A Unique Modelling Strategy to Dynamically Simulate the Performance of a Lobe Pump for Industrial Applications

The performance of a newly designed tri-lobe industrial lobe pump of high capacity is simulated by using commercial CFD solver Ansys Fluent. A combination of user-defined-functions and meshing strategies is employed to capture the rotation of the lobes. The numerical model is validated by comparing the simulated results with the literature values. The processes of suction, displacement, compression and exhaust are accurately captured in the transient simulation. The fluid pressure value remains in the range of inlet pressure value till the processes of suction and displacement are over. The instantaneous process of compression is accurately captured in the simulation. The movement of a particular working chamber is traced along the gradual degree of lobe’s rotation. At five different degrees of lobe’s rotation, pressure contour plots are reported which clearly shows the pressure values inside the working chamber. Each pressure value inside the working chamber conforms to the particular process in which the working chamber is operating. Finally, the power requirement at the shaft of rotation is estimated from the simulated values. The estimated value of power requirement is 3.61 BHP FHP whereas the same calculated theoretically is 3 BHP FHP. The discrepancy is attributed to the assumption of symmetry of blower along the thickness.

Time-Domain Analysis of Body Freedom Flutter Based on 6DOF Equation

The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.

Numerical Investigation of the Aerodynamic Performance Affected by Spiral Inlet and Outlet in a Positive Displacement Blower

The flow in the positive displacement blower is very complex.The existing two-dimensional numerical simulation cannot provide the detailed flow information,especially flow characteristics along the axial direction,which is unfavorable to improve the performance of positive displacement blower.To investigate the effects of spiral inlet and outlet on the aerodynamic performance of positive displacement blower,three-dimensional unsteady flow characteristics in a three-lobe positive displacement blower with and without the spiral inlet and outlet are simulated by solving Navier-Stokes equations coupled with RNG k-ε turbulent model.In the numerical simulation,the dynamic mesh technique and overset mesh updating method are used.The computational results are compared with the experimental measurements on the variation of flow rate with the outlet pressure to verify the validity of the numerical method presented.The results show that the mass flow rate with the change of pressure is slightly affected by the application of spiral inlet and outlet,but the internal flow state is largely affected.In the exhaust region,the fluctuations of pressure,velocity and temperature as well as the average values of velocity are significantly reduced.This illustrates that the spiral outlet can effectively suppress the fluctuations of pressure,thus reducing reflux shock and energy dissipation.In the intake area,the average value of pressure,velocity and temperature are slightly declined,but the fluctuations of them are significantly reduced,indicating that the spiral inlet plays the role in making the flow more stable.The numerical results obtained reveal the three-dimensional flow characteristics of the positive displacement blower with spiral inlet and outlet,and provide useful reference to improve performance and empirical correction in the noise-reduction design of the positive displacement blowers.

Numerical study on DPM dispersion and distribution in an underground development face based on dynamic mesh

In 2012,the International Agency for Research on Cancer(IARC)classified diesel particulate matter(DPM)as a carcinogen to human.With the increased usage of diesel equipment in underground mines,miners have a high risk of over-exposure to DPM,which has drawn many concerns from the public.This study used computational fluid dynamics(CFD)to analyse the DPM dispersion and concentration distribution characteristics in an underground development face based on an onsite experiment.The DPM emitted from a moving loader under a forcing auxiliary ventilation system was simulated.The motion of the load-haul-dump(LHD)in the tunnel was represented by a dynamic mesh method.The species transport approach was applied to study the DPM behaviours.High DPM concentration zones were then identified based on the simulation results.The results could provide guidelines for work practices and be helpful to an optimum auxiliary ventilation design to reduce underground miner exposure.

Mesh Generation and Dynamic Mesh Management for KIVA-3V

To improve mesh quality for KIVA-3V a method has been developed for rapid mesh generation and dynamic mesh management with moving valves for internal combustion engines. Two phases are included in rapid mesh generation： the initial mesh generation and the mesh pre-treatment. In the second step （pre-treatment）, the connectivity of those cells is generated by a new algorithm added to the KIVA-3V code after the initial mesh generated. In dynamic mesh management phase, a new rezoning algorithm is developed and the basic principle is that the rezoning starts from the moving part. The movement of the adjustment is treated as an ＂earth quake wave＂ propagating to the surrounding vertexes. The amount of coordinate adjustment of the surrounding vertexes is determined by the movement of the epicenter and the distance between the vertexes and the ＂epicenter＂. Finally, a real IC engine mesh is generated and managed aceording to the new method. It gives a new theory and a new method for creating and managing the mesh in IC engine.

