Analysis Of Flow Field Research Articles

Optimization of rotor profile design and analysis of transient flow fields in an asymmetric singular double claw vacuum pump

The claw vacuum pump is widely used in vacuum industries due to its high-performance, compact structure, and oil-free operation. This study delves into the rotor profile and internal flow field characteristics of an asymmetric singular double claw vacuum pump. Theoretical profile equations for the male-female rotor of claw vacuum pumps were given, and a three-dimensional transient simulation of the internal flow field was carried out using the dynamic mesh reconstruction method. The simulation result was also verified by experiments. Analysis shows that: the radial clearance significantly affects the volumetric efficiency of the claw vacuum pump, with a larger effect than the axial clearance; the maximum instantaneous temperature corresponds to radial clearance, leading to maximum thermal deformation concentrated at the claw tip; thermal deformation is the predominant factor contributing to maximum deformation; the smaller the coefficient of thermal expansion, the less the rotor material affects the claw vacuum pump clearance. Based on these insights, we have innovatively optimized two elements of the theoretical claw vacuum pump rotor profile, i.e., the curvature of the cusp B and three optimized configurations of the complex EH section. The optimization results provide a solid theoretical basis for advancing the design and practical application of this pump type.

Stability enhancement using a new combined casing treatment strategy in an ultra-highly loaded transonic compressor rotor

Low-reaction compressors are promising for achieving high loads but face severe flow instability challenges. This study investigates a low-reaction transonic compressor rotor using casing treatment technologies to control unstable flow dynamics precisely. First, a design integrating self-recirculating and circumferential groove casing treatments near the leading edge is implemented. This design enhances flow capacity at the tip passage inlet. However, it causes a “stall transposition” phenomenon. The unstable flow structures shift from shock-tip leakage vortex interactions at the front to corner separation at the rear. Consequently, the stall mechanism transitions from an end-wall stall to a blade stall. To address this issue, a new casing treatment layout is proposed. Grooves are added after the mid-chord of the initial front casing configuration. This adaptation suppresses emerging unstable flow structures and extends the stall margin by approximately 12.07 %. Detailed flow field analysis shows that the rear grooves effectively reduced the trailing edge separation vortex. They also limit downstream corner separation and mitigate disturbances from tip leakage flows in the rear of the passage.

Influence of internal bypass conditions on the double bypass matching characteristics of variable cycle high-pressure compression system

The variable cycle high-pressure compression system (VCHCS) consists of a core driven fan stage (CDFS) and a high-pressure compressor (HPC), which are crucial components for controlling the variable cycle engine's bypass ratio. However, the double bypass (DB) matching mechanism of the VCHCS remains insufficiently understood. This study focuses on investigating the DB matching characteristics of the VCHCS under different representative internal bypass conditions. The findings demonstrate that as the internal bypass conditions transition from near choke to near stall, the external bypass stability margin of the VCHCS decreases progressively, and the external bypass characteristic curve of the HPC exhibits an approximate “counter-clockwise rotation” pattern. Furthermore, the operating state of the CDFS and the redistribution of internal and external bypass flow rate, collectively determine the matching state of the compressor system. Building upon the aforementioned summarization regarding the impact of internal bypass conditions on the matching characteristics of the VCHCS, this research integrates flow field analysis to explicate the mechanism of stall under typical operating conditions. The investigation reveals that, when the internal bypass condition under design point and the external bypass condition approaches the stall boundary, an excessive accumulation of low-energy fluid occurs at the external bypass outlet guide vane, subsequently triggers the occurrence of stall. Specifically, when the internal bypass conditions under the near stall point, the predominant limitation on further elevation or reduction of external bypass back pressure lies in the extensive blockage of a massive low-energy fluid on the suction surface of the HPC second stage stator.

