Underwater sewage systems release a lot of water into the environment, which may alter the properties of the water and have an impact on marine ecosystems. This study numerically investigates the hydrodynamic behavior of tandem buoyant jets discharged under regular wave conditions typical of shallow coastal outfalls. Six scenarios combining jet speeds of 0.7-1.06 m/s, wave periods of 1-2 s, and wave heights of 0.02-0.04 m were simulated (Cases 1-6) using a two-phase volume of fluid (VOF) model. The free-surface elevation generated by the computational model matches published experimental data with < 5% deviation, confirming the robustness of the approach. Results show that 1 s waves intensify oscillatory forcing, increasing vertical velocity fluctuations by 35-40%, relative to 2 s waves due to more rapid crest-trough cycling. Increasing wave height from 0.02 m to 0.04 m enhances vertical displacement amplitudes by 20-25%, producing stronger disruption of the jet core. Higher jet velocity (1.06 m/s) increases the centerline vertical momentum by 30-35%, reducing the influence of wave-induced shear. Far-field vertical velocity decreases by more than 50% relative to the jet centerline under all wave conditions due to dominant wave-induced orbital motion. The findings provide new quantitative insight into jet-wave interactions, contributing to improved outfall design in wave-dominated nearshore environments.
Sloshing is a nonlinear and complex phenomenon that gives rise to loads at the fluid-structure interface leading to enormous pressure buildup in partially filled tanks. In the present study, the sloshing response of four types of axisymmetric tank geometries-cylinder, sphere, capsule, and 1:10 scaled model of NASA Space Launch System liquid hydrogen tanks-have been compared in various degrees of freedom. Due to symmetry of the vessels considered, the degrees of freedom were reduced to four: pitch, spin, heave, and surge motions. Total volume and water volume were the same for all tank geometries. Computational analyses of the fluid domain were performed using ANSYS Fluent. The effects of sloshing on the free surface, impact pressure, and wall moment are presented. The impact pressure is maximum for the spherical tank when subjected to surge motion, 40 kPa. The wall moment effect on the centroid of the tank is maximum for the capsule-shaped tank when subjected to spin motion, 14 Nm. Thus surge motion is critical in comparison to other motions for defining the tank's structural integrity. The particle fluctuation is decreased as the free surface area is increased, which is why spherical geometry offered greater structural stability in comparison to other shapes.
This study investigates the influence of bluff-body length on wake dynamics for improving piezoelectric energy harvesting (PEH) in vortex-induced vibration (VIV) systems. A triangular bluff body with lengths varying from 150 mm to 10 mm is analyzed using computational fluid dynamics (CFD) simulations in ANSYS Fluent to quantify the pressure difference amplitude in the wake region, which directly governs VIV forcing and electrical output. The results show a clear increase in wake pressure fluctuations as the bluff-body length decreases, indicating stronger vortex shedding and higher excitation potential for PEH. Experimental measurements validate the CFD trends, confirming the relationship between bluff-body geometry and wake-induced pressure loading. The findings provide a design guideline for optimizing triangular bluff bodies to improve VIV-based piezoelectric power generation.
This study investigates the influence of conduit height and length on the characteristics of viscous shear induced internal hydraulic jump and transition behavior during countercurrent stratified gas-liquid flow in miniature conduits. The shallow water theory for two-phase viscous flow has been adopted for the analysis. The results reveal that, as gas-liquid flow rate ratio (q(g)/q(l)) increases, the scaled jump location (the distance of jump from the inlet with respect to incoming liquid height, xj/h(i)) decreases while jump strength (ratio of liquid height just after jump to that before jump, h(2)/h(1)) increases, each reaching a critical point corresponding to a minimum and maximum, respectively. Beyond these critical values of q(g)/q(l), the behavior of both parameters becomes dependent on the magnitude of scaled channel height (H/hi). For lower values of H/h(i), scaled jump location begins to increase and jump strength to decrease, eventually becoming constant, whereas for higher H/h(i), both transition directly into constant values immediately after their respective critical values. The slopes of gas-liquid interface profiles both upstream and downstream of jump are noted to be influenced by q(g)/q(l), whereas the channel length impacts only the downstream profile. Furthermore, a new correlation is proposed for the critical flooding parameter as a function of scaled conduit height. The study thus provides new insights into the role of geometric parameters on two-phase flow behavior and offers valuable guidance for the design of miniature flow systems involving gas-liquid interactions.
