Calculation Of Flow Field Research Articles

Алгоритм маршового розрахунку надзвукового обтікання ракети з відхиля-ємою носовою частиною

This paper presents a marching algorithm for the calculation of supersonic flow past a tilting-nose rocket. A feature of the algorithm is that the marching direction of supersonic flow calculation for the nose does not coincide with that for the main part of the rocket surface. Because of this, at first flow past the nose is calculated in a cylindrical coordinate system, the flow field parameters being stored at marching cross-sections. The start and the end of the parameter storage interval in the flow field are determined from the condition of the intersection of the bow shock wave with a plane in which an initial flow field is to be specified for the calculation of flow past the main part of the rocket surface. The flow field is interpolated in two stages, First, in the cylindrical coordinate system bound to the main part of the rocket surface in the initial data plane, the radial coordinates of the bow shock wave are determined at meridional sections. From the radial coordinates of points on the rocket surface and the bow shock wave, new computational grid node coordinates are determined at meridional sections in the cylindrical coordinate system of the main part. Using the new computational grid coordinates specified in the cylindrical coordinate system of the main part, old coordinates specified in the cylindrical coordinate system of the nose are determined with the use of expressions that relate the two coordinate systems to each other. The flow parameters at a point with the calculated coordinates are calculated using linear interpolation of the stored flow field parameters in the cylindrical coordinate system bound to the nose. The calculated flow field is used as initial data for the marching calculation of the main part of the rocket, The paper presents the results of calculation of the aerodynamic characteristics of a tilting-nose rocket in a supersonic flow at different values of the nose angle. The proposed algorithm may be used in a prompt calculation of the aerodynamic characteristics of rockets with tilting elements. In doing so, use may be made of a standard program of rocket flow calculation with an added block for the storage and interpolation of the flow field in a tilted cylindrical coordinate system with a shifted origin, which allows the marching direction to be changed.

Experimental Evaluation of MHD Modeling of EMS During Continuous Casting

Electromagnetic stirring (EMS) has been recognized as a mature technique in steel industry to control the as-cast structure of steel continuous casting (CC), and computational magnetohydrodynamic (MHD) methods have been applied to study the EMS efficiency. Most MHD methods de-coupled the calculations of electromagnetic and flow fields or simplifications were made for the flow–electromagnetic interactions. However, the experimental validations of the MHD modeling have been rarely reported or very limited. In this study, we present a benchmark, i.e., a series of laboratory experiments, to evaluate the MHD methods, which have been typically applied for steel CC process. Specifically, a rotating magnetic field (RMF) with variable intensity and frequency is considered. First experiment is performed to measure the distribution of magnetic field without any loaded sample (casting); the second experiment is conducted to measure the RMF-induced torque on a cylindrical sample (different metals/alloys in solid state); the third experiment is (based on a special device) to measure the RMF-induced rotational velocity of the liquid metal (Ga75In25), which is enclosed in a cylindrical crucible. The MHD calculation is performed by coupling ANSYS Maxwell and ANSYS Fluent. The Lorentz force, as calculated by analytical equations, ANSYS Fluent addon MHD module, and external electromagnetic solver, is added as the source term in Navier–Stokes equation. By comparing the simulation results with the benchmark experiments, the calculation accuracy with different coupling methods and modification strategies is evaluated. Based on this, a necessary simplification strategy of the MHD method for CC is established, and application of the simplified MHD method to a CC process is demonstrated.

Calculation of Flow Field and Vibration Analysis of Heat Exchanging Tube in Low Temperature Multi-effect Seawater Desalination Evaporator

Abstract In this paper, a 1000t/d low-temperature multi-effect seawater desalination pilot plant (MED) is taken as the research object, a multi-phase flow (VOF) model is selected to describe the shell side flow field of the evaporator, and the overall direct simulation of the flow field on the shell side of MED is carried out by using the fluid mechanics calculation software Fluent. The vapor velocity field distribution around the evaporator tube bundle is obtained by calculation under stable test conditions. The influence of seawater spray density and evaporation temperature on flow field distribution and the vibration of tube bundle under different working conditions are researched. Research result shows that the spray density has little effect on steam velocity, but the maximum steam velocity is significantly affected by evaporation capacity of seawater. At the same time, when the evaporation capacity reaches a certain value, the phenomenon of flow resonance will occur in some areas of the evaporator, which will cause damage to the heat exchange tube bundle.

