Abstract Fog harvesting is a sustainable approach for potable-water supply in fog-prone coastal and elevated regions, but its fog-capture efficiency (ηcap) depends strongly on droplet-size distribution, mesh geometry, and wind speed. This study uses Eulerian–Lagrangian simulations to examine the effects of fog-mesh wire diameter (df 0.2–1.0 mm), shade coefficient (SC = 0.3–0.7), and freestream velocity (2–5 m s−1) on the capture of droplets with diameters from 2 to 40 μm. To interpret the results in a transferable form, droplet behavior is organized by Stokes number into three regimes: regime 1 (low-St and streamline-following droplets with weak capture), regime 2 (intermediate-St droplets that are highly sensitive to mesh geometry and aerodynamics), and regime 3 (high-St droplets dominated by inertial impaction). Large droplets show the highest instantaneous capture across most cases, whereas intermediate droplets govern the sensitivity to SC, df, and U. Fine and intermediate wires (df = 0.2–0.6 mm) with SC close to 0.6 provide the best balance between geometric interception and aerodynamic permeability. Increasing velocity enhances impaction until wake formation and flow diversion limit additional gain. The results are interpreted using a nondimensional framework, based on the droplet Stokes number, mesh-fiber Reynolds number, pressure-drop coefficient, and shade coefficient. The reported fog-capture efficiency (ηcap) values should be interpreted as the dry-mesh capture efficiencies (instantaneous capture at the onset of fogging, or under lean fog loading) since the current study excludes the dynamic impact of prolonged wetting, liquid deposition and growth on the fibers, mesh pore-clogging, and droplet re-entrainment effects. Notwithstanding, the current analysis effectively identifies a desirable design window corresponding to intermediate Stokes numbers, moderate-to-high aerodynamic permeability, and SC = 0.6.
Abstract This paper presents an explicit Lambert-W inversion of the classical Fanno relation for steady, adiabatic, quasi-one-dimensional (Q1D) flow of a calorically perfect ideal gas in a constant-area duct with wall friction. The formulation isolates the downstream Mach number as a function of the upstream Mach number, the specific-heat ratio, and the prescribed friction-length parameter 4fL/D. The appropriate real branch of the Lambert-W function is selected from the inlet sonic regime: the W−1 branch for subsonic inlet flow and the W0 branch for supersonic inlet flow. The resulting expression eliminates the conventional iterative inversion of the implicit Fanno equation for admissible, unchoked cases. Numerical comparisons with the classical implicit Fanno relation show agreement to numerical precision for representative subsonic and supersonic cases. The expression may be useful for instruction, code verification, preliminary sizing and rapid evaluation of idealized compressible duct systems, and reduced-order analysis of microchannels where wall friction is a dominant effect.
Abstract The present work proposes and numerically investigates a series of novel passive micromixers based on the triangular-shaped separation and recombination (TSAR) configuration. These designs are further integrated with the Minkowski fractal principle into the triangular obstacle geometries to promote enhanced mixing performance. The study begins with three fundamental configurations: converging triangular separation and recombination (TSAR-CC), diverging triangular separation and recombination (TSAR-DD), and a union of converging–diverging triangular separation and recombination (TSAR-CD) micromixers, each designed to induce chaotic advection along the mixing channel. Subsequently, the variants of each base design are introduced inspired by the Minkowski fractal theory, featuring two, four, and eight steps within triangular obstacles. These modifications create distinct flow perturbations and local recirculation zones that further strengthen chaotic advection and improve mixing uniformity. The numerical simulations are carried out in openfoam v24 workbench for mixing of fluids having identical properties, while the Reynolds number range of 1 to 100 is set for the analysis. The mixing performance of the micromixers is evaluated qualitatively and quantitatively through concentration contours, while the streamlines and velocity vectors are also presented to reveal the flow dynamics. Among all the designs, TSAR-CD demonstrates superior results, particularly in low Reynolds number range (Re < 25). The improvement in the mixing quality is further reported in the wide range of Reynolds numbers (more than 90%), as the TSAR-CD is modified with the Minkowski fractal. Finally, all the proposed micromixers are being evaluated together based on the mixing index and pressure drop to determine the overall optimum design.
