Steady Flow Field Research Articles

Application of Permeable Spur Dike in Mountain River Training

Based on the investigation and indoor experiment, the flow structure and properties of erosion or deposition associated with permeable spur dike were researched. According to the new demands about engineering structure in mountain rivers regulation, the potential action of permeable spur dike in mountain river training was analyzed. The results can be showed that, as the permeable structure, the influence of permeable spur dike to main flow and flood level is less than the solid one, and the local scour depth is less too, so the permeable spur dike has larger safety. In the back of permeable spur dike, it can form a slow flow field, instead of a circumfluence field, and the deposition volume is less than solid one, so the steady slow flow field can benefit to the small aquatic animal lives. The pervious rate can be adjusted to complete training goals when the project faces to different training demands. And the material of spur dike is not limited, it can use the local materials to build, which can reduce the construction cost. The permeable spur dike have a good applicability in the control of mountain river, it can meet the requirements of flood prevention, ecology, environment, cost saving and so on, it have a greatly application prospect.

A Graph-Based Interface for Visual Analytics of 3D Streamlines and Pathlines.

Visual exploration of large and complex 3D steady and unsteady flow fields is critically important in many areas of science and engineering. In this paper, we introduce FlowGraph, a novel compound graph representation that organizes field line clusters and spatiotemporal regions hierarchically for occlusion-free and controllable visual exploration. It works with any seeding strategy as long as the domain is well covered and important flow features are captured. By transforming a flow field to a graph representation, we enable observation and exploration of the relationships among field line clusters, spatiotemporal regions and their interconnection in the transformed space. FlowGraph not only provides a visual mapping that abstracts field line clusters and spatiotemporal regions in various levels of detail, but also serves as a navigation tool that guides flow field exploration and understanding. Through brushing and linking in conjunction with the standard field line view, we demonstrate the effectiveness of FlowGraph with several visual exploration and comparison tasks that cannot be well accomplished using the field line view alone. We also perform an empirical expert evaluation to confirm the usefulness of this graph-based technique.

Design and Simulation of Supersonic Swirling Separator

Supersonic swirling separator has been developed for natural gas dehydration in recent years. Compared to Twister-I supersonic swirling separator, Twister-II type overcomes the disadvantage of uncontrolled shock and the steady swirling flow field contributes to high efficiency of gas-liquid separation. The design method is discussed. For the Laval nozzle, the contraction section is designed by double cubic curve method, while the method for expansion section is tapered tube method the same as the divergent tube, throat is smooth circular arc; the length of straight swirling pipe section for separation is 3-8 times of the diameter. The paper simulates the applicability of the supersonic swirling separator by Fluent. Studies have shown that the lower environmental temperature, the lower the outlet temperature, the easier water to cool, and the higher the separation efficiency. If the volume flow rate rises, the inlet velocity and the mass flow rate can be effectively improved. We can control the shock location by adjusting the pressure at the outlet of divergent pipe. The shock appears at the inlet in the working condition designed. When the outlet pressure is lower, the shock occurs in divergent tube; on the opposite, it moves forward. Beyond a certain degree, shock occurs at the Laval nozzle, the device fails to work.

Design trade-off study between efficiency and rotor forcing attenuation in a transonic turbine stage

A multi-objective optimisation procedure was applied to the 3D design of a transonic turbine vane row, considering efficiency and stator outlet pressure distortion, which is directly related to the forcing induced in the rotor. The characteristic features that define different individuals along the Pareto Front were described, analysing the differences between high efficiency airfoils and low interaction. Pressure distortion was assessed by means of a model that requires only of the computation the steady flow field in the domain of the stator. The reduction of aerodynamic rotor forcing was validated via unsteady multistage aerodynamic computations carried out with NUMECA FINETM/Turbo. A well known loss prediction method was used to perform total loss decomposition to quantify the influence on efficiency of reducing rotor forcing. Results show that when striving for efficiency, the rotor was affected by few, but intense shocks. On the other hand, when the objective was the minimisation of distortion, multiple shocks appeared.