Under the combined effects of environmental loads such as wind and flow, the motion response of inland river vessels in port increases, directly affecting the mooring safety of the vessels and even leading to major accidents such as cable breakage, collision damage, and capsize. A new numerical simulation method for the mooring force of inland river dolphin wharf is established based on the static equilibrium theory. According to the tonnage and types of the vessel, its underwater area facing current and its above-water area facing the wind are determined. The external loads such as wind and flow are calculated using empirical formulas. The tension of the mooring ropes is calculated using the Wilson formula, which considers the nonlinear characteristics of the ropes. Through solving the static equations, the motions of the moored vessel, including lateral and longitudinal movements, roll, and yaw, are obtained. Then the tension values of each rope are calculated, which is consistent with the measured results. The mean relative error of the key cables is less than 15%. Finally, the force characteristics of each rope of a certain wharf-moored vessel are analyzed under different wind speeds and directions, and flow velocity and direction conditions. The maximum force value of each rope is obtained, providing reasonable parameters for wharf design and operation.
The paper considers the near-critical fluid flows that remain at the margins of experimental and theoretical studies. The related publications are briefly revised, and the problem relevance is specified. When describing all the phenomena in this class originating from the unified hypothesis on the hydrostatic pressure distribution in the initial cross section, one faces five paradoxes formulated in the text. The essence of those paradoxes is revealed by analyzing the experimental data concerning various near-critical hydrodynamic phenomena. Such flows can be correctly described in terms of two controlling factors: the Froude Number (Fr1) and the coefficient of non-hydrostatics (s1) (the degree of deviation from the hydrostatics in the initial cross section).
This paper investigates the behavior of turbulent airflow around the NACA 23012 wing to evaluate the aerodynamic performance of a helicopter blade. The fluid-solid interaction, influenced by the rotational speed and blade geometry, creates complex pressure differences in the impact area on the blade surface. An analytical study was conducted to determine the aerodynamic loads acting on the helicopter blade. A finite element model was developed to calculate their natural frequencies and mode shapes, and the blade reaction forces were analyzed as well. Lift and drag coefficients were calculated for different angles of attack, ranging from 0 degrees to 20 degrees, corresponding to a Reynolds number Re = 106 and a Mach number M = 0.12. Time variations were not considered in the simulation, and the atmospheric pressure and airflow velocity were assumed to be constant. Comparisons between these computational fluid dynamics simulations and NASA experimental data showed a close agreement, with a margin of error of less than 4%. In addition, the results regarding the airfoil surface temperature due to air particle friction indicated that the nominal heat flux did not exceed 200 W, and therefore the flow reconnection occurred across all modulation frequencies. This study provides valuable insights into the aerodynamic behavior of helicopter blades under different operating conditions.
The dynamic behavior of the droplet and the liquid filament in the liquid jet process is widely encountered in natural phenomena and scientific problems. In this work, the liquid jet process is investigated by employing a phase field-based lattice Boltzmann model, and the influences of Reynolds number (Re), Weber number (We), and Ohnesorge number (Oh) on the dynamic behavior of the droplet and the liquid filament in this process are discussed comprehensively. Firstly, the static droplet is simulated and the results are validated against the Laplace law, then the liquid filament breakup processes at different wavenumbers are discussed, and the produced droplet sizes are analyzed quantitatively for validation. The results show that the Re affects the produced droplet number and the penetration length in the liquid jet process, and a high Re number leads to pronounced droplet fragmentation and an increased penetration length. The droplet shape is affected by the We number, and a high We number results in unstable and irregularly shaped droplets. The liquid jet fragmentation and the droplet size are affected much by the Oh number, and a high Oh number results in small droplet sizes, which further enhances the liquid jet breakup.
The aerodynamic characteristics of plain and stepped cylindrical constructions are crucial in architectural design, marine applications, and structural engineering. The present study examines the impact of stepped-cylinder geometry on drag and wake characteristics under supercritical flow conditions. Experiments were performed on three stepped cylinders (Model 1, 2, 3) and one plain cylinder in a wind tunnel at Reynolds numbers between 1.0 & times; 106 and 1.4 & times; 106. Static probes quantified pressure distributions around a stepped cylinder, whereas numerical simulations employing the RANS methodology with a k-epsilon turbulence model validated the results. These results indicate that step configurations substantially influence pressure distribution, drag coefficient (CD), and wake region. Of the evaluated geometries, Model 3 had the highest efficacy in drag reduction and wake suppression. These findings offer insights into flow control strategies for applications involving bluff bodies at high Reynolds numbers.
Polarity characteristics of expansion valves have demonstrated significant potential in microfluidic control applications, yet practical implementation challenges persist in engineering systems. This study systematically investigates the coupled effects of expansion ratio and scale on flow nonlinearity and polarity characteristics through numerical simulations of sudden expansion channels. Numerical simulations were conducted using computational fluid dynamics software for models with expansion ratios (lambda) ranging from 0 to 4 in both forward and reverse directions, covering Reynolds numbers (Re) from 0.001 to 1000. The results demonstrate that in models with lambda not equal 0, the generation and development of flow nonlinearity and polarity characteristics exhibit inherent coupling. Under constant Re conditions, both the equivalent hydraulic aperture (b(h)) and pressure difference ratio (D-i) progressively increase with higher expansion ratios, though the rate of augmentation gradually diminishes. The sudden expansion channel achieves maximum enhancement in both polarity and nonlinear effects at lambda = 2. Beyond this critical expansion ratio (lambda > 2), further increases in T produce diminishing returns in optimizing these characteristics. Scaling studies reveal that a 10 & times; enlarged lambda = 2 model maintains identical nonlinear and bipolar behaviors as the prototype, confirming geometric similarity. These findings provide critical insights for optimizing microfluidic valve performance through strategic geometric parameter modulation.
