Largeeddy simulation was used to model turbulent atmospheric surface layer (ASL) flow over canopies composed of streamwisealigned rows of synthetic trees of height,
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Magnetic reconnection is an important process in astrophysical environments, as it reconfigures magnetic field topology and converts magnetic energy into thermal and kinetic energy. In extreme astrophysical systems, such as black hole coronae and pulsar magnetospheres, radiative cooling modifies the energy partition by radiating away internal energy, which can lead to the radiative collapse of the reconnection layer. In this paper, we perform two and threedimensional simulations to model the MARZ (Magnetic Reconnection on Z) experiments, which are designed to access cooling rates in the laboratory necessary to investigate reconnection in a previously unexplored radiatively cooled regime. These simulations are performed in GORGON, an Eulerian twotemperature resistive magnetohydrodynamic code, which models the experimental geometry comprising two exploding wire arrays driven by 20 MA of current on the Z machine (Sandia National Laboratories). Radiative losses are implemented using nonlocal thermodynamic equilibrium tables computed using the atomic code Spk, and we probe the effects of radiation transport by implementing both a local radiation loss model and
 Award ID(s):
 2213898
 NSFPAR ID:
 10501826
 Publisher / Repository:
 Cambridge University Press
 Date Published:
 Journal Name:
 Journal of Plasma Physics
 Volume:
 90
 Issue:
 2
 ISSN:
 00223778
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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, and systematically arranged to quantify the response to variable streamwise spacing,$h$ , and spanwise spacing,$\delta _1$ , between adjacent trees. The response to spanwise and streamwise heterogeneity has, indeed, been the topic of a sustained research effort: the former resulting in formation of Reynoldsaveraged counterrotating secondary cells, the latter associated with the$\delta _2$  and$k$ type response. No study has addressed the confluence of both, and results herein show secondary flow polarity reversal across ‘critical’ values of$d$ and$\delta _1$ . For$\delta _2$ and$\delta _2/\delta \lesssim 1$ , where$\gtrsim 2$ is the flow depth, the counterrotating secondary cells are aligned such that upwelling and downwelling, respectively, occurs above the elements. The streamwise spacing$\delta$ regulates this transition, with secondary cell reversal occurring first for the largest$\delta _1$ type cases, as elevated turbulence production within the canopy necessitates entrainment of fluid from aloft. The results are interpreted through the lens of a benchmark prognostic closure for effective aerodynamic roughness,$k$ , where$z_{0,{Eff.}} = \alpha \sigma _h$ is a proportionality constant and$\alpha$ is height root mean square. We report$\sigma _h$ , the value reported over many decades for a broad range of rough surfaces, for$\alpha \approx 10^{1}$ type cases at small$k$ , whereas the transition to$\delta _2$ type arrangements necessitates larger$d$ . Though preliminary, results highlight the nontrivial response to variation of streamwise and spanwise spacing.$\delta _2$ 
Wellresolved direct numerical simulations (DNS) have been performed of the flow in a smooth circular pipe of radius
and axial length$R$ at friction Reynolds numbers up to$10{\rm \pi} R$ using the pseudospectral code OPENPIPEFLOW. Various turbulence statistics are documented and compared with other DNS and experimental data in pipes as well as channels. Small but distinct differences between various datasets are identified. The friction factor$Re_\tau =5200$ overshoots by$\lambda$ and undershoots by$2\,\%$ the Prandtl friction law at low and high$0.6\,\%$ ranges, respectively. In addition,$Re$ in our results is slightly higher than in Pirozzoli$\lambda$ et al. (J. Fluid Mech. , vol. 926, 2021, A28), but matches well the experiments in Furuichiet al. (Phys. Fluids , vol. 27, issue 9, 2015, 095108). The loglaw indicator function, which is nearly indistinguishable between pipe and channel up to , has not yet developed a plateau farther away from the wall in the pipes even for the$y^+=250$ cases. The wall shear stress fluctuations and the inner peak of the axial turbulence intensity – which grow monotonically with$Re_\tau =5200$ – are lower in the pipe than in the channel, but the difference decreases with increasing$Re_\tau$ . While the wall value is slightly lower in the channel than in the pipe at the same$Re_\tau$ , the inner peak of the pressure fluctuation shows negligible differences between them. The Reynolds number scaling of all these quantities agrees with both the logarithmic and defectpower laws if the coefficients are properly chosen. The onedimensional spectrum of the axial velocity fluctuation exhibits a$Re_\tau$ dependence at an intermediate distance from the wall – also seen in the channel. In summary, these highfidelity data enable us to provide better insights into the flow physics in the pipes as well as the similarity/difference among different types of wall turbulence.$k^{1}$ 
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