Integrated analysis on static/dynamic aeroelasticity of curved panels based on a modified local piston theory

A flow field modified local piston theory, which is applied to the integrated analysis on static/dynamic aeroelastic behaviors of curved panels, is proposed in this paper. The local flow field parameters used in the modification are obtained by CFD technique which has the advantage to simulate the steady flow field accurately. This flow field modified local piston theory for aerodynamic loading is applied to the analysis of static aeroelastic deformation and flutter stabilities of curved panels in hypersonic flow. In addition, comparisons are made between results obtained by using the present method and curvature modified method. It shows that when the curvature of the curved panel is relatively small, the static aeroelastic deformations and flutter stability boundaries obtained by these two methods have little difference, while for curved panels with larger curvatures, the static aeroelastic deformation obtained by the present method is larger and the flutter stability boundary is smaller compared with those obtained by the curvature modified method, and the discrepancy increases with the increasing of curvature of panels. Therefore, the existing curvature modified method is non-conservative compared to the proposed flow field modified method based on the consideration of hypersonic flight vehicle safety, and the proposed flow field modified local piston theory for curved panels enlarges the application range of piston theory.

Numerical Simulation of Turbulence-Induced Flocculation and Sedimentation in a Flocculant-Aided Sediment Retention Pond

A model combining multi-dimensional discretized population balance equations with a computational fluid dynamics simulation (CFD-DPBE model) was developed and applied to simulate turbulent flocculation and sedimentation processes in sediment retention basins. Computation fluid dynamics and the discretized population balance equations were solved to generate steady state flow field data and simulate flocculation and sedimentation processes in a sequential manner. Up-to-date numerical algorithms, such as opera tor splitting and LeVeque flux-corrected upwind schemes, were applied to cope with the computational demands caused by complexity and nonlinearity of the population balance equations and the instability caused by advection-dominated transport. In a modeling and simulation study with a two-dimensional simplified pond system, applicability of the CFD-DPBE model was demonstrated by tracking mass balances and floc size evolutions and by examining particle/floc size and solid concentration distributions. Thus, the CFD-DPBE model may be used as a valuable simulation tool for natural and engineered flocculation and sedimentation systems as well as for flocculant-aided sediment retention ponds.

Investigation into galloping characteristics of iced quad bundle conductors

A nonlinear finite element method for galloping of iced bundle conductor transmission lines is presented. Wind tunnel tests for galloping of quad bundle conductor segments with crescent-shaped and sector-shaped ice models were carried out, and validity of the finite element method is demonstrated by the consistency of the galloping responses determined by the numerical method and those measured by the wind tunnel tests. Numerical models of four sections of iced transmission lines with different Irvine parameter λ2, which determines if internal resonance exists, are set up. Galloping of the iced transmission lines in steady wind flow and stochastic wind field is numerically simulated by the presented finite element method. Based on the numerical results, galloping characteristics of the iced transmission lines with and without internal resonance in steady and stochastic wind fields are discussed. It is found that the galloping mode and frequency of an iced quad bundle conductor transmission line in a stochastic wind field are similar to those in a steady wind flow, but the galloping amplitude may be different. Moreover, the Irvine parameter λ2 may be used to estimate some galloping characteristics, such as galloping mode and coupling movement induced by internal resonance.

The Three-Dimensional Unsteady Numerical Analysis of the Internal Flow Field of the New Control Valve

The medium flow of control valve is a typical complex unsteady flow, the internal flow is very unstable which leads to trim or body with vibration of different amplitude, therefore, control valve has been a failure-prone components in the turbine inlet steam system. This paper take the new valve as the research object, by computational fluid dynamics (CFD) software, the numerical simulation of the internal steam steady state flow field of valve normal work a typical opening in the process of opening is made, and obtain the internal flow field visualization distribution and flow characteristics of control valve. Extract unstable place pressure pulsation of the flow field, get the pulse frequency, and provide the basis for the design, optimization and application of low vibration noise control valve.

