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In the present work, uncertainty quantification of a venturi tube simulation with the cavitating flow is conducted based on Bayesian inference and point-collocation nonintrusive polynomial chaos (PC-NIPC). A Zwart–Gerber–Belamri (ZGB) cavitation model and RNG k-ε turbulence model are adopted to simulate the cavitating flow in the venturi tube using ANSYS Fluent, and the simulation results, with void fractions and velocity profiles, are validated with experimental data. A grid convergence index (GCI) based on the SLS-GCI method is investigated for the cavitation area, and the uncertainty error (UG) is estimated as 1.12 × 10−5. First, for uncertainty quantification of the venturi flow simulation, the ZGB cavitation model coefficients are calibrated with an experimental void fraction as observation data, and posterior distributions of the four model coefficients are obtained using MCMC. Second, based on the calibrated model coefficients, the forward problem with two random inputs, an inlet velocity, and wall roughness, is conducted using PC-NIPC for the surrogate model. The quantities of interest are set to the cavitation area and the profile of the velocity and void fraction. It is confirmed that the wall roughness with a Sobol index of 0.72 has a more significant effect on the uncertainty of the cavitating flow simulation than the inlet velocity of 0.52.

In the operating nuclear power plant, piping and components installed in the in-service testing (IST) systems connected to the reactor coolant system are potentially exposed to fatigue caused by thermal stratification flow, possibly threatening its integrity. The emergency core cooling system (ECCS) is one of candidates for which the thermal stratification phenomenon can occur. During the ECCS operating period, buoyancy due to density difference may have significant influence on thermal-hydraulic characteristics of the mixing flow. Therefore, in this study, the need to consider proper buoyancy models in governing equations, especially turbulent transport equations, for accurate prediction of single phase thermal stratification by ECCS injection was numerically studied using ANSYS CFX R17.2.

The Korea Institute of Nuclear Safety (KINS) is tasked with the technical supporting for approving the safety of specific components or design modifications in nuclear power plant. When a licensee submits analysis to the Nuclear Safety & Security Commission (NSSC) for acceptance, KINS staff reviews this analysis and sometimes conducts independent audit calculations. Though recently licensing applications supported by using Computational Fluid Dynamics (CFD) software are increasing for nuclear safety problems, there is no CFD software which obtains a licensing from the domestic regulatory body until now. Additionally, there is no domestic regulatory guideline for the comprehensive evaluation of CFD software. Therefore, from the nuclear regulatory perspective, it is necessary to perform the systematic assessment and prepare the domestic regulatory guideline for checking whether valid CFD software is used for nuclear safety problems. In this paper, regulatory audit calculation activities on the applicability of CFD software to nuclear safety problems was briefly explained.

Nuclear power plant operators conduct in-service testing (IST) to verify the safety functions of safety–related pumps and valves and to monitor the degree of vulnerability over time during reactor operation. The system to which the pump and valve to be tested are installed has various sizes of orificesfor flow control and decompression. Rapid flow acceleration and accompanying pressure drop may cause cavitation inside the orifice, which may result in orifice degradation and structural damage. Though licensing applications supported by using Computational Fluid Dynamics (CFD) software are gradually increasing for IST–related problems, there is no CFD software which obtains a licensing from the domestic regulatory body until now. In this paper, to assess the prediction performance of different commercialCFD software for the analysis of cavitating flow inside a square–edged orifice, the simulation was conducted with ANSYS CFX and FLUENT R18.1. The results predicted were then compared with the measured data.

The rotating stall generated by the centrifugal pump impeller reduces efficiency and causes severe flow fluctuations and noise due to surging. In the present work, the six-bladed impeller in the centrifugal pump was simulated by RANS, LES, and Hybrid RANS/LES turbulence models using ANSYS CFX. The turbulence models considered were the Shear Stress Transport (SST), Detached Eddy Simulation (DES), Stress-Blended Eddy Simulation (SBES), Scale Adaptive Simulation (SAS), and Wall-Adapted Local Eddy-viscosity (WALE). The design load condition and the quarter-load condition were applied for the boundary conditions, and the experimental results were compared and analyzed using velocity profile and turbulent kinetic energy at the impeller mid-height. Under the design load condition, all turbulence models predicted results similar to the experimental results. In the off-design load condition, LES predicted the experimental value most accurately, followed by SST-RM of RANS with high accuracy, and the hybrid RANS/LES model showing lower prediction accuracy; SBES predicted excessive recirculation flow. However, if sufficient grid resolution is achieved, hybrid RANS/LES model can simulate the rotating stall under the off-design flow condition than RANS models. Both DES and SAS model show relatively low mesh dependent results with acceptable accuracy. Graphical abstract