Numerical Prediction of Hydrodynamic Forces on A Ship Passing Through A Lock

While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the ship may be remarkable, which may have an adverse effect on navigation safety. However, the complicated hydrodynamics is not yet fully understood. This paper focuses on the hydrodynamic forces acting on a ship passing through a lock. The unsteady viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k-e turbulence model. User-defined function （UDF） is compiled to define the ship motion. Meanwhile, the grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Numerical study is carried out for a bulk carrier ship passing through the Pierre Vandamme Lock in Zeebrugge at the model scale. The proposed method is validated by comparing the numerical results with the data of captive model tests. By analyzing the numerical results obtained at different speeds, water depths and eccentricities, the influences of speed, water depth and eccentricity on the hydrodynamic forces are illustrated. The numerical method proposed in this paper can qualitatively predict the ship-lock hydrodynamic interaction. It can provide certain guidance on the manoeuvring and control of ships passing through a lock.

Predicting the Growth of Ash Deposits in Drop Tube Furnace Using Dynamic Mesh Technique

Modeling and experiments of the growth of ash deposits during the combustion in a drop tube furnace are presented in this paper.An existing deposition model for ash deposit was used,which involves relationship among the force of gravity,elastic rebound and adhesion forces acting at the moment of ash particle impaction.Important parameters of this model were determined by the experimental data.The influence of particle size and velocity on deposit geometry was investigated.The growth of ash deposits involving various inlet velocities,tube diameters and tube arrangements were simulated with dynamic mesh technique in Fluent.The simulation results show that particle normal impacted velocity plays an important role due to elastic bounce force term.Deposited geometry was influenced by side velocity(velocity of inlet⁃2),and large velocity has an obvious effect to change the shape of deposition and postpone the steady time.

Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

Numerical and Experimental Investigation of Interactions Between Free-Surface Waves and A Floating Breakwater with Cylindrical-Dual/Rectangular-Single Pontoon

This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.

Experimental and Numerical Study on Pectoral-Fin Propulsive System

Generally the underwater bio-robots take the tail fin as propulsor, and combined with pectoral fin they can manoeuvre agilely and control their position and movement at will. In nature, a lot of fishes realize to suspend itself in water to go forward and to move back up by the pectoral fin moving complexly. So that it is significant theoretically and valuable for practical application to investigate the propulsive principle and hydrodynamic performance of pectoral fin, and find the method utilizing the pectoral fin to manoeuvre the underwater bio-robot agilely. In this paper, a two degree of freedom （DoF） motion model is established for a rigid pectoral fin, and the hydrodynamic performances of the pectoral fin are studied by use of the pectoral fin propulsive experimental platform developed by Harbin Engineering University, simultaneously the hydrodynamic performance of the pectoral fin is analyzed when some parameters change. Then, through the secondary development of FLUENT （CFD code） software, the hydrodynamic performances of rigid pectoral fin in viscous flows are calculated and the results are compared with the latest experimental results. The research in this paper will provide the theoretical reference for the design of the manoeuvring system imitating pectoral fin, at the same time will become the foundation for the development of the small underwater bio-robot.

Shock-Wave/Rail-Fasteners Interaction for Two Rocket Sleds in the Supersonic Flow Regime

Rocket sleds belong to a category of large-scale test platforms running on the ground.The applications can be found in many fields,such as aerospace engineering,conventional weapons,and civil high-tech products.In the present work,shock-wave/rail-fasteners interaction is investigated numerically when the rocket sled is in supersonic flow conditions.Two typical rocket sled models are considered,i.e.,an anti-D shaped version of the rocket sled and an axisymmetric slender-body variant.The dynamics for Mach number 2 have been simulated in the framework of a dynamic mesh method.The emerging shock waves can be categorized as head-shock,tailing-shock and reflected-shock.An unsteady large-scale vortex and related shock dynamics have been found for the anti-D shaped rocket sled.However,a quasi-steady flow state exists for the slender-body shaped rocket sled.It indicates that the axisymmetric geometry is more suitable for the effective production of rocket sleds.With the help of power spectral density analysis,we have also determined the characteristic frequencies related to shock-wave/rail-fasteners interaction.Furthermore,a harmonic phenomenon has been revealed,which is intimately related to a shock wave reflection mechanism.

