Commercial Computational Fluid Dynamics Code Research Articles

CFD code-to-code benchmarking on simulation of fire and smoke propagation for nuclear applications

Abstract The nuclear industry has seen an increased use of Computational Fluid Dynamics (CFD) technology as a high-fidelity tool for design-basis and beyond design-basis accident simulations. For fire hazards, detailed experimental investigation in a realistic environment is often impractical. Therefore, the use of an advanced 3D CFD modeling approach to predict smoke and fire propagation has risen, especially for nuclear power plant fire modeling applications. CFD simulations can include major contributing and mitigating mechanisms regarding the fire propagation and its consequences, in fine detail and under realistic geometry conditions. In addition, accurate simulations of unsteady 3D fire and smoke spread, in conjunction with evacuation analyses, can be used to establish effective emergency evacuation strategies. In the present study, the fire and smoke propagation in a main control room was modelled using Reynolds-Averaged Navier-Stokes Equation based twoequation turbulence models and a Large Eddy Simulation model implemented in a commercial CFD code, Siemens STAR-CCM+. The predictions from STAR-CCM+ were compared with those obtained in a previous study using the NIST Fire Dynamic Simulator (FDS) code. Although higher temperature was predicted at the fire source by STAR-CCM+, the current study predicted trends similar to the FDS results with some minor differences at the operator location. A follow-up study is currently underway to investigate the factors affecting the differences, including further assessment of codes against available benchmark experiments.

Enhanced Delayed Detached Eddy Simulation for Cavities and Labyrinth Seals

Abstract A range of popular hybrid Reynolds-averaged Navier–Stokes -large eddy simulation (RANS-LES) methods are tested for a cavity and two labyrinth seal geometries using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the standard Spalart–Allmaras (SA) and Menter shear stress transport (SST) versions of delayed detached eddy simulation (DDES) and the Menter scale adaptive simulation (SAS) model. A recently formulated, enhanced, variant of SA-DDES presented in the literature and a new variant using the Menter SST model are also investigated. The latter modify the original definition of the subgrid length scale used in standard DDES based on local vorticity and strain. For all geometries, the meshes are considered to be hybrid RANS-LES adequate. Very low levels of resolved turbulence and quasi-two-dimensional flow fields are observed for the standard DDES and SAS models even for the test cases here that contain obstacles, sharp edges, and swirling flow. Similar findings are observed for both the commercial and in-house high-order CFD codes. For the cavity simulations, when using standard DDES and SAS, there is a significant under prediction of turbulent statistics compared with experimental measurements. The enhanced versions of DDES, on the other hand, show a significant improvement and resolve turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed for profiles of the vertical velocity component. For the first labyrinth seal geometry swirl velocities are more accurately captured by the enhanced DDES versions. For the second labyrinth seal geometry, the mass flow coefficient prediction using the enhanced models is significantly improved (up to 30%). Standard, industrially available hybrid RANS-LES models, when applied to the present canonical cases can produce little to no resolved turbulent content. The standard SA- and Menter-based DDES models can yield lower levels of eddy viscosity when compared to equivilent steady RANS simulations which means that they are not operating as RANS or LES. It is recommended that hybrid RANS-LES models should be extensively tested for specific flow configurations and that special care is exercised by CFD practitioners when using many of the popular hybrid RANS-LES models that are currently available in commercial CFD packages.

Experimental and Numerical Investigation of DARPA Suboff Submarine Propelled with INSEAN E1619 Propeller for Self-Propulsion

