Computational Fluid Dynamics Analysis Method Research Articles

Investigation of the leakage in the flow distribution pair of radial piston hydraulic motors through CFD analysis and experiments

The internal leakage of a radial piston motor (RPM) is an unavoidable structural characteristic, and the amount of internal leakage has a critical effect on the volumetric efficiency of the motor. Using the distribution plate as the force body, an equation for the balance between the preload spring force and the hydrodynamic force is analytically derived, the variation range of the clearance of the flow distribution pair (FDP) is determined, and a model for the internal leakage flow of the FDP is developed. Based on computational fluid dynamics (CFD) simulations, the effects of the oil film thickness, inlet pressure, motor speed, and oil temperature on the leakage volume are investigated. An efficiency test system for RPMs is built and tests are performed on motor prototypes. The experimental results show that the error between experimental and simulation results decreases gradually with increasing motor speed. When the motor runs at the rated speed, the error is stable within 5%. The experimental results verify the correctness of both the theoretical and CFD models. The CFD analysis method can be used as a technical means to optimize the motor volumetric efficiency and the preload spring design.

High-Fidelity Numerical Investigation on Elucidating Sodium Heat Transfer Characteristics for 37-Pin Wire-Wrapped Fuel Bundle in the PLANDTL Facility

This study involved a Reynolds-averaged Navier-Stokes- (RANS-) based computational fluid dynamics (CFD) analysis of the 37-pin wire-wrapped fuel bundle of the PNC Plant dynamics test loop (PLANDTL) facility. Previously, mainly the hydrodynamic phenomena of the wire-wrapped fuel bundle were analyzed, but the present study additionally included heat transfer analysis through conjugate heat transfer. The main purpose of the study was to benchmark the experimental data of the PLANDTL 37-pin wire-wrapped fuel bundle to investigate the heat transfer phenomena. In addition, the aim was to verify the accuracy of the RANS-based CFD analysis method using the STAR-CCM+ simulation software in comparison with the experimental data. The grid used for verification was an innovative grid system consisting of hexahedra using Fortran-based code. The development of the RANS-based CFD methodology included grid sensitivity analysis, turbulence model sensitivity analysis, and turbulent Prandtl number sensitivity analysis. Information on the temperature, mass flow rate, and area of the CFD results for each subchannel was provided for the top of the heated section and is expected to serve as a reference for future studies aiming to perform the validation and verification of a PLANDTL facility. In addition, the dependence of the peak temperature on the azimuth angle of each pin was analyzed.

Numerical modelling of multiphase flow hydrodynamics by CFD analysis methods in a double-elbow pipeline

Introduction. Prediction of multiphase flow patterns in pipelines of gas and oil industry is a complicated hydrodynamic process. Hydraulics of gas-liquid flows and erosion processes in pipelines with many bends in which gas, water, oil and air move are insufficiently studied. There are known studies of movement in single-phase flow conditions with one elbow, which is insufficient for design of modern pipeline systems. Therefore, there is a need for in-depth analysis of interaction of media in multiphase flow and transported sand particles. In this paper the effects of elbows on multiphase flow hydraulics and erosion of pipe sections are investigated using computational fluid dynamics (CFD) modelling tools for 100 seconds’ of process.
 
 Materials and methods. A liquid volume model (VOF) was used to simulate three-phase flow: air-water with solids in a pipe with two elbows. Turbulence effects have been accounted for with the RNG k–ε model. The model verification methods from previous studies have been used. For the numerical solution, the Ansys Fluent version 20.1 software package has been used. The results of CFD modelling of the volumetric gas content have shown a good agreement with the available experimental data.
 
 Results. The results showed that the change in the flow regime remains unchanged before the first elbow and after the se-cond elbow in the cork flow. However, for the initial churn flow regime, the flow regime varies at different segments of the flow area before and after each elbow.
 
 Conclusions. The preliminary churn flow in the upper vertical section was transformed to wavy stratified flow in the horizontal section between the two elbows and wavy annular flow in the vertical pipe after the second elbow. The flow pattern in slug flow maintained same after the first elbow, but the Taylor bubbles are lengthier in the horizontal section between the first and second elbows.