Study on flow distribution of irrigation canal system based on image velocimetry

• The YOLOV5 algorithm combined with the monocular ranging principle is used for fast flow measurement of UAV images for UAV hovering type measurement of local river surface flow fields. • Based on the smooth circular arc channel distribution model, the velocity distribution law of Yongji section, Yonggang section and Yonglan section is studied and summarized. • Based on The Rule of Tyson polygon, combined with the representative point of average velocity, the measurement of flow through water section is calculated, and the contactless measurement is realized. With the development of computer technology, it has become possible to measure surface flow velocity using video technology. Ripples are produced when flowing, and flow velocity can be determined based on the ripples and floating objects in water. A UAV velocity measurement system based on optical flow method and YOLOV5 algorithm in deep learning has been established, to realize the monitoring of surface flow field of large rivers. The optical flow method and the deep learning algorithm are used to track the target, convert the pixel distance to actual distance by monocular ranging, and calculate the actual flow velocity. The method was successfully applied to the surface flow field measurement of the Yongji canal in the river-loop irrigation area of Inner Mongolia, and the results showed that the orthophoto graphic images obtained by the method were of high quality, the flow field calculation results were reasonable, and the calculation results agreed well with the measurements.

Analysis of Vortex-Generation Using Adaptive Finite Element Method to Simulate Hemodynamics of Sigmoid Sinus Diverticulum

In various practical physical problems, the formation of the vortical flow inside the flow field has different effects and consequences. The diverticular vortex has been considered one of the causative factors of venous pulsatile tinnitus (PT). Thus, we aimed to solve the diverticular vortex by using the adaptive finite element method. We investigated the physical phenomena of the diverticular flow field generated during the cardiac cycles and transient changes of various physical phenomena before and after the vortex. The three-dimensional (3D) computational reconstructive geometry was created by combining computed-tomography images using MIMICS 19.0 software. Flow field calculation was performed with the software COMSOL 5.6 by implementing the 3D unsteady k-𝜔𝜔 turbulent model. The results showed that the overall state of blood flow in the sigmoid sinus and the pressure in the diverticulum changed secondarily to the cardiac cycles. Before the vortex was generated inside the diverticulum, the magnitude and the fluctuation of the inertial force in all directions become larger than those in regions without a vortex. After the appearance of the vortex, the fluctuation of its inertial force tended to be moderate at different points, and the results were similar to those regions without a vortex. The calculation of error estimates in this study met convergence, and different time intervals also exhibited expected results. The study result provides a basis for understanding the effect and cause prior to the vortex generation on venous PT.

Simulation and experimental research on aerodynamic noise of gas turbine 1.5-stage axial compressor

The aerodynamic noise of the axial compressor is one of the significant noise sources of gas turbines, and it has gradually attracted the attention of the majority of researchers. In this paper, the aerodynamic noise characteristics of a 1.5-stage axial compressor were studied through simulations and experiments. A full-channel calculation of a three-dimensional unsteady flow field was computed using the Reynolds-averaged Navier Stokes (RANS) method. Spectral analysis of the static pressure in the tip clearance area was in good agreement with experimental data, which verifies the accuracy of the calculations. The volume and surface sound sources were extracted from computational fluid dynamics calculations to estimate the far-field acoustic characteristics of the compressor. The simulated results of the sound field were verified by a comparison with experimental data. The results show that the sound source intensity of the compressor’s guide vanes is much lower than that originating in the rotor and stator, which indicates that the interaction between the rotor and stator is much stronger than that of the guide vane and rotor. This conclusion is consistent with the unsteady flow field analysis. To investigate the influence of complex geometric structures on sound propagation, three sets of finite element grids were employed for noise prediction. The calculations considering all structures are in the best agreement with the experimental data, which shows that complex structures cannot be ignored when calculating aeroacoustic predictions.

