) the surface is located outside of the jet’s rotational hydrodynamic field, and (3) the jet turbulent field is not modified by the surface.
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