Search

This study investigates the characteristics of a turbulent boundary layer in a curved circular pipe under an inflow of Ma = 3.0. The pipe consisted of a straight part and a curved part with a turning angle of 36° and a radius of curvature, γ = R/Rc, of γ = 0.0825. The nanoparticle-based planar laser scattering technique was applied to visualize the structure of the instantaneous flow field, and a large eddy simulation was conducted to uncover the physical aspects of development of the turbulent boundary layer. The distributions of density and vorticity, baroclinic pressure caused by the density and pressure gradients, and other physical quantities were analyzed. The asymmetry of the turbulent boundary layer in the curved part of the pipe, as influenced by curvature, secondary flow, and oblique shock, was obtained as the boundary layer on the inner wall gradually thickened while that on the outer wall gradually thinned. The secondary flow took the mainstream outer bend of the curved pipe and drew the low-energy fluid in the boundary layer to its inner bend, which led to the gradual thickening of the turbulent boundary layer from the outer to the inner bend along the circumferential direction. A low-speed region was formed in the downstream region of the inner part. The intersection between the oblique shock wave and the shear layer led to a high baroclinic pressure that promoted the generation of the vortex and forced the boundary layer to turn and inhibit the separation in the inner part. [ABSTRACT FROM AUTHOR]

The high-strain-rate dynamic response of a hydroxyl-terminated polyether (HTPE) propellant during impact loading is essential for assessing the structural reliability and impact safety of HTPE propellant. In this study, a modified split Hopkinson pressure bar (SHPB) apparatus has been developed to research the stress–strain behavior of the HTPE propellant over strain rates ranging from 470 to 5910 s−1 at room temperature, and the validity of the SHPB test is analyzed in detail. Meanwhile, the evolution of deformation to failure of the HTPE propellant was recorded by a high-speed digital camera synchronized with the SHPB test, which revealed the correlation between mechanical response and failure mode. Scanning electron microscopy was applied to investigate the microscopic failure mechanism of the post-test HTPE propellant, which indicated two characteristic failure modes: cracking propagates along the (1) debonding surface and (2) transgranular damage path. Finally, based on the stress–strain plots derived from the SHPB tests, the ultimate stress, strain energy density, and adiabatic temperature-rise effect of the HTPE propellant were seen to show strong strain rate dependence by following an empirical power law function. [ABSTRACT FROM AUTHOR]

The effects of alkyl side-chain length on the interactions between imidazolium ionic liquids (ILs) and β-cyclodextrin (β-CD) were studied at ambient pressure and up to 2.5GPa. No noticeable changes in the C-H band frequencies of 1-methyl-3-propylimidazolium hexafluorophosphate ([MPIM][PF6]) were observed upon β-CD addition under ambient pressure. Nevertheless, β-CD addition inhibited the formation of the [MPIM][PF6] aggregated structure under pressures of ≤0.7 GPa. As the pressure was raised to 1.1–2.5 GPa, [MPIM][PF6] aggregated and formed self-associated configurations. This pressure-induced dissociation was not detected in the 1-butyl-3-methylimidazolium hexafluorophosphate and β-CD mixture ([BMIM][PF6]-β-CD) due to the long side chain in the [BMIM] cation. This indicates that the alkyl side-chain length of the imidazolium ILs plays a non-negligible role in controlling the order and strength of IL-β-CD interactions. It is well known that the validity of infrared spectroscopy for detecting the inclusion complexation is questionable in the literature. However, this study demonstrates that the combination of high pressure and IR spectroscopy may provide a suitable way to monitor the IL-β-CD interactions. [ABSTRACT FROM AUTHOR]