Search Results (174)

In this study, a computational thermo-fluid dynamics simulation of a wide-slot jet impingement heating process is performed. The present configuration consists of a turbulent incompressible air jet impinging orthogonally on an isothermal cold plate at a Reynolds number of around 11,000. The two-dimensional mean turbulent flow field is numerically predicted by solving Reynolds-averaged Navier–Stokes (RANS) equations, where the two-equation eddy viscosity k-$\omega$ model is utilized for turbulence closure. As the commonly used shear stress transport variant overpredicts heat transfer at the plate due to excessive turbulent diffusion, the recently developed generalized k-$\omega$ (GEKO) model is considered for the present analysis, where the primary model coefficients are suitably tuned. Through a comparative analysis of the various solutions against one another, in addition to reference experimental and numerical data, the effectiveness of the generalized procedure in predicting both the jet flow characteristics and the heat transfer at the plate is thoroughly evaluated, while determining the optimal set of model parameters. By improving accuracy within the RANS framework, the importance of model adaptability and parameter tuning for this specific fluid engineering application is demonstrated. This study offers valuable insights for improving predictive capability in turbulent jet simulations with broad engineering implications, particularly for industrial heating or cooling systems relying on wide-slot jet impingement. Full article

In the present study, three-dimensional turbulent, subcritical open-channel flow (Fr = 0.19) through submerged rigid vegetation is numerically investigated using the ANSYS FLUENT solver (v. 22. 1). The Volume of Fluid (VOF) method is applied for free-surface tracking, while the standard k-ε turbulence model is employed for turbulence closure. Vegetation is modeled as vertical rigid cylinders fixed at the bottom of the channel. Regarding the arrangement of the stems, two cases are examined. In the first case, a linear arrangement of three equally spaced vegetative stems is located transversely at the center of the channel, while in the second case, a parallel arrangement of fifteen equidistant vegetative stems is located downstream of the channel center. In both cases, the vertical velocity profile within the submerged vegetation layer deviates significantly from that of the upper non-vegetated layer, which generally adheres to the logarithmic velocity distribution. In the second case, flow field repeatability is observed after the third stem series, particularly in terms of velocity profiles. Additionally, the structure of turbulence is noticeably affected in the vicinity of the stems, resulting in higher eddy viscosity values near each stem’s crest area. Furthermore, a localized drop in the free surface is recorded above the vegetated region, while a slight rise is observed upstream of each stem series, consistent with subcritical open-channel flow. Full article

Reflective Tomography LiDAR (RTL) imaging, an innovative LiDAR technology, offers the significant advantage of an imaging resolution independent of detection distance and receiving optical aperture, evolving from Computed Tomography (CT) principles. However, distinct from transmissive imaging, RTL requires precise alignment of multi-angle echo data around the target’s rotation center before image reconstruction. This paper presents an adaptive contour closure algorithm for automated multi-angle echo data registration in RTL. A 10.38 km remote RTL imaging experiment validates the algorithm’s efficacy, showing that it improves the quality factor of reconstructed images by over 23% and effectively suppresses interference from target/detector jitter, laser pulse transmission/reception fluctuations, and atmospheric turbulence. These results support the development of advanced space target perception capabilities and drive the transition of space-based LiDAR from “point” measurements to “volumetric” perception, marking a crucial advancement in space exploration and surveillance. Full article

The dynamic response of pump valve motion directly influences the volumetric efficiency of drilling pumps and serves as a critical factor in performance enhancement. This study presents a coupled fluid–structure interaction (FSI) analysis of a novel secondary cushioned pump valve for drilling systems. A validated 3D transient numerical model, integrating piston–valve kinematic coupling and clearance threshold modeling, was developed to resolve the dynamic interactions between reciprocating mechanisms and turbulent flow fields. The methodology addresses critical limitations in conventional valve closure simulations by incorporating a geometrically adaptive mesh refinement strategy while maintaining computational stability. Transient velocity profiles confirm complete sealing integrity with near-zero leakage (<0.01 m/s), while a 39.3 MPa inter-pipeline pressure differential induces 16% higher jet velocities in suction valves compared to discharge counterparts. The secondary cushioned valve design reduces closure hysteresis by 22%, enhancing volumetric efficiency under rated conditions. Parametric studies reveal structural dominance, with increases in cylindrical spring stiffness lowering discharge valve lift by 7.2% and velocity amplitude by 2.74%, while wave spring optimization (24% stiffness enhancement) eliminates pressure decay and reduces perturbations by 90%. Operational sensitivity analysis demonstrates stroke frequency as a critical failure determinant: elevating speed from 90 to 120 rpm amplifies suction valve peak velocity by 59.87% and initial closing shock by 129.07%. Transient flow simulations validate configuration-dependent performance, showing 6.3 ± 0.1% flow rate deviations from theoretical predictions (Q_{t_max} = 40.0316 kg/s) due to kinematic hysteresis. This study establishes spring parameter modulation as a key strategy for balancing flow stability and mitigating cushioning-induced oscillations. These findings provide actionable insights for optimizing high-pressure pump systems through hysteresis control and parametric adaptation. Full article

