Turbulent pipe flow is still an essentially open area of research, boosted in the last two decades by considerable progress achieved on both the experimental and numerical frontiers, mainly related to the identification and characterization of coherent structures as basic building blocks of turbulence. It has been a challenging task, however, to detect and visualize these coherent states. We address, by means of stereoscopic particle image velocimetry, that issue with the help of a large diameter (6 in.) pipe loop, which allowed us to probe for coherent states at various moderate Reynolds numbers (5300 < Re < 29 000) of the single-phase Newtonian flow. Although these states have been observed at flow regimes around laminar–turbulent transition (Re $\approx$ 2300) and also at high Reynolds number pipe flow (Re $\approx$ 35 000), at moderate Reynolds numbers, their existence had not been observed yet by experiment. By conditionally averaging the flow fields with respect to their dominant azimuthal wavenumber of streamwise velocity streaks, we have been able to uncover the existence of ten well-defined coherent flow patterns. It turns out, as a remarkable phenomenon, that their occurrence probabilities and the total number of dominant modes do not essentially change as the Reynolds number is varied. Their occurrence probabilities are noted to be reasonably well described by a Poisson distribution, which suggests that low-speed streaks are created as a Poisson process on the pipe circular geometry.

Turbulent pipe flows exhibit organizational states (OSs) that are labeled by discrete azimuthal wave number modes and are reminiscent of the traveling wave solutions of low Reynolds number regimes. The discretized time evolution of the OSs, obtained through stereoscopic particle image velocimetry, is shown to be non-Markovian for data acquisition carried out at a structure-resolved sampling rate. In particular, properly defined time-correlation functions for the OS transitions are observed to decay as intriguing power laws, up to a large-eddy time horizon, beyond which they decorrelate at much faster rates. We are able to establish, relying upon a probabilistic description of the creation and annihilation of streamwise streaks, a lower-level Markovian model for the OS transitions, which reproduces their time-correlated behavior with meaningful accuracy. These findings indicate that the OSs are distributed along the pipe as statistically correlated packets of quasistreamwise vortical structures.

Previous studies on particle-laden flows have focused mainly on either small, heavy particles or large, and weakly buoyant particles. We present measurements in the regime of large and heavy particles, investigating the particle-turbulence dynamics over a parameter space covering a wide range of particle volume fractions, Stokes and Froude numbers at low to moderate Reynolds numbers. We consider the flow in a vertical pipe, thus allowing for the investigation of the two-way coupling between particles and the carrier phase turbulence while excluding the effect of gravity-induced settling on the wall-normal migration of particles. Pressure drop measurements indicate a linear increase in the skin friction coefficient with the volume fraction of particles. The growth rate of the skin friction coefficient was found to scale inversely with the Froude number. Using time-resolved particle image velocimetry measurements, we show that the carrier phase turbulence is modulated even at particle concentrations as low as 0.3%, indicating that particle-induced stresses due to the distortion of fluid streamlines cannot be neglected. Additionally, using Voronoi tessellations to quantify the particle concentration field, we observe a strong deviation from the Poisson behavior for cases both with and without turbophoresis. The results of particle tracking show that the particles move in roughly straight-line trajectories, which deviate from the flow streamlines with a mean angle of about 2° and a maximum angle of about 9°. The particles were also observed to be situated away from vortex cores indicating the occurrence of the centrifuge mechanism.

The variability of solar energy limits its reliability as a thermal resource, motivating the use of thermal energy storage (TES) to extend heat availability beyond periods of direct irradiance. This study numerically compares latent and sensible TES integrated into a solar dish system from a resource-oriented perspective across representative Mexican climates. Rather than focusing only on stored energy, the analysis evaluates how each storage strategy affects the temporal availability and post-irradiation persistence of usable thermal energy over 24 h charge–discharge cycles. A salt-based PCM (58.1LiNO₃–41.9KCl) was assessed against steel-based sensible storage under identical operating conditions. Under average-day forcing, the minimum PCM mass required to effectively utilize latent heat while sustaining a 320 W test load was found to be 13 kg. Under these conditions, the PCM case showed smoother thermal transients and longer post-irradiation energy availability, enabling nocturnal operation. In contrast, a mass-matched 13 kg steel store showed negligible post-irradiation availability, while a volume-matched 55 kg steel configuration achieved similar nocturnal operation only by substantially increasing mass, with limited improvement in accumulated energy. Hot-day forcing extended the operating window, whereas cold-day forcing yielded negligible charging so that operation could not be sustained within a single daily cycle.