  Recent research indicates that low-inertia viscoelastic channel flow
experiences supercritical non-normal mode elastic instability from laminar to
sustained chaotic flow due to finite-size perturbations. The challenge of this
study is to elucidate a realization of such a pathway when the intensity of the
elastic wave is too low to amplify velocity fluctuations above the instability
onset. The study identifies two subregions in the transition flow regime at
Weissenberg number $Wi>Wi_c$, the instability onset. In the lower subregion at
$Wi_c\leq Wi\leq 300$, we discover periodic spikes in the streamwise velocity
time series $u(t)$ that appear in the chaotic power spectrum as low-frequency,
high-intensity peaks resembling stochastic resonance (SR). In contrast, the
spanwise velocity power spectrum, $E_w$, remains flat with low-intensity,
noisy, and broad elastic wave peaks. The spikes significantly distort the
probability density function of $u$, initiating and amplifying random streaks
and wall-normal vorticity fluctuations. The SR appearance is similar to
dynamical systems where chaotic attractor and limit cycle interact with
external white noise. This similarity is confirmed by presenting a phase
portrait in two subregions of the transition regime. In the upper subregion at
$Wi>400$ the periodic spikes disappear and $E_w$ becomes chaotic with a large
intensity elastic wave sufficient to self-organize and synchronize the streaks
into cycles and to amplify the wall normal vorticity according to a recently
proposed mechanism.
