Carotid artery stenosis substantially alters local hemodynamics and can increase blood-flow energy loss (BFEL). How heart-rate-dependent inflow redistributes viscous loss, wall-related net loss, and Reynolds-stress transfer remains unclear. Nine patient-specific carotid models spanning mild, moderate, and severe stenosis were examined using a bidirectional fluid–structure interaction framework. Flow-rate waveforms were converted to inlet velocities using case-specific common carotid artery areas; three-element Windkessel outlet models supported 27 simulations at 67, 100, and 140 beats per minute (bpm). Clinical Doppler ultrasound measurements were compared with predicted external and internal carotid velocity waveforms in one mild-stenosis case. A literature-based reconstructed phantom benchmark additionally assessed outlet-pressure predictions. Molecular viscous dissipation (Eμ), wall-related net energy loss (EW), and shear stress transport (SST)-modeled Reynolds-stress energy transfer (ERS) accounted for 10.14%–82.97%, 3.04%–32.81%, and 0.02%–66.37% of BFEL, respectively. Viscous loss dominated most cases, while BFEL generally increased from (3.0–10.5) × 10−5 J/cycle at 67 bpm to (5.4–17.7) × 10−5 J/cycle at 100 bpm and (7.0–23.0) × 10−5 J/cycle at 140 bpm, reflecting changes in flow magnitude and pulsatile timing. Wall-related loss varied comparatively little, whereas ERS responded strongly under selected conditions. In Case 7 at 140 bpm, ERS/BFEL was 66.37% with baseline SST and 62.52% with transition SST. A separate scale-resolving improved delayed detached-eddy simulation estimated mean-flow-to-fluctuation transfer and turbulence-associated irreversible dissipation at approximately 58.0% and 45.0% of BFEL, respectively. Thus, Reynolds-averaged Navier–Stokes-derived ERS is a model-dependent interscale-transfer metric rather than a physical turbulent-dissipation fraction.
CO2-enhanced coalbed methane recovery (CO2-ECBM) is a vital approach for synergizing deep methane extraction with geological carbon storage. This study characterized the multi-scale pore structure and fractal attributes of coal specimens across various ranks to clarify pore architecture evolution. Subsequently, gas pressure cyclic loading–unloading seepage experiments were conducted to replicate complex stress conditions induced by periodic bottom-hole pressure fluctuations. Results indicate that cyclic stress induces substantial nonlinear hysteresis and irreversible permeability damage, with permeability decreasing by up to 8.53% after 3 cycles. Crucially, this hysteresis is revealed not merely as a mechanical response, but as a manifestation of non-equilibrium fluid–solid interaction, where delayed matrix swelling competes with irreversible micro-fracture compaction. Furthermore, a dynamic seepage prediction model incorporating fractal characteristics, stress, and adsorption was established. The study explicitly articulates the underlying physical contributions by treating the internal swelling coefficient and fracture compressibility as dynamic state variables rather than constants. The model's strong agreement with experimental data validates its ability to capture permeability evolution and hysteresis under cyclic paths, overcoming limitations of traditional steady-state models. Ultimately, this research elucidates the microscopic seepage mechanism driven by stress and adsorption, providing the physical insight that permeability evolution under cyclic loading is governed by the competition between stress-induced fracture compaction and adsorption-induced matrix swelling, both dynamically altered by cumulative damage. This study reveals the permeability evolution mechanism, guiding CO2-ECBM parameter optimization. The proposed dynamic model overcomes traditional limitations, significantly enhancing productivity prediction and carbon storage evaluation under complex stress.
Gas jet impingement on liquid pools is a key technology widely used in chemical and metallurgical processes. However, most existing research on this technology is based on jets issuing from straight circular nozzles, in which boundary layer development leads to significant momentum dissipation. In this study, gas jet impingement under reduced boundary layer effects is investigated using a converging variable-cross section nozzle. First, numerical simulations are performed to characterize the flow fields of both the gas jet and the liquid pool and to reveal the underlying impingement mechanism. The simulation results are then validated against experimental data. Next, a theoretical model for predicting the gas–liquid interfacial morphology under a converging variable-cross section nozzle is developed based on the force balance at the stagnation point, and the model constant is determined by nonlinear global optimization using measured interfacial parameters. Furthermore, experiments are conducted to analyze the interfacial morphology at different outlet Reynolds numbers. The results elucidate the coupling mechanism between boundary-layer suppression and interfacial momentum transfer, providing a new theoretical basis for the accurate prediction and active regulation of gas–liquid interfacial morphology in multiphase impact systems.
This work investigates the dynamics of gas bubble formation on a capillary immersed in a quiescent liquid under a nonuniform electric field. Ethyl alcohol was used as the working fluid. To create a nonuniform electric field, two electrodes were immersed in the liquid: a stainless-steel capillary through which air was injected, and a copper ring positioned above the capillary. Using a high-speed camera, the bubble formation and rise were filmed at different voltages, gas flow rates, and capillary diameters. It was shown that applying an electric field can significantly reduce the size of the bubble formed. Based on the force balance, the electrostatic force required to form the resulting bubble was estimated. Also, based on the electric field calculated using finite element method magnetics, the integrated electrostatic force acting on the bubble was obtained. It was shown that this force is insufficient to form bubbles of the desired size. This demonstrates the existence of additional mechanisms that reduce the bubble detachment diameter in an electric field. During their rise, the bubbles do not move in a single line, but scatter in different directions. The growth of the vertical velocity component in the presence of a nonuniform electric field and the appearance of the radial velocity component prevent the coalescence of bubbles near the capillary. These effects make it possible to efficiently generate monodisperse gas–liquid mixtures with submillimeter-sized bubbles, thus generating a finely dispersed gas–liquid mixtures.
This paper presents a numerical study of supersonic flow past a sharp flat plate at zero incidence using a two-fluid turbulence model written in von Mises variables and solved with an implicit marching finite-difference scheme. Velocity, skin-friction, temperature, and turbulent Prandtl number distributions were obtained for M = 2 and M = 5 with adiabatic (Tw/Tr=1) and cooled (Tw/Tr=0.5 and 0.2) walls, Tr being the recovery temperature, in the range Rex≤3⋅107 (Reθ up to about 2 × 104). Laminar-to-turbulent transition was captured by varying the amplitude of the initial disturbance from 0.05% to 5%. The skin-friction coefficient was compared with the van Driest II correlation, with direct numerical simulation (DNS) data at matched Mach number and wall-temperature ratio, and with the recent skin-friction scaling law of Zhao and Fu. For adiabatic walls, the model agrees with van Driest II within 9% (mean deviation 4%–5%) for 4000≤Reθ≤12 000. For cooled walls, the model predicts a skin friction 11%–21% lower than van Driest II. This reproduces the tendency, found in DNS, of van Driest II to over-predict the skin friction on cold walls but overestimates its magnitude: the model under-predicts the DNS skin friction by 3%–26% (14% on average) for 0.15≤Tw/Tr≤0.5. Besides the skin friction, the two-fluid model describes phenomena that are not described by empirical correlations: the dependence of the transition onset on the intensity of the incoming disturbances and the anisotropy of turbulent heat transfer in a compressible boundary layer, which cannot be represented by models based on the Boussinesq hypothesis. The computed turbulent Prandtl number varies strongly in the transition region and tends to a constant value of 0.855 in the turbulent zone.