Abstract In wall-modeled large-eddy simulation (WMLES), the velocity is sampled at a distance from the wall in the turbulence resolving region. Then, using this velocity as a boundary condition, Reynolds-averaged Navier-Stokes equations in thin boundary-layer form are solved down to the wall to obtain the near-wall solution. The Prandtl mixing-length model is often used to determine the eddy viscosity in the wall-model region. In the present work, we derive a new curvature-corrected mixing-length model based on the axisymmetric law of the wall. This new formulation improves agreement with experimental measurements at the radius-based Reynolds number Rea = 4.330 × 103, particularly in the log-law region just below the wall-model sample location. At higher Reynolds numbers, i.e., Rea = 1.060 × 105, 2.185 × 105, the curvature-corrected wall model converges to the baseline model. Importantly, we also introduce a method to estimate, a priori, the increment in wall shear stress due to the use of the curvature-corrected mixing-length model over the planar model. The estimation method predicts increments of less than 1% for Reynolds numbers greater than Rea ≈ O(105) and an increment greater than 10% for Reynolds numbers of order O(103). This is confirmed through WMLES.
Abstract Pressure losses vary significantly among fittings, yet such data are rarely provided by manufacturers. This gap largely stems from the lack of a measurement method that balances accuracy and practicality. Conventional testing requires each fitting to be connected to straight tubes of compatible material and connection type, with multiple upstream and downstream pressure taps. Given the wide range of materials, geometries, and connection types used in modern fittings, fabricating dedicated instrumented test sections for each fitting is impractical. This paper presents a streamlined and widely applicable method that enables consistent and accurate testing of various fittings using the same instrumented straight tubes. The method is demonstrated using three elbow fittings (glue-joint chlorinated polyvinyl chloride (CPVC), solder-joint copper, push-to-connect brass) and a polyethylene (PEX) tube bend, all with ¾-in. (19 mm) nominal tube size. A comprehensive uncertainty analysis is presented. Results show that measurement uncertainty in pressure loss is strongly influenced by the extent to which the flow is fully developed at the pressure measurement locations. Screening data based on the straight-tube friction factors effectively identifies and removes data associated with developing flow, thereby reducing the uncertainty. The measured pressure loss coefficients agree with predictions from existing methods based on bend radius. By simplifying the test setup and streamlining the data analysis, the method lowers the practical barrier for manufacturers to generate pressure-loss data, improving the accuracy of design and evaluation of fluid piping systems.
Abstract Technology development accelerates economic growth and advances human life. As the Fluids Engineering Division (FED) of the American Society of Mechanical Engineers (ASME) marks its 100th anniversary, we review here the Division's achievements over the years and discuss plans for our future directions. In the documents published about the celebration of our 90th Anniversary, we acknowledged the contributions of many of our former and present Division members. The present document briefly summarizes the 90th Anniversary Celebration. In this 100th Anniversary Celebration, we focus on our current organizational status, with particular emphasis on activities designed to appeal to young engineers and students to continue in the fluids engineering profession. Systematic evaluations have been conducted to assess the primary drivers of technological advancement within the FED over the past 100 years, encompassing progress in computational algorithms and applications, as well as innovations in experimental methodologies and instrumentation. These areas reflect those that appeared in the Journal of Fluids Engineering or its predecessors and are not meant to be a comprehensive review. This paper also presents a summary of various viewpoints on selected fluids engineering topics that will emerge in the future.
