Verification Of CFD Research Articles

초대형 선박 폐열 열전발전시스템 내부 열전달 현상 규명

As environmental regulations on exhaust gas are being enforced around the world, and marine transportation is gradually being strengthened. It is believed that various methods will be attempted to the emission regulations. The thermoelectric power generation system can convert thermal energy into electrical energy. It can be applied without limiting the functions of the equipment and parts in the existing ship and has the advantage of not incurring large maintenance costs, which have spread to ship applications. In order to optimize the design of the thermoelectric power generation system, the heat transfer phenomenon due to the internal position was analyzed through CFD, and cross-validation was carried out through comparison with actual experimental values. Before conducting CFD of the thermoelectric power generation system, By setting the porous domain for the fin was applied to TEM to derive accurate results while reducing the calculation load. Comparing the fin that was applied to TEM and porous domain CFD results confirmed that the fin and porous domain CFD results have a great agreement with a maximum error of less than 0.5%. After that, performed a CFD of the entire thermoelectric power generation system, analyzed the heat transfer phenomena in a thermoelectric generator, and based on the results, conducted a comparison verification with the experimental results. The result of the comparison indicates the maximum error in the cooling jacket and power generation. This is analyzed in the experimental and CFD adiabatic efficiency difference, the heat loss difference at different locations in the actual experiment. In this study establishes an analysis methodology through comparative verification of experiments and CFD, It is expected that can optimize the design of thermoelectric power generation systems through the established methodology.

Studying the Swirl Flow Hydrodynamics in the Guiding Channel Area Downstream of Mixing Spacer Grids of a PWR Reactor Fuel Assembly

The results from studying the coolant flow in fuel assemblies downstream of mixing spacer grids of a PWR reactor are presented. The aim of the study is to estimate the effect from using different designs of mixing grids. For this purpose, experimental investigations were carried out on an aerodynamic test facility with scaled models of fuel assembly fragments containing mixing spacer grids of different designs. Two adjacent cells of the guiding channel zone were selected as the representative study area. The specific structural feature of these cells is that the turbulizers installed on the intensifying grids have different spatial orientation. The general flow pattern is represented by the vector fields of tangential velocities and by the distribution of relative velocities in the gaps between the fuel rods and the guiding channel. For estimating the effect from using the grid designs with respect to coolant flow mixing, the intracell vortex formation coefficients and intercell mixing coefficients were analyzed. It has been shown from the performed analysis that, owing to the use of the alternative design with a pair of cell deflectors oriented in a changed direction, the intercell transfer coefficient and the intracell vortex formation coefficient were increased by a factor of 1.13 and 2.2, respectively, in comparison with those in the basic design. Hence, the use of the grid of the alternative design is more preferable for obtaining better mixing of the coolant flow. The accumulated database on coolant flow in the Square FA serves for engineering substantiation of the PWR reactor cores. The results from experimental studies are used for verification of CFD codes developed both in Russia and abroad and of programs for detailed cell-wise analysis of the cores for reducing the conservatism in substantiating their thermal reliability.

Verification and Validation of CFD Based Form Factors as a Combined CFD/EFD Method

Predicting the propulsive power of ships with high accuracy still remains a challenge. Well established practices in the 1978 ITTC Power Prediction method have been questioned such as the form factor approach and its determination method. This paper investigates the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method where the experimental determination of form factor is replaced by double body RANS computations. Following the Quality Assurance Procedure proposed by ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. Following the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions using the CFD based form factors in combination with ITTC-57 line and numerical friction lines are investigated. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.