The Defense Advanced Research Projects Agency (DARPA) Suboff Submarine propelled by the Italian Ship Model Basin (INSEAN) E1619 propeller is extensively used in submarine validation studies. Although there are several numerical studies where the DARPA Suboff submarine is used in combination with E1619 propeller there are no experimental data available in open literature for the self-propulsion condition. In this article, the self-propulsion characteristics of the DARPA Suboff submarine model with INSEAN E1619 propeller obtained with experimental and numerical methods are presented and discussed by means of Taylor wake fraction, thrust deduction, hull efficiency, relative rotative efficiency, and propulsive efficiency. To experimentally investigate the submarine form, a self-propulsion experimental setup is designed and manufactured. Resistance and self-propulsion experiments are conducted in Istanbul Technical University Ata Nutku Ship Model Testing Laboratory. Resistance tests are carried out for three different speeds, and the results show good agreement with the published experimental results. Propulsion tests are conducted by using the load-varying self-propulsion test method for constant speed and seven different propeller rotation rates. Rotational speed, thrust, and torque forces at self-propulsion point are investigated. For the numerical computations a commercial Computational Fluid Dynamics (CFD) code is used. Propeller open water characteristics and nondimensional velocities behind the propeller are calculated. Self-propulsion point of the submarine and propeller assembly is also solved numerically and the results are compared with the results obtained from the experiments, and it is seen that especially the propeller rate of revolution and thrust force are predicted with very good approximation.

A Study on Thermal-flow Characteristics in a Reaction Chamber of Gas Scrubber Designed Based on Similitude Theory

Objectives A gas scrubber which is normally composed of a reaction chamber and a scrubbing part is being used to purify the waste gases from the processes. An efficient design of the reaction chamber is essential in a scrubber system due to the overall operation stability and high destruction & removal efficiency (DRE). The purpose of the study was to obtain the basic design data of deriving the improved design by analyzing a small-scale model of the commercial reaction chamber. Methods In the present study, the small-scale model of the simplified the reaction chamber was designed and fabricated based on similitude theory, and the thermal-flow characteristics were numerically analyzed inside the chamber using commercial Computational Fluid Dynamics (CFD) code. Results and Discussion Based on two dimensionless numbers for the geometric similarity and three dimensionless numbers for the kinematic similarity, the small-scale model of the reaction chamber was designed and fabricated. From the numerical and experimental results, thermal-flow characteristics such as temperature gradient and thermal efficiency were evaluated. To validate the numerical method applied herein, the numerical results of the temperature at specific monitoring points were compared with the experimental data. The average error rates (2.5~9.8%) between them was shown and the numerical results of temperature distribution are in good agreement with the experimental data. Conclusions In this study, the small-scale model, which was designed and manufactured based on similarity theory was analyzed. From these results, the basic design data for drawing the improved design ideas were acquired The results of this study can be used as basic data for analyzing thermal and flow characteristics in a variety of scrubber systems. Key words: Semiconductor Industry, Gas Scrubber, Reaction Chamber, Similitude Theory, Computational Fluid Dynamics (CFD)

Transient thermal-hydraulic analysis for fuel assembly blockage accident by coupling CFD code with the neutron kinetics model

Lead-based reactor coolants have many excellent characteristics but the coolants may seriously erode the fuel cladding and the structural materials and the flow area will be reduced by the corrosion products. This phenomenon is called blockage accident.In this paper, the blockage accident of single subassembly for a lead-based reactor has been analyzed by applying the commercial computational fluid dynamics (CFD) software coupled with the point reactor kinetics model. Firstly, the neutronics/thermal-hydraulics coupling model was established by user defined function (UDF) of FLUENT software based on the point reactor kinetics function with one group delayed neutron. Then the neutronics/thermal-hydraulics coupling model was validated with a single fuel pin model by comparing the fuel power, the cladding temperature and the coolant temperature with the calculation results of the RELAP5 code. Secondly, after considering mesh independence, turbulence models and other factors, the steady state of a single subassembly with 61 fuel pins at full power for a lead-based reactor designed by INEST/FDS Team was simulated in the normal operating conditions. Finally, a single subassembly for the center blockages of the flow channel was simulated by the neutronics/thermal-hydraulics coupling model. The temperature distributions and the maximum temperature were compared with that of the normal operating conditions and the effect of axial position for blockage was analyzed. It shows that the core outlet temperature and the highest temperature of cladding are increasing after blockage accident happening. And the highest temperature of cladding is lower calculated by neutronics/thermal-hydraulics coupling model than the condition without considering reactivity feedback. And the maximum cladding temperature for the 500 mm axially location blockage accident is higher.