Numerical Simulation and Flow Field Analysis of Porous Water Jet Nozzle Based on Fluent

The water jet nozzle is a penetrating drilling tool, which sends the pumped water to the nozzle through a high-pressure hose. It can work in a variety of working environments. When it dredges the blockage in the pipeline, its structural parameters will affect the jet flow field in the pipeline. Taking the self-propelled water jet nozzle as the research object, SolidWorks was used to establish the nozzle model with different parameter structures. Based on Fluent, the k-ε turbulence model was used to simulate the jet of nozzles with different nozzle sizes and arrangements in the pipeline. The distribution of the jet flow field and the change in velocity and displacement of nozzles with different parameters in the pipeline were compared, and then computational fluid dynamics (CFD) were used to process the simulation data for further research. The results show that when the inclination angle of the rear nozzle is 35°, the attenuation of the front jet velocity and the fluctuation of the wall fluid velocity are the smallest. When the nozzle aperture is increased from 2 mm to 3.5 mm, the vortex area inside the pipe is reduced, and the velocity attenuation of the front jet is also reduced, with the velocity attenuation rate decreasing by about 10%. This study provides a reference for the design and parameter optimization of self-propelled water jet nozzles.

Effects of serration angle on noise reduction mechanism of trailing edge serration

This study investigates the effects of serration angle on the three-dimensional flow field and noise reduction mechanism of a NACA6512-63 airfoil using large eddy simulation (LES) and spectral proper orthogonal decomposition (SPOD) techniques. The serration angle is defined as the ratio of serration wavelength (λ) to serration amplitude (h). The mean flow field analysis on suction side of serration reveals the outward flow towards the serration edges and the downwash flow between the valleys that generate the counter-rotating vortex pair. This flow alteration changes the serration effective angle of the serration, consequently affecting the noise reduction performance. Additionally, by comparing the general solution of Lyu’s semi-analytical equation with the SPOD mode results, the noise reduction mechanism is examined, and the frequency range in which noise reduction occurs is analyzed. The linearly distributed multipole-like pressure patterns, similar to those in the semi-analytical solution, are observed in the low-frequency range for all three cases, with the λ/h = 0.3 case exhibiting the most effective noise reduction. The findings suggest that the local deviation of the turbulence axis, caused by the strong outward flow near the serration edges, can hinder the formation of the optimal pressure field distribution required for effective noise reduction.

Study on stable thrust of separated undulating fins

Constrained by their inherent motion characteristics, undulating fins generate fluctuating thrust during movement, which is disadvantageous for precise underwater positioning and control. Drawing inspiration from the principles of biomimicry and leveraging the excellent maneuverability and propulsion capabilities of dragonflies, this study establishes a separated undulating fins model based on the dragonfly's unique front and rear wing structures. The impact of different phases of the separated undulating fins on thrust is studied by numerical simulation methods and quantitatively evaluate thrust stability using the range and standard deviation. Refining relevant theoretical derivations, the mapping relationship between the phase and thrust stability is established. The intrinsic mechanism behind the generation of stable thrust by separated undulating fins is revealed through flow field analysis. A new undulating fin validation platform is designed and constructed, with experimental results demonstrating a good concordance with numerical simulation outcomes. The study reveals that separated undulating fins can effectively reduce thrust fluctuations, with the range of thrust being only 48% of that of traditional undulating fins and the standard deviation being only 35% of that of traditional undulating fins. This research provides a novel approach and theoretical support for the precise control of underwater robots equipped with undulating fins.

Flow field analysis and aerodynamic drag optimization of non-pneumatic tires

Flow field analysis and aerodynamic drag optimization of non-pneumatic tires

Unsteady measurement in a transonic axial compressor with optimized axial slot casing treatment

Casing treatment has been widely adopted to enhance the operating range of compressors by extending the stall margin. In this article, a high-precision experimental investigation was conducted in a transonic compressor. Unsteady pressure is measured in the casing wall using a cluster of time-resolved transducers with axial and circumferential spatial resolution. The experimental data show that the optimized axial slot casing treatment improves the stall margin without peak efficiency penalty for all measured speedlines. A comprehensive flow field analysis indicates that the surge boundary of transonic compressor is sensitive to the position of shock wave and tip leakage flow. After the application of optimized axial slot casing treatment, the flow structure can be significantly modified, which specifically manifests as both the mitigation in shock wave detachment and redistribution of tip leakage flow trajectory toward the trailing edge of the blade. Furthermore, power spectral density analysis is conducted to examine the unsteady effect. The amplitude of characteristic frequency band induced by the unsteady fluctuation of tip leakage flow and shock wave is considerably suppressed, which can also be regard as the stability enhancement mechanism of casing treatment.