Accurate prediction of cavitating flows is essential for improving the performance and durability of marine and hydrodynamic systems. This study investigates the influence of different cavitation models—Kunz, Merkle, and Schnerr–Sauer—on the numerical prediction of cavitation around a hemispherical head-form body using computational fluid dynamics (CFD). Additionally, the effects of turbulence modeling approaches, including Reynolds-averaged Navier–Stokes (RANS) and partially averaged Navier–Stokes (PANS), are examined to assess their capability in capturing transient cavitation structures and turbulence interactions. The results indicate that the Schnerr–Sauer model, which incorporates bubble dynamics based on the Rayleigh–Plesset equation, provides the most accurate prediction of cavitation structures, closely aligning with experimental data. The Merkle model shows intermediate accuracy, while the Kunz model tends to overpredict cavity closure, limiting its ability to capture unsteady cavitation dynamics. Furthermore, the PANS turbulence model demonstrates superior performance over RANS by resolving more transient cavitation phenomena, such as cavity shedding and re-entrant jets, leading to improved accuracy in pressure distribution and vapor volume fraction predictions. The combination of the PANS turbulence model with the Schnerr–Sauer cavitation model yields the most consistent results with experimental observations, highlighting its effectiveness in modeling highly dynamic cavitating flows. Full article

Background: Velopharyngeal insufficiency (VPI) is a failure of the sphincter mechanism, causing speech patterns like hypernasality and decreased intelligibility. Causes include structural, neurologic, and mechanical issues. Treatment options include non-surgical and surgical interventions, but complications can arise. A new approach using the buccal flap (BF) has been suggested for palatal length augmentation. This systematic review assessed speech outcomes after BF palatal lengthening. Methods: A thorough investigation was conducted by methodically reviewing numerous databases, including PubMed, Scopus, Web of Science, and Embase, until December 2024. The goal of our analysis was to find studies that assess the short- and long-term efficacy of BF on speech outcomes on patients with VPI. We used the NIH Quality Assessment Tool to assess the quality of the evidence, ensuring the dependability of the results reached during these investigations. Results: This systematic review identified 23 studies (total sample size of 995) that assessed the speech outcomes of BF on VPI. The BF significantly improves speech outcomes in patients with VPI. Hypernasality improved significantly post-surgery, with outcomes measured using different scales and methods, including both subjective and objective tools. Benefits were observed within three months postoperatively, with sustained benefits up to 15 months in several studies. Speech intelligibility also improved notably, with mean differences up to 1.09 (p < 0.001). Reductions in audible nasal air emissions were observed, though some variability was noted across studies. Secondary outcomes, including better velopharyngeal closure and decreased facial grimacing, further highlight its efficacy. However, inconsistent findings for nasal turbulence and limited long-term data suggest that benefits may plateau over time. These findings support the BF as an effective intervention, though further research is needed on extended outcomes. Conclusions: BF is an effective surgical intervention for VPI, significantly improving hypernasality, speech intelligibility, and audible nasal air emissions. While benefits are evident across diverse populations, long-term outcomes and secondary features, such as nasal turbulence, show variability, emphasizing the need for individualized approaches and continued follow-up. This technique offers a reliable option for functional and speech rehabilitation, though further research is needed to optimize its long-term efficacy and broader outcomes. Full article

An aorto-right ventricular fistula, a rare condition in humans, is characterized by communication between the ascending aorta and the right ventricle through a defect in the aortic wall. This report describes three cases of dogs with continuous murmurs: a 6-month-old Coton de Tulear, a 5-year-old Maltese, and a 6-month-old Jindo. Notably, all of the dogs presented with no severe clinical signs. Echocardiography revealed a turbulent jet through restrictive perimembranous ventricular septal defects (VSD) during systole and aorto-right ventricular fistulas secondary to ruptured sinuses of Valsalva aneurysm during diastole. In one case, a surgical closure of the VSD simultaneously resolved the aorto-right ventricular fistula. Follow-up echocardiography in the other two cases revealed mild left heart volume overload and a slight increase in the pulmonary-to-systemic blood flow ratio. However, the dogs remained asymptomatic. In conclusion, aorto-right ventricular fistulas with VSDs should be considered in the differential diagnosis of continuous murmurs in dogs. Full article