Numerical and Experimental Investigation on Radiated Noise Characteristics of the Multistage Centrifugal Pump

The radiated noise of the centrifugal pump acts as a disturbance in many applications. The radiated noise is closely related to the hydraulic design. The hydraulic parameters in the multistage pump are complex and the flow interaction among different stages is very strong, which in turn causes vibration and noise problems because of the strong hydraulic excitation. Hence, the mechanism of radiated noise and its relationship with hydraulics must be studied clearly. In order to find the regular pattern of the radiated noise at different operational conditions, a hybrid numerical method was proposed to obtain the flow-induced noise source based on Lighthill acoustic analogy theory, which divided the computational process into two parts: computational fluid dynamics (CFD) and computational acoustics (CA). The unsteady flow field was solved by detached eddy simulation using the commercial CFD code. The detailed flow information near the surface of the vane diffusers and the calculated flow-induced noise source was extracted as the hydraulic exciting force, both of which were used as acoustic sources for radiated noise simulation. The acoustic simulation employed the finite element method code to get the sound pressure level (SPL), frequency response, directivity, et al. results. The experiment was performed inside a semi-anechoic room with a closed type pump test rig. The pump performance and acoustic parameters of the multistage pump at different flow rates were gathered to verify the numerical methods. The computational and experimental results both reveal that the radiated noise exhibits a typical dipole characteristic behavior and its directivity varies with the flowrate. In addition, the sound pressure level (SPL) of the radiated noise fluctuates with the increment of the flow rate and the lowest SPL is generated at 0.8Qd, which corresponds to the maximum efficiency working conditions. Furthermore, the experiment detects that the sound pressure level of the radiated noise in the multistage pump rises linearly with the increase of the rotational speed. Finally, an example of a low noise pump design is processed based on the obtained noise characteristics.

A numerical study on NOx formation behavior in a lean-premixed gas turbine combustor using CFD-CRN method

A chemical reactor network (CRN) was developed, guided by computational fluid dynamics (CFD), to predict the NOx formation in lean-premixed gas turbine combustors. CFD analysis was conducted using the ANSYS Fluent version 14.5, a commercial CFD code. The developed CRN consisted of 41 chemical reactor elements, which acted as different reaction zones in the combustor. CRN predictions were carried out using CHEMKIN code and the GRI 3.0 chemical kinetics mechanism. The CFD-CRN method was evaluated over a range of equivalence ratios by comparing the predicted NOx emissions with experimental data. Good agreement between the predictions and measurements indicates the validity of the modeling approach. The CFD-CRN method was employed to analyze NOx formation characteristics in the different regions of the combustor. The analysis of reaction path indicated that in the main flame zone NO was generated greatly by a combination of thermal, prompt, N2O and NNH pathways; in near post-flame zone, NO production by thermal and N2O pathway persists, and NO production by prompt and NNH falls off quickly as the flame continue to completion. In IRZ, where occurs the highest temperature, the thermal pathway is dominated due to high maximum temperature (1800 K) and reduced radical concentration. Through the pathway study for overall NOx emissions, at an equivalence ratio of Φ = 0.5 the sum of N2O and NNH pathway contribution exceeds 81.4 %, but N2O pathway outperformed the NNH pathway. At an equivalence ratio of Φ = 0.6 the contributions of four pathways were almost identical; at an equivalence ratio of Φ = 0.7 the sum of thermal and prompt exceeded 64.3 %, but the thermal pathway was superior to the prompt pathway.

Computational Fluid Dynamics (CFD) Modelling of Mixture Formation in Gasoline Direct Injection (GDI) Engine

