Search Results (206)

To clarify the effects of splitter blades on hydraulic performance and internal energy dissipation in a double-suction pump as turbine (PAT), full-passage CFD models of a PAT and a PAT with splitter blades were established and experimentally validated. Same-flow-rate cross-comparisons at the BEP flow rates of the configurations distinguished geometric effects from flow-rate effects. Impeller loss redistribution was analyzed using entropy generation, LEGR, TKE, and radial-flow characteristics. The splitter blades shifted the BEP flow rate from 1350 to 1708 m³/h, an increase of 26.52%, and increased the maximum efficiency from 85.61% to 87.72%. Turbulent and wall entropy generation dominated the loss, whereas direct viscous entropy generation contributed less than 1%. At the prototype BEP flow rate, the normalized volumetric entropy-generation coefficient over Regions I–O decreased by 10.31%; at the splitter-blade BEP flow rate, the reduction reached 60.71%, with Region M decreasing by 66.33% and providing the dominant absolute loss reduction. At the higher flow rate, splitter blades restricted the lateral expansion of low-velocity regions, weakened large-scale separation and continuous high-LEGR shear structures, and confined the remaining high-loss regions to blade leading edges, splitter-blade wakes, and local flow-recombination zones. These results show that splitter blades improve high-flow-rate performance by suppressing separation- and shear-related volumetric dissipation and redistributing impeller energy losses. Full article

Aneurysmal bone cysts (ABCs) are benign but locally aggressive osteolytic lesions that are rarely reported in dogs and may progress or recur following surgical treatment. This case report describes the diagnosis, surgical management, postoperative progression, and long-term outcome of an ABC affecting the left ulna of a four-month-old Labrador Retriever. Radiography and computed tomography revealed a rapidly progressive, expansile osteolytic lesion with marked cortical thinning. Histopathological examination supported the diagnosis of ABC, with no evidence of malignancy. Initial treatment consisted of corticotomy, intralesional curettage, autologous bone grafting, and stabilization of the cortical segment with lag screws. Despite complete clinical resolution of lameness, surveillance radiographs six weeks postoperatively demonstrated progression of the lesion proximal to the original surgical site. Revision surgery involving a larger cortical window and more extensive curettage was subsequently performed, followed by bone grafting. Histopathology again confirmed ABC without malignant transformation. The dog regained normal limb function, and serial radiographic and computed tomographic examinations demonstrated progressive osseous remodeling with no evidence of further progression or recurrence through 35 months of follow-up. This case highlights the importance of adequate surgical excision and scheduled postoperative imaging, as ABC progression may occur despite apparent clinical recovery. Full article

Accurately simulating convective initiation (CI) in capped High Plains dryline environments remains a significant challenge for convection-permitting numerical weather prediction. As a follow-up work to Lu and White, this study utilizes the Model for Prediction Across Scales (MPAS) at a 3 km grid resolution to evaluate the sensitivity of dryline morphology and CI to two planetary boundary layer (PBL) parameterization schemes: the non-local Yonsei University (YSU) and the local Mellor-Yamada-Nakanishi-Niino (MYNN) frameworks. Radar observations and simulated maximum reflectivity show that while the YSU scheme successfully replicates the timing and spatial development of convective cores triggered along the elevated terrain slope at 21:30 UTC, the MYNN scheme completely suppresses deep convection throughout the study period. Vertical thermodynamic profiles indicate that YSU establishes a deeply mixed boundary layer that weakens the regional capping inversion, enabling surface parcels to break the stable lid and reach their level of free convection (LFC). Conversely, the MYNN scheme confines moisture to a thin layer near the surface beneath an unyielding temperature inversion, preventing parcels from achieving free buoyancy. For the 3 km “grey zone” of turbulence resolution, both PBL schemes successfully resolve horizontal convective rolls (HCRs) near the primary dryline boundary. YSU’s non-local mixing permits these HCR perturbations to couple vertically into deep, cap-breaching updraft plumes, while MYNN’s local turbulent kinetic energy (TKE) closure traps them as shallow horizontal waves. It was shown that the MYNN failure is driven by an intrusive synoptic wind bias, generating anomaly wind velocities of 24–28 m/s throughout the column. These winds act as a mechanical sweeper across the terrain slope which shears, flattens, and dilutes the moisture pool below 2000 m Mean Sea Level (MSL) and physically reduces fuel from the western initiation zone. In contrast, the YSU scheme maintains a well-regulated, moderate wind profile (8–12 m/s aloft), preserving a state of mesoscale equilibrium that allows moisture to ascend the terrain slope and continuously feed developing convective cells. Our findings demonstrate that the choice of PBL parameterization plays significant role in not only local vertical mixing but also the structural translation of macroscale synoptic forcing versus localized thermodynamic regulation in complex terrain. Full article