This study investigates the effectiveness of the large eddy simulation version of the Weather Research and Forecasting model (WRF-LES) in reproducing the atmospheric conditions observed during a Perdigão field experiment. When comparing the results of the WRF-LES with observations, using LES settings can accurately represent both large-scale events and the specific characteristics of atmospheric circulation at a small scale. Six sensitivity experiments are performed to evaluate the impact of different planetary boundary layer (PBL) schemes, including the MYNN, YSU, and Shin and Hong (SH) PBL models, as well as large eddy simulation (LES) with Smagorinsky (SMAG), a 1.5-order turbulence kinetic energy closure (TKE) model, and nonlinear backscatter and anisotropy (NBA) subgrid-scale (SGS) stress models. Two case studies are selected to be representative of flow conditions. In the northeastern flow, the MYNN NBA simulation yields the best result at a height of 100 m with an underestimation of 3.4%, despite SH generally producing better results than PBL schemes. In the southwestern flow, the MYNN TKE simulation at station Mast 29 is the best result, with an underestimation of 1.2%. The choice of SGS models over complex terrain affects wind field features in the boundary layer more than above the boundary layer. The NBA model generally produces better results in complex terrain when compared to other SGS models. In general, the WRF-LES can model the observed flow with high-resolution topographic maps in complex terrain with different SGS models for both flow regimes. Full article

This study conducts a numerical analysis to understand the effect of flow through the impeller–diffuser side gap on the performance and internal flow of a centrifugal pump. Three-dimensional steady-state Reynolds-averaged Navier–Stokes simulations are performed, employing the shear stress transport turbulence model for turbulence closure. To analyze the effects of side-gap flow on the main passage flow, a simplified fluid domain for the side gap is constructed and applied with a one-dimensional loss model for the leakage flow. The numerical results are validated with experimental data for performance curves and velocity components at the diffuser inlet. For a detailed analysis of the leakage flow, flow simulations are carried out for three cases: flow absence, inflow, and outflow (leakage) in the impeller–diffuser gap. Significant performance deviations are observed according to the flow direction in the gap, and the detailed fluid flow structures are examined to assess its impact on the performance. Full article

A balanced flowmeter not only inherits the advantages of orifice plate flowmeters but also stabilizes the flow field, reduces permanent pressure loss, and effectively increases the cavitation threshold. To perform an in-depth analysis of flow characteristics through the perforated plate and achieve performance optimization for the liquid hydrogen (LH₂) measurement, a numerical calculation framework is established based on the mixture model, realizable turbulence closure, and Schnerr–Sauer cavitation model. The model is first evaluated through comparison with the liquid nitrogen (LN₂) experimental results of a self-developed balanced flowmeter as well as the measuring setup. The flow coefficient and pressure loss coefficient are especially considered, and a comparison is made with the orifice plane considering cavitation and non-cavitation conditions. The cavitation cloud and temperature contours are also presented to illustrate the difference in the upper limit of the Re between water, LN₂, and LH₂ flow. The results show that compared to LN₂ and water, LH₂ has a larger cavitation threshold, indicating a wider range of Re number measurements. Full article

The present work investigates the influence of rectangular deflectors on the performance of a Savonius turbine mounted in an L-shaped channel, which represents a geometry like that found in one oscillating water column (OWC) device. It also performs a geometric investigation of the entrance region of the channel. More precisely, it investigates the effect of the height/length ratio (H₁/L₁) of the entering region of the channel on the system performance for three different configurations: (1) without the use of deflectors, (2) with just one deflector upstream the turbine, and (3) with one deflector upstream and another downstream the turbine. The geometric investigation is performed based on the constructal design method, and the entering channel area (A₁) is the problem constraint. The performance indicators are the mechanical power in the Savonius turbine and the available power in the device. For all cases, it is considered turbulent airflow in the domain, being solved by the unsteady Reynolds Averaged Navier–Stokes mass and momentum equations. The numerical solution was obtained with the finite-volume method using the Ansys FLUENT software (version 2021 R1). The k-ω shear stress transport turbulence closure model is used. The results demonstrated that the mechanical and available powers depend on the H₁/L₁ ratio, regardless of the usage of deflectors. For instance, differences of up to 16.35% in mechanical power and 7.25% in available power were observed between the best and worst performance configurations in the case without deflectors. The use of deflectors resulted in increases of two and three times in available and mechanical powers, respectively, when the cases with one and two deflectors are compared with those without deflectors. This demonstrates that the enclosed domain and the insertion of the deflectors can enhance the performance of the Savonius turbine. Full article