Enhancing transonic compressor rotor efficiency by flow analysis-driven blade section modification

Abstract Transonic axial compressors are widely used in aero-engines and gas turbines, and their efficiency has a significant influence on the equipment energy utilization rate and fuel cost. In this research, blade section modification based on flow analysis is carried out on the Rotor 67 for improving efficiency. First, the numerical calculation method used is verified with experimental data to ensure the accuracy of the simulation. Then, according to the analysis of simulated flow field and shock structure, the blade section shapes are altered to optimize the blade passage wide distribution for the sections from hub to mid-span. In addition, the blade surface angle is altered to reduce the supersonic flow expansion angle for decreasing shock strength. With these optimizations, the efficiency of modified transonic rotor increases by 0.9 percentage at the design point and 1.0 percentage at near stall point (N = 1.0), respectively. Slightly higher efficiency at off-design speeds (N = 0.9 and 0.8) are also obtained, with maintaining the stall margin.

Proper orthogonal decomposition analysis of flow characteristics of aerostatic bearings based on Large Eddy Simulation

The driving mechanism of the vibration of aerostatic bearings is still unclear. Although there are several interpretations, none of them is conclusive. The difficulty lies in the complicated information concealed beneath the turbulence flow. To this end, the proper orthogonal decomposition (POD) method was systematically implemented in the aerostatic bearing flow field analysis in the present study, and some new findings have been proposed. First, the accuracy of our large eddy simulation (LES) has been validated through quantitative comparisons with the experimental references in terms of pressure distribution. Then, the mode decomposition has been conducted at a circumferential symmetry plane and bottom surface and the influence of supply pressure has been uncovered. It turns out that the vortices within the recess dominate the flowfield when the supply energy Ps=3atm, which could be recognized as the driving mechanisms of vibrations. The convection and shearing process in the vicinity of the recess inlet becomes intense and corresponding vortices become predominant in the cases of Ps=4atm and 5atm. Eventually, the influences of film thickness have also been discussed when Ps=4atm. Different from the case of h = 10 μm, the low-frequency vortices near the recess outlet could be detected when the film thickness is increased to 20 µm. The control of corresponding flow structures might be helpful for the vibration suppression.

Numerical Study of Air–Vapor–Particle Flow in Gas Cyclone

AbstractThis paper presents a numerical study of the complex multiphase flow of air, vapor, and particles in an innovative gas cyclone called CAP cyclone. The air–vapor flow is modeled as a mixture by the Reynolds‐averaged Navier‐Stokes equations with the mixture species transport and the Eulerian wall film model using FLUENT. Particle flow is modeled by the Lagrangian particle tracking method and the condensational growth of particle droplets is modeled via a user‐defined function. The model is validated by reaching good agreement with experimental results. Flow field analysis shows that the added vapor does not change the major vortex characteristics in the cyclone, but the vapor distribution is not uniform. The vapor concentration is much higher in the upper part than in the lower part of the cyclone, leading to insufficient condensational growth in the lower part. A secondary vapor injection is proposed to improve the vapor concentration in the lower part, which is shown to be effective in improving the collection efficiency. The model and the results are helpful to the understanding and optimization of the CAP cyclone technology, and also the vapor and particle droplet flow in turbulent flows.

Computational Fluid Dynamics Simulation on Blade Geometry of Novel Axial FlowTurbine for Wave Energy Extraction

Wave energy converters (WECs) utilizing the Oscillating Water Column (OWC) principle have gained prominence for harnessing kinetic energy from ocean waves. This study explores an innovative approach by transforming the pivoting Denniss–Auld turbine blades into a fixed configuration, offering a simplified alternative. The fixed-blade design emulates the maximum pivot points during the OWC’s exhalation and inhalation phases. Traditional Denniss–Auld turbines rely on complex hub systems to enable controllable blade rotation for performance optimization. This research examines the turbine’s efficiency without mechanical actuation. The simulations were conducted using ANSYS™ CFX 2023 R2 to solve the three-dimensional, incompressible, steady-state Reynolds-Averaged Navier–Stokes (RANS) equations, employing the k-ω SST turbulence model to close the system of equations. A grid convergence study was performed, and the numerical results were validated against available experimental and numerical data. An in-depth analysis of the intricate flow field around the turbine blades was also conducted. The modified Denniss–Auld turbine demonstrated a broad operating range, avoiding stalling at high flow coefficients and exhibiting performance characteristics like an impulse turbine. However, the peak efficiency was 12%, significantly lower than that of conventional Denniss–Auld and impulse turbines. Future research should focus on expanding the design space through parametric studies to enhance turbine efficiency and power output.