This study compares the standart (STD) piston with a specially designed MR-1 piston that better meets modern requirements. Firstly, the experimental comparison was conducted at 3000 rpm, with static fuel injection timing advance (ITA) of (30°, 25°, 20°, 17.5°) CA BTDC, and engine load conditions of 100%, 75%, 50%, 25%. Subsequently, the combustion chambers (CCs) were simulated at the same ITA to examine in-cylinder phenomena in more detail. Analysis was performed at full load, where emissions are critical. Reducing the ITA to decrease combustion temperature and NOx emissions resulted in higher soot and UHC emissions, particularly for the STD chamber. However, this trend was not observed with the MR-1 chamber. NOx was reduced further thanks to the lower local peak temperatures, and there was no increase in soot without a significant loss in performance. The increase in UHC was negligible compared to the STD, while CO decreased. The advantages of the MR-1 can be attributed to its ability to increase air movement in the vertical direction, which is better suited for the bowl geometry and spray direction. This results in improved mixture formation in the cylinder by increasing turbulent kinetic energy (TKE) to an optimal level. Additionally, the temperature distribution is more uniform when considering dimensions, heat release duration is shortened and lower pressure and pressure rise rate are achieved. Full article

Fish can perceive and respond to local flow structures when selecting microhabitats, yet how scale-dependent hydrodynamic heterogeneity shapes behavioral habitat choice remains poorly understood. In this study, a multi-scale rock-array flow field was constructed using flume experiments, and the volitional swimming behavior of Schizothorax grahami was observed. Hydrodynamic parameters including velocity magnitude (U_mag), turbulent kinetic energy (TKE), and kinetic energy gradient (KEG) were analyzed. The results indicated that fish distribution changed with rock size: at a rock-element diameter of 0.12 m, fish were dispersed without forming stable high-utilization core areas; at 0.24 m, fish aggregated in the lee-side regions behind the rock elements; and at 0.50 m, fish shifted toward the upstream faces. The hydrodynamic variables significantly associated with fish microhabitat selection varied with rock-array scale: in the 0.24 m rock arrays, KEG differed significantly between high- and low-use units under all flow conditions; in the 0.50 m rock arrays, U_mag and TKE showed consistent and significant between-group differences across flow conditions. Moreover, cross-scale overlap analysis revealed that the utilization range of velocity magnitude had the highest overlap, followed by TKE, with KEG exhibiting the lowest overlap. Collectively, these findings support a hierarchical interpretation of fish microhabitat selection characterized by “velocity rigidity–turbulence elasticity,” providing a potential perspective for understanding differences in the hydrodynamic variables associated with fish microhabitat selection across studies. These results indicate that both mean velocity constraints and local turbulence-creating structures should be considered in river habitat restoration and roughness element configuration. Full article