Effects of Twisted and Cylindrical Blades on the Flow Characteristics inside Blade Inlet and Outlet for a Centrifugal Pump

In this paper, the performance between cylindrical and twisted blades are analyzed for the same centrifugal pump. The three-dimensional steady and unsteady flow fields under 0.7Qd, Qd and 1.3Qd are simulated. The blade inlet and outlet flow and pressure pulsation inside the centrifugal pumps are discussed by using mathematical statistics and frequency domain analysis methods. The research is verified by experiments. The results show that the twisted blade controls blade outlet better than cylindrical blade at small flow and design flow, cylindrical blade controls blade outlet better than twisted blade at large flow. In the blade inlet and outlet, as the flow changes, the instability of cylindrical blade loading is higher than that of twisted blade. The cylindrical blade inlet pressure is affected by the shaft frequency more than that of the twisted blade. At shaft frequency and blade frequency, pressure pulsation coefficient of cylindrical blade outlet is higher than that of twisted blade outlet. The cylindrical and twisted blades effect on the blade inlet and middle gradually accumulates, resulting twisted blade outlet has larger pressure pulsation. The result can guide the optimum design of centrifugal pump to consider the performance balance between twisted and cylindrical blades.

A numerical analysis on the hydrodynamic characteristics of net cages using coupled fluid–structure interaction model

A numerical approach is proposed to simulate the hydrodynamic characteristics of a net cage in a steady current. The numerical approach is based on the joint use of the porous-media fluid model and the lumped-mass mechanical model. The deformation of a net cage can be calculated using the lumped-mass mechanical model and the flow field around a fishing net can be simulated using the porous-media fluid model. Using an appropriate iterative scheme, the coupled fluid–structure interaction between the flow and net cage can be solved, and the steady flow field inside and around a net cage can be obtained. Using the proposed numerical approach, numerical simulations of flow through a single net cage in different currents, single net cage with different weight modes and multiple net cages are investigated. Validation of the numerical model is conducted by comparing the numerical results with the corresponding physical model measurements. The comparisons demonstrate that both the configuration of the net chamber and the flow-velocity results are in accordance with those of the corresponding physical model tests. It was determined that more accurate results can be obtained by considering the coupled fluid–structure interaction between the flow and the net cage.

Numerical simulation of the interaction between flow and flexible nets

A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid–structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests.

Level set-based topology optimization of steady state incompressible viscous flows under outflow rate inequality constraint

Historically, fluidic devices such as switches, amplifiers, and oscillators, have an advantage, compared with electronic devices, in terms of maintenance-free operation and operating life. Therefore, prior to the great progress in electronic technologies that has occurred during the past several decades, the structure and function of fluidic devices were the subject of extensive research. In particular, the structures of these fluidic devices are often composed of complicated flow channel layouts. Recently, fluidic devices are again attracting significant attention, stimulated by progress in the development of MEMS technologies. In this study, to develop an energy-efficient structure for a MEMS-scale fluidic device, we apply a topology optimization method to an optimal design problem for a steady state incompressible viscous flow field. We use a level set-based topology optimization method incorporating the concept of the phase field method for the topology optimization so that clear boundaries between the solid and fluid domains are expressed in the optimal configurations. To define the topology optimization problem for a fluid regime, the expressions of the primary and adjoint problems are formulated concretely, to minimize viscous energy dissipation. Moreover, to ensure the intended design outflow rate at a designated outlet, the optimization problem includes an outflow rate inequality constraint in this paper. Following the concept of the standard adjoint variable method, a stable optimization process that satisfies the outflow rate inequality constraint is achieved. Two numerical examples, one for two-terminal and the other for multi-terminal flow, are provided to demonstrate the usefulness of the proposed level set-based topology optimization method.