Pressure distribution and flow dynamics in a nasal airway using a scale resolving simulation

Airflow through the nasal cavity exhibits a wide variety of fluid dynamic behaviors due to the intricacy of the nasal geometry. The flow is naturally unsteady and perhaps turbulent, despite Computational Fluid Dynamics (CFD) in the literature being assumed as having a steady laminar flow. Time-dependent simulations can be used to generate detailed data with the potential to uncover new flow behavior, although they are more computationally intensive than steady-state simulations. Furthermore, verification of CFD results has relied on a reported pressure drop (e.g., nasal resistance) across the nasal airway although the geometries used are different. This study investigated the unsteady nature of inhalation at flow rates of 10 l/min, 15 l/min, 20 l/min, and 30 l/min. A scale resolving CFD simulation using a hybrid Reynolds-averaged Navier–Stokes--large eddy simulation model was used and compared with experimental measurements of the pressure distribution and the overall pressure drop in the nasal cavity. The experimental results indicated a large pressure drop across the nasal valve and across the nasopharynx, with the latter attributed to a narrow cross-sectional area. At a flowrate of 30 l/min, the CFD simulations showed that the anterior half of the nasal cavity displayed dominantly laminar but disturbed flow behavior in the form of velocity fluctuations. The posterior half of the nasal cavity displayed turbulent activity, characterized by erratic fluctuating velocities, which was enhanced by the wider cross-sectional areas in the coronal plane. At 15 l/min, the flow field was laminar dominant with very little disturbance, confirming a steady-state laminar flow assumption is viable at this flow rate.

X-Ray tomography reconstruction of multiphase flows and the verification of CFD

X-Ray tomography reconstruction of multiphase flows and the verification of CFD

X-Ray tomography reconstruction of multiphase flows and the verification of CFD

X-Ray tomography reconstruction of multiphase flows and the verification of CFD

IAEA CRP benchmark of ROCOM PTS test case for the use of CFD in reactor design using the CFD-Codes ANSYS CFX and TrioCFD

Over the last 15 years, considerable effort has been expended in assembling the available information on the use of CFD in the nuclear reactor safety field. Typical application areas here are heterogeneous mixing and heat transfer in complex geometries, buoyancy-induced natural and mixed convection, etc., with specific reference to Nuclear Reactor Safety (NRS) accident scenarios such as Pressurized Thermal Shock (PTS), boron dilution, hydrogen build-up in containments, thermal fatigue and thermal striping issues, etc. The development, verification and validation of CFD codes in respect to Nuclear Power Plant (NPP) design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. Therefore, a set of ROCOM CFD-grade test data were made available to set up an International Atomic Energy Agency (IAEA) benchmark, relating to PTS scenarios. The benchmark deals with the injection of the relatively cold Emergency Core Cooling (ECC) water, which can induce buoyancy-driven stratification. Data obtained from the PTS experiment were compared in the study presented here with predictions obtained from the CFD software packages ANSYS CFX and TrioCFD. In addition a test case without buoyancy forces was selected to show the influence of density differences.The results of the two test cases and the numerical calculations show that mixing efficiency is strongly influenced by buoyancy effects. At higher mass flow rates without density differences the injected slug propagates in the circumferential direction around the core barrel. Buoyancy forces reduce this azimuthal propagation. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. Both CFD codes were able to predict the observed flow patterns and mixing phenomena.

CFD analysis of pressure drop across grid spacers in rod bundles compared to correlations and heavy liquid metal experimental data