Numerical Solution of the Asymmetric Water Impact of A Wedge in Three Degrees of Freedom

Impact problems associated with water entry have important applications in various aspects of naval architecture and ocean engineering. Estimation of hydrodynamic impact forces especially during the first instances after the impact is very important and is of interest. Since the estimation of hydrodynamic impact load plays an important role in safe design and also in evaluation of structural weight and costs, it is better to use a reliable and accurate prediction method instead of a simple estimation resulted by analyzing methods. In landing of flying boats, some phenomena such as weather conditions and strong winds can cause asymmetric instead of symmetric descent. In this paper, a numerical simulation of the asymmetric impact of a wedge, as the step of a flying boat, considering dynamic equations in two-phase flow is taken into account. The dynamic motion of the wedge in two-phase flow is solved based on finite volume method with volume of fluid （VOF） scheme considering dynamic equations. Then the effects of different angles of impact and water depth on the velocity change and slamming forces in an asymmetric impact are investigated. The comparison between the simulation results and experimental data verifies the accuracy of the method applied in the present study.

二维冲箱式造波机的间隙和形状效应数值研究

The installation of plunger-type wave makers in experimental tanks will generally include a gap between the back of the wedge and the wall of the tank.In this study,we analyze the influence of this gap on the wave making performance of the plunger using two-dimensional(2 D)CFD calculations for a range of nearly linear wave conditions and compare the results with both experimental measurements and linear potential flow theory.Three wedge-shaped profiles,all with the same submerged volume,are considered.Moreover,the generated waves are compared with the predictions of linear potential flow theory.The calculations are made using the commercial ANSYS FLUENT finite-volume code with dynamic meshes to solve the Navier-Stokes equations and the volume of fluid scheme to capture the air-water interface.Furthermore,the linear potential flow solution of Wu(J Hydraul Res 26:481-493,1988)is extended to consider an arbitrary profile and serve as a reference solution.The amplitude ratios of the generated waves predicted by the CFD calculations compare well with the predictions of linear potential flow theory for a simple wedge,indicating that viscous effects do not influence this ratio for small-amplitude motions in 2 D.By contrast,significant higher harmonic components are produced by larger amplitude motions.Also,the simple wedge is found to produce the smallest spurious higher harmonic content in the far-field wave.

Numerical Simulation of PMM Tests for A Ship in Close Proximity to Sidewall and Maneuvering Stability Analysis

As the maneuverability of a ship navigating close to a bank is influenced by the sidewall, the assessment of ship maneuvering stability is important. The hydrodynamic derivatives measured by the planar motion mechanism （PMM） test provide a way to predict the change of ship maneuverability. This paper presents a numerical simulation of PMM model tests with variant distances to a vertical bank by using unsteady RANS equations. A hybrid dynamic mesh technique is developed to realize the mesh configuration and remeshing of dynamic PMM tests when the ship is close to the bank. The proposed method is validated by comparing numerical results with results of PMM tests in a circulating water channel. The first-order hydrodynamic derivatives of the ship are analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure and the variations of hydrodynamic derivatives with the ship-sidewall distance are given. The straight line stability and directional stability are also discussed and stable or unstable zone of proportional-derivative （PD） controller parameters for directional stability is shown, which can be a reference for course keeping operation when sailing near a bank.

Safety estimation of high-pressure hydraulic cylinder using FSI method

Hydraulic cylinder is a primary component of the hydraulic valve systems.The numerical study of hydraulic cylinder to evaluate the stress analysis,the life assessment and the performance of operation characteristics in hydraulic cylinder were described.The calculation of safety factor,fatigue life,piston chamber pressure,rod chamber pressure and the change of velocity of piston with flow time after the beginning of hydraulic cylinder were incorporated.Numerical analysis was performed using the commercial CFD code,ANSYS with unsteady,dynamic mesh model,two-way FSI(fluid-structure interaction)method and k-εturbulent model.The internal pressure in hydraulic cylinder through stress analysis show higher than those of the yield strength.

Influence of Different Velocities on Muzzle Flow Field

A two?dimensional axisymmetric numerical simulation was successfully carried out on the muzzle flow field of a 300 mm?caliber counter?mass propelling gun. Based on the FLUENT software,using the finite volume method(FVM)and the realizable k?ε turbulence model,we adopted the holistic movement of a partitioned mesh processing method coupled with the intermediate ballistic model and the six degree?of?freedom model(6?DOF). We compared the flow field characteristics at the velocity of 1 730.4,978.3,and 323.4 m/s. The results indicate that the pressure of the hypersonic initial flow field is much higher than that of the subsonic and supersonic initial flow fields. In the case of the subsonic(323.4 m/s)flow field,the tiny disturbance spreads throughout the whole domain. But in the cases of the supersonic(978.3 m/s) and the hypersonic(1 730.4 m/s) flow fields,it cannot spread to the upstream disturbance source,and the disturbance domain of the supersonic flow field is wider than that of the hypersonic. It is noted that the subsonic flow field has a rounded shock wave before the projectile. However,in the supersonic and hypersonic flow fields,a shear layer is formed which begins from the head of the projectile and extends outward from the side of the projectile. Then a multi?layer shock wave is formed composed of coronal shock waves,bottom shock waves,reflected shock waves,and Mach disk.