In this study, the author investigated the wake characteristics of a shrouded wind turbine and performed a high-resolution large-eddy simulation (LES) investigation using a supercomputer. The turbulent kinetic energy (TKE) of the shrouded wind turbine was significantly greater than that of a conventional wind turbine (non-shrouded wind turbine) in the range of x/D = 0 to 5 (where x is the distance downstream of the hub center and D is the rotor diameter), due to large-scale vortices generated and released from the brim of the shrouded wind turbine and the separated flow from the nacelle. For example, the TKE was 4.4 times larger at x/D = 2. Significant differences were also observed in the wake width. The wake width of the shrouded wind turbine was approximately 2.4 times wider than that of the conventional wind turbine. In contrast, the shrouded and conventional wind turbines exhibited nearly similar behaviors in the far-wake region downstream of x/D = 5. Furthermore, a calculation was performed for the shrouded wind turbine while omitting the brim connected to the diffuser. While flow separation from the diffuser is clearly observed, the numerical results for the shrouded wind turbine without the brim connected to the diffuser showed a flow pattern very similar to that of a conventional wind turbine. Full article

A novel bilateral-symmetric, multi-slot fishway (BMSF-R11) was recently developed, which has more migration space for fish, and lower mainstream velocity and turbulence than traditional vertical-slot fishways (VSFs) under the condition of the same slot width. This study aims to verify that, relative to a VSF, the BMSF-R11 is more favorable for the upstream migration of moderately swimming fishes. Three-dimensional numerical simulations were performed to determine hydrodynamic properties in both a VSF and the BMSF-R11, and laboratory fish-passage experiments using silver carp (Hypophthalmichthys molitrix, a moderately swimming fish species) were conducted to provide fish-passing characteristics. As expected, the BMSF-R11 possessed much higher fish-passing efficiency than the VSF (e.g., the passage success rate (PSR) was 90–93% vs. 57–63% and the entrance efficiency (EE) was 90–98% vs. 55–63%), due to the former’s much better hydrodynamic performance. There are two primary roughly linear fish-passing paths in a VSF, but four primary S-shape fish-passing paths are present in the BMSF-R11. Furthermore, this study reveals the inherent relationships among fish-passing efficiency parameters, fish-swimming trajectory, fish-occurrence frequency, and hydrodynamic properties in both a VSF and the BMSF-R11. This study contributes to conserving fishery resources and aquatic biodiversity, especially for migratory fish with moderate swimming abilities. Full article

This study investigates the aerodynamic and thermal impacts of tire sidewall cooling fins on a passenger vehicle using high-fidelity computational fluid dynamics (CFD) simulations. Continuous heat accumulation from tire rotation and road friction can degrade structural durability. To address this thermal challenge, a parametric study was conducted on the DrivAer notchback vehicle model across various fin angles from −67.5° to 67.5°. The results revealed a distinct design space that offers simultaneous aero-thermal improvements. Specifically, the 22.5° fin configuration demonstrates a dual-benefit performance, achieving a 3.79% net reduction in overall vehicle drag alongside a 17.36% increase in the average heat transfer coefficient (HTC). Conversely, the −22.5° configuration yields the maximum cooling enhancement with a 30.49% increase in average HTC but incurs a 2.52% drag penalty. Microdrag and Turbulent Kinetic Energy (TKE) analyses successfully explain the underlying fluid mechanisms governing these trade-offs. These findings provide practical design guidelines for flow control on rotating wheels, showing that tire sidewall geometries can enhance full-vehicle aerodynamic efficiency and tire thermal reliability. Full article

Throughfall kinetic energy (TKE) is a physically based index of raindrop-driven splash erosion potential in forest ecosystems. In Japanese cypress plantations, TKE shows substantial spatial heterogeneity beneath the canopy, but the stand structural factors controlling this variability remain poorly understood. Under-canopy structures, such as the dead-branch layer in unmanaged stands, may contribute to localized variation in throughfall erosivity. This study quantified TKE in two unmanaged Japanese cypress plots and examined whether stand structural attributes, particularly the lowest dead-branch height (H_db), explained within-stand variability. Throughfall (TF) gauges and sand-filled splash cups were co-located at 20 measurement points in each plot, and gross rainfall (GR) and free kinetic energy (FKE) were measured in an adjacent open space. TKE beneath the canopy exceeded FKE, indicating canopy enhancement of rainfall erosivity. Stand-mean TKE was similar between the two plots, whereas TKE varied markedly among measurement points within stands. H_db showed a significant but modest positive association with TKE (r = 0.447, R² = 0.20, p < 0.01) in both plots. These results suggest that the under-canopy structure, including H_db, is associated with within-stand spatial heterogeneity in throughfall erosivity. The normalized stand-mean TKE (unit $\overline{\mathrm{T}\mathrm{K}\mathrm{E}}$) values were consistent with the reported relationship between stem density (SD) and unit $\overline{\mathrm{T}\mathrm{K}\mathrm{E}}$. These findings highlight the importance of considering H_db and SD in spatially explicit assessments of potential splash erosion risk. Full article