Early studies of the flow in rod bundles with spacer grids suggest that the pressure drop can be decomposed in contributions due to flow area variations by spacer grids and frictional losses along the rods. For these shape and frictional losses simple correlations based on theoretical and experimental data have been proposed. In the OECD benchmark study LACANES it was observed that correlations could well describe the flow behavior of the heavy liquid metal loop including a rod bundle with the exception of the core region, where different experts chose different pressure-loss correlations for the losses due to spacer grids. Here, RANS–CFD simulations provided very good data compared to the experimental data. It was observed that the most commonly applied Rehme correlation underestimated the shape losses. The available correlations relate the pressure drop across a grid spacer to the relative plugging of the spacer i.e. solidity emax. More sophisticated correlations distinct between spacer grids with round or sharp leading edge shape. The purpose of this study is to (i) show that CFD is suitable to predict pressure drop across spacer grids and (ii) to access the generality of pressure drop correlations. By verification and validation of CFD results against experimental data obtained in KALLA we show (i). The generality (ii) is challenged by considering three cases which yield identical pressure drop in the correlations. First we test the effect of surface roughness, a parameter not present in the correlations. Here we compare a simulation assuming a typical surface roughness representing the experimental situation to a perfectly smooth spacer surface. Second we reverse the flow direction for the spacer grid employed in the experiments which is asymmetric. The flow direction reversal is chosen for convenience, since an asymmetric spacer grid with given blockage ratio, may result in different flow situations depending on flow direction. Obviously blockage develops differently along flow direction due to the asymmetry, so that the same numerical mesh can be used for two distinct simulations. The study shows that prediction of pressure drop across spacer grids by RANS–CFD using well resolved meshes in the spacer grid region yields more accurate results than any available correlation.

416 自動車用送風機の電力回生に関する研究 : 翼周りの流れ測定によるCFD解析の検証と翼型改良(GS 自動車技術)

416 自動車用送風機の電力回生に関する研究 : 翼周りの流れ測定によるCFD解析の検証と翼型改良(GS 自動車技術)

CFD modelling of two-phase liquid-liquid flow in a SMX static mixer

CFD modelling of two-phase liquid-liquid flow in a SMX static mixer The paper provides an overview of the application of Computational Fluid Dynamics tools for predicting transport processes in two-phase flow in a SMX static mixer. The overview is achieved by taking a brief look at factors: mesh generation, development of sub-models, post-processing including validation and quantitative verification of CFD results with experimental data. Two types of numerical approach were used in the simulations: the Reynolds averaged Navier-Stokes in the steady-state mode with the standard k-??turbulence model and Large Eddy Simulations in the unsteady mode. Both CFD techniques were applied to calculate flow velocities, pressure drop and homogenisation level in a SMX static mixer of the liquid-liquid mixture. The steady state drop size distribution was obtained by implementation procedure containing the population balance equation, where transport equations for the moments of the drop size distribution are solved and the closure problem is overcome by using the Quadrature Method of Moments.

1138 3軸胸鰭運動装置の流体力特性について(J04-2 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス(2),J04 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス)

This paper describes the use of a three-motor driven mechanical pectoral fm as a device for maneuvering and stabilizing an underwater vehicle. The mechanical pectoral fm consists of three servomotors generating feathering, rowing, and flapping motions. The time varied hydrodynamic force properties of three types of fin motion and two kinds of fluid circumstances were measured. Measured data is useful for validation or verification of CFD or some numerical methods in case of estimating hydrodynamic force generated by a pectoral fin.

PIV Study of Wake-Rotor Interactions in a Transonic Compressor at Various Operating Conditions

Details of the unsteady flowfield between an upstream wake generator and a downstream rotor that are closely spaced in a transonic compressor are studied at various operating conditions using particle-image velocimetry. Flow-visualization images and particle-image velocimetry data facilitate analysis of the details of shed vortices, wake motion, and wake-shock interaction phenomena. Such analysis not only aids the understanding of the effect of blade-row interactions on compressor performance but also allows verification of time-accurate CFD codes that are used to characterize transonic compressors. As the operating point changes from choke to stall and the rotor-bow shock moves upstream, distinct vortex-shedding patterns are observed that affect the wake deviation and rotor incidence. With close spacing between the wake generator and the rotor, vortex shedding from the wake generator and the passage of the rotor-bow shock are strongly synchronized and blade-passage phase-locked measurements are possible. The resulting multiple images of the flow corresponding to any blade position are averaged to yield vortex and rotor-bow-shock locations at various back pressures. Using various postprocessing methods, specific shed vortices and wake topological features are isolated and details of the wake-shock interaction are captured.