Upstream Rheotaxis of Catalytic Janus Spheres.

Fluid flow is ubiquitous in many environments that form habitats for microorganisms. Therefore, it is not surprising that both biological and artificial microswimmers show responses to flows that are determined by the interplay of chemical and physical factors. In particular, to deepen the understanding of how different systems respond to flows, it is crucial to comprehend the influence played by swimming pattern. The tendency of organisms to navigate up or down the flow is termed rheotaxis. Early theoretical studies predicted a positive rheotactic response for puller-type spherical Janus micromotors. However, recent experimental studies have focused on pusher-type Janus particles, finding that they exhibit cross-stream migration in externally applied flows. To study the response to the flow of swimmers with a qualitatively different flow pattern, we introduce Cu@SiO2 micromotors that swim toward their catalytic cap. On the basis of experimental observations, and supported by flow field calculations using a model for self-electrophoresis, we hypothesize that they behave effectively as a puller-type system. We investigate the effect of externally imposed flow on these spherically symmetrical Cu@SiO2 active Janus colloids, and we indeed observe a steady upstream directional response. Through a simple squirmer model for a puller, we recover the major experimental observations. Additionally, the model predicts a "jumping" behavior for puller-type micromotors at high flow speeds. Performing additional experiments at high flow speeds, we capture this phenomenon, in which the particles "roll" with their swimming axes aligned to the shear plane, in addition to being dragged downstream by the fluid flow.

Numerical simulation and flow noise computation during transient launching process of torpedo in deep-sea simulator

The transient launching process of a torpedo in a deep-sea simulator is a complex nonlinear fluid–solid coupling problem. Complex problems, such as projectile movement and gap flow, must be dealt with in the numerical computation. The launching channel is usually simplified to reduce computational cost, which affects the accuracy of the simulated flow field and acoustic computation results. The complete inner structure of the launching channel was retained in the numerical computations in this study to make the computation results much realistic. The spring mesh method and the radial basis function method were applied to update the mesh for the projectile movement, and a fine simulation was conducted on the launching flow field. The computation results related to torpedo movement were validated based on the test results, and the evolution of each flow structure in the deep-sea simulator was analysed. Based on the simulated flow field, acoustic computations were completed using the acoustic analogy method, and the acoustic characteristics, e.g. the propagation direction and sound source contribution of the launching noise, were analysed.

One-dimensional and three-dimensional coupling simulation research of centrifugal cascade hydraulics

Abstract Centrifuge cascade hydraulics research is very important for the cascade system design and safety analysis. The one-dimensional centrifugal cascade dynamic hydraulics calculation program can be used to achieve the rapid verification of the cascade system dynamic operation or accident condition. While the computational fluid dynamics (CFD) program is mainly used to analyze the local three-dimensional fluid phenomena such as the centrifugal cascade pipe and equipment. To comprehensively utilize the advantages of the two simulation methods, based on the one-dimensional calculation software SimuWorks of centrifugal cascade hydraulics and three-dimensional flow field calculation software Fluent, a one-dimensional and three-dimensional coupling simulation program for centrifugal cascade hydraulics was developed by using the API functions provided by SimuWorks simulation software and the user-defined function (UDF) of Fluent. The coupling method is used to analyze the movement of solid particles in the main feed pipe of the separation stage. By comparing the calculation results of the coupling program with the calculation results of the traditional one-dimensional dynamic hydraulics program, it can be seen that the coupling program can correctly predict the influence of feeding orifice plate clogging on the system parameters and can more intuitively show the flow field characteristics in the important parts of the system. The motion characteristics of the solid particles obtained in the simulation verification are consistent with the experimental analysis results, which further verifies the accuracy of the coupling program. The coupling program can provide a new calculation method and analytical tool for the study of centrifugal cascade hydraulics.