This study experimentally examines turbulent flow structures induced by the coupled interaction of transverse bank slope, rigid vegetation, and bed roughness heterogeneity in a compound channel. Three-dimensional velocity components were measured using Acoustic Doppler Velocimetry (ADV) in a 13 m long flume under three transverse bank slopes (0°, 10°, and 25°), both with and without submerged rigid vegetation. Quantitatively, the presence of vegetation on the sloped bank reduced local flow velocity by 40–50% due to drag caused by vegetation canopy, while the accelerating flow in the main channel reduced by 25–35%. The combined effect of a steep 25° slope and vegetation amplified the turbulent kinetic energy (TKE) by ~55% and maximum Reynolds shear stress (RSS) by 50–70% at the sand–gravel interface compared to bare-bed conditions, generating a rigorous lateral shear layer. These quantitative insights provide critical design guidance for river restoration, bank protection, and flood management. The identified interactions between bank slope and vegetation establish a predictive framework for mitigating localized scour and bank erosion while optimizing channel conveyance capacity in ecologically managed river systems. Full article

This study investigates the impact of internal muffler geometry on flow-related dissipation characteristics potentially relevant to acoustic behavior using steady-state Computational Fluid Dynamics (CFD) simulations. Four variants were analyzed: an empty tube, considered to be a baseline model, a three-chamber baffle system, a single spiral channel, and a complex multi-channel insert manufacturable only via advanced additive technologies. Simulations were conducted in SimScale using a compressible flow model with the k-ω SST turbulence formulation. Key outputs included static pressure distribution and turbulent kinetic energy (TKE), both of which were evaluated as qualitative surrogate indicators associated with flow-induced energy dissipation phenomena. The results indicate that geometries incorporating spiral features modify flow redistribution patterns, pressure gradients and localized turbulence intensity, suggesting potential applicability for future acoustic optimization studies. The study highlights how additive manufacturing enables the integration of geometrically complex internal structures otherwise unattainable through conventional methods. By comparing pressure drop and TKE patterns with internal design features, the research offers a preliminary CFD-based framework for geometry screening and conceptual evaluation of muffler insert designs for automotive exhaust systems. This approach provides computational support for rapid comparative assessment prior to experimental validation and detailed acoustic analysis. Full article

Denil fishways exhibit limited passage efficiency for weak-swimming and benthic species, partly due to severe near-bed hydrodynamics generated by the sharp V-notch apex of conventional baffles. Modifying bottom geometry is a promising optimization pathway, but previous studies often lack rigorous comparison under constrained baffle openness ratios. This study employed CFD with the RNG $k-\epsilon$ turbulence model to evaluate conventional V-shaped (TDF), equivalent U-shaped (SCDF), and rectangular (RDF) baffles under a unified openness ratio. A layered hydrodynamic evaluation framework demarcated by the effective blocking height was developed to distinguish flow responses in the upper jet-dominated and lower baffle-controlled layers. Results show that the upper-layer conveyance indicators remain broadly comparable across configurations, whereas the lower-layer indicators show configuration-related differences within the tested discharge range. The RDF and SCDF reduce lower-layer mean velocity and TKE relative to the TDF baseline across the tested discharge range, with the RDF achieving the larger velocity reduction and the SCDF the larger TKE reduction. The maximum relative reduction in lower-layer TKE, approximately 22%, occurs under intermediate discharge. These results suggest that bottom baffle geometry can provide a potential means of adjusting near-bed hydraulic conditions in Denil fishways, although the ecological consequences require further verification. Full article

This study examines the effects of jet Reynolds number (Re) and jet hole diameter (d) on flow and heat transfer in the leading-edge full-impingement cooling channel of a gas turbine nozzle guide vanes (NGV). Experiments via transient liquid crystal and numerical simulations were conducted. Results reveal that the peak Nusselt number (Nu) initially increases and then reaches a fixed value from root to tip in the spanwise direction. The area-averaged Nu presents the descending trend of the shower-head surface, pressure surface, and suction surface. In addition, the bleeding from film holes causes significant local flow acceleration and Turbulence Kinetic Energy (TKE) enhancement of 10.69%, resulting in local heat transfer elevation. The heat transfer enhancement region on both pressure and suction surfaces is inclined towards the shower-head at a 5% span region. Increasing the jet hole diameter (d) results in a decrease in both averaged Nu and TKE on the target surface. Simultaneously, the Nu gradient increases. When d = 1.6 mm, there is a recirculation zone near the hub on the suction surface and a strong crossflow near the hub on the pressure surface. The jet flow on the target surface is bending towards the shower-head. When d = 0.8 mm, the overall heat transfer is highest. However, considering heat transfer uniformity, a jet hole diameter of d = 1.2 mm offers better application. Full article

The performance of the meteorological measurements of an Unmanned Aircraft System (UAS) is studied in this paper by comparison with the simultaneous data collected by a wind mast, a radiosonde sensing package and ground-based, remote-sensing meteorological instruments at the radiosonde station of King’s Park, Hong Kong. They are found to meet the “breakthrough” level requirement of the World Meteorological Organization. The UAS is then used to collect meteorological data for the first time at a sandbox project location in Hong Kong for low altitude economy (LAE), namely, an area of complex terrain at an isolated island called Peng Chau. Some interesting features are identified in the vertical profiling flight of wind speed and turbulent kinetic energy (TKE), which forms the basis for developing meteorological support for LAE at this site in the future. High-resolution numerical weather prediction (NWP) simulation is then performed and evaluated statistically by comparison with UAS measurements at these two locations. The simulation of wind direction and TKE appears to be rather challenging as demonstrated in this comparison exercise. The root-mean-square-error of the simulated TKE is found to be of a similar order of magnitude as the absolute value itself, and the wind direction from the outer domain is found to have limited “correction” with the use of high-resolution terrain data in the NWP simulation with the mesoscale model. Further research directions for the simulation are discussed, with the objective of providing weather forecasting services for supporting LAE developments in Hong Kong. Full article

Accurate characterization of coherent vortex structures in high-speed turbulent boundary layers presents a persistent challenge due to the flow’s high dimensionality and nonlinear dynamics. This study investigates an optimized decomposition framework that integrates modal decomposition techniques with a novel vortex identification strategy to extract dynamically significant features. The numerical solution from a previously conducted high-fidelity simulation of MVG-controlled supersonic flow serves as the testbed. Principal Component Decomposition and Non-negative Matrix Factorization are applied across multiple flow variables to evaluate their effectiveness in isolating coherent structures. The results show that, across the velocity-based cases, 3–4 modes capture 70% of the TKE with MSE about 0.1, while the Liutex case requires 14 modes but achieves a lower MSE of about 0.04. Overall, using the same number of modes yields similar reconstruction performance across all cases. The influence of various normalization and rescaling methods on decomposition performance is also examined. Optimization is guided by two primary criteria: the interpretability of spatial modes and MSE in reconstructing vortex structures. By employing low-rank matrix representations, this optimization study aims to enhance interpretability and reduce computational costs. This approach establishes a mathematically rigorous and efficient platform for analyzing vortex dynamics, achieving significant dimensionality reduction while preserving key features of turbulent transport. Full article