外部湍流作用下轴对称射流中的标量混合与卷挟

A DNS Study of entrainment in an axisymmetric turbulent jet as an episodic process

This investigation is based on a DNS of a steady self-preserving incompressible axisymmetric turbulent jet at a Reynolds number of 2400. The DNS data enable accurate maps of the outer irrotational flow field, and also the vorticity field in the turbulent core of the jet. It is found necessary to define two separate boundaries of the jet. The first is an inner boundary (turbulent/nonturbulent, T/NT), from where vorticity rises steeply towards to the core. The second is an outer rotational/irrotational boundary, beyond which the flow may be considered irrotational. The velocity field beyond the …

水面波在入水过程中改变空气卷入

Water entry of small hydrophobic spheres on an axisymmetric wavefield

研究球体撞击带表面波的水面时空气卷入情况，通过分析不同参数下形成的空腔，发现局部界面变形受飞溅幕几何调制影响空气卷入，证明波影响由局部波斜率描述，结合韦伯数和邦德数建立预测框架。

Entrainment into particle-laden turbulent plumes

We use laboratory experiments to investigate the entrainment of ambient fluid into an axisymmetric turbulent plume that contains dense particles with a settling velocity that is considerably smaller than the plume velocity. We consider the effect of particle size, particle concentration, and the orientation of the plume buoyancy flux - either in the same or opposite direction to the particle buoyancy flux. When the plume buoyancy flux is in the opposite direction to the particle buoyancy flux, entrainment into the plume increases by up to 40%. The rate of entrainment increases linearly with th…

Unified description of turbulent entrainment

We present a mathematical description of turbulent entrainment that is applicable to free shear problems that evolve in space, time or both. Defining the global entrainment velocity $\overline V_g$ to be the fluid motion across an isosurface of an averaged scalar, we find that for a slender flow, $\overline V_g=\overline u_ζ- \overline{D}h_t/\overline{D}t$, where $\overline D/\overline D t$ is the material derivative of the average flowfield and $\overline u_ζ$ is the average velocity perpendicular to the flow direction across the interface located at $ζ=h_t$. The description is shown to repro…

The influence of freestream turbulence on the near-field growth of a turbulent cylinder wake: turbulent entrainment and wake meandering

The effect of freestream turbulence on the spreading of the near wake of a circular cylinder is investigated through particle image velocimetry (PIV) data. Different ``flavours'' of freestream turbulence, in which the turbulence intensity and integral length scale are independently varied, are subjected to the cylinder. The time-averaged spreading of the near wake is decoupled into the growth through entrainment and the envelope of the spatial extent of the instantaneous wake due to wake ``meandering'', induced by the presence of large-scale coherent structures, i.e. the von Karman vortex stre…

Turbulent transport and entrainment in jets and plumes: a DNS study

We present a new DNS data set for a statistically axisymmetric turbulent jet, plume and forced plume in a domain of size $40 r_0 \times 40 r_0 \times 60 r_0$, where $r_0$ is the source diameter. The data set provides evidence of the validity of the Priestley and Ball entrainment model in unstratified environments (excluding the region near the source), which is corroborated further by the Wang and Law and Ezzamel \emph{et al.} experimental data sets, the latter being corrected for a small but influential co-flow that affected the statistics. We show that the turbulence in the core region of th…