Understanding and accurately quantifying fluid flow in small, multiscale bifurcated structures subjected to peristaltic boundary conditions is critical in diverse engineering and biomedical applications, ranging from pipe flow to vascular hemodynamics to respiratory airflow. Traditional computational fluid dynamics (CFD) methods, while accurate, are often computationally expensive and limited in their handling of complex geometries and boundary conditions. In this study, we propose a novel geometry and physics-informed neural network (G-PINN) framework that seamlessly integrates geometric constraints and the governing nonlinear partial differential equations (PDEs) into a unified deep learning model to predict steady and transient fluid flow in Y-shaped bifurcated ducts. The G-PINN is trained solely on sparse velocity data without requiring pressure field supervision, yet it effectively reconstructs grid-independent pressure and velocity distributions throughout the domain. Comparative analyses with reference CFD solutions from ansys fluent demonstrate that the G-PINN accurately captures flow separation, secondary recirculation, and pressure drops across bifurcations under both steady and pulsatile inflow conditions. Moreover, the model demonstrates robust generalization across different flow regimes in distal ducts as small as 0.25 mm. This work underscores the synergy between physics-based machine learning and traditional fluid dynamics, paving the way for efficient, data-driven modeling of complex flow systems.
Abstract This study uses numerical simulation to investigate active flow control on a finite square cylinder, examining the effect of partial-span suction at the side leading edge on the aerodynamic forces and wake structure of the square cylinder at a Reynolds number of 250. The objective is to clarify how the spanwise distribution of suction interacts with the three-dimensional wake dynamics induced by the finite-span geometry. The results show that partial-span suction can effectively reduce the aerodynamic forces acting on the square cylinder and can outperform full-span suction. The best drag control effect occurs at a suction ratio of Γ = 1 (where Γ is the absolute value of the suction velocity divided by the freestream velocity), with a drag coefficient reduction of nearly 20%. The strongest suppression of fluctuating lift occurs at Γ = 0.75, with a reduction of over 85%, which is superior to the full-span suction. Suction forms three vortices near the square cylinder ends, reversing streamwise friction drag from negative to positive. The improved performance of the partial-span arrangement is associated with a different reorganization of the three-dimensional wake, including the downwash-upwash interaction, the side-pressure fluctuation distribution, and the friction-drag response. Proper orthogonal decomposition and principal correlation decomposition analyses indicate that fluctuating lift is mainly related to a few modes representing small-scale flow structures. The essence of the fluctuating lift reduction due to suction is the disruption of small-scale flow structures in the wake.
By using a fluid-structure interaction model, the dynamics of a swimming machine inspired by the tank-treading behavior of erythrocytes (red blood cells) during its transit through a pore in a wall are numerical investigated. Unlike traditional locomotion methods in aquatic environments, which rely mostly on hydrodynamic pressure for propulsion, this design utilizes fluid shear stress on its surface, enabled through circulatory motion of its membrane to generate thrust force. The numerical results show that this novel method has unique advantage in negotiating obstacles such as pores when swimming at relatively low Reynolds numbers ( O(10) or less). Specifically, when the swimmer passes through a pore, it is accelerated by the interaction between its membrane and the solid boundary despite the fact that the drag force is significantly increased during this process. Meanwhile, although the instantaneous power expenditure is increased, due to the reduced transit time, the total energy consumption during the transit is reduced, leading to lower cost of transport. These characteristics suggest that this bio-inspired locomotion method has great potential in applications where it is necessary to swim through confined space with obstacles at low Reynolds numbers.
