Internal Flow Research Articles

Optimization of 3D Printing Nozzle Structure and the Influence of Process Parameters on the Forming Performance of Underwater Concrete

Underwater concrete 3D printing (3DPC) technology, as a pioneering construction process, has demonstrated significant potential in various fields, such as marine engineering, underwater restoration projects, and ecological construction. However, the complexity and variability of the underwater environment pose stricter quality standards for the printed structures. To address this, this study employed a self-developed framed concrete 3D printer and utilized response surface methodology to optimize the structural dimensions of the printing nozzle. Through in-depth analysis of the internal flow field of printing nozzles with various size combinations using ANSYS Fluent 2022R1 software, an optimal parameter configuration was determined, including a nozzle diameter (D) of 55 mm, an inclination angle (θ) of 20°, and a length (L) of 34 mm, ensuring uniform extrusion of the concrete material. Furthermore, this study applied an orthogonal experimental design to systematically investigate the combined effects of screw speed, printing speed, and nozzle height on the print quality and mechanical properties (compressive strength and flexural strength) of underwater concrete 3D printing. The experimental results, presented based on direct observation and analysis, identified the optimal combination of process parameters: a printing speed of 16 mm/s, a nozzle height of 10 mm, and a screw speed of 50 r/min. This combination ensures efficient printing while maintaining the mechanical properties of the printed samples. This study not only provides solid scientific and practical guidance for optimizing the nozzle structure and process parameters of underwater concrete 3D printing technology but also offers innovative solutions to underwater construction challenges in the field of marine resource development and utilization.

Analysis and Optimization Design of Internal Flow Evolution of Large Centrifugal Fans Under Inlet Distortion Effects

Large curvature, high pre-swirl large high-speed centrifugal fans are the preferred choice for industrial gas quenching furnaces, as they need to operate under non-uniform inlet conditions for extended periods. The resulting inlet distortion disrupts the symmetric flow of the gas, leading to reduced fan stability and phenomena such as flow separation and rotational stall. This issue has become a key research focus in the field of large centrifugal fan applications. This paper introduces an eddy viscosity correction method, and compares it with experimental results from U-shaped pipe curved flow. The corrected SST k-ω model shows a maximum error of only 4.7%. Simulation results show that the fan inlet generates a positive pre-swirl inflow with a relative distortion intensity of 3.83°. The flow characteristics within the impeller passage are significantly affected by the swirl angle distribution. At the maximum swirl angle, the leakage flow at the blade tip develops into a stall vortex that spans the entire passage, with an average blockage coefficient of 0.29. At the minimum swirl angle, the downstream leakage flow at the blade tip is suppressed on the suction side by the main flow, leading to a reduced vortex structure within the passage and an average blockage coefficient of 0.21. To address the design challenges of large high-speed centrifugal fans under inlet distortion, a blade design method based on secondary flow suppression is proposed. Eleven impeller flow surfaces are selected as control parameters, and the centrifugal impeller blade profile is redesigned. Numerical simulations and experimental results of the gas quenching furnace’s flow and temperature fields indicate that the modified impeller significantly reduces the blade tip leakage flow strength, with the average blockage coefficient decreasing to 0.07 and 0.04, respectively. The standard deviation of the average flow velocity at the test section is reduced by 42.78% compared to the original, and the temperature fluctuation at the workpiece surface is reduced by 53.09%. Both the flow and temperature field uniformity are significantly improved.

Structural Optimization and Fluid–Structure Interaction Analysis of a Novel High-Speed Switching Control Valve

Laver fluffy is an indispensable link in the processing of laver products. After fluffing, the laver acquires an appealing color, which is conducive to better marketability. During the primary mechanical processing of laver, a valve capable of rapid opening and closing is required to ensure that the laver’s surface becomes fluffy and lustrous post-processing. However, valve products that can meet the specific requirements of laver fluffing are scarce. This study proposes a novel principle for a high-speed switching control valve. This valve can quickly turn on or cut off the high-pressure gas path during laver processing while also taking into account the response speed and service life. The structure and principle of the new control valve were introduced. Different flow field models in the valve were designed, and their flow characteristics and flow field performance under various schemes were compared and discussed by using Fluent. Subsequently, an optimized control valve structure model was proposed. Based on this, a strength analysis of the control valve was conducted via fluid–structure interaction, revealing the response characteristics of the valve under the working state. The results indicate that, when different cone angles and bell shapes were selected for the upper chamber inlet of the control valve, the number and intensity of vortices in the upper chamber can be reduced. The height of the upper chamber affected the formation of the throttle between the top and bottom surfaces of the upper chamber. When the height of the upper chamber was 32 mm, the energy loss in the upper chamber remains basically stable. Simultaneously changing the inlet shape and height of the upper chamber can effectively prevent the throttle formed by the height of the upper chamber, which was conducive to increasing the valve outlet flow rate. Through the analysis of the flow field with different valve chamber structures, the improved control valve adopted the bell-shaped inlet, with an upper chamber height of 32 mm and curved transition for the internal flow channel. Compared to the original fluid domain, when the opening was 100%, the outlet flow rate of the 10° conical tube and bell-shaped inlet increased by 12.77% and 12.59%, respectively. The outlet flow rate at the curved transition position rose by 15.35%, and the outlet flow of the improved control valve increased by 32.70%. When the control valve was operating under a preload pressure of 1 MPa, at 20% opening, the maximum equivalent stress of the valve body was 52.51 MPa, and the total deformation was 12.56 microns. When the preload pressure exceeded 1.5 MPa, the equivalent stress and total deformation of the control valve body and T-shaped valve stem exhibited an upward trend with further increases in the preload pressure.

Study on friction pressure drop characteristics of gas flow through multi-size irregular high-purity magnesia bed layer

Abstract As the primary production equipment for high-purity magnesia, shaft kilns are extensively employed in metallurgical and chemical processes. Understanding and optimizing the internal flow dynamics and heat transfer mechanisms within high-purity magnesia shaft kilns can significantly enhance production efficiency and product quality while reducing energy consumption and mitigating environmental impacts. Particularly, the airflow characteristics in shaft kilns directly impact burner selection, bed height, fan selection, and fan power consumption, consequently affecting heat transfer properties within the kilns. The airflow pressure drop across the high-purity magnesia particle bed under varying operational conditions was systematically investigated via experimentation utilizing a self-built experimental setup. Initially, the fundamental macroscopic attributes of high-purity magnesia particles, including particle size distribution, density, sphericity, and voidage, were meticulously quantified. Subsequently, employing the aforementioned experimental platform, the impacts of differing gas apparent flow velocities and particle equivalent diameters on gas flow pressure drop were assessed and analyzed. Incorporating considerations for the wall effect, the existing frictional pressure drop correlation was recalibrated through fitting procedures to derive an experimental correlation characterizing gas flow pressure drop within the high-purity magnesia particle bed layer, with subsequent verification of its applicability. The findings reveal a linear relationship between the wall-corrected frictional pressure drop, f w and the wall-corrected particle Reynolds number, Rew, with a gradual increase in the slope of the curve. Considering the substantial deviation between experimental data and previously established resistance correlation equations, a novel resistance correlation applicable to the high-purity magnesia bed was formulated through data fitting. The pressure drop correlation obtained in the present work can well predict the gas flow resistance in the multi-size high-purity magnesia bed with an error of less than 7 %.

Unsteady Flow and Pressure Pulsation Characteristics in an Ultra-High-Speed Centrifugal Pump Considering the Weak Compressibility Effect

Abstract Ultra-high-speed centrifugal pumps are frequently utilized in the chemical, aerospace, and other industries due to their significant head and compact geometrical size. The pump's complex flow structures and excitation characteristics are critical for stable operation. Under the impact of ultra-high pressurization and rotating speeds, the fluid inside the pump exhibits weak compressibility and the corresponding effects on the pump's internal flow structure and pressure pulsation patterns remain unclear. This study employs the Delayed Detached Eddy Simulation (DDES) numerical method to investigate the effects of the medium's weak compressibility on the internal flow field structure of an ultra-high-speed centrifugal pump, with a particular focus on pressure pulsations. Results indicate that under weak compressibility conditions, the density and velocity distribution of the fluid inside the pump are influenced. Moreover, the weak compressibility of the medium impacts the pressure pulsation signals under the design condition, especially for the monitoring points around the volute tongue where the amplitude is approximately 60~85% of that in the incompressible state, besides, a significant impact under low flow rate is generated. By comparing the blade passing frequency amplitude and the root mean square (RMS) energy within the 0-100 kHz frequency band, it is evident that considering weak compressibility effects results in overall lower pressure pulsation energy within the pump compared to the incompressible state. This finding suggests that the weak compressibility effect of the fluid has a suppressive influence on pressure pulsation in ultra-high-speed centrifugal pump.

Migration and deformation of a droplet enclosing an active particle

The encapsulation of active particles, such as bacteria or active colloids, inside a droplet gives rise to a non-trivial shape dynamics and droplet displacement. To understand this behaviour, we derive an asymptotic solution for the fluid flow about a deformable droplet containing an active particle, modelled as a Stokes-flow singularity, in the case of small shape distortions. We develop a general solution for any Stokes singularity and apply it to compute the flows and resulting droplet velocity due to common singularity representations of active particles, such as Stokeslets, rotlets and stresslets. The results show that offsetting of the active particle from the centre of the drop breaks symmetry and excites a large number of generally non-axisymmetric shape modes as well as particle and droplet motion. In the case of a swimming stresslet singularity, a run-and-tumble locomotion results in superdiffusive droplet displacement. The effect of interfacial properties is also investigated. Surfactants adsorbed at the droplet interface counteract the internal flow and arrest the droplet motion for all Stokes singularities except the Stokeslet. Our results highlight strategies to steer the flows of active particles and create autonomously navigating containers.

Numerical simulation of voluntary respiration in a model of the whole human lower airway.

The lung model construction is limited to the local scale, and the numerical simulation of autonomous breathing is mostly computed from top to bottom in recent research. In this study, models of the entire lower airway from G0-G23 were constructed, and computational simulations were performed for the alveolar model using coupled fluid-solid analysis with pressure changes on the wall and for the rigid bronchial model using computational fluid dynamics by transmitting the boundary conditions step from bottom to top. This paper provides the results under spontaneous respiration, including the ventilation volume of the tracheobronchial tree, the situation of the internal flow field, and the mechanical characteristics of the lung tissues. The mechanical characteristics and the lung functions computed by the models were consistent with clinical or experimental data. This model could provide quantitative analysis results of respiratory mechanics in the lower respiratory tract of the human, which offers a reference for mechanical studies, such as the morphological changes and differentiation of cell types induced by force stimulation and tumor induction. Furthermore, various pathological models can be developed based on this model.

Image findings and pathological findings of lymphoepithelial cysts with hyper internal echo-a comparison with dermoid cysts.

To summarize the ultrasonography (US) and magnetic resonance imaging (MRI) findings of lymphoepithelial cysts (LECs) and dermoid cysts (DCs) and to discuss the hyperinternal echo in LECs based on histopathological findings. Patients who underwent US and MRI before resection and whose lesions were pathologically diagnosed as LECs or DCs were included (January 2010 to December 2023). Internal echo, convective flow, and Doppler signals were evaluated on US, while on MRI, we measured the apparent diffusion coefficient (ADC). Surprisingly, all lesions (4 LECs and 7 DCs) had hyperinternal echoes. Convective flow and Doppler signals were observed in 2 of the 4 cases of LEC, and the ADC was high in these cases (2.4 × 10-3 and 2.0 × 10-3mm2/s). In the two cases where they were not, the ADC was low (1.4 × 10-3 and 0.81 × 10-3mm2/s). Various cells, such as lymphocyte cells, foam cells, erythroid cells, and keratin, have been found in the cystic cavity, which are thought to be the cause of hyperecho. Considering the ADC, the presence or absence of convection and Doppler signals is thought to reflect the ease of movement of the contents. In the DCs, neither internal convection nor obvious Doppler signals were observed. ADCs were quite low for cysts, which was a characteristic finding (1.1 ± 0.13-3mm2/s). It is well known that DCs appear hyperechoic on US owing to the presence of keratin; however, it is necessary to recognize that some LECs are depicted as hyperechoic masses and have convective flow and Doppler signals depending on the content.

Principles of hydrodynamic particle manipulation in internal Stokes flow

Principles of hydrodynamic particle manipulation in internal Stokes flow

Experimental and numerical studies on the hydraulics of stepped spillways with baffle walls and blocks

ABSTRACT The present experimental study investigates the effect of baffle walls and baffle blocks with different heights on the hydraulics and energy dissipation of stepped spillways. Image processing technique was employed to detect internal flow motion, and experiments were simulated to extract detailed information to examine the effect of baffles on flow motion and energy dissipation. The results indicated that placing baffle blocks initiated transverse flows in the spillway, leading to an increase in energy dissipation rate. It was found that the energy dissipation rate increased with increasing the baffle block’s height and reducing the baffle’s width. The optimum baffle’s geometry was achieved when the baffle’s width was 5% of the spillway width and the baffle’s height was 76% of the step height. At the maximum discharge, the optimum baffle geometry was able to dissipate 39% more energy than that of a spillway without baffles. Three zones of Redirected Flow (RF), Mixing Zone (MZ), and Recirculation Zone (RZ) were identified under the pseudo-bottom line, and the size of defined zones plays an important role in energy dissipation rate. Furthermore, the results showed the formation of four complete cycles with approximately 25% of the spillway’s width on each step of the spillway.

Study on the correlation between color Doppler flow imaging and histopathology of choroidal melanoma

Objective: To explore the correlation between the characteristics of color Doppler flow imaging (CDFI) and histopathological manifestations of choroidal melanoma (CM). Methods: This was a retrospective case series study. The clinical and histopathological data of 49 patients (49 eyes) with CM who underwent enucleation at Tianjin Eye Hospital from February 2004 to March 2022 were collected. All patients underwent CDFI examination and histopathological examination to measure the number of tumor blood vessels. The relationships between the blood flow signals shown by CDFI and the internal blood flow characteristics of the tumor, tumor size, clinical stage, extra-scleral extension grade of the tumor, and cell type were analyzed. The consistency between CDFI and histopathological results was compared using the Adler semi-quantitative method. Paired Wilcoxon signed-rank test and Hodges-Lehman method were used for statistical analysis. Results: Among the 49 CM patients, 28 were male (57.1%) and 21 were female (42.9%). The age was (52.1±11.0) years old, and all cases were unilateral. Regarding the tumor shape detected by CDFI, 26 cases (53.1%) were mushroom-shaped, 11 cases (22.4%) were dome-shaped, and 12 cases (24.5%) were flat and diffuse-shaped. Among the 49 patients, 9 cases (18.4%) had blood flow signal grade Ⅰ, 16 cases (32.7%) had grade Ⅱ, and 24 cases (48.9%) had grade Ⅲ. The location with abundant blood flow inside the tumor was in the superotemporal quadrant in 19 cases (39.6%). The blood flow in the peripheral part of the tumor was more than that in the central part in 34 cases (69.4%). There were 13 large-sized tumors (26.5%), among which 6 cases had grade Ⅰ blood flow signal; 36 medium-sized tumors (73.5%), among which 20 cases (55.6%) had grade Ⅲ blood flow signal. There were 38 cases (77.6%) in the intraocular stage, among which 20 cases (52.6%) had grade Ⅲ blood flow signal; 4 cases in the glaucoma stage, among which 3 cases had grade Ⅰ blood flow signal; 6 cases in the extra-ocular extension stage, among which 4 cases had grade Ⅰ blood flow signal; 1 case in the systemic metastasis stage, showing grade Ⅲ blood flow signal. The extra-scleral extension grade of the tumor was grade Ⅰ (tumor cells involving the sclera) in 31 cases (63.3%), among which 17 cases (54.8%) had grade Ⅲ blood flow signal. There were 32 cases (65.3%) of mixed cell type, among which 17 cases (53.1%) had grade Ⅲ blood flow signal. Histopathological examination showed that the number of blood vessels was 9.0 (6.5, 11.0), the number of blood vessels measured by CDFI was 7.0 (4.0, 9.0), and the difference was 2.0 (1.0, 4.0) [95%CI: 1.5-3.0], and the difference was statistically significant (Z=4.376, P<0.001). The consistency analysis between CDFI and histopathological results showed that the grading was consistent in 40 cases (81.6%) and inconsistent in 8 cases (16.3%). Conclusions: There is a high correlation between the CDFI characteristics of CM patients and histopathological examination, but the former cannot completely replace the latter in measuring the blood vessel situation inside the tumor.

Investigation of Turbulence Characteristics Influenced by Flow Velocity, Roughness, and Eccentricity in Horizontal Annuli Based on Numerical Simulation

Annular flow channels, which are distinct from circular pipes, represent a complex flow structure widely applied in fields such as food engineering and petroleum engineering. Discovering the internal flow patterns is conducive to the study of heat and mass transfer laws, thereby playing a crucial role in optimizing flow processes and selecting equipment. However, the mechanism underlying the influence of annular turbulent flow on macro-pressure drop remains to be further investigated. This paper focuses on the roughness of both inner and outer pipes, as well as positive and negative eccentricities. Numerical simulation is employed to study the microscopic characteristics of the flow field, and the numerical model is validated through indoor experimental measurements of pressure drop laws. Further numerical simulations are conducted to explore the microscopic variations in the flow field, analyzed from the perspectives of wall shear force and turbulence characteristics. The results indicate that an increase in inner pipe roughness significantly enhances the wall shear force on both the inner and outer pipes, and vice versa. In the concentric case, wall shear force and turbulence characteristics exhibit central symmetry. Eccentricity leads to uneven distributions of velocity, turbulence intensity, and shear force, with such unevenness presenting axial symmetry under both positive and negative eccentricities. Additionally, eccentricity demonstrates turbulence drag reduction characteristics. This study enhances our understanding of the mechanism by which annular turbulent flow influences pressure drop. Furthermore, it offers theoretical backing for the design and optimization of annular space piping, thereby aiding in the enhancement of the performance and stability of associated industrial systems.

Flow Structures in a Compressible Elliptical Cavity Flow

This experimental and numerical study determines the time-averaged flow patterns within an elliptical cavity at a freestream Mach number of 0.83. The elliptical cavity model has a length-to-depth ratio of 4.43, which is classified as an open cavity flow. The flow within the elliptical cavity exhibits distinctive features due to its unique geometry. A large clockwise-rotating recirculation vortex is created, which is a common feature of an open cavity flow. Tornado-like vortices are observed at positions farther from the centerline than those in a rectangular cavity because of the geometric effect of the diverging sidewalls in the front half of an elliptical cavity, which increases the spanwise motion by directing internal flow from the centerline towards the sidewalls. Additional vortex structures, such as a front corner vortex, a rear corner vortex and secondary tornado-like vortices near the sidewalls, are identified. These structures contribute to complex flow interactions, including vortex–vortex, vortex–wall, and shear layer interactions. The three-dimensional effect affects the cellular structures within the cavity, which is similar to the effect for a rectangular cavity with a large length-to-width ratio.

Influence of Impeller–Diffuser Side-Gap Flow with a Simplified Leakage Model on the Performance and Internal Flow of a Centrifugal Pump

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.

Applications of different vortex identification methods in cavitation of a self-priming pump

To investigate the internal flow mechanisms during cavitation in self-priming pumps, this study employs numerical simulations based on the RNG k-ε turbulence model coupled with the Schnerr–Sauer cavitation model. The vapor–liquid two-phase flow characteristics at the critical cavitation condition are analyzed under various flow rates and rotational speeds. Based on the vorticity method, Q criterion, λ2 criterion, Δ criterion, λci criterion, and Ω criterion, predictions and comparative analyses of the vortex structures during cavitation in self-priming pumps have been conducted. Additionally, the energy loss in various regions of the pump before and after cavitation onset has been analyzed using the theory of entropy production. The results demonstrate that the Ω criterion, Q criterion, and λ2 criterion yield consistent vortex identification outcomes across different regions. In contrast, the Δ criterion and λci criterion produce more fragmented vortices, most notably in the gas–liquid separation chamber area, whereas the vorticity method is most susceptible to disturbances from strong shear layers; Energy losses are not directly related to vorticity but show a significant correlation with vortex intensity; Changes in flow rate and the onset of cavitation have the greatest impact on average entropy production in the reflux hole region, particularly under high flow conditions; The difference in energy loss of the impeller is the largest before and after cavitation occurs; When the cavitation coefficient is constant, the vapor volume fraction in the impeller region exhibits a positive correlation with both flow rate and rotational speed.