Automotive engine faces stringent regulations on emission with improved fuel consumption. As such, the Gasoline Direct Injection (GDI) engines which have the potential to meet these requirements are being improved on especially the mixture formation to the burning of the mixture. In GDI, late injection compared with early injection scheme generates charge stratification which contributes to the optimised fuel consumption and combustion. As a result, this strategy in GDI engines is considered to be promising with increasing research focus. This paper aims at evaluating the computational fluids dynamics (CFD) modelling of two-phase transient injection process in generic GDI engines with the late injection to study the features of fuel atomisation process, injection velocity and its influence on turbulence. The commercial CFD code Star CCM+ was used to perform this simulation due to its advanced polyhedral mesh technology and the user-friendly interface. Transient liquid and gas flow inside the combustion chamber was simulated using the Eulerian multiphase segregated flow model with k-epsilon turbulence. The contour plots show that during the injection period turbulence for each phase was independent of the spray shape predicted to be asymmetric under non-vaporisation conditions. In addition, increasing injection velocity of liquid fuel causes stronger turbulence for the liquid phase. The results also show that the variation of turbulence for gas-phase is mainly centred in the region of the inlet during the injection process and non-homogenous turbulent characteristics were observed for the late injection with the volume fraction of the liquid phase also seen to be asymmetric.

Numerical Validation and Study of Particulate Flow in Cyclone Separator using Commercial Computational Fluid Dynamics Code

The cyclone separator is widely used for particle separation in industries because of ease in manufacturing and maintenance free working capability. It has also been an automobile component used in air intake system. It’s necessary to understand the flow of air and particles inside the cyclone separator for the design of cyclone separator. Its performance depends upon operational and geometrical parameters. This study is focused on geometric parameter in which a numerical simulation has been carried out to understand the effect of air and particle flow on varying the cone height of cyclone separator using ANSYS 15.0. The analysis involves determining pressure drop at different inlet velocity with corresponding change in cone height of the cyclone separator. The results were obtained for different velocity condition with maximum of 8% of error. Moreover, collection efficiency for cyclone separator was also determined by varying particle size from 0.01 to 10 micron. Decreasing cyclone height led to increase in tangential velocity thus increasing the cyclone efficiency.

Aerodynamic Optimal Design for Horizontal Axis Wind Turbine Airfoil Using Integrated Optimization Method

In this work, a new approach for aerodynamic optimization of horizontal axis wind turbine (HAWT) airfoil is presented. This technique combines commercial computational fluid dynamics (CFD) codes with differential evolution (DE), a reliable gradient-free global optimization method. During the optimization process, commercial CFD codes are used to evaluate aerodynamic characteristics of HAWT airfoil and an improved DE algorithm is utilized to find the optimal airfoil design. The objective of this research is to maximize the aerodynamic coefficients of HAWT airfoil at the design angle of attack (AOA) with specific ambient environment. The airfoil shape is modeled by control points which their coordinates are design variables. The reliability of CFD codes is validated by comparing the analytical results of a typical HAWT airfoil with its experimental data. Finally, the optimal design of wind turbine airfoil is evaluated about aerodynamic performance in comparison with existing airfoils and some discussions are performed.

Effect of ignition position on vented hydrogen–air deflagration in a 1 m3 vessel

This study investigates the effect of the ignition position on vented hydrogen-air deflagration in a 1 m3 vessel and evaluates the performance of the commercial computational fluid dynamics (CFD) code FLACS in simulating the vented explosion of hydrogen-air mixtures. First, the differences in the measured pressure-time histories for various ignition locations are presented, and the mechanisms responsible for the generation of different pressure peaks are explained, along with the flame behavior. Secondly, the CFD software FLACS is assessed against the experimental data. The characteristic phenomena of vented explosion are observed for hydrogen-air mixtures ignited at different ignition positions, such as Helmholtz oscillation for front ignition, the interaction between external explosion and combustion inside the vessel for central ignition, and the wall effect for back-wall ignition. Flame-acoustic interaction are observed in all cases, particularly in those of front ignition and very lean hydrogen-air mixtures. The predicted flame behavior agree well with the experimental data in general while the simulated maximum overpressures are larger than the experimental values by a factor of 1.5–2, which is conservative then would lead to a safe design of explosion panels for instance. Not only the flame development during the deflagration was well-simulated for the different ignition locations, but also the correspondence between the pressure transients and flame behavior was also accurately calculated. The comparison of the predicted results with the experimental data shows the performance of FLACS to model vented mixtures of hydrogen with air ignited in a lab scale vessel. However, the experimental scale is often smaller than that used in practical scenarios, such as hydrogen refueling installations. Thus, future large-scale experiments are necessary to assess the performance of FLACS in practical use.