Unsteady Flow Simulations in a Three-lobe Positive Displacement Blower

To improve the performance of the positive displacement blower, it is imperative to understand the detailed internal flow characteristics or enable a visualization of flow status. However, the existing two-dimensional unsteady, three-dimensional steady or quasi-unsteady numerical simulation and theoretical analysis cannot provide the detailed flow information, which is unfavorable to improve the performance of positive displacement blower. Therefore, the unsteady flow characteristics in a three-lobe positive displacement blower are numerically investigated by solving the three-dimensional, unsteady, compressible Navier-Stokes equations coupled with RNG k-e turbulent model. In the numerical simulation, the dynamic mesh technique and overset mesh updating method are adopted. Due to the air being compressed in the process of the rotors rotating, the variation of the temperature field in the positive displacement blower is considered. By comparing the experimental measurements and the numerical results on the variation of flow rate with the outlet pressure, the maximum relative error of the flow rate is less than 2.15% even at the maximum outlet pressure condition, which means that the calculation model and numerical computational method used are effective. The numerical results show that in the intake region, the fluctuations of the inlet flow are greatly affected by the direction of the velocity vectors. In the exhaust region, the temperature changes significantly, which leads to the increase of the airflow pulsation. Through analysis on the velocity, pressure and temperature fields obtained from the numerical simulations, three-dimensional unsteady flow characteristics in the positive displacement blower are revealed. The studied results will provide useful reference for improving the performance and empirical correction in the design of the positive displacement blower.

Simulations of the Transient Flow Generated from a Started Flat Plate

Transient operations are commonly founded in fluid machineries such as the starting, stopping, and variations of rotor speeds, etc. Flow generated from a started fiat plate is of fundamental importance. Experiments have been done to observe the flow evolution in current researches. And in order to explore the flow in more detailed scale, some vortex methods with high resolution and other numerical methods were developed to solve various related problems by some researchers. But the promotion of vortex method to engineering application is rare due to its complexity and difficulty in specifying the boundary conditions. In order to build up a method of numerical study for such problems, a simplified model is built up with a flat plate. The development of two-dimensional viscous incompressible flow generated from an impulsively started and uniformly accelerated infinitesimally thin flat plate is simulated numerically. A dynamic mesh（DM） method based on the spring analogue and local remeshing is applied to realize the mesh motion caused by the started plate. Researches show that the mesh quality will decline under large grid shear force during the updating process. To conquer this problem, a region near the plate is separated to guarantee the mesh quality at location of interest which is the innovation of the present paper. All computations at least cover a period during which the plate translates 6 times its length. The simulated instantaneous velocity profiles, flow structures and drag coefficients under several Reynolds numbers （20 ≤ Re ≤ 126） and accelerations （20 m/s2≤ a ≤ 152 m/s2） are presented and compared with existing results in literatures. Comparisons are found to be satisfactory, confirming the validity of the current proposed method（region separated DM）. The proposed DM method is firstly used to study the transient flow generated from a started flat plate and can be used in further study of transient characteristics during transient operations of turbo machineries.

NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFI-CIENTS USING CFD SIMULATION

The submarine Hydrodynamic coefficients are predicted by numerical simulations. Steady and unsteady Reynolds Averaged Navier-Stokes （RANS） simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism （PMM） experiment performed on the SUBOFF submarine model. The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving, pure swaying, pure pitching and pure yawing. The hydrodynamic forces and moments acting on the maneuvering submarine are obtained. Consequently, by analyzing these results, the hydrodynamic coefficients of the submarine maneuvering motions can be determined. The computational results are verified by comparison with experimental data, which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.

Aeroacoustic and aerodynamic optimization of propeller blades

It is of great significance to develop a high-efficiency and low-noise propeller optimization method for new-generation propeller aircraft design.Coupled with free form deformation method,dynamic mesh interpolation technology,optimization algorithm,surrogate model,aerodynamic calculation and aeroacoustic prediction model module,the integrated aerodynamic and aeroacoustic design method of propeller is built.The optimization design for the six-blade propeller is carried out.The non-reduction in efficiency,thrust coefficient and the minimum of aerodynamic noise is treated as the optimization design objective.The spatial vorticity distribution of the propeller before and after the design is also analyzed by using unsteady computational fluid dynamics method.The results show that the optimized propeller can effectively reduce the aerodynamic noise level.The maximum total sound pressure level can be reduced by 5 dB without reducing its aerodynamic performance.The developed method has good application potential in low-noise optimization design of propeller and other rotating machinery.