Improvement of separation performance of the hydrocyclone with dual enlarged outlets and an arc overflow tube

The application of hydrocyclones can be traced back more than 100 years. Due to their unique advantages, they have been widely used in various separation industries. However, the classification efficiency of hydrocyclones is relatively low due to structural limitations. Therefore, improving the classification performance of hydrocyclones has become a research hotspot and challenge. As critical components, the vortex finder and underflow outlet significantly affect the classification performance of hydrocyclones. This paper designs a series of vortex finder and underflow outlet structures to improve classification accuracy. Numerical analysis and experimental verification methods are used, with pressure field, velocity field, turbulence field, and classification efficiency as evaluation criteria, to investigate the mechanisms underlying the classification performance of hydrocyclones with different structures. Results show that the pressure drop of the Type D (double outlet expansion) hydrocyclone is the smallest, indicating lower energy consumption under identical operating conditions, thereby reducing operating costs. The Type D with an arc vortex finder shifts the LZVV inward, enlarging the separation space for coarse particles while reducing it for fine particles. The circulating flow of the Type D hydrocyclone decreases by 2.26 percentage points compared to the Type A (Base) hydrocyclone, and the short-circuit flow decreases by 4.43 percentage points, resulting in a more stable internal flow field. Type D has a smaller cut size and a higher steepness index, demonstrating stronger cutting ability and higher classification accuracy. Experimental verification shows that the −6 μm underflow content of the Type D hydrocyclone is 13.93 percentage points lower than that of the Type A hydrocyclone, while the −75 μm overflow content decreases by 3.97 percentage points. The issues of fine particles in the underflow and coarse particles in the overflow are effectively mitigated. The data obtained in this study provide theoretical and empirical support for the development of novel hydrocyclone structures.

Experimental Visualization Study on Flow Characteristics Inside a Self-Priming Sewage Pump

To investigate the motion patterns of flexible fibers inside a sewage pump and their impact on internal flow characteristics, visualization experiments were conducted to compare the pump flow when transporting water—0.3% CMC solution and 0.3% CMC solution containing flexible fibers under different operating conditions. The results showed that changes in the rheological properties of the 0.3% CMC solution primarily affected fluid viscous dissipation. Under the same rotational speed, the flow rate increased by only 2.4%, but power consumption decreased by 9.1%, resulting in a 6.4% improvement in efficiency. The curvature and distribution of fibers within the impeller flow channel remained stable. Their impact on the flow was characterized by an overall reduction in velocity within the impeller region, with the peak velocity decreasing by up to 26.3%. The primary cause of pump failure due to fibers was their tendency to repeatedly accumulate and detach at the tongue, leading to blockages. Fiber length had a more significant impact on the blockage rate than mass concentration.

Study on Erosion Results of Temporary Venting Device in Shale Gas Pipeline Station

A temporary venting device for shale gas pipeline station is designed. After one year of adhibition, there are pits in the elbow of the venting pipe, which is presumed to be caused by the erosion of the elbow by untreated shale gas in the gas collector. The erosion model is simplified. The sand is set as the discrete phase, and the gas and liquid are set as the continuous phase. Based on the VOF model and the DPM discrete phase model of multiphase flow, the erosion rate of U-shaped pipe is studied by ANSYS Fluent. The internal flow field of multiphase flow in the pipe is studied. The influence of solid particle velocity, mass flow, particle diameter, curvature-to-diameter rate and pipe diameter on the erosion rate of the elbow is studied by using the control variable method. The influence of various factors on the erosion rate is analyzed by grey correlation analysis. It provides a basis for reducing the erosion rate of U-shaped pipeline and prolonging the service life of pipeline.

Can ACR TI-RADS predict the malignant risk of medullary thyroid cancer?

Can ACR TI-RADS predict the malignant risk of medullary thyroid cancer?

Transient rear cavity vortex flow in a spherical-casing nuclear reactor coolant pump

The next-generation nuclear reactor coolant pumps (NRCP) have gradually transitioned to mixed-flow designs due to their advantages of a wide operating range, broad flow range, and high efficiency. These pumps often adopt unconventional spherical casings, resulting in complex internal flow dynamics. Therefore, a comprehensive analysis of NRCPs' internal flow field structure is critical for evaluating their operational stability. This investigation uses large eddy simulation to analyze the transient flow inside the spherical casing mixed-flow NRCP. A new type of large-scale strip-like vortex inside the rear cavity of the spherical casing has been found, named the rear cavity vortex, and its pressure pulsation characteristic is analyzed. The rear cavity vortex has three stages. This investigation identifies 7.09 Hz as the characteristic frequency of the rear cavity vortex, recognized as its self-rotation frequency. Additionally, 24.82 Hz is identified as the characteristic frequency of front vortex shedding. The results of this investigation indicate that optimizing the geometric design of the spherical casing might help weaken the intensity of the rear cavity vortex, thereby mitigating its impact on the operational stability of the NRCP. This provides valuable guidance for improving the efficiency and operational reliability of the NRCP.