Flamelet generated manifold simulation of highly swirling spray combustion: Adoption of a mixed homogeneous reactor and inclusion of liquid-flame heat transfer

In real urban environments, wind velocities often exhibit significant time-dependent variations. However, the impact of these fluctuations on ventilation performance is not frequently addressed in the literature. To accurately predict the building ventilation performance, this paper intends to elucidate the influence of the unsteady approaching flow. Four distinct inflows, characterized by periodic sinusoidal fluctuations, are evaluated using large-eddy simulation (LES). A single-sided building model with natural ventilation is constructed and validated through a wind tunnel experiment. Four periodic inflows consist of combinations of two frequencies (f = 0.1 and 0.3 Hz) and two amplitudes (A = 0.06 and 0.09). This paper mainly compares the results of airflow patterns and ventilation performance with those of stable inflows. The results indicate that periodic inflows cause greater fluctuations in the velocity fields on the leeward side. At higher frequencies and lower amplitudes, the vertical distribution of indoor bottom vortices is relatively dispersed. It shows that periodic flows lead to noticeable changes in the ventilation rate, with a deviation between instantaneous and average Q* ranging from 13.8% to 16.5%. Compared to the stable inflow, the impacts of periodic inflows on ventilation performance vary over time; 6% and 9% variations in incoming velocities result in deviations of up to 17.5% in ventilation rates. The frequencies and amplitudes of the periodic inflows do not exhibit a linear relation with ventilation rate. Therefore, it is prudent to be cautious about adopting averaged incoming wind velocities in predicting ventilation performance. This study helps in the more accurate prediction of single-sided natural ventilation.

Periodic approaching flows and pollutant dispersion of a single-sided generic building with natural ventilation

Dai,

Luo,

Zhu

et al. 2024

Research on the excitation force and vortex dynamics characteristics of pump-jet propulsor induced by shafting whirling vibration: Non-uniform blade tip clearance

Zou,

Xue,

Yang

et al. 2024

The propulsion shafting whirling vibration causes non-uniform dynamic changes in the rotor tip clearance, which directly have a significant influence on the excitation force and vortex dynamic characteristics of the pump-jet propulsor. In the current study, based on improved delay detached eddy simulation, the influence of non-uniform blade tip clearance on the excitation force and vortex dynamics characteristics of the pump-jet propulsor is studied under design conditions. The results show that the application of propulsion shafting whirling vibration induces significant changes in the excitation force of the pump-jet propulsor. The rotor blades modulate the excitation forces of the stator blades and duct. The transverse and vertical excitation forces are more significant than the longitudinal excitation force. The magnitude change in the circular orbit shows a linear relationship with the excitation force magnitude. The characteristic frequency of the transverse and vertical excitation forces of each component is the shaft rotation frequency. In contrast, the characteristic frequency of the longitudinal excitation force is twice the shaft rotation frequency. In the elliptical orbit, the excitation force of each component is compressed or stretched in the time domain, and the dominant frequency is shifted in the frequency domain; there is no longer a linear relationship between the vibration magnitude change and the excitation force magnitude. Furthermore, an energy generation mechanism in the wake field of the pump-jet propulsor induces vortex frequency due to the whirling vibration of the propulsion shafting system.

Numerical study on effects of leading-edge manufacturing defects on cavitation performance of a full-scale propeller. II. Simulation for the full-scale propeller with defects

Jin,

Peng,

Qiu

2024

Paper II of this two-part paper investigated the effects of leading-edge (LE) manufacturing defects on the open-water cavitation performance of a full-scale propeller based on the geometry of David Taylor Model Basin propeller by using the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes solver. Various simulation parameters, including domain size, grid size, stretch ratio, first-grid spacing, y+, and turbulence model, were carefully examined for their effects on the solutions, leading to the development of the best modeling practices for the full-scale propeller with LE defects. Employing these recommended best-practice settings, simulations were conducted on the full-scale propellers with 0.10, 0.25, and 0.50 mm LE defects. Compared to the predictions from Paper I [Jin et al., “Numerical study on effects of leading-edge manufacturing defects on cavitation performance of a full-scale propeller—Paper I: Simulation for the model- and full-scale propellers without defect,” Phys. Fluids 36, 105179 (2024).], which did not account for LE defects, the results showed that the LE defects within International Standards Organization (ISO) 484 Class S tolerances narrow the cavitation buckets. As a consequence, such LE defects can result in more than 40% reduction in cavitation inception speed, which is similar to the conclusions drawn from earlier two-dimensional (2D) studies [Jin et al., “2D CFD studies on effects of leading-edge propeller manufacturing defects on cavitation performance,” in SNAME Maritime Convention (The Society of Naval Architects and Marine Engineers, 2020).]. Note that Paper I [Jin et al., “Numerical study on effects of leading-edge manufacturing defects on cavitation performance of a full-scale propeller—Paper I: Simulation for the model- and full-scale propellers without defect,” Phys. Fluids 36, 105179 (2024).] presents the simulations for the model- and full-scale propellers without LE defects.