Visualization of an annular viscoplastic jet

The current study investigates the global flow field characteristics of a submerged annular viscoplastic jet. The mass and momentum conservation equations, governing the steady laminar flow field, along with the Bingham rheological model, are numerically solved using a finite-difference scheme. Central and outer recirculation regions typically characterize the flow of a Newtonian annular jet. However, the current visualizations demonstrate the existence of new and unique-to-viscoplastic-fluids flow features. When the yield numbers are small, central and outer recirculation regions exist. However, the extent of the outer region and recirculation intensity of the outer and central regions are found to substantially diminish with the yield number. At intermediate yield numbers, a stagnant, attached-to-the-wall region replaces the outer recirculation while a central, yet weaker one, exists. At high yield numbers, stagnant regions replace the recirculating ones, i.e., flow recirculation throughout the whole flow field is eliminated once a critical yield number is exceeded.

Characterization of oscillatory instability in lid driven cavity flows using lattice Boltzmann method

In the present work, lattice Boltzmann method (LBM) is applied for simulating flow in a three-dimensional lid driven cubic and deep cavities. The developed code is first validated by simulating flow in a cubic lid driven cavity at 1000 and 12,000 Reynolds numbers following which we study the effect of cavity depth on the steady-oscillatory transition Reynolds number in cavities with depth aspect ratio equal to 1, 2 and 3. Turbulence modeling is performed through large eddy simulation (LES) using the classical Smagorinsky sub-grid scale model to arrive at an optimum mesh size for all the simulations. The simulation results indicate that the first Hopf bifurcation Reynolds number correlates negatively with the cavity depth which is consistent with the observations from two-dimensional deep cavity flow data available in the literature. Cubic cavity displays a steady flow field up to a Reynolds number of 2100, a delayed anti-symmetry breaking oscillatory field at a Reynolds number of 2300, which further gets restored to a symmetry preserving oscillatory flow field at 2350. Deep cavities on the other hand only attain an anti-symmetry breaking flow field from a steady flow field upon increase of the Reynolds number in the range explored. As the present work involved performing a set of time-dependent calculations for several Reynolds numbers and cavity depths, the parallel performance of the code is evaluated a priori by running the code on up to 4096 cores. The computational time required for these runs shows a close to linear speed up over a wide range of processor counts depending on the problem size, which establishes the feasibility of performing a thorough search process such as the one presently undertaken.

Computational study of steady streaming from oscillating microbubbles with uniform and wavy wall motions

Steady streaming flow fields of a 5μm bubble oscillating with uniform radial wall motion and a 500μm bubble oscillating with wavy wall motion were simulated using a computational fluid dynamics method that incorporated fluid–structure interactions. The steady streaming flow fields for both bubbles were calculated, and they exhibited upward jet flow with two symmetrical counter-rotating vortices. The maximum streaming velocity ranged from a few to tens of millimeters per second. The simulated flow fields were compared with the theory and experimental measurements using particle image velocimetry. The simulation results agreed well with the theoretical and experimental data. Therefore, the proposed computational method would provide a useful tool to predict steady streaming flow fields of oscillating bubbles.

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domain with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired.

Evaluation of Numerical Modeling Methods for the Management of Produced Water Discharges in the Coastal Region with a Canadian Case Study

This study aims at evaluating two numerical methods for 3D simulation of marine pollutant dispersion problems: the random walk particle tracking (RWPT) method and an explicit second-order finite difference method (FDM) for assessing produced water discharges from offshore oil platform. Test cases in a steady flow field were used to evaluate the efficiency and accuracy of simulating pollutant concentration profiles obtained using both the FDM and RWPT method in comparison with an analytical solution. Additionally, a field study was conducted to simulate the lead concentration distribution of produced water discharged from an oil platform off Canada’s east coast, based on the Princeton Ocean Model modeling the ocean flow in the study area with field verifications. Results indicate that, with proper configuration of grid resolution and particle resolution, both FDM and RWPT method can provide accurate results with reasonable computational costs for complex field cases. Particularly, the satisfactory 3D simulations of marine pollutant dispersion in the far field by both FDM and RWPT numerical methods enable effective assessment and management of offshore waste discharges.

