Numerical Simulation Of Flow Field Research Articles

Parallel Numerical Simulation of Complex Unsteady Multi-Component Three-Dimensional Flow Field of Nonequilibrium Chemical Reaction

Parallel Numerical Simulation of Complex Unsteady Multi-Component Three-Dimensional Flow Field of Nonequilibrium Chemical Reaction

A method for numerical simulation of mode transition process of compression system of variable cycle engine based on throttle valve model

In order to study the aerodynamic characteristics of the compression system of a variable-cycle engine during its mode transition, a low-order model was established based on the throttle valve theory to describe the throttle characteristics of the mode selection valve at its different opening degrees. The model was applied to the outlet of a double-bypass variable-cycle fan in the form of characteristic boundary. A 3D low-order hybrid computational model was established for the numerical simulation of flow fields in the mode transition process of the compression system. The calculation accuracy and effectiveness of the throttle valve model were verified by comparing its calculation results with those of the 3D valve model. The simulation method was further applied to the prediction and analysis of the fan performance variation during the single and double bypass mode transitions of the variable-cycle fan. The simulation results show that: the throttle coefficient, which represents the throttle intensity, has something to do only with the flow area ratio of the valve but has nothing to do with its angle. Therefore, the throttle valve model is universal for valves with different motion angles; the throttle valve model can accurately predict the variation trend of the aerodynamic characteristics of the fan in all stages of the mode transition process. Compared with the 3D valve model, the prediction error of the pressure ratio of the fan in all stages is less than 1.93%, and the efficiency error is less than 1.05%. In the valve closing process, the second-stage rotor performance changes more dramatically, and the first-stage rotor performance changes with lag.

Numerical simulation of flow field of molten steel in the caster mould

In order to analyse the molten steel flow in the mould, a 2D model including the mould and the SENwas established. The fluctuation of molten steel on the meniscus of the mould and the steel flow velocity field in the mould and nozzle were analyzed. The calculation results show that: (1) the steel flow velocity field in the mouldwas the highest in the nozzle area. When liquid steel flows out of the SEN, its flow velocity decreases gradually. (2) There were three regions flow in the mould. There were two reflux areas outside the nozzle, the dividing line is the free surface, and the other reflux area is 0.2 m∼0.9 m. The liquid steel within 0.9 m∼1.5 m flows vertically downward. (3) The free surface near the nozzle is high, while the free surface away from the nozzle is low. The free surface is the lowest at 0.1 m and the highest at 0.06 m.

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.

Modeling and numerical simulation of flow field in three types of standard new design cyclone separators

In this paper, numerical simulation of flow field in three types of standard new design cyclone separators namely 1D2Dn, 1D3Dn and 2D2Dn are investigated. In these standard cyclones, the length of cylindrical top part of the body is equal to 1, 1 and 2 times of the body diameter, respectively; and the length of the cylindrical bottom part is 2, 3 and 2 times of the body diameter. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that among the three standard new design cyclones, cyclone 2D2Dn has the highest efficiency followed by 1D3Dn one with about only 2% lower efficiency. Cyclone 1D2Dn possesses the lowest efficiency among all. Similarly, the highest pressure drop occurs in cyclone 2D2Dn. Cyclones 1D3Dn and 1D2Dn followed 2D2Dn one with a marked difference of about 20%. In result section, the details of the flow field including velocity, pressure contours, turbulence, velocity vectors and particle trajectory will be presented.

Numerical simulation of flow field in a Laval nozzle based on one-dimensional Euler equation

Numerical simulation refers to a computer research method which runs calculation based on a specific mathematical model to simulate actual physical processes. It is a powerful tool to analyse complex engineering problems. In this paper, a numerical method for solving the steady one-dimensional Euler equations using a two-step second-order difference scheme is developed. The method is implemented by a Python code. The method is applied to numerical simulation of flows in a Laval nozzle and used to investigate the influence of shapes of Laval nozzle. It is found that the physical quantities of the nozzle flow show a positive correlation trend with different throat positions. In terms of the temperature, density, and pressure, they increase during the initial evolutions, then reach the maximum point and produce significant fluctuations, indicating the flow flows into the transonic stage. Subsequently, those physical properties gradually tend to a stable value during the supersonic stage. Moreover, it is observed that the closer the throat is to the exit, the lower the Mach number at which it eventually stabilizes. Finally, a suggestion about the best shape of the nozzle which can realize the max efficiency is concluded. Despite using an inviscid flow model, the steady pressures are quite satisfactorily predicted over the range of frequencies studied.