Purpose - To investigate the effect of aspect ratio on the quantitative analogy between developing laminar flows in orthogonally rotating straight ducts and stationary curved ductsDesign methodology approach - A fractional step method is used to obtain the numerical solution of the governing equations by decoupling the solution of the momentum equations from the solution of the continuity equation. In order to clarify the similarity of the two flows, dimensionless parameters KLR and Rossby number, Ro, in a rotating straight duct were used as a set corresponding to Dean number, KLC, and curvature ratio, λ, in a stationary curved duct.Findings - Under the condition that the aspect ratio was larger than one and that the magnitude of Ro or λ was large enough to satisfy the \"asymptotic invariance property\" the quantitative analogy between the two flows was established clearly.Research limitations implications - As the aspect ratio decreased below one, the difference between the secondary flow intensities of these two flows increased, and therefore, the analogy between the two flows was not as evident as that for the larger aspect ratios.Practical implications - Based on this methodology, the characteristics of the developing flow in orthogonally rotating ducts of higher aspect ratio can be predicted by considering the flow in stationary curved ducts, and vice versa.Originality value - The results obtained in this study will suggest an optimal criterion for the application of this approach to the flow similarity analysis in rectangular ducts with arbitrary aspect ratios.

In general, the turbulent flow inside PWR (Pressurized Water Reactor) fuel assembly depends on the mixing vane configuration and the pattern of the mixing vane arrangement on the strap of the spacer grid. In this study, in order to examine the turbulent flow structure inside fuel assembly with the split-type mixing vanes, simulations were conducted with the commercial CFD (Computational Fluid Dynamics) software, ANSYS CFX R.14. Two different types of turbulence models, i.e. SAS (Scale-Adaptive Simulation)-SST (Shear Stress Transport) and DES (Detached Eddy Simulation), were used. The predicted results were compared with the measured data from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. Although there were locally differences between the prediction and the measurement, ANSYS CFX R.14 predicted the time averaged velocity field in the reliable level. The predicted horizontal and vertical velocity components were more in agreement with the measured data than the axial velocity component. There was no significant difference in the prediction accuracy of both turbulence models.

A numerical study of a quantitative analogy of fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross-section was carried out. In order to compare the two flows, the dimensionless parameters KTR=Re1 4 √Ro and the Rossby number, Ro=wm Ωdh, in the rotating straight duct flow corresponded to KTC=Re1 4 √λ and the curvature ratio, λ=R dh, in the stationary curved duct flow, so that they had the same dynamical meaning as those parameters for fully developed laminar flow. For the large values of Ro or λ, the flow field satisfied the \"asymptotic invariance property\"; there were strong quantitative similarities between the two flows, such as in the flow patterns and friction factors for the same values of KTR and KTC. Based on these similarities, it is possible to predict the flow characteristics in rotating ducts by considering the flow in stationary curved ducts, and vice versa.

An experimental analysis using three-dimensional laser Doppler velocimetry (LDV) measurement and computational analysis using the Reynolds stress model of the commercial flow solver, FLUENT, have been conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition (⊘ = 0.25) and two off-design conditions (⊘ = 0.21 and 0.30). As the blade loading increased, the onset position of the rolling-up of tip leakage flow moved upstream and the trajectory of tip leakage vortex (TLV) center was more inclined toward the circumferential direction. Because the casing boundary layer became thicker and the mixing between the through-flow and the leakage jet with the different flow direction was enforced, the streamwise vorticity decayed more rapidly with the blade loading increasing. A distinct TLV was observed downstream of the blade trailing edge at ⊘ = 0.30, but it was not found at ⊘ = 0.21 and 0.25. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region in a reliable level. Influence of the relative motion of the casing wall on the structure of tip leakage flow was also investigated. Since it enhanced the strength of TLV by dragging the fluid through the tip clearance region, the magnitudes of the streamwise vorticity for the stationary casing wall were considerably larger than those for the rotating casing wall. Therefore, for the rotating casing wall, the high momentum region related with the blockage effect of TLV was reduced in comparison with that of the stationary casing wall.

In Korea, the web-foot octopus (Amphioctopus sp.) is commonly consumed as jjