DOI: 10.1515/tp-2026-0079 ISSN: 3052-878X
Implications of compressibility on the quiescent thermal and momentum cores
Justin E. Ka Ip Sun, Wei Shyy, Lin Fu Abstract
The quiescent thermal core (QTC), similar to the quiescent core in momentum transport, has recently been identified in compressible channel turbulence by Li et al. (
Phys. Rev. Fluids
, 2025, vol. 10, p. 064612) at bulk Mach number
Ma
b
= 3, and semilocal friction Reynolds number
R
e
τ
*
=
861
${\mathrm{R}\mathrm{e}}_{\tau }^{{\ast}}=861$
. We extend the analysis of the QTCs to a larger range of Mach numbers and Reynolds numbers, specifically to 0.8 ≤
Ma
b
≤ 3,
140
≤
R
e
τ
*
≤
783
$140\le {\mathrm{R}\mathrm{e}}_{\tau }^{{\ast}}\le 783$
, where the QTC can be readily identified, exhibiting “quiescent” characteristics. We found that the QTC is heavily influenced by Mach numbers and therefore compressibility effects, unlike the quiescent momentum core (QMC), which does not exhibit variations with respect to
Ma
b
. As
Ma
b
and therefore thermal effects increase, the QTC becomes noticeably thinner with a less stable core, as the intermittency and temperature variations increase. The QTCs are also much more continuous and are less dominated by anti-symmetrical frames, which can be attributed to the fundamental differences in the mechanism for momentum and thermal transport in the outer regions. We also investigated the QMCs within the same range, where we found significant large-scale coherence between the QMC and QTC interfaces within the same half of the channel. Conditional spanwise vorticity and linear coherence spectrum analysis reveal that the QTC is indirectly linked to the QMC via a secondary uniform momentum zone (UMZ), prompting further investigations into the QTCs and secondary UMZs in a Reynolds analogy-like manner. Coherence studies into the QMC and QTC interfaces on opposite halves of the channel also provide further insights into the physical mechanisms that span across the channel centreline. We also highlight some differences in the core identification methodology and Reynolds number effects in this study, especially compared to the incompressible regime. Nevertheless, this study showcases that thermal transport, regardless of flow parameters, exhibits a quiescent core akin to momentum transport, where we demonstrate its similarities and differences to momentum transport in compressible turbulent channel flows.