Numerical Simulation of Flow Field in the Laval Nozzle Based on Euler Equation

A nozzle is a versatile fluid device that is utilized to control the characteristics of a fluid flow. In order to enhance the performance or better the design of the nozzle, it is critical to carry out extensive research into its inner flow. Thus, the investigation of the nozzle flow remains an important challenge. This article used a numerical simulation method based on Euler equations to solve the internal flow of the divergent, convergent-divergent, and convergent nozzles. Specifically, we simplify all three equations of the one-dimensional Euler equation (the continuity equation, the momentum equation, and the energy balance equation) by assuming a constant nozzle shape, then discretizing them using a central differential scheme. After conducting systematic research on the influence on the internal nozzle flow due to the change of nozzle shape, we found that the mass flow rate varied as it fluctuated and peaked at the middle point of the Laval nozzle. However, with the nozzle becomes flatter, the mass flow rate appeared to restore conserved. Moreover, it appeared that the flatter the Laval nozzle is, the smaller acceleration and smaller decrease of the pressure of the fluid flow gets. In short, the results suggested that it is dependable to apply this numerical method when analysing a relatively flat Laval nozzle.

Design and Performance Research of Flexible Drill Pipe Joint Based on Bionic Theory

Fatigue fracture is the main failure form of mining drill pipe joints, which directly leads to the occurrence of drill pipe drop accidents. Based on the principle of engineering bionics, the spine structure and kinematic behavior characteristics of cheetah were studied; the bionic design and trial production of drill pipe joints were carried out. For the bionic drill pipe joint, it separates the torsion transmission function from the connection function, and when the torsion transmission function of the joint fails, the connection function is still effective, so as to achieve the effect of “breaking the bones and connecting the ribs.” The mechanical and flow field properties of the bionic drill pipe joint were analyzed. Mechanical test results showed that, for the bionic drill pipe joint, the average tensile capacity was 555.48 kN and the average torsion capacity was 8914.13 N·m, which met the mechanical performance requirements. The flow field numerical simulation results showed that, when the drilling fluid velocity field and pressure field were stable and change evenly, there is no risk of leakage. The study results can provide a new research idea for the research and development of mine drill pipe joint with long life and antidropping function.

Numerical Simulation of Connected Flow in the Inlet and Outlet of the Pumping Storage Power Station

Pumping and storage power stations with different hydraulic units are simultaneously in power generation and pumping operation (same-in-one pumping operation) is an effective means to alleviate the adverse effects caused by the sudden power imbalance of the power grid and adapt to the emergency dispatching requirements of the power grid. In this mode of operation, the water flow in the different inlet and outlet ports is reversed, and water flow communication will be formed in the front pool. Aiming at the problem that the connected flow is difficult to measure in physical model test and prototype observation, a three-dimensional flow field numerical simulation is used to determine the flow connection path and orifice velocity distribution, and the area-weighted average method is used to obtain the connected flow calculation method for different paths. Taking the inlet and outlet of a pumped storage power station as an example, this method is used to analyze the flow rate of the orifice and its proportion. The results show that when the pumped storage power station is running in the same pumping operation, the flow rate of some orifices will exceed 80% of its total flow. It is easy to cause the cooling water of the unit to circulate between the hydraulic units and keep heating up, thus reducing the cooling effect of the unit.

