2 research outputs found
Scalar mixing and entrainment in an axisymmetric jet subjected to external turbulence
The effect of zero-mean-flow external turbulence on the topology of the
scalar turbulent/turbulent interface (TTI) has been recently studied in
axisymmetric jets (Kohan & Gaskin, J. Fluid Mech., vol. 950, 2022, A32). The
present study aims to understand the process of turbulent entrainment into a
jet, as affected by background turbulence, using scalar statistics.
Planar-laser-induced fluorescence was employed to capture the orthogonal cross
sections of the jet at a fixed downstream station with varying background
turbulence intensities and length scales. The conditional scalar profiles
revealed that the thickness of the scalar TTI is greater than that of the
traditional turbulent/non-turbulent interface (TNTI), and the interfacial
thickness is an increasing function of the background turbulence intensity.
Although nibbling remains the primary entrainment mechanism in the far field,
increased occurrence of concentration 'holes' within the interfacial layer in
the presence of ambient turbulence suggests a more significant role of
large-scale engulfment in the turbulent/turbulent entrainment process. Enhanced
contribution of the area of detached jet patches (i.e. 'islands') to that of
the main jet is hypothesized to be evidence of intense detrainment events in
the background turbulence. This can potentially explain the reduced net
entrainment into the jet, which manifests as less negative values of scalar
skewness within the jet core