Micro Particle Image Velocimetry Measurements of Steady Diastolic Leakage Flow in the Hinge of a St. Jude Medical® Regent™ Mechanical Heart Valve

A number of clinical, in vitro and computational studies have shown the potential for thromboembolic complications in bileaflet mechanical heart valves (BMHV), primarily due to the complex and unsteady flows in the valve hinges. These studies have focused on quantitative and qualitative parameters such as velocity magnitude, turbulent shear stresses, vortex formation, and platelet activation to identify potential for blood damage. However, experimental characterization of the whole flow fields within the valve hinges has not yet been conducted. This information can be utilized to investigate instantaneous damage to blood elements and also to validate numerical studies focusing on the hinge's complex fluid dynamics. The objective of this study was therefore to develop a high-resolution imaging system to characterize the flow fields and global velocity maps in a BMHV hinge. In this study, the steady leakage hinge flow fields representing the diastolic phase during the cardiac cycle in a 23 mm St. Jude Medical regent BMHV in the aortic position were characterized using a two-dimensional micro particle image velocimetry system. Diastolic flow was simulated by imposing a static pressure head on the aortic side. Under these conditions, a reverse flow jet from the aortic to the ventricular side was observed with velocities in the range of 1.47-3.24 m/s, whereas low flow regions were observed on the ventricular side of the hinge with viscous shear stress magnitude up to 60 N/m². High velocities and viscous shearing may be associated with platelet activation and hemolysis, while low flow zones can cause thrombosis due to increased residence time in the hinge. Overall, this study provides a high spatial resolution experimental technique to map the fluid velocity in the BMHV hinge, which can be extended to investigate micron-scale flow domains in various prosthetic devices under different hemodynamic conditions.

Time-Averaged and Time-Accurate Aerodynamic Effects of Forward Rotor Cavity Purge Flow for a High-Pressure Turbine—Part I: Analytical and Experimental Comparisons

The effect of rotor purge flow on the unsteady aerodynamics of a high-pressure turbine stage operating at design corrected conditions has been investigated, both experimentally and computationally. The experimental configuration consisted of a single-stage high-pressure turbine with a modern film-cooling configuration on the vane airfoil and the inner and outer end wall surfaces. Purge flow was introduced into the cavity located between the high-pressure vane and the high-pressure disk. The high-pressure blades and the downstream low-pressure turbine nozzle row were not cooled. All of the hardware featured an aerodynamic design typical of a commercial high-pressure ratio turbine and the flow path geometry was representative of the actual engine hardware. In addition to instrumentation in the main flow path, the stationary and rotating seals of the purge flow cavity were instrumented with high frequency response flush-mounted pressure transducers and miniature thermocouples in order to measure the flow field parameters above and below the angel wing. Predictions of the time-dependent flow field in the turbine flow path were obtained using FINE/Turbo, a three-dimensional Reynolds-averaged Navier–Stokes computational fluid dynamics CFD code that had the capability to perform both a steady and unsteady analysis. The steady and unsteady flow fields throughout the turbine were predicted using a three blade-row computational model that incorporated the purge flow cavity between the high-pressure vane and disk. The predictions were performed in an effort to mimic the design process with no adjustment of boundary conditions to better match the experimental data. The time-accurate predictions were generated using the harmonic method. Part I of this paper concentrates on the comparison of the time-averaged and time-accurate predictions with measurements in and around the purge flow cavity. The degree of agreement between the measured and predicted parameters is described in detail, providing confidence in the predictions for the flow field analysis that will be provided in Part II.

Three-Dimensional Shock Wave Detection Based on the Theory of Characteristics

This paper describes a method to detect three-dimensional, steady inviscid shock waves from computational fluid dynamics data. The method is based on the principle that the collision of the characteristics of the same family causes the generation of a shock wave in a two-dimensional flow. In a three-dimensional flowfield, however, there is an infinite number of characteristics. Therefore, the plane on which the streamline can be treated locally as a planar curve is introduced, and the characteristic as an intersection between the Mach cone and this plane is defined. As a result, the shock waves in a three-dimensional, steady flowfield can be treated by a similar methodology as that in a two-dimensional flowfield.