Flow field analysis and flow prediction of pressure reducing valves in power-law media

A robust hydraulic system is necessary for industrial gluing equipment in order to transfer and regulate a variety of chemical fluid media. Certain operational conditions call for a certain flow output. In hydraulic systems, pressure reduction valves are frequently employed to regulate flow and pressure output. In order to analyze the flow of high viscosity special media inside the valve body, a colloidal medium that complies with the power-law constitutive law and a novel type of pressure-reducing valve appropriate for high viscosity fluids were chosen as the research objects in this study. First, the valve channel's flow performance and flow field characteristics were researched with a combination of simulation and experiments. Then the impact of pressure differences, opening, and temperature variations on flow rate was investigated. The proposed flow prediction formulas can be used to forecast the flow rate in engineering applications accurately which is verified by the comparison of the numerical and experimental results. Lastly, an analysis was done on the pressure reducing valve's capacity to regulate pressure under various operating circumstances. The research can offer a specific reference for the analysis of flow field characteristics inside valves in high viscosity media and the design of pressure-reducing valve bodies in non-Newtonian media. Furthermore, the research results can help determine whether the pressure reducing valve's operating condition is normal.

Numerical Simulation and Test Analysis of Flow Field in an Aluminum Electrolytic Cell with Graphitized Cathode Carbon Block

Numerical Simulation and Test Analysis of Flow Field in an Aluminum Electrolytic Cell with Graphitized Cathode Carbon Block

Flow field analysis and performance evaluation of a mini-hydrocyclone for ultra-low inlet flow rate

It is difficult for hydrocyclone to separate oil-water under the condition of ultra-low inlet flow rate, which commonly exist in the field of energy engineering. Mini-hydrocyclone is an effective technology to solve this problem. The flow field characteristics and oil droplet migration trajectory in the mini-hydrocyclone are the key to guide its efficient work. An innovative mini-hydrocyclone are studied via computational fluid dynamics (CFD) and experiment method. The good separation performance of mini-hydrocyclone for ultra-low inlet flow rate and tiny particle size of oil droplets is verified and analyzed. Furthermore, The distribution of velocity, oil volume fraction and oil migration trajectories in the mini-hydrocyclone are analyzed systematically. The effects of oil droplet size, inlet flow rate and split ratio on the separation performance of mini-hydrocyclone are investigated. The results show that the maximum separation efficiency of the mini-hydrocyclone for 1.0 L/min ultra-low inlet flow rate is 99.98 %, when the split ratio is 30 %, the oil phase volume fraction is 2 %. Moreover, the morphological and distribution of oil core in mini-hydrocyclone are basically consistent between simulation and experiment results, under the conditions of different operating parameters. The minimum error of numerical simulation and experiment results is less than 2.23 %, the accuracy of the numerical simulation method is verified.

Influence of porous media and substrate rotation on AlN growth in MNVPE reactors based on CFD simulations

AlN is an important III-V wide-bandwidth semiconductor material. Its maximum (ultra-wide) direct bandgap of up to 6.2 eV at room temperature and excellent physical properties make it have great application prospects in the fields of high-power high-frequency electronics and high-efficiency optoelectronic devices. In this paper, based on Computational Fluid Dynamics (CFD), the finite volume method was employed to investigate the process of growing AlN thin films by MNVPE using CFD simulation software for three-dimensional numerical simulation. By optimizing the chamber structure, it was devoted to improving the growth rate and uniformity of AlN thin films. Different thicknesses of porous media were placed in front of the substrate respectively, and the flow field analysis showed that the presence of eddy currents can be effectively suppressed to reduce the pre-reaction, and the best growth effect was achieved when the thickness reached 7 cm. With the increasing of porosity, more gas reached the substrate surface and improved the growth rate of AlN films. Secondly, for the 90° substrate, substrate rotation created a pumping effect and the growth rate was higher with the increase of the rotation speed. At 160 rpm, the growth rate reached 11.29 μm/h and the coefficient of variation decreased to less than 5 %.