The correct prediction of the wind speed and turbulence levels over complex terrain is essential for accurately assessing wind turbine wake recovery, power production, safety, and wind farm design. In this paper, two modified RANS turbulence models are proposed, which are innovative variants of the conventional SST k-ω model and the linear Reynolds stress model (RSM) featuring optimized closure constants. Then, these two modified models and their origin models are applied to compare and analyze wind flows from a 3D hill wind tunnel experiment and two field measurements over typical complex terrain, including Askervein hill and Bolund island, with the aim of analyzing the sensitivity of wind flows to different RANS turbulence models. The study focuses on analyzing the effects of different turbulence models on the self-sustainability of wind speed and turbulent kinetic energy upstream of the computational domain and on the accuracy of wind flow prediction over complex terrain. The results show that our modified RSM model shows better agreement with the available experimental data on the upstream and leeward sides of all simulated hills. The wind speed on the leeward slope is particularly sensitive to the turbulence model, with a maximum difference in the relative root mean square error (RRMSE) that can reach 11% among the four models. The accuracy of the turbulent kinetic energy depends on the self-sustainability of the upstream turbulent kinetic energy and the predictive ability of the turbulence model for separated flows, and the maximum difference in the RRMSE of the four models can reach 47%. In addition, the advantages and disadvantages of the tested models are discussed to provide guidance for model selection during wind flow simulations in complex terrain. Full article

Casting AISI 52100 steel represents a challenge, particularly at the start of the casting sequence, due to its low melting point. The steel spilling over the tundish bottom cools down rapidly and freezes in the stopper rods, obliging the closure of a strand. Therefore, an additional function of turbulence inhibitors is to induce steel masses at a slow cooling rate. This paper deals with the physical and mathematical modeling of unsteady state-flows using two turbulence inhibitors (TIs) during the sequence start. One of the TIs makes steel spill forming thin layers of liquid on the tundish bottom, while the other forms a thicker layer. Based on the Flow of Volume Model, the mathematical simulation was satisfactorily replicated in the water model. Full article

The current paper focuses on the assessment of radial mesh influence on the description of the transient event obtained by an axisymmetric model. The objective is to reduce computational effort while accurately calculating hydraulic transients in smooth–turbulent pressurized pipes. The analyzed pipe system has a reservoir–pipe–valve configuration with an inner diameter of 0.02 m and a total length of 14.96 m, with the initial discharge being equal to 120 × 10⁻³ L/s (Re = 7638). An extensive study is carried out with 80 geometric sequence meshes by varying the total number of cylinders, the geometric common ratio, and the pipe axial discretization. The benefit of increasing the geometric common ratio is highlighted. A detailed comparison between two meshes is presented, in which the best mesh (i.e., the one with the lowest computational effort) has a three-fold higher value of the geometric common ratio. The two meshes show small differences for the instantaneous valve closure, limited to a time interval immediately after the arrival of the pressure surge and only during the first pressure wave. The dynamic characterization of the transient phenomenon demonstrates the in-depth consistency between the model results and the hydraulic transients’ phenomenon in terms of the piezometric head, the wall shear stress, and the mean velocity time-history, in comparison to the results obtained with the shear stress, lateral velocity, and axial velocity profiles. Full article

This paper presents a comparison of two turbulence models implemented in two different frameworks (Eulerian and Lagrangian) in order to simulate the motion in calm water of a displacement hull. The hydrodynamic resistance is calculated using two open-source Computational Fluid Dynamics (CFD) software packages: OpenFOAM and DualSPHysics. These two packages are employed with two different numerical treatments to introduce turbulence closure effects. The methodology includes rigorous validation using a Wigley hull with experimental data taken from the literature. Then, the validated frameworks are applied to model a ship hull with a 30 m length overall (LOA), and their results discussed, outlining the advantages and disadvantages of the two turbulence treatments. In conclusion, the resistance calculated with OpenFOAM offers the best compactness of results and a shorter simulation time, whereas DualSPHysics can better capture the free-surface deformations, preserving similar accuracy. Full article