  The present work focuses on a specific bouncing behaviour as a particle
settling through a three-layer stratified fluid in the absence of neutral
buoyant position, which was firstly discovered by Abaid, N., Adalsteinsson D.,
Agyapong A. & McLaughlin, R.M. (2004) in salinity-induced stratification. Both
experiments and numerical simulations are carried out. In our experiments,
illuminated by a laser sheet on the central plane of the particle, its bouncing
behaviour is well captured. We find that the bouncing process starts after the
wake detaches from the particle. The PIV results show that an upward jet is
generated at the central axis behind the particle after the wake breaks. By
conducting a force decomposition procedure, we quantify the enhanced drag
caused by the buoyancy of the wake ($F_{sb}$) and the flow structure
($F_{sj}$). It is noted that $F_{sb}$ contributes primarily to the enhanced
drag at the early stage, which becomes less dominant after the detachment of
the wake. In contrast, $F_{sj}$ plays a pivotal role in reversing the
particle's motion. We conjecture that the jet flow is a necessary condition for
the occurrence of bouncing motion. Then, we examine the minimal velocities
(negative values when bounce occurs) of the particle by varying the lower
Reynolds number $Re_l$, the Froude number $Fr$ and the upper Reynolds number
$Re_u$ within the ranges $1 \leq Re_l\leq 125$, $115 \leq Re_u\leq 356$ and $2
\leq Fr\leq 7$. We find that the bouncing behaviour is primarily determined by
$Re_l$. In our experiments, the bouncing motion is found to occur below a
critical lower Reynolds number around $Re^ \ast _{l}=30$. In the numerical
simulations, the highest value for this critical number is $Re^ \ast
_{l}=46.2$, limited in the currently studied parametric ranges.