Flow Field Numerical Simulation and Performance Analysis of Progressing Cavity Pump

SummaryProgressing cavity pump (PCP) is the essential booster equipment in oil–gas mixing delivery. Changes in relevant parameters in PCP operations directly affect the working performance and service life of the pump. On the basis of computational fluid dynamics (CFD) in this study, we apply dynamic grid technology to establish a 3D flow field numerical calculation model for the CQ11-2.4J PCP, which is used in the field of the Hounan Operation Area in Changqing oil field, China. The effects of several operating parameters, such as oil viscosity, pump rotation speed, differential pump pressure, and void fraction of oil, on the pressure and the velocity distribution of the PCP flow field are examined. Various performance parameters in the transport of the oil–gas two-phase mixture are used in the analysis, including volumetric flow rate, slippage, shaft power, volumetric efficiency, and system efficiency. The results show that the pressure and speed distribution in the pump chamber of the PCP is relatively homogenous under different working conditions, whereas the pressure and speed exhibited sharp changes at the stator and rotor sealing line and adjacent areas in the pump chamber. Increasing the viscosity of the oil and the speed of the rotor can effectively improve the flow characteristics of the PCP, but extremely high pump rotation speed would cause a decline in system efficiency. Increasing the differential pressure and the void fraction of oil would result in a decrease in the volumetric flow rate and efficiency of the PCP. Considering the variation law of the PCP's performance parameters, the optimal interval for each operating parameter of the PCP is as follows: Oil viscosity at 50–100 mPa·s, pump rotation speed at 200–300 rev/min, differential pressure at 0.2–0.3 MPa, and the void fraction of oil not more than 50%. This research can provide technical support for the optimization of the working conditions of the PCP on site.

Study on the Intelligent Modeling of the Blade Aerodynamic Force in Compressors Based on Machine Learning

In order to obtain the aerodynamic loads of the vibrating blades efficiently, the eXterme Gradient Boosting (XGBoost) algorithm in machine learning was adopted to establish a three-dimensional unsteady aerodynamic force reduction model. First, the database for the unsteady aerodynamic response during the blade vibration was acquired through the numerical simulation of flow field. Then the obtained data set was trained by the XGBoost algorithm to set up the intelligent model of unsteady aerodynamic force for the three-dimensional blade. Afterwards, the aerodynamic load could be gained at any spatial location during blade vibration. To evaluate and verify the reliability of the intelligent model for the blade aerodynamic load, the prediction results of the machine learning model were compared with the results of Computation Fluid Dynamics (CFD). The determination coefficient R2 and the Root Mean Square Error (RMSE) were introduced as the model evaluation indicators. The results show that the prediction results based on the machine learning model are in good agreement with the CFD results, and the calculation efficiency is significantly improved. The results also indicate that the aerodynamic intelligent model based on the machine learning method is worthy of further study in evaluating the blade vibration stability.

Numerical Simulation of Performance of an Air–Water Separator with Corrugated Plates for Marine Diesel Engines

For low speed diesel engines under severe ocean conditions, high efficiency air–water separators must be equipped to separate excess moisture contained in the air and reduce the corrosion. Optimal design of air–water separator is an indispensable part in the development of marine main engines. In view of the complex gas–liquid two-phase turbulent motion within an air–water separator with corrugated plates, a mathematical model is established and numerical simulations of flow field, droplet trajectory and secondary transport are realized. The separation efficiency and pressure drop of the air–water separator under different structure parameters and different working conditions are studied. The results show that reducing the spacing of corrugated plate is helpful to improve the separation efficiency. The bending and hydrophobic hooks of the corrugated channel are important to improve the separation efficiency. The separation of droplet is mainly concentrated on the first two stages of the air–water separator, and the separation efficiency at the third stage is significantly reduced. Research results will further support corrugated plate theory, experimental research and optimization design of similar separators.

Far-field drag decomposition using hybrid formulas and vorticity based area sensors

Numerical simulation of flow-field has become an indispensable tool for aerodynamic design. Usually, wall surface integration is a tool used to calculate values of pressure drag and skin friction drag, but the aerodynamic mechanism of drag production is still confusing. In present work, in order to decompose the total drag into viscous drag, wave drag, induced drag, and spurious drag, a far-field drag decomposition (FDD) method is developed. This method depends on axial velocity defect and area sensor functions. The present work proposes three hybrid formulas for velocity defect to tackle the negative square root issue by analyzing the existing axial velocity defect formulas. For dealing with the issue of detection failure for near-wall cells, a novel vorticity based viscous area sensor function is proposed. The new area sensor function is also independent of the turbulence model, which ensures easy application to general simulation methods for flow-field. Three tests cases are there to validate the proposed FDD method. The three dimensional transonic CRM test case shows that the present improvement is crucial for accurate drag decomposition. Excellent agreement between total decomposed drags and results from the near-field method or experimental data further confirms the correctness.