Effect of Axial Clearance Variation on Dual-Rotor Flowmeter Performance.

This study examines the impact of axial clearance variations on the performance characteristics of a dual-rotor flowmeter (DRT-FM) through numerical simulations, with the validity of the numerical results verified by calibration experiments. The results indicate that within the range of 200 L/h to 1600 L/h, the K factors of different groups increase as clearance increases. The K factor of the 0.80 mm group is the largest, showing an average increase of around 6% compared to that of the 0.50 mm group. Additionally, Linearity E also decreased, with a minimum of 1.07% in the 0.65 mm group, significantly lower than the 3.33% in the 0.50 mm group. Furthermore, the pressure loss increased slightly, with the 0.65 mm group having the largest pressure loss; however, at a flow rate of 1600 L/h, the pressure loss only increases by 0.186 kPa compared to that of the 0.50 mm group. Flow field analysis reveals that changes in axial clearance predominantly affect pressure distribution. Larger clearances reduce low-pressure regions on upstream and downstream transition surfaces, thereby reducing energy loss due to pressure changes. Entropy analysis further demonstrates that higher axial clearance decreases energy loss in the upstream and downstream stationary domains, optimizing the DRT-FM's energy characteristics.

Improvement of sand-washing performance and internal flow field analysis of a novel downhole sand removal device

With the progression of many shale gas wells in the Sichuan-Chongqing region of China into the middle and late stages of exploitation, the problem of sand production in these wells is a primary factor influencing production. Failure to implement measures to remove sand from the gas wells will lead to a sharp decline in production after a certain period of exploitation. Moreover, As the amount of sand produced in the well increases, the production layer will be potentially buried by sand. To boost the production of shale gas wells in the Sichuan-Chongqing region and improve production efficiency, a novel downhole jet sand-washing device has been developed. Upon analyzing the device's overall structure, it is revealed that the device adopts a structural design integrating a jet pump with an efficient sand- washing nozzle, providing dual capabilities for jet sand- washing and sand conveying via negative pressure. To enhance the sand- washing and unblocking performance of the device, various sand- washing fluids and the structures of different sand- washing nozzles are compared for selection, aiming to elevate the device's sand- washing and unblocking performance from a macro perspective. Subsequently, drawing on simulation and internal flow field analysis of the device's sand- washing and unblocking process through CFD and the control variable method, it is ultimately found that the length diameter ratio of the cylindrical segment of the nozzle outlet, the outlet diameter, and the contraction angle of the nozzle greatly influence the device's sand- washing and unblocking performance. And the optimum ranges for the length-diameter ratio of the cylindrical segment of the nozzle outlet, the outlet diameter, the contraction angle of the nozzle, and the inlet diameter are 2 to 4, 6 mm to 10 mm, 12° to 16°, and 18 mm and 22 mm, respectively. The findings of the research not only provide new insights into existing sand removal processes but also offer a novel structure for current downhole sand removal devices and a specific range for the optimal size of the nozzle.

Flow field design and simulation in electrochemical machining for closed integral components

Using closed integral components (CICs) not only simplifies the structure and reduces the weight of aeroengine components but also reduces the number of parts and improves overall engine performance. However, there are currently few publicly available reports on the electrochemical machining (ECM) of CIC blades. The key factor influencing the stability of ECM is the flow-field, which is difficult to design for a CIC because its two sides are closed, thereby limiting the direction of electrolyte flow into the processing area. To achieve the ECM of CICs, flow modes involving either lateral or composite liquid supply (LLS or CLS) are proposed, followed by flow-field and cathode-deformation simulation analyses. The simulation results show that the CLS flow-field is more reasonably designed and its electrolyte distribution is more uniform. The maximum cathode deformation under CLS flow-field is only ca. 15 µm. The experiments were conducted to improve the efficiency of CIC ECM and compare the LLS and CLS flow-fields. During processing, the feed rate was increased from 0.2 min/mm to 0.45 min/mm, and the surface roughness (Ra) decreased from ca. 1.29 µm to ca. 0.37 µm. The experiments show that the CLS flow-field offers higher processing efficiency and better surface quality.

Comparative sustainability analysis of serpentine flow-field and straight channel PEM fuel cell designs

Comparative sustainability analysis of serpentine flow-field and straight channel PEM fuel cell designs