Uncertainty quantification analysis with arbitrary polynomial chaos method: Application in slipstream effect of propeller aircraft

The slipstream effect of propeller aircraft has a major impact on aircraft aerodynamic characteristics. Predicting the interaction of propeller slipstream on flow field over a complete aircraft has been an important topic in the field of fluid mechanics. In the flight test, we found that parameters in the flight data of propeller aircraft exhibit significant stochastic characteristics, and the mechanism of the influence of these stochastic parameters on aerodynamic characteristics of propeller aircraft needs to be further studied. Therefore, we combine arbitrary Polynomial Chaos method with Computational Fluid Dynamics (CFD) according to the characteristics of stochastic parameter distribution, propose an uncertainty CFD analysis method, and apply it to the aerodynamic uncertainty analysis of propeller aircraft. Results show that the standard deviation (Std) of the pressure coefficient [Formula: see text] on the wing surface will form an extreme region at windward side and separation position, respectively, which will gradually decrease with the flow direction. Furthermore, the slipstream will reduce the local Std on wing surface, and the downwash caused by slipstream will change the Std distribution on the leading edge of the horizontal tail.

A heat dissipation design strategy based on computational fluid dynamics analysis method for shunt active power filter

Aiming at the heat dissipation design problem of shunt active power filter, this paper proposes a computational fluid dynamics (CFD) simulation method of module flow–heat transfer coupling under forced air cooling. The power filter has carried out a detailed heat generation analysis, and given the analysis and simulation results, the heat dissipation system of the parallel active power filter is designed. The experimental results of the compensation performance prove that the designed modular system has an excellent dynamic, steady-state performance, and temperature rise. The experimental results are consistent with the simulation analysis, which demonstrates the effectiveness of the heat dissipation design of the parallel active power filter module proposed in this paper.

A parametric study for a flettner rotor in standalone condition using CFD

In this study, the performance prediction and parametric study of a Flettner rotor in standalone condition was conducted based on a computational fluid dynamics (CFD) approach. A method for predicting the rotor performance based on steady RANS simulation was established, and the present method was validated with a reference rotor model in which wind tunnel test results were published. The CFD results depending on the turbulence models including k-omega shear stress transport (SST), k-epsilon, Spallart-Almaras and Reynolds stress model, and the non-dimensional wall distance (y+) as well as boundary conditions were compared with the experimental results. A model scale condition with a similar rotor diameter was considered to apply the CFD analysis method to the target rotor dimension. The CFD results based on the Reynolds number (Re) and y + values were compared in the model scale. In addition, a comparative analysis was performed on the model and prototype size under the same Re condition. Consequently, an appropriate condition for the CFD analysis was proposed and the lift, drag, torque and energy efficiency of the target rotor design were predicted. Based on this, parametric investigations for the rotor aspect ratios from 4 to 6 and the diameter ratio of the disk and rotor cylinder from 1.5 to 8 were conducted. The effect of aspect ratio was examined by varying the rotor diameter while maintaining the height. Furthermore, the torque components generated by the rotor cylinder and disk owing to the aerodynamic load were analyzed.

An Experimental Study on Physical Properties of Optimized Sintered Wick Structured Heat Pipe using Computational Fluid Dynamics Analysis Method and Additive Manufacturing Method

An Experimental Study on Physical Properties of Optimized Sintered Wick Structured Heat Pipe using Computational Fluid Dynamics Analysis Method and Additive Manufacturing Method

A Fundamental Study on Physical Properties of Optimized Sintered Wick Structured Heat Pipe Using Computational Fluid Dynamics Analysis Method

This paper reports the evaluation of physical properties for optimized sintered wick structured heat pipe. The structural design of the heat pipe was executed using CATIA V5 computer aided design software. Upon designing, finite element analysis conducted to evaluate performance of heat pipe were evaluated using ANSYS R19 computer aided manufacturing software.

Predictions of NOx and CO emissions from a low-emission concentric staged combustor for civil aeroengines

