High-resolution direct numerical simulation data of a turbulent plane jet at Reynolds numbers $ \textit{Re}_H= 10^4$ and $10^5$, based on the nozzle width, are employed to investigate the behaviour of the structure functions in the flow region with external intermittency. In the intermittent turbulent region, the conditional second-order longitudinal and transverse structure functions exhibit self-similar behaviour at small and intermediate scales. Moreover, as the order increases from the second to the sixth, the conditional higher even-order structure function profiles progressively deviate from self-similarity and the predictions of Kolmogorov’s universal equilibrium theory. The conditional third-order structure function only displays self-similarity within the small-scale dissipation range, albeit the range of self-similarity extends to progressively larger values of $r/\eta ^T$ for a higher Reynolds number, where $\eta ^T$ denotes conditional Kolmogorov length scale and $r$ is the separation distance. As the intermittency factor decreases, the unsteady term in the Kármán–Howarth equation becomes more significant, leading to a larger deviation from Kolmogorov’s $4/5$ law. The extrapolation results based on the empirical formula for the structure function $\langle \delta u^{\prime n}\rangle (r)$ indicate that the finite-Reynolds-number effect on the structure function may differ between the intermittent and fully turbulent regions. The structure functions in the intermittent region may follow the predictions of K41 theory, i.e. $\langle \delta u^{\prime n}\rangle (r) \sim r^{n/3}$, which is consistent with the results observed in the fully turbulent region. However, the realisation of Kolmogorov’s predictions is more difficult in the intermittent region than in the fully turbulent region and requires a much higher local Reynolds number. It is further found that the conditional third-order structure function profiles recover self-similarity at intermediate scales when the local Reynolds number exceeds $10^5$. These findings provide valuable insights into the understanding and modelling of mixing transition problems.

Ensemble-variational (EnVar) assimilation of wall-pressure measurements in direct numerical simulations of Mach 6 flow over a cone–flare is performed. The experimental data include pressure spectra and intensities from seven wall-mounted PCB sensors positioned upstream, within and downstream of the separation region induced by the compression corner. Assimilation of the first two sensors only, all upstream of separation, is insufficient to accurately predict the downstream flow. Assimilating all the sensor data is shown to be essential to correctly predict separation onset and the downstream wall-pressure data. Similar to the experiments, the assimilated flow features intense rope-like structures in the attached region. The simulations additionally predict a localised amplification of disturbances beneath the separation shock, where experimental data are not available. This amplification results from the interaction of the boundary-layer instability modes with the compression shock. The simulations also capture the sharp decrease in wall-pressure intensity across separation, and the amplification of low-frequency three-dimensional disturbances within the recirculation bubble. Additionally, the computations highlight the uncertainty in the post-separation predictions due to the low-frequency unsteadiness of the separation shock. Oscillations of the streamwise velocity modulate the boundary-layer thickness, which in turn introduces variability in disturbance amplification.

A neutrally buoyant rigid spheroid suspended in a wall-bounded plane Poiseuille flow undergoes cross-stream migration, driven by inertia. We examine theoretically the migration of a spheroid of aspect ratio $\kappa$ in the limit of small but finite particle Reynolds number (${\textit{Re}}_{\!p}$), and for small confinement ratios ($\lambda$), with the channel Reynolds number, ${\textit{Re}}_c = {\textit{Re}}_{\!p}/\lambda ^2$, assumed arbitrary; here, $\lambda =L/H$ with $L$ being the semimajor axis of the spheroid and $H$ denoting the separation between channel walls. For small $\lambda$, the asymptotic separation between the rotation-cum-orbital-drift and migration time scales implies that, to begin with, inertia rapidly drives the spheroid towards the tumbling orbit (orbit constant, $C=\infty$) with negligible migration; migration is subsequently driven by a time-averaged lift velocity, the average being over the orientations sampled in the inertially stabilized tumbling orbit. While spheroids with $\kappa \sim O(1)$ rotate with the Jeffery angular velocity to a very good approximation, deviations from Jeffery rotation, for both large and small $\kappa$, lead to a time-averaged inertial lift profile with equilibrium locations (zero crossings) that differ from the classical Segre–Silberberg predictions for a sphere. Beyond a threshold ${\textit{Re}}_c$, both slender spheroids and thin disks attain a steady orientation in the neighbourhood of the walls, and with increasing ${\textit{Re}}_c$, these rotation-arrested regions grow in extent, moving in towards the channel centreline. In contrast to spheres, but consistent with experiments, onset of rotation arrest causes the aforementioned equilibrium positions to move towards the centreline; further, for thin disks alone, the equilibrium positions themselves become rotation-arrested beyond a threshold ${\textit{Re}}_c$. The $\kappa$-dependence of the equilibrium positions can be leveraged towards developing passive shape-sorting protocols on microfluidic platforms.

Earthquakes and the destruction they wreak on communities and landscapes are regular features of both modern news output and historical accounts. Archaeology can add to our understanding of such disasters, demonstrated here in the discussion of architectural damage noted during recent excavations at Panaztepe, an Early Bronze Age settlement in Western Anatolia. Distinct destruction horizons illustrate the primary and secondary impacts of two earthquakes during the third millennium BC: the first was followed by reconstruction and adaptation, the second by abandonment. By focusing on evidence of seismic activity, the authors examine the resilience of communities inhabiting this geologically fragile region.