Internal flow analysis of a porous burner via CFD

Purpose This study aims to introduce a metal porous burner design. Literature is surveyed in a comprehensive manner to relate the current design with ongoing research. A demonstrative computational fluid dynamics (CFD) analysis is presented with projected flow conditions by means of a common commercial CFD code and turbulence model to show the flow-related features of the proposed burner. The porous metal burner has a novel design, and it is not commercially available. Design/methodology/approach Based on the field experience about porous burners, a metal, cylindrical, two-staged, homogenous porous burner was designed. Literature was surveyed to lay out research aspects for the porous burners and porous media. Three dimensional solid computer model of the burner was created. The flow domain was extracted from the solid model to use in CFD analysis. A commercial computational fluid dynamics code was utilized to analyze the flow domain. Projected flow conditions for the burner were applied to the CFD code. Results were evaluated in terms of homogenous flow distribution at the outer surface and flow mixing. Quantitative results are gathered and are presented in the present report by means of contour maps. Findings There aren’t any flow sourced anomalies in the flow domain which would cause an inefficient combustion for the application. An accumulation of gas is evident around the top flange of the burner leading to higher static pressure. Generally, very low pressure drop throughout the proposed burner geometry is found which is regarded as an advantage for burners. About 0.63 Pa static pressure increase is realized on the flange surface due to the accumulation of the gas. The passage between inner and outer volumes has a high impact on the total pressure and leads to about 0.5 Pa pressure drop. About 0.03 J/kg turbulent kinetic energy can be viewed as the highest amount. Together with the increase in total enthalpy, total amount of energy drawn from the flow is 0.05 J/kg. More than half of it spent through turbulence and remaining is dissipated as heat. Outflow from burner surface can be regarded homogenous though the top part has slightly higher outflow. This can be changed by gradually increasing pore sizes toward inlet direction. Research limitations/implications Combustion via a porous medium is a complex phenomenon since it involves multiple phases, combustion chemistry, complex pore geometries and fast transient responses. Therefore, experimentation is used mostly. To do a precise computational analysis, strong computational power, parallelizing, elaborate solid modeling, very fine meshes and small time steps and multiple models are required. Practical implications Findings in the present work imply that a homogenous gas outflow can be attained through the burner surfaces while very small pressure drop occurs leading to less pumping power requirement which is regarded as an advantage. Flow mixing is realizable since turbulent kinetic energy is distinguished at the interface surface between inner and outer volumes. The porous metal matrix burner offers fluid mixing and therefore better combustion efficiency. The proposed dimensions are found appropriate for real-world application. Originality/value Conducted analysis is for a novel burner design. There are opportunities both for scientific and commercial fields.

Advanced design optimization of combustion equipment for biomass combustion

Designof engineered combustion equipment normally involves laborious “build and try” designs to identify the best possible configuration. The number of design iterations can be reduced with engineering experience of what might work. The expensive cut-and-try approach can be improved using computational aided engineering tools coupled with optimization techniques to find the optimal design. For example, the “best” air duct configuration with the lowest pressure loss and smallest fan size for an air-fed biomass gasifier may take several weeks using the standard computational fluid dynamics (CFD) “cut and try” approach. Alternatively, coupling an efficient design optimization algorithm with an existing CFD model can reduce the time to find the best design by more than 50% and can allow the engineer to examine more design options than possible using the “cut-and-try” approach. Combining an efficient optimization algorithm with an existing CFD model of a biomass gasifier to find the “optimal” design is the focus of this work. Shape optimization has been performed by combining the optimization tool Sculptor® with the commercial CFD code STARCCM+. This work illustrates how the “linked” approach is used to examine design factors to optimize an entrained flow biomass gasifier to improve overall system performance in a methodical comprehensive fashion.

Numerical investigation on bottom shear stress induced by flushing gate for sewer cleaning.