This study is aimed to establish a detailed chemical reactor network model based on the analysis of complex reaction flowfield structures in aeroengine combustors, so that the emissions of nitrogen oxides and carbon monoxide from advanced civil aeroengines can be predicted quickly and accurately. In this study, a low-emission concentric staged combustor with three axial swirlers is designed for civil aeroengines, and numerical simulations of the three-dimensional reaction flowfields of the combustor during four load phases of takeoff, climb, approach, and idle, are conducted. Based on the numerical results, a simple chemical reactor network model with seven perfectly stirred reactors and a detailed chemical reactor network model using up to 15 perfectly stirred reactors are established. Using the developed chemical reactor network models and the detailed JP10 chemical reaction mechanism—composed of 374 step elementary reactions and 82 species, the emission variations of nitrogen oxides and carbon monoxide are predicted and compared with those estimated using an empirical formula and with the numerical results as a function of the combustion load. Using a combined chemical reactor network–computational fluid dynamics analysis method, the variations of the formation path, the mechanism, and the amounts of nitrogen oxides in the combustor and in the perfectly stirred reactors, are analyzed as a function of the combustion load. In addition, the effects of fuel and air pilot-to-total ratio on nitrogen oxides emissions for the 100% load condition are also analyzed. It is found that at high loads, the production rate of the thermal NO is the highest, while at low loads, the production rate of the prompt NO is the highest. The nitrogen oxide is mainly produced in the pilot zone and the recirculation zone, while its production in the outer main stage zone is low. The results show that the NOx emissions predicted by the complex chemical reactor network model are most consistent with those elicited using the empirical formula.

A novel methodology for architectural wind environment study by integrating CFD simulation, multiple parametric tools and evaluation criteria

Nowadays wind environment research usually requires lots of comparisons of simulations to study influences on wind environment of building shapes and arrangements. This research aims to develop a novel methodology by integrating computational fluid dynamics (CFD) simulation, parametric tools and evaluation criteria. The integration of multiple tools can provide abundant functions and an efficient modelling-simulation-analysis solution for comparison studies. The methodology is consisted of parametric design, CFD simulation method and analysis method. It is further demonstrated in the case study of square form and scattered configuration to study the relationship between influences on winds and building variables through iterative analysis. For square form, the increase of edge length increases the influence, because more winds are obstructed by larger windward surfaces; the increase of rotation angle reduces the influence, because it is easier for winds to flow around non-vertical windward surfaces. For scattered configuration, the increase of building intervals reduces the influences on winds, because it is easier for winds to flow through larger intervals. In summary, the novel methodology provides an accurate and efficient integrated solution for wind environmental studies of contemporary buildings to explore basic laws for architects to improve their design on the early stage.

Effect of clearance jet on aerodynamic performance of centrifugal fan

The change of the depth of the inlet collector inserted into the impeller will change the gap shape between the collector and the impeller, and then affect the performance of the ventilator. Taking the small centrifugal ventilator as the object, the influence of the depth of the impeller inserted into the collector on the aerodynamic performance of the ventilator is studied in this paper. Firstly, the depth of the collector inserted into the front disk of the impeller is adjusted to 2 mm, 3 mm and 4 mm respectively to change the geometry of the clearance. Then, based on the computational fluid dynamics analysis method, the influence of the insertion depth of the above three different concentrators on the aerodynamic performance of the ventilator is analyzed. The analysis results show that the gap leakage is positively correlated with the depth of the impeller inserted into the collector, and the aerodynamic performance of the ventilator can be significantly improved by reducing the insertion depth of the collector under the conditions of design flow rate and large flow rate, but under the condition of small flow, the decrease of insertion depth weakens the effect of gap jet on the flow field in impeller, resulting in the decrease of fan efficiency and static pressure.

Measurement and Prediction of Total Friction Losses in Drip Irrigation Laterals with Cylindrical Integrated in-line Drip Emitters using CFD Analysis Method

The objective of this study was to predict total friction losses in drip irrigation laterals with cylindrical integrated inline emitters at different spacing using Computational Fluid Dynamics (CFD) simulation method. Two types of drip irrigation laterals with different technical specifications were used in the study. In the laboratory, the total friction losses were measured in the laterals for different velocities. In CFD analysis, standard k-ε, RNG k-ε, realizable k-ε, Reynolds Stress (RSM) with Linear Pressure-Strain (LPS) turbulence models and standard wall function, non-equilibrium wall function, enhanced wall treatment were considered. CFD simulation results were compared with experimental total friction losses in laterals. The highest prediction was obtained by RSM turbulence model with LPS using standard wall function with the lowest values of MAPE (2.96%) and RMSE (369 Pa).

A Review of CFD Analysis Methods for Personalized Ventilation (PV) in Indoor Built Environments

Computational fluid dynamics (CFD) is an effective analysis method of personalized ventilation (PV) in indoor built environments. As an increasingly important supplement to experimental and theoretical methods, the quality of CFD simulations must be maintained through an adequately controlled numerical modeling process. CFD numerical data can explain PV performance in terms of inhaled air quality, occupants’ thermal comfort, and building energy savings. Therefore, this paper presents state-of-the-art CFD analyses of PV systems in indoor built environments. The results emphasize the importance of accurate thermal boundary conditions for computational thermal manikins (CTMs) to properly analyze the heat exchange between human body and the microenvironment, including both convective and radiative heat exchange. CFD modeling performance is examined in terms of effectiveness of computational grids, convergence criteria, and validation methods. Additionally, indices of PV performance are suggested as system-performance evaluation criteria. A specific utilization of realistic PV air supply diffuser configurations remains a challenging task for further study. Overall, the adaptable airflow characteristics of a PV air supply provide an opportunity to achieve better thermal comfort with lower energy use based on CFD numerical analyses.

Design optimization for subsea gate valve based on combined analyses of fluid characteristics and sensitivity

A subsea gate valve is an extremely important part of a subsea Xmas tree system. An optimization method for subsea gate valve is proposed based on combined analysis of fluid characteristics and sensitivity. Fluid characteristics are studied via Computational Fluid Dynamics (CFD) method to simulate the flow field inside a gate valve. In order to verify that the CFD analysis method is applicable to this paper, a qualitative experiment has been conducted. The type of gate valve is preferred by combining with velocity pathlines, pressure field distribution, and gate deformation contours. The number of sensitivity analysis experiments for key design parameters of the gate is reduced by orthogonal experimental design. The factors affecting the peak flow velocity inside the valve and the maximum deformation of the gate are determined. The range method is used to analyze and evaluate the factor sensitivity, and the combination of the minimum peak flow velocity and the reduced maximum gate deformation is obtained. Experimental results show that the preferred combined design can reduce the peak flow velocity in pipes by approximately 8.0%, with a maximum gate deformation reduction of approximately 50%. This method can provide a new way of optimizing the flow characteristics and design of valve gates.

Application of Exactly Linearized Error Transport Equations to Sonic Boom Prediction Workshop

The computational fluid dynamics (CFD) prediction workshops sponsored by the AIAA have created invaluable opportunities to discuss the predictive capabilities of CFD in areas in which it has struggled, for example, sonic boom prediction. While there are many factors that contribute to disagreement between simulated and experimental results, such as modeling or discretization errors, quantifying the errors contained in a simulation is important for those who make decisions based on the computational results. The linearized error transport equations (ETE) combined with a truncation error estimate is a method to quantify one source of error. The ETE are implemented with a complex-step method to provide an exact linearization with minimal source code modifications to CFD and multidisciplinary analysis methods including atmospheric propagation of sonic boom signatures. Uniformly refined grids from the 2nd AIAA Sonic Boom Prediction Workshop demonstrate the utility of the linearized ETE for multidisciplinary analysis, capturing the general trends of the discretization error when flow features are resolved while also demonstrating issues related to error prediction near strong shocks or when under-resolved flow features are present.

Application of an Airfoil to the Tidal Turbine Design by Analyzing Two-dimensional Performance in the Water

The tidal turbine, the first device converting the in-line flow energy into rotational motion, is one of the crucial components that affects the performance of the tidal current power system. The tidal turbine is designed by using BEMT (Blade Element Momentum Theory) developed for wind turbine that has large similarities. But the differences exist in range of Reynolds number and in working fluid that should be considered for tidal turbine design. Since the airfoil profile has been developed for wind turbine, it might contain essential errors in 2-dimensional characteristics. In this study, using validated CFD (Computational Fluid Dynamics) analysis method with experimental data obtained from flume tank, the 2-dimensional airfoil performance was evaluated considering operating conditions of the tidal turbine for design optimization. Based on the obtained characteristics of the airfoil, the horizontal axis tidal turbine of 10m diameter was designed. Performance of the designed turbine has been analyzed, and the results are summarized in this paper.

Application of the developed CFD analysis methodology to H2 explosion accidents in an open space

We developed a CFD (Computational Fluid Dynamics) analysis methodology for predicting an overpressure buildup due to a hydrogen explosion as well as the blast wave propagation from the near field to the far field of the hydrogen explosion site with an error range of about ±30% on the basis of test results with the small-scale obstacle at the stoichiometry condition in an open space in the previous research. In this paper, we confirmed the applicability of the developed CFD analysis method to the evaluation of the safety distance between a VHTR (Very High Temperature Reactor) and a hydrogen production facility through the CFD analysis conducted on the HTTR (High Temperature Test Reactor) and the hydrogen production facility in JAEA (Japan Atomic Energy Agency) under an assumption of a hypothetical hydrogen explosion. The application study showed physically reasonable results when compared to the test data performed by SRI (Stanford Research Institute) International, and the CFD analysis methodology is a more useful tool in the evaluation of the safety distance than the MEM (Multi-Energy Method) because the MEM has some drawbacks that it cannot predict an asymmetric explosion phenomenon due to a complicated geometry and an ambient temperature effect on an overpressure buildup. Finally, the developed CFD analysis methodology will be applied to evaluate the safety distance between a VHTR and a hydrogen production facility after KAERI (Korea Atomic Energy Reaches Institute) completes a design work of a VHTR and a production facility.