Experimental Investigation on Laser Metal Deposition of Ti-6Al-4V Alloy with Coaxial Local Shielding Gas Nozzle

An inert gas environment is required during the laser metal deposition of titanium alloys due to oxidation. A nozzle with local shielding device is more flexible than the inert gas chamber, and size of the components produced is not restricted. In this study, a coaxial double-deck gas shielding nozzle was designed to provide a local shielding for the laser metal deposition of Ti-6Al-4V alloy. Numerical simulation of flow field under four different gas flow rates was carried out, and the corresponding Ti-6Al-4V single clads as well as components were produced. Experimental results revealed that the effective protection length increased and then became steady with the gas rate getting larger. Every component showed significant change in the degree of surface discoloration. Among that when the gas flow rate exceeded 30 L/min, surface of the formed bulk components showed yellowish and shiny silver and the internal oxygen content was below 2000 ppm, which had a minimal raise from the powder. In addition, the microhardness of the components showed little increase compared with the rolled substrate.

Numerical studies and validation of combustor and annular isolator interactions of hydrocarbon based axisymmetric dual combustion ramjet

Combustor Intake interactions study is very important for design of Ramjet/Scramjet propulsion systems. High Combustion-induced back pressures make the shock train propagate upstream further and interfere the flow of inlet and the scramjet would unstart. The study has more relevance especially for the propulsion systems like Dual Combustion Ramjet (DCR) due to its wider range operation of Mach number. In this paper, numerical simulation of flow field in an axisymmetric scramjet/ramjet combustor with annular isolator is carried out. Configuration chosen for simulation is Dual Combustion Ramjet, which has a dump subsonic combustor, main supersonic Combustor and an annular isolator. Objective of the work is to evolve a CFD procedure for combustor-isolator interaction and validation of the model with experimental data. Geometry of model DCR is taken from literature for simulations and studies are carried out for Isolator inlet Mach No. 1.79 and 2.23. Favre Averaged equations are solved using Commercial code–ANSYS FLUENT. Premixed composition of air and Kerosene is introduced into dump combustor. Reactive flow is modelled using 7 species and 4 step chemistry. Numerical simulations have been carried out with various turbulence models namely k–ε (Standard), (RNG) k–ε, kω-Standard, kω-SST and combustor wall pressures were compared with experimental results. Error in estimation of starting location of Shock train, Maximum Pressure, Average pressure in combustor is compared. (RNG) k–ε predicted shock train location with an error difference of 5% compared to k–ε (Standard). Further, effect on shock train position in isolator with change in gas generator equivalence ratio is also studied for free stream Mach numbers 4 and 5. Shock train moves upstream in Isolator with increase in gas generator equivalence ratio. Various parameters such as Wall static Pressure, Shock train location, length and static pressure along shock train centre, Velocity profile and Combustion efficiency are compared for reactive flow turbulence models.

Numerical simulation of flow field over slender bodies at transonic Mach number and low angle of attacks

The transonic flow field over a launch vehicle is complicated due to presence of a normal shockwave on the heat shield. To predict the aerodynamic loads, the shockwave position needs to be predicted accurately. The present work aims at predicting the flow field over a typical launch vehicle at an angle of attack (AOA), and analyzing the effect of AOA on flow field, shockwave position and aerodynamic and moment coefficients. The launch vehicle considered here is a long slender body with spherical nose followed by the conical, cylindrical and boat-tail portions. Simulations are performed at a Mach number of 0.95with AOA of 0°, 2°, and 4°. Commercial Computational Fluid Dynamics package ANSYS Fluent is used for simulations. Density-based algorithm is used to obtain the steady state solutions with explicit time stepping.κ-ω SST turbulence model is used to close the turbulent stresses terms. The surface pressure distribution in axial direction is analyzed to understand the effect of AOA on the aerodynamic and moment coefficients. It is observed that as AOA increases, the normal shockwave moves towards nose. The drag coefficient and pitching moment coefficients are found to increase with increase of AOA.