CFD simulation of a swirling vortex cavitator and its degradation performance and pathway of tetracycline in aqueous solution

Abstract The vortex cavitation technology shows a great development potential for antibiotic wastewater treatment. We have designed a novel swirling vortex cavitator for tetracycline degradation in aqueous solution. By Computational Fluid Dynamics (CFD) simulation using ANSYS CFX flow field calculation software, it was found that the vortex cavitator could form a low-pressure area far lower than the saturated vapor pressure at experimental temperature, resulting in generation of obvious vortex cavitation effect, which also proved by the concentration of hydroxyl radical of 4.58 μmol/L measured by methylene blue method. Moreover, the tetracycline degradation process may be mainly caused by the oxidation of hydroxyl radicals. The batch experiments results showed when the degradation time was 30 min, the vortex cavitator had a good degradation ability of tetracycline in pH range of 5.0–9.0. The degradation efficiency of 2.0 mg/L tetracycline solution was 76.45% within 50 min at pH 7.0. The possible intermediate products of tetracycline were determined by HPLC-MS Spectrometry. A series of reactions including hydroxylation, decarbonylation and C–N bond cleavage, ring-opening, and removing two methyl groups in the carbon atom ring, occur during the degradation.

Coherent structures decomposition of the flow field in Francis turbine runner under different working conditions

The dynamic mode decomposition (DMD) method is adopted to do flow field decomposition in the runner of Francis turbine. The coherent structures corresponding to main frequency components in runner passage under different working conditions are extracted, and the relative error of the reconstructed flow field and the predicted flow field are analyzed. The results show that the DMD method successfully decomposes the position and shape of the coherent structure corresponding to a single frequency in the unsteady flow, and its temporal and spatial evolution. Under part load (PL), best efficiency point (BEP), and high load (HL) working conditions, the coherent structures with high frequency induced by rotor-stator interaction (RSI) are the most stable, which located at the entrance of the runner passage. The low-frequency coherent structures mostly appear inside the runner passage, which is mainly caused by the short blade wake and flow separation under off-design conditions. The averaged flow field contains the most flow energy (larger than 90%), and unsteady coherent structures consume or transport less energy. The flow field in runner passage predicted by the DMD method is consistent with the computational flow field, which relative error is stable at 10−2. The study of coherent structures in runner passage of Francis turbine is beneficial to achieve a better design of runner and more stable operation of power plants.

Numerical simulations of thermal environment of the rocket impingement jet with afterburning under different water spray angles

To investigate the effect of afterburning and water injection on the thermal environment of the rocket jet flow, three-dimensional hybrid RANS/LES method and a nine-species and ten-step chemical mechanism are used to establish the thermodynamic model of the exhaust plume. The evaporation and condensation of the water flow are simulated by using the Eulerian dispersed phase (EDP) model. The comparison between numerical results and experimental data confirms the validity of this model. Then, the jet flow fields under different water spray angles are calculated. The results show that the afterburning mainly occurs in the mixing layer between the exhaust plume and air. The water spray has an obvious cooling effect on the impingement plate with increasing of the injection angle. Meanwhile, the stability of the jet flow could be affected by large spray angles. The temperature of the impingement plate has a significant dropped after spraying water, by approximately 450 to 750 K. With the increases of the spray angle, the peak temperature in impingement surface gradually decreased and maximum reduction is 17.84%. The rigorous thermal environment of the rocket afterbody is improved after injecting water with a large angle. The results can offer theoretical references for calculation of the jet flow field with water spray, and have vital guiding significance for the water cooling system design.