Cavitation within the injector has a significant impact on the performance and stability of the liquid ammonia supply system. This study investigates the transient cavitation flow of liquid ammonia in a multiple-orifice injector using a combination of experimental and numerical simulation methods. First, a three-dimensional computational fluid dynamics (CFD) model of the injector was developed, which couples the volume of fluid (VOF) multiphase flow model, the realizable k-epsilon turbulence model, and the Zwart-Gerber-Belamri cavitation model. Then, the accuracy of the model was verified using experimental data from visualizations of liquid ammonia cavitation flow. On this basis, the effects of varying inlet pressure (40-80 MPa) and outlet pressure (1-3 MPa) on cavitation evolution were systematically studied to investigate the transient cavitating flow of liquid ammonia in the multi-orifice injector. The results indicate that the inlet pressure is the dominant factor determining cavitation flow characteristics. As the inlet pressure increases, the cavitation intensity, exit velocity, and mass flowrate all increase. Nozzles 1-3 are highly sensitive to changes in inlet pressure. Nozzles 4 and 5 achieve better flow output and stability owing to the expansion space in the pressure chamber. In contrast, the influence of outlet pressure is relatively small, with overall variations in all indicators not exceeding 3.2%. The buffering effect of the pressure chamber effectively mitigates the impact caused by outlet pressure fluctuations. This study clarifies the role of pressure conditions on the cavitation phenomenon in liquid ammonia injectors and provides direct guidance for designing high-performance and stable injection systems.
This study numerically investigates the impact of wall-based perturbation length on the response and recovery of turbulent pipe flow toward developing an effective passive flow manipulation system. The Reynolds number is 25,000, and length of the wall perturbation, introduced as a pipe-insert, varies between 2D and 12D, where D is the pipe diameter. The wall perturbations are based on Fourier modes that are designed to induce wall-normal gradients of Reynolds stresses, leading to local mixing, near-wall flow deceleration, and axial flow acceleration. The turbulent field downstream of each pipe-insert is analyzed and compared, revealing a higher magnitude of Reynolds shear and normal stress for longer perturbations. The rate of transport of Reynolds shear stress follows the same power-law trend for longer inserts, but at higher magnitudes. The increase in perturbation length delays mean flow recovery, while increasing turbulent kinetic energy and localized frictional drag reduction. Thus, there is an optimal length for maximizing frictional drag reduction, while minimizing pressure drop due to wall-based perturbations.
Abstract This study investigates the effect of compressibility on the kinetic energy correction factor, α, in both laminar and turbulent gaseous flows. In Bernoulli's equation, α is defined as the ratio of kinetic energy based on the integrated nonuniform velocity distribution to that based on a uniform distribution. For incompressible flows, α assumes the characteristic values of 2 for laminar flow with a parabolic velocity profile and approximately 1 for turbulent flow with a nearly uniform profile. In compressible gas flows, however, the velocity and temperature distributions can deviate substantially from their incompressible counterparts. To quantify these effects, numerical simulations were performed using the arbitrary Lagrangian–Eulerian (ALE) method to solve the two-dimensional compressible momentum and energy equations. The simulations covered a wide range of Reynolds numbers for both laminar and turbulent regimes under adiabatic wall conditions, with tube diameters ranging from 10 μm to 10 mm and a fixed length-to-diameter ratio (L/D) of 200. The results show that, in laminar flow, velocity profiles progressively depart from the classical parabolic form as the Mach number increases along the tube length. In turbulent flow, velocity distributions deviate from the conventional power-law profile, with the extent of deviation depending on the Reynolds number. Overall, the findings indicate that α decreases with increasing Mach number in laminar flow, whereas it remains essentially constant and largely independent of Mach number in turbulent flow.