An analytical and numerical study on the influence of flow indices of a non-Newtonian fluid in the presence of Soret and Dufour effects during heat and mass transfer, in the absence of the thermal Rayleigh number, is conducted in a saturated anisotropic porous layer. The Darcy model, the Boussinesq approximation, and the Oswald-de Waele model were used. Heat and mass fluxes are constant on the horizontal walls, while the vertical walls are assumed to be adiabatic and impermeable. The analytical investigation is based on the parallel flow approximation in the horizontal cavity, while the numerical method involves solving the nonlinear equation using the Newton-Raphson method in MATLAB. We observed that the numerical solution admits real solutions for n < 1 and n > 1 when the thermal Rayleigh number is zero. A parametric study is conducted to show the effect of a non-Newtonian fluid with Soret and Dufour parameters, in the absence of thermal Rayleigh number, on the stream function at the center of gravity, speed, temperature, concentration, as well as the Nusselt and Sherwood numbers. The results highlight the predominant role of Soret and Dufour effects in heat and mass transfer, even in the absence of the thermal Rayleigh number, and emphasize the importance of these mechanisms for the optimal design of systems involving non-Newtonian fluids in anisotropic porous media.
A generalized range-minimized normalization framework (GRMNF) integrates data collection, normalization, systematic parameter variation, graphical analysis, polynomial exponent optimization, and nondimensionalization to minimize vertical spread in parameter-dependent curves. By compressing normalized curves into near-horizontal lines, the framework identifies relationships unaffected by parameter variations. Although validated here through horizontal cylinder impacts, the GRMNF is designed for universal application to fluid-structure interaction problems. It examines how parameters such as the cylinder's radius, mass, and impact velocity and the liquid's density affect the cylinder's behavior. The results examine the effects of each parameter individually and collectively, introducing two dimensionless relationships for maximum pressure and maximum force. The methodology demonstrates robustness in force prediction while highlighting challenges in pressure field. Finally, a derived model estimates the circumferential pressure distributions on the cylinder using peak pressure values and angular positions, achieving close agreement with simulation data.
This study presents a numerical investigation of turbulent flow in water-based nanofluids within circular pipes, using a two-phase Eulerian-granular mixture model. Correlations for the Nusselt number were developed using machine learning techniques, with Al2O3, CuO, and graphene nanoparticles under varying operating conditions. A comprehensive dataset comprising approximately 1300 data points was generated by simulating nanofluid flows at concentrations ranging from 0% to 5%, inlet velocities between 1 and 40 m/s, and pipe diameters from 5 to 20 mm. The wall of the pipe was kept at constant heat flux. Key input parameters included pipe diameter, nanoparticle concentration, Reynolds number, and Prandtl number, and the output parameter was the Nusselt number. Several machine learning algorithms-polynomial regression, artificial neural networks, k-nearest neighbors, Adaptive Boosting (AdaBoost), Extreme Gradient Boosting, random forest, and linear regression-were evaluated. Among these, AdaBoost achieved the best performance, with a minimum mean absolute error (MAE) of 287.26 and a maximum coefficient of determination (R2) of 0.876. The developed Nusselt number correlations showed good agreement with numerical experimental data, with maximum errors of +/- 5% at low concentrations and +/- 8% to +/- 15% for 95% of the total dataset. The correlations are valid for nanoparticle concentrations between 0.05% and 5%, Reynolds numbers from 3000 to 300,000, and Prandtl numbers between 6 and 25.
The influence of a direct shock wave on the transformation of disturbances in the parameters of a supersonic gas flow is studied. The influence of disturbances in the velocity, density, pressure, temperature, and Mach number ahead of the wave on disturbances in the parameters behind it is shown. The velocity and density disturbances behind the shock wave depend extremely on the Mach number (with a maximum). This is in qualitative agreement with the experimental data on the transformation of turbulence. The value of the maximum point increases with increasing disturbances in the velocity ahead of the shock wave. With increasing disturbances in the density and temperature, this increase becomes less intense. As the disturbances in the density and temperature ahead of the shock wave increase, the disturbances in the velocity behind it increase. The shock wave increases disturbances in the flow temperature. With increasing disturbances in the density ahead of the shock wave, the influence of the Mach number weakens. The passage of the shock wave increases disturbances in the pressure in the flow. It is shown that disturbances in the pressure behind the shock wave increase with increasing disturbances in the velocity, density, and Mach number ahead of the wave.