Influence of horizontal eddy viscosity and bottom friction coefficients on morphodynamic evaluations

The horizontal eddy viscosity (ε) and bottom friction coefficient (Kbr) are important hydrodynamic parameters in the computation of flow fields that dictate the morphodynamics. The effect of the variations in ε and Kbr as well as their combination on the prediction of hydrodynamics and morphodynamics in the Cochin harbor and adjoining nearshore area (9.9312° N, 76.2673° E) has been investigated in detail. A tidal circulation model to solve the shallow water equation is applied with the different parameterizations of ε and Kbr. In order to understand its effect, ε is expressed as a function of depth averaged velocity and length scale of computation mesh, whereas Kbr is expressed as a function of depth. The validation of the model is carried out with the measured currents. The improvement in the hydrodynamic and morphodynamic predictions is demonstrated by implementing the spatially and temporally varying ε The predictions are further improved by implementing a spatially varying Kbr. It is seen that the simulations with varying ε and Kbr predict the morphodynamic behavior close to the field values. The performance of the model predictions is discussed in terms of R2, RMSE and BSS (Brier Skill Score).

Modeling the electron density distribution of high-enthalpy plasma jets through chemical reaction method

The plasma electron number density can be measured using probes, lasers, and microwaves. When the plasma jet temperature is higher than the upper limit of the temperature allowed by the probe, the probe cannot be used to measure the electron number density. Laser and microwave measurement methods are difficult to obtain the distribution characteristics of the electron number density. In this paper, a calculation method for equilibrium chemical reactions is proposed. The transport and thermodynamic properties are calculated according to the mole fraction of each species in the equilibrium conditions, and the electron number density distribution is obtained by the numerical calculation of chemical reactions and flow fields. Finally, the results of laser measurement and numerical calculation are compared, and the results are consistent. The numerical calculation results can reflect the electron number density distribution of the plasma jet.

Numerical simulations of flow field and flow-induced vibration in rectangular channel with single cylinder

A vortex street structure in a narrow channel can not only enhance the mixing efficiency of the turbulence, but also cause flow-induced vibration. In this study, a rectangular channel with a single cylinder was used as the research object. The generation and influence factors of the turbulent vortex street structure in the channel and the flow-induced vibration of a cylindrical structure caused by the vortex street structure were numerically studied. First, based on the experimental data and numerical results, the accuracy of the numerical method used in this study for the flow field calculation and fluid–structure coupling calculation was verified. Second, the influence of the rod–wall gap size (W/D) on the vortex street structure formation and turbulent mixing efficiency was studied based on the validated numerical method. Finally, the flow-induced vibration of a cylindrical structure caused by a vortex street structure in a narrow channel was numerically studied using a weak coupling algorithm, and the influence of W/D on the vibration characteristics of the cylindrical structure was obtained. The results showed that an RSM-ε anisotropic turbulence model could accurately capture the vortex street in a narrow channel. The value of W/D had a significant effect on the formation of the vortex street structure. When W/D is greater than 1.150, the vortex street structure disappears. The presence of vortex street structure can significantly enhance the mixing efficiency of turbulent flow. The vortex street structure also caused the buckling of the cylinder in the normal direction of the narrow channel.

An insight into the flow field characteristics of the high temperature liquid Sodium (Na) with cavitation effects in the 600 MW fast reactor system

The paper explores the flow field characteristics of liquid Sodium pump, the flow field calculation model is established. The head and efficiency curves of sodium pump obtained by simulation are compared with the test data to verify the accuracy of the model. Flow characteristics inside the impeller, guide vane and the volute are investigated and summarized. The pressure distribution and velocity distribution characteristics of the steady flow field and the pressure fluctuation and fluid force characteristics of the unsteady flow field are further analyzed, which provides the basis for the calculation of flow induced vibration and sound field. The dynamic processes of Sodium cavitation effects are stimulated and studied systematically. The causes of fluid excited vibrations in Sodium pump are preliminarily revealed. Researches have remarkable guiding significances for the analysis of flow characteristics of Sodium pump system of the new generation 600 MW nuclear main pump system.