Abstract A three-dimensional laminar flow for 37 Reynolds numbers (Re: 0.1, 0.2…1, 2…10, 20…100, 200…1000), primarily in the low-Reynolds-number regime, with water flow through six rectangular microchannels (aspect ratio (α): 1, 0.75, 0.5, 0.25, 0.2, 0.125) has been modeled, with 222 simulations conducted to develop correlations for the fully developed friction factor (fRe) and the incremental pressure drop number to determine apparent fRe. Results from the present simulations were validated by comparing the fully developed velocity profile, friction factor, and incremental pressure drop number for Re > 100 in rectangular channels reported in the literature. Three new correlations were derived from a vast array of numerical data generated by these simulations. First, a new fRe correlation was developed to include all aspect ratios, 0.125≤α≤8, with a mean and maximum deviation of 0.14% and 0.26%, respectively, from the numerical results. Next, a correlation for the fully developed incremental pressure drop number, K(∞), was developed as a function of aspect ratio 0.125≤α≤8 and Reynolds number (0.1≤Re≤1000). This correlation was in good agreement with the numerical data, with a mean deviation of 1.75% and a maximum deviation of 4.99%. The final correlation was for the incremental pressure drop number, K(z), in the developing region as a function of the nondimensional axial distance (Z*≥0.05Lh+), the aspect ratio (0.125≤α≤8), and the Reynolds number (0.125≤α≤8). The correlation was in good agreement with the numerical data, with a mean deviation of 0.80% and a maximum deviation of 5.93%. The local fapp,zRe can be determined using the three correlations, with a maximum deviation of 8.23% for 0.1≤Re≤1000 and 0.125≤α≤8, compared with the numerical results. These correlations will be useful in channel heat exchanger design to determine the required pumping power accurately.
Abstract Swirling flows underpin engineering systems, yet their dominant instability—the precessing vortex-core (PVC) associated with vortex-breakdown—can cause detrimental flame wrinkling, pressure oscillations, and increased pollutant formation. This work examines how swirler centerbody (CB) geometry alters PVC dynamics in a nonreacting, isothermal swirl-combustor. Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations with shear-stress-transport (SST) k–ω model are performed for double-bullet and cylindrical CBs, with grid-independence and validation against reported measurements. PVC characteristics are extracted using two-point cross-spectral analysis of axial-velocity fluctuations near inner shear layer, time-domain signals for persistence, and low-pressure isosurfaces for associated vortex-core (VC) visualization. Both configurations exhibit a dominant m=1 correlated oscillatory component. Double-bullet case shows a strong PVC at ≈122 Hz, whereas cylindrical CB shifts it to ≈25 Hz and substantially attenuates the oscillation. Low-pressure isosurfaces show a clear asymmetric single-helical VC in double-bullet case, while cylindrical-CB case possesses a more symmetric near-swirler core with a weakly asymmetric downstream extension, i.e., deformed single-helical VC. The resolved fluctuations remain largely persistent in both cases. Further, the weak persistent response in cylindrical CB case is not fully explained by expected eigenmode-based suppression/intermittency. Accordingly, eigenmode-based interpretation here appears to be sensitive to mean-flow linearization and turbulence model used in URANS for predicting mean-flow topology; therefore, PVC behavior deduced from linear eigenmodes and mean-flow state should be interpreted here only qualitatively.
Abstract Ice accretion is a critical factor that compromises the flight safety of hybrid wing body (HWB) aircraft. This study aims to characterize the icing behavior of an HWB configuration and, on this basis, to further investigate the effectiveness of a leading-edge droop strategy in enhancing the ice tolerance of iced airfoils. An Eulerian droplet approach coupled with a shallow-water icing model was employed to numerically predict glaze-ice accretion on the HWB aircraft surface. Based on the resulting ice geometry, the Reynolds-averaged Navier–Stokes (RANS) method was applied to systematically examine the aerodynamic responses of iced airfoils under different leading-edge droop angles. The numerical results demonstrate that leading-edge droop can effectively suppress flow separation on the upper surface of iced airfoils, albeit at the expense of intensified separation on the lower surface. For cases characterized by extensive upper-surface separation, leading-edge droop markedly improves the aerodynamic performance of iced airfoils. In contrast, when upper-surface separation is limited while lower-surface separation is dominant, this strategy fails to alleviate the overall flow separation and may even exacerbate it, leading to further deterioration of lift and drag characteristics.