Numerical Simulation of Flow Field and Ion Transport for Different Ion Source Sampling Interfaces of a Mass Spectrometer.

Understanding ion transport mechanisms in the flow expansion section of the first vacuum region of a mass spectrometer (MS) with an atmospheric pressure ionization source is essential for optimizing the MS sampling interface design. In this study, numerical simulations of three types of ions in two different MS interface designs have been carried out. In contrast to previously reported numerical studies, nonequilibrium gas dynamics due to rarefied gas effects has been considered in modeling the flow expansion and a realistic space charge effect has been considered in a continuous ion injection mode. Numerical simulations reveal that a flat plate interface has a higher peak buffer gas velocity but a narrower zone of silence compared to the conical interface. Shock wave structures are clearly captured, and the Knudsen number distribution is displayed. Simulation results show that in the axial direction the buffer gas effect is much stronger than the electric force effect in the current configuration. The conical interface leads to both a strong ion acceleration in the zone of silence and a strong ion deceleration downstream. In the radial direction, both the electric force and buffer gas drag force play an important role. The conical interface introduces a relatively stronger ion focusing effect from the radial buffer gas effect and a stronger ion dispersion from the radial electric force than the flat plate interface. The net effect for the current configuration is an increase in ion losses for the conical interface. Nanoelectrospray ionization experiments were carried out to validate the ion transmission efficiency.

Research on the Normal Use of a Plug Discharge Tunnel

This study analyzed the normal use of an unusual flood-releasing tunnel with a plug dissipator. Firstly, normal physical model tests based on the Froude criterion (1 : 50) were finished. Secondly, depression physical model tests based on the Froude criterion (1 : 50) and cavitation similarity criterion were finished. Thirdly, 3-dimensional numerical simulation of flow field was finished, and free surface profile was captured, which was based on RNGk-εtwo-equation turbulence model and VOF method. The focus of this study is on the relationship between normal use and cavitation characteristics (e.g., pressure, turbulence kinetic energy, and cavitation number). The results show that lowering the reservoir water level, reduced by 20.41 m at most, increases the risk of cavitation of a plug discharge tunnel, which means with the decrease of the flow cavitation number, the possibility of structural damage will increase dramatically, while reducing the outlet height can effectively raise the flow cavitation number, ensuring the safety of normal use. Under the conditions of free outflow, for theH1/evalues of 4.45, 4.00, and 3.55, the conditions in which the tunnel meets the requirements of anticavitation areh/D ≤ 0.42,h/D ≤ 0.39, andh/D ≤ 0.35, respectively. In addition, the discharge capacity of the tunnel is not significantly reduced with the lowering of outlet height, implying that operation under a low water head of the plug discharge tunnel, as low as 3.55 ofH1/ein the test, is feasible. The results obtained in this study can serve as reference information in engineering design of the plug discharge tunnel.

Numerical Study of Flow Field in New Design Dynamic Cyclone Separators

In this paper the numerical simulation of flow field in the new design dynamic cyclone separator is investigated. The effects of different geometrical parameters such as impeller diameter, number of vanes, length and the location of impeller is investigated. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) were solved. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that in new design dynamic cyclone, the collection efficiency is higher and the pressure drop is lower in compare with other studied on cyclones. Installing impeller at the lower positions leads to a decrease in efficiency. With increase in impeller diameter, pressure drop in dynamic new design decreases. Finally, with increase in impeller length, efficiency increases and pressure drop decreases.

Numerical simulation of flow field in chemical vapor reactor for nanoparticle synthesized

This paper provided a numerical simulation of fluid dynamics in the chemical vapor reactor for nanoparticle synthesis. Standard k-? turbulence equation and eddy-dissipation model with standard wall function were used to investigate the reaction process of turbulent diffusion for alumina production. Here the tempera?ture and the operating conditions are discussed. Numerical results show that the model can well describe synthesis of nanometer alumina. The chemical reactions for alumina by this reactor are mainly concentrated in the range of 200 mm after the nozzle. The materials are completely mixed after 400 mm in the reactor.