One of the most common strategies for sewer cleaning is to generate flushing flows using flushing gates to store water in the upstream sewer pipe. Therefore it is important to obtain the flow information on the flushing waves and their eroding effects. In this study, the flow characteristics of the flushing wave and the flushing effect were investigated by a transient flow calculation using a commercial computational fluid dynamics (CFD) code. The values of bottom shear stress were obtained and the effect of several factors are discussed. The water depth and the slope were related to the release rate of the storage volume, while the flushing volume determined the flushing distance at long sewer distances. The initial downstream water level was found to dramatically reduce the flushing effect. Equations based on the storage depth were developed to estimate the flushing effect, and suggestions for the installation and operation of flushing gates are provided.

Assessment of steady VOF RANS turbulence models in rendering the internal flow structure of pressure swirl nozzles

This study deals with a series of two-phase flow, computational fluid dynamics (CFD) simulations, to assess the performance of the steady Reynolds averaged Navier–Stokes (RANS) scheme. The study utilizes a high-pressure swirl nozzle at inlet injection pressure of 15 bar. In this particular nozzle, the volume of the swirl chamber is adjustable to change the spray pattern from a hollow cone to full cone at its minimum and maximum volume, respectively. The spray angle of this nozzle was measured from 1,000 images captured experimentally via a high-speed camera. Commercial CFD code (STAR CCM+ version 11.04) was used to solve the Navier–Stokes equations implementing volume-of-fluid method to simulate the internal flow structure. An extensive description is provided regarding grid sensitivity analysis and essential correlations with experimental results are introduced. Two of the most popular RANS turbulence models, namely realizable k-ε (RK-ϵ) and k-ω shear stress transport (SST), are then used and their ability to render the complex internal flow field is compared. The grid dependency study shows that none of the two models are grid independent due to the unsteady behavior of the internal flow field. Both models are inaccurate for predicting the liquid film thickness, and when the k-ω SST is superior for predicting of the spray angle.

CFD Simulations of Molten Salt Reactor Experiment Core

At present, no clear guidelines exist for modeling non-water-cooled small modular reactors (SMRs) despite the rising need for high-fidelity simulation tools to support regulators and the industry. Most SMR concepts currently under the Canadian prelicensing review adopted non-water-cooled–reactor technologies [molten salt reactor (MSR), gas-cooled reactor, and liquid metal–cooled reactor] that are new for Canada. There is a need for a modeling tool set that is broadly applicable for the assessment of advanced technologies used in SMRs. Computational fluid dynamics (CFD) can be used in performance evaluation and safety analysis of non-water-cooled SMRs for modeling three-dimensional (3-D) fluid flow and heat transfer in geometries of arbitrary complexity without resorting to geometry-specific empirical correlations. This study investigates the capabilities of existing models within a commercial CFD code to simulate the flow and heat transfer characteristics in a MSR configuration. The Oak Ridge National Laboratory (ORNL) Molten Salt Reactor Experiment (MSRE) configuration was simulated in this study using a stand-alone CFD approach, and CFD predictions were assessed with ORNL data. Intricate geometry details within the MSRE core were included in the computational model to study the associated geometric effects. The results obtained in this study showcased the ability of CFD to predict 3-D effects within the computational domain especially at the lower plenums. The predicted trends for the temperature rise in the fuel and moderator within the core were in good agreement with the ORNL data. The results presented in this paper constitute the first step in developing Canadian Nuclear Laboratories’ capability for CFD modeling of non-water SMRs.

Study of flow field and heat transfer characteristics for an interacting pair of counter-rotating dual-swirling impinging flames