Abstract Supercooled droplets are liquid droplets existing below their equilibrium freezing point without solidification, which occur widely in natural and industrial environments and play critical roles in atmospheric science, cryopreservation, and aviation safety. Supercooled droplets exhibit unique characteristics, such as rapid freezing triggered by impingement or other disturbances. To better reveal the dynamic and thermal processes experienced by supercooled droplets, controlled laboratory generation of supercooled droplets is essential for systematic investigations. In this study, we developed a novel freezing-levitation system to produce supercooled droplets without direct contact or support. Both high-speed imaging and infrared thermography were applied to characterize the supercooling process and the subsequent droplet impinging dynamics. Different types of water droplets, i.e., de-ionized-water and tap-water, were used in the experiments and compared in terms of their supercooling and freezing behaviors. The observations revealed that, while a clear recalescence event occurred for the tap water droplet during supercooling, the de-ionized water droplet remained in a liquid state for an extended period. Droplet impact experiments showed that both supercooled and nonsupercooled droplets spread similarly during the inertial stage. However, their retraction varied, i.e., the supercooled droplet showed suppressed recoil, while the nonsupercooled droplet underwent full capillary retraction before freezing. These findings demonstrate that the developed freezing-levitation system can consistently and precisely produce supercooled droplets that can offer reliable experimental conditions in examining the thermal and hydrodynamic features of supercooled droplets in both static and dynamic environments.
Abstract A new formulation of the energy equation corresponding to the known Rayleigh–Plesset (RP) equation is presented, thus directly linking bubble dynamics with energy considerations. An energy balance is formulated by leveraging the fact that the RP equation is a sum of distinct kinematic terms, where each system property, namely, density, pressure, viscosity, and surface tension, is associated with one or more kinematic terms. By differentiating the energy equation and matching its units to those of the known RP, energy functions-based RP equation is recovered; this function has unknown energy terms. Comparing the two equations gives these terms, resulting in an explicit, time-dependent energy equation. The derivation reported herein can be applied to modified RP equations as well, which are similar to the classical form of RP equation but include modified or additional factors (such as oscillating pressure and liquid compressibility). Proof of the energies' uniqueness and physical integrity is demonstrated. Finally, an example using a modified RP equation, namely the Rayleigh–Plesset–Keller (RPK) equation, which accounts for liquid compressibility, is presented. This example demonstrates a more complex modification, where system properties cannot always be explicitly isolated, thus demonstrating its wider applicability.
This study addresses the inherent limitations of conventional single-plane measurements, which predominantly rely on two-dimensional (2D) data, in fully capturing the three-dimensional (3D) physical essence of rotor-stator cavity flows. To overcome this constraint, the research innovatively integrates 2D particle image velocimetry (PIV) with 3D tomographic PIV (tomo-PIV), establishing a synergistic measurement framework. Experiments were conducted at speeds of 300-900 r/min and gap ratios (G) of 0.07-0.11. The 2D PIV technique tracked the planar evolution of large-scale coherent structures, while tomo-PIV enabled observation of 3D vortex stretching and breakup processes, achieving mutual validation between planar observations and volumetric reality. Through integrated analysis using proper orthogonal decomposition (POD) and the Omega vortex identification criterion, key findings reveal under the tested conditions, a small gap ratio imposes strong wall confinement, effectively suppressing 3D instabilities and maintaining quasi-2D vortex ring structures. The 2D POD modes exhibit high fidelity to the actual 3D vortex morphology. Conversely, larger gap ratios allow centrifugal stretching to dominate, leading to vortex distortion, fragmentation, and accelerated transition to turbulence. Energy spectrum analysis further confirms that anisotropic stretching at high rotational speeds inhibits energy transfer to smaller scales. This combined measurement approach not only identifies G = 0.07 as an effective condition for suppressing 3D instabilities, but also directly links 2D modal dynamics to 3D vortex structures. The findings provide a validated theoretical framework for diagnosing multiscale flow instability and optimizing energy efficiency in rotor-stator systems.