A Scalable Moving Boundary Treatment in the Lattice Boltzmann Method

Based on the lattice Boltzmann Method (LBM), a new moving boundary treatment is proposed by studying the influence of the moving boundary in a low-speed incompressible fluid. Simulating flow past a static cylinder, flow past a moving cylinder, and flow in a curved moving pipe shows that the LBM has high reliability and stability with moving boundary conditions. In order to reduce parallel computing time and take full advantage of the characteristics of the model, the solid grids are allocated according to the number of computing cores. Two parallel speedup ratios were tested, keeping the overall task volume unchanged to increase the number of cores and keeping the single-core task volume unchanged. In the first speedup ratio, the efficiency of the flow field calculation at 112 cores reached more than 80%. The second speedup ratio indicated that the proportion of communication in the program was tiny and suitable for large-scale parallel computing. The study of the moving boundary problem can effectively help solve the fluid-structure coupling problem. Due to the particularity of the model, it can be used to simulate the fluid-structure coupling problem of blood vessel flow effectively.

Hexcomb-Pattern Roughness Effects on Blunt-Body Transition and Heating

An experimental investigation of hexcomb-pattern surface roughness effects on boundary-layer transition and convective heating has been performed. Two representative entry vehicle geometries, a spherical-cap aeroshell and a sphere-cone aeroshell, were considered. Multiple cast ceramic models of each geometry were fabricated with various roughness pattern densities and depths that simulated an ablated hexcomb-structure thermal protection system. Wind-tunnel testing was performed at Mach 6 over a range of Reynolds numbers sufficient to produce laminar, transitional, and turbulent flow. Aeroheating and boundary-layer transition onset data were obtained using global phosphor thermography. The experimental heating data are presented herein, as are comparisons to laminar and turbulent smooth-wall heat transfer distributions from computational flowfield simulations. The experimental data were used to develop a unified boundary-layer transition correlation for both sand-grain distributed roughness and hexcomb-pattern roughness.

Numerical simulations over a three body launch vehicle for incompressible flows

In the present work, three dimensional numerical simulations over a launch vehicle at 70 m/s are performed for 3 scale models. The vehicle has a cylindrical core body and two strap on boosters. The scaled models chosen so that they represent a wind tunnel blockage ratio of 3%, 4% and 5% respectively. Simulations are performed using commercial CFD software Ansys Fluent. Three dimensional structured mesh is generated using ICEMCFD software. The solver depends on finite volume technique, and SIMPLE calculation is utilized to address the couple continuity and energy conditions. K-w SST model is utilized for disturbance demonstration. The computed flow field is analyzed in terms of velocity, pressure and turbulent kinetic energy contours. Surface pressure acquired from the three simulation (relating to every blockage ratio) arrangements in balance plane is compared to understand the impact of blockage ratio on the stream field and drag coefficients. As the blockage is increased, it was observed that maximum velocity is increasing. Lowest blockage found to give highest drag coefficient.

Numerical investigation into flow and solidification behavior of billet continuous casting with and without mold electromagnetic stirring

AbstractMold electromagnetic stirring (M‐EMS) in the continuous casting process improves the metallurgical quality of the caster as it acts as a dendrite breaker and increases the heat transfer. In this study, a numerical model of molten steel flow and solidification of continuous casting billet caster is developed. Further, this model is coupled with M‐EMS to investigate the influence of stirring on molten steel flow dynamics and solidification in the mold. The magnetic field calculations are performed in ANSYS Maxwell and computational fluid dynamics solver Fluent is used for flow field and heat transfer calculations. The fluid flow, temperature field, and solidification are investigated and compared with without M‐EMS case. The results indicate that the application of M‐EMS significantly changes flow dynamics in the mold. Strong swirl flow is dominant and a significant increment in tangential velocity is observed in the presence of M‐EMS. High intense rotational flow about the strand center gives rise to the superheat transfer near the solidification front, which further enhances the temperature in this region and thereby decreases the solidification thickness in the M‐EMS‐affected zone