Experimental and numerical studies have been conducted to investigate the flow field and heat transfer characteristics of a pair of counter rotating dual-swirling flames impinging on a flat surface. Effect of separation distance (H/Dh = 3, 4, 6 and 8), inter-jet spacings (S/Dh = 4, 7 and 10) and Reynolds number on flow interactions and impingement heat transfer have been studied under stoichiometric conditions. The inner non-swirling flames are seen to bend towards interacting side due to asymmetric interactions developed in a pair of dual-swirling flames. Commercial computational fluid dynamics (CFD) code (FLUENT®) has been used to simulate the interacting dual-swirling impinging flames. Numerical simulation predicted the deflection of inner flames to be primarily due to large distorted RCZ developed from asymmetric interactions. Comparisons of co-and-counter swirling configurations suggest that the presence of plate has a stronger influence on flow structure of impinging flames than sign of rotation. High resolution heat fluxes have been obtained using steady state 1-D heat balance from temperature readings obtained on rear side of quartz impingement plate through IR thermal camera. 1-D heat balance has been corrected for lateral conduction taking place inside the impingement plate using an iterative procedure. For counter swirl case, cross-flow leaves as a straight flow along the transverse direction due to the nature of interactions. Cross-flow causes heat flux contours in the interaction region to be asymmetric and preferential heating is observed along the transverse direction. The increase in Re(o) causes wider flame spread and severe interactions result in increased tendency for preferential heating of the impingement plate. High average heat fluxes are obtained at smallest H/Dh and S/Dh whereas minimum relative deviation is observed at S/Dh = 10 for H/Dh = 4.

A Comparative Study of Program FloSim Results Against SYRF Wide Light Project Data

In November, 2015, the Sailing Yacht Research Foundation (SYRF) published the tank test data from their "Wide Light Yacht Project" for the hydrodynamics of a modern, high performance, semi-planing yacht. This comprehensive data set, comprising canoe body with and without appendages in upright, heeled and yawed conditions, provides an important validation base for Computational Fluid Dynamics (CFD) codes. The SYRF report includes a number of comparative results from commercial CFD codes. In this paper, we present results computed using an advanced Boundary Element Method (BEM), FloSim, these calculations being compared against the test matrix of "Wide Light" measured data and also STAR-CCM+ RANS calculated results. Computer model preparation is discussed and FloSim and RANS case execution times and computer requirements are compared. FloSim is an unsteady, time-stepping BEM with a non-linear vortex wake rollup procedure and a coupled integral boundary layer method for viscous effects. The free surface wave development is treated with a non-linear procedure that includes a breaking-wave model to deal with excess wave energy issues. The program was developed specifically to bridge the gap between basic potential flow panel methods and RANS codes, with the objective of providing accurate, practical solutions on a laptop computer within a reasonable turnaround time and cost. In essence, the results presented in this paper demonstrate the development objectives have been achieved. The comparisons of FloSim's essentially "low-order" results against test data and STARCCM+ RANS calculations, provide a measure of tradeoff between calculation accuracy versus cost and turnaround time for a case.

Parametric Geometric Model and Shape Optimization of Airfoils of a Biomimetic Manta Ray Underwater Vehicle

As a new kind of autonomous underwater vehicle, bionic submersible has many merits such as high efficiency and low costs. In order to obtain such advantages, it is a good way to simulate the shapes of marine animals and apply them to the design of artificial underwater vehicle. In this paper, an optimization system of airfoils is proposed by the improved class-shape-transformation (CST) parameterization method and genetic algorithm (GA). The appearance of a manta-ray-inspired underwater vehicle is rebuilt using the optimal sectional airfoils obtained by the proposed optimization system. Computational simulations are carried out to investigate the hydrodynamic performance of the submersible using the commercial computational fluid dynamics (CFD) code Fluent. The results demonstrate that the maximum thickness of the vehicle increases by 9%, which means the loading capacity is increased. Moreover, the underwater vehicle shows better hydrodynamic performance, and the lift-drag ratio of initial design is increased by more than 10% using the presented optimization system of airfoils.

Numerical Simulation of Flow Field in Air-Jet Loom Main Nozzle

Abstract To improve airflow injection capacity of the main nozzle and decrease backflow phenomenon, a new main nozzle structure with two throats is designed. Negative pressure value and negative pressure zone length are first proposed evaluating the strength of backflow phenomenon. Commercial computational fluid dynamic (CFD) code “Fluent” is performed to simulate the flow field inside and outside the main nozzle. Exit velocity increases about 10 m/s in new main nozzle. Airflow core length of the new main nozzle is 35% higher than that of commonly used main nozzle. Smaller negative pressure value and shorter negative pressure zone length mean a weaker backflow phenomenon in the new main nozzle. Bigger air drag force indicates stronger weft insertion ability in the new main nozzle.