Verification of CFD analysis methods for predicting the drag force and thrust power of an underwater disk robot

This paper examines the suitability of using the Computational Fluid Dynamics (CFD) tools, ANSYSCFX, as an initial analysis tool for predicting the drag and propulsion performance (thrust and torque) of a concept underwater vehicle design. In order to select an appropriate thruster that will achieve the required speed of the Underwater Disk Robot (UDR), the ANSYS-CFX tools were used to predict the drag force of the UDR. Vertical Planar Motion Mechanism (VPMM) test simulations (i.e. pure heaving and pure pitching motion) by CFD motion analysis were carried out with the CFD software. The CFD results reveal the distribution of hydrodynamic values (velocity, pressure, etc.) of the UDR for these motion studies. Finally, CFD bollard pull test simulations were performed and compared with the experimental bollard pull test results conducted in a model basin. The experimental results confirm the suitability of using the ANSYS-CFX tools for predicting the behavior of concept vehicles early on in their design process.

커먼레일 디젤인젝터의 분사성능 개선을 위한 내부유로형상 최적화에 관한 수치적 연구

The common-rail injectors are the most critical component of the CRDI diesel engines that dominantly affect engine performances through high pressure injection with exact control. Thus, from now on the advanced combustion technologies for common-rail diesel injection engine require high performance fuel injectors. Accordingly, the previous studies on the numerical and experimental analysis of the diesel injector have focused on a optimum geometry to induce proper injection rate. In this study, computational predictions of performance of the diesel injector have been performed to evaluate internal flow characteristics for various needle lift and the spray pattern at the nozzle exit. To our knowledge, three-dimensional computational fluid dynamics (CFD) model of the internal flow passage of an entire injector duct including injection and return routes has never been studied. In this study, major design parameters concerning internal routes in the injector are optimized by using a CFD analysis and Response Surface Method (RSM). The computational prediction of the internal flow characteristics of the common-rail diesel injector was carried out by using STAR-CCM+7.06 code. In this work, computations were carried out under the assumption that the internal flow passage is a steady-state condition at the maximum needle lift. The design parameters are optimized by using the L16 orthogonal array and polynomial regression, local-approximation characteristics of RSM. Meanwhile, the optimum values are confirmed to be valid in 95% confidence and 5% significance level through analysis of variance (ANOVA). In addition, optimal design and prototype design were confirmed by calculating the injection quantities, resulting in the improvement of the injection performance by more than 54%.

Numerical analysis of blood flow distribution in 4- and 3-branch vascular grafts

Trifurcated arch grafts (3-branch grafts) are now being used to repair the thoracic aorta in addition to conventional arch grafts (4-branch grafts). The anatomical shape of the 3-branch graft is different from the original vessel, so it is necessary for clinical application to evaluate blood flow distribution in the graft to assess whether there is adequate blood flow to the target organs. To achieve this, we developed a computational fluid dynamics (CFD) method to evaluate blood flow distribution in the grafts. Aortic blood flow was measured by phase-contrast magnetic resonance imaging (PC-MRI), and flow distribution into the branched vessels was obtained. The MRI image was used to create a patient-specific image model that represents the geometry of the aortic arch. The CFD analysis method was employed to determine a boundary condition of the blood flow analysis in the aorta using a patient-specific image model. We also created simplified models of 4-branch and 3-branch grafts and used our CFD analysis method to compare blood flow distribution among simplified models. It was found that blood flow distribution in the descending aorta was 71.3% for the 4-branch graft and 67.7% for the 3-branch graft, indicating that a sum of branching flow in the 3-branch graft was almost the same as the one in the 4-branch graft. Therefore, there is no major concern about implanting a new 3-branch graft. Our CFD analysis method may be applied to estimate blood flow distribution of a newly developed vascular graft prior to its clinical use and provide useful information for safe use of the graft.