Fluid Dynamics最新文献

The work aims to increase the performance of an aerofoil using the active method of a dual injection system. The three-dimensional numerical study that uses the Reynolds average Navier– Stokes equation along with the k-epsilon turbulence model is performed. This turbulence model is employed to identify the lift and drag coefficients at various angles. The results show that the dual injection system with the same mass flow produces better performance than the variable mass flow injection system. The obtained results proved that the proposed method used to increase the lift coefficient of 50% higher than the baseline and 14% improvement over the variation mass flow method. The novelty of the method is to effectively implement the dual injection system (DIS) over the top surface of an aerofoil by changing the various mass flow parameters to increase the performance of an aerofoil. The proposed concept can be an alternate solution for the existing co-flow jet method, which can be used for any type of commercial and military aircraft.

A mathematical model of circulation flow in a non-magnetic fluid that occupies a cylindrical channel is proposed. The flow is induced by the injection of a ferrofluid drop under the influence of an alternating magnetic field. One end face of the channel is closed by an impermeable wall, simulating a thrombosed blood vessel. The aim of this study is to develop a scientific basis for a progressive method for enhancing drug delivery to thrombi in blood vessels using magnetically induced circulation flow.

When a ramjet engine inlet operates under off-design conditions, the large-scale separation zone formed by the shock wave/boundary layer interaction significantly degrades engine performance, making separation control critically important. Based on a five-stage mixed-compression inlet designed for shock-on-lip condition under inviscid assumptions, six secondary flow circulation configurations with different locations for suction and blowing ports were designed. For comparison, two boundary layer suction configurations were also developed as baseline models. The numerical results demonstrate that under sub-rated conditions (M = 4), the suction port should be located away from the shoulder, while the blowing port should be positioned within the isolator. Comparing with the boundary layer suction method, the secondary flow circulation method increased the total pressure recovery coefficient by 11.00%, reduced the total pressure distortion index by 14.80%, and improved the mass flow coefficient by 1.75%. Under super-rated conditions (M = 8), the suction port should also be away from the shoulder, but the blowing port should be located on the first wedge. Compared with the boundary layer suction, the secondary flow circulation method resulted in a 6.59% decrease in the total pressure recovery coefficient. However, it reduced the total pressure distortion index by 4.24% and increased the mass flow coefficient by 0.98%. Furthermore, a feasible wide-speed-range flow control method with the use of the secondary flow circulation is proposed, offering a potential flow control strategy for enhancing the performance of ramjet inlets across a broad operational envelope.

External control bodies can adjust the operational environment by changing the incoming wind speed and direction, and so are considered to enhance the aerodynamic performance of H-type vertical axis wind turbines (VAWTs) with V-riblets structure and blunt trailing-edge. For a single blunt trailing-edge wind wheel with the V-riblets structure, the effects of four control bodies at the longitudinal position with different shapes are first explored on the wind energy utilization and velocity distributions in wake region, and those of the lateral position and size of the control body with optimal shape are further analyzed on the wind energy utilization, velocity distributions in wake region, and flow characteristics. For wind turbines with interaction, the effects of the number and arrangement of control bodies with optimal shape and size are investigated on the velocity distributions and output characteristics. The results show that control bodies with different shapes improve the wind energy utilization, and the rectangular control body has the most significant effects. The wind energy utilization increases first and then decreases with the lateral distance between the control body and the wind turbine, and increases with the size of the rectangular control body. The number and arrangement of control bodies obviously change the interaction mechanism among wind turbines and the flow field, affecting the velocity distributions around wind wheels, thereby improving the overall output performance.

Simulation of the developed laminar channel flow with a single-row array of inclined oval‑trench dimples with variable values of the trench length is carried out at the fixed dimple area and dimple depth. To evaluate the heat transfer enhancement, VP2/3 (Velocity–Pressure 2D/3D) in‑house code is used to solve Navier–Stokes and energy equations with the use of the multiblock computational technologies. The performed numerical analysis showed that four types of dimples with small, moderate, medium, and large values of the trench length could be distinguished. The flow and heat transfer features for small dimples are comparable to those of the spherical dimples with thermohydraulic efficiency of about 1.0. A significant change of the vortex structure is observed for moderate dimples which is accompanied with a significant increase of the thermohydraulic efficiency. For medium dimples a secondary separation area is formed whereas the thermohydraulic efficiency slightly grows. For large dimples the maximum value of the thermohydraulic efficiency of about 1.73 is observed for the trench length of about 5.0 whereas it decreases for larger values of the trench length. The origin of the significant heat transfer intensification is attributed to the formation of the extraordinary static pressure difference between the dimple leading and trailing edges with the value normalized by the doubled dynamic pressure of about 0.35–0.4.

An elliptical nozzle (the aspect ratio AR is equal to 2) with an equivalent diameter of 10 mm is experimentally investigated at the Mach number M = 0.4 with the secondary fluidic injection of M = 0.6 minijets with four air tabs placed diametrically opposite to another at the nozzle exit plane. The high-speed jet facility is used to characterize the jet behaviour of the manipulated jet with the uncontrolled open jet. The effects of the minijet mass flow rate and the diameter ratio (air tab diameter/nozzle exit diameter) are analysed. In this experimental investigation four air tabs of 0.4, 0.5, 1 mm diameters being placed at the elliptical convergent nozzle exit at 90° to each another. As distinct from the circular nozzle, non-uniform vortices may be generated from the larger and shorter curvature of the major and minor axis of the elliptical nozzle, thus increasing the mass entrainment from the ambient to the main jet core. Air tabs not only generating the streamwise vortices and also induces Kelvin–Helmholtz instability due to the momentum difference in the primary jet due to the secondary jet thus promoting the mixing which reflects in the rapid reduction in pressure in the potential core region of the jet. Compared to the uncontrolled jet, the percentage of reduction in potential core is obtained as 40, 45, and 80% with the 0.4, 0.5 and 1 mm air tabs, respectively. Also, from the radial profile, a significant jet distortion is observed due to the amount of the energy added in the primary jet and the penetration of the secondary jets which is more significant in the minor axis as compared to the major axis of the elliptical nozzle. From the pressure plots and the analytical investigation, it is documented that 1 mm air tabs which sustain more momentum flux thus enhancing the entrainment ratio to the primary jet as compare to the 0.4 and 0.5 mm air tabs-controlled jets.

The gas-solid two-phase flow characteristics within the compression cavity of a solid carbon dioxide (CO₂) molding machine are investigated using numerical simulation. Initially, based on computational fluid dynamics (CFD), the effects of varying inlet inclination angles (0–60°) on the flow field structure within the cavity are analyzed, with a particular focus on examining the evolution of the velocity field, the pressure distribution, and the gas trajectory patterns. Subsequently, the discrete phase model (DPM) is applied to track the motion of snowflake-shaped dry ice particles, enabling a detailed examination of particle spatial distribution under flow interactions. Results indicate that an increase in the inlet inclination angle significantly enhances the main flow diffusion within the cavity, improving particle phase dispersion uniformity. However, further increases in the angle lead to a concomitant rise in the static pressure gradients, raising the risk of high-pressure injection events. An analysis of gas motion trajectories shows that, at the 45 and 60° inlet angles, the flow field exhibits a typical vortex-diffusion composite pattern. The primary gas flow forms stable spiral trajectories that enhance particle dispersion, while secondary flows effectively reduce particle deposition at the cavity bottom. In terms of the particle distribution, particles accumulate near the exhaust hole at the angle of 45°, increasing the cavitation risk, whereas at the angle of 60°, they concentrate primarily on the right side while maintaining optimal dispersion uniformity throughout the cavity. Comprehensive evaluation identifies the angle of 60° as the optimal inlet inclination for aerodynamic performance. This work provides critical theoretical foundation and engineering guidance for the aerodynamic optimization of solid CO₂ molding equipment.

In practical applications, droplets often collide with surfaces in an asymmetric (eccentric) manner rather than striking centrally, leading to complex impact dynamics that significantly affect the droplet behavior and contact time. However, most previous studies have primarily concentrated on symmetric (central) impacts, overlooking the nuances introduced by eccentric collisions. To address this gap, this study employs a three-dimensional pseudopotential lattice Boltzmann method (LBM) to investigate the dynamics of droplets impacting superhydrophobic surfaces (SHS) adorned with a single cubic protrusion under eccentric collision conditions. Here, the effects of the Weber number We, eccentricity, and the cubic protrusion size on the droplet contact time and rebound dynamics are systematically explored. Several distinct rebound modes, including off-center toroidal rebounds and horseshoe-shaped rebounds, driven by asymmetric momentum redistribution, are identified. The results show that under strong eccentricity, the droplet achieves rapid detachment via a slanted rebound mode that bypasses liquid ring formation, resulting in a reduction in the contact time up to 65.05% as compared to flat SHS. The findings further reveal that the coupling of lateral sliding and vertical retraction enhances energy conversion efficiency and accelerates rebound. The study provides new physical insights into the mechanisms of contact time reduction and offers practical design guidelines for engineered surfaces with superior liquid repellency.

The winglets located at aircraft wing ends are used to increase the aerodynamic performance and reduce fuel consumption by regulating negatively affecting the performance at the wings end. Therefore, aircraft wings have a critical importance on aerodynamic efficiency. The most efficient winglet model should be used in each of the flight positions. This study is aimed to investigate the effects of concave, convex, and plain winglet geometry on wing performance. The effects of plain, concave and convex winglet models with cant angles of 30°, 45°, and 60° were experimentally investigated at the angles of attack ranging from 0 to 20°. The aerodynamic lift and drag coefficients generated by each design were measured in wind tunnel tests conducted at a Reynolds number of 2.5 × 10⁵, and the effect of the winglet’s shape on wing performance was compared. The data obtained reveal that various wingtip designs have significant effects on the aerodynamic properties of the wing. At low, moderate and high angles of attack, the highest lift is achieved with the 30° cant angle winglet. The best results for all winglet models in terms of the aerodynamic quality were obtained in the plain winglet model. Furthermore, the aerodynamic quality generally increases with decrease in the cant angles. It is anticipated that these findings, obtained from winglet models with various geometric designs, could contribute to the development of more efficient winglet geometry.

This study presents a three-dimensional numerical investigation of droplet breakup in asymmetric Y-junction microchannels using a coupled volume of fluid-level set method. The motivation arises from the limited understanding of how geometric asymmetry and viscosity contrast jointly influence droplet splitting, which has been extensively explored only in symmetric T-junctions. The effects of the viscosity ratio ({{lambda }}) and the outlet width ratio ({{w}_{2}}{text{/}}{{w}_{1}}) on the critical capillary number ({text{Ca}}) and the droplet length ratio l/w governing the transition between the breakup and non-breakup regimes were systematically analyzed. The results reveal that the higher viscosity ratios promote breakup by enhancing the viscous stresses with respect to interfacial tension, while the larger outlet width ratios favor non-breakup as droplets tend to move into the wider branch. A modified predictive model, developed by extending the existing T-junction framework, successfully captures the regime transition behavior in asymmetric Y-junctions. Furthermore, the daughter droplet length ratio after breakup deviates increasingly from ideal geometric scaling with greater outlet asymmetry. These findings provide new insight into the coupled influence of the viscosity ratio and geometric asymmetry on droplet dynamics and offer a predictive approach for designing microfluidic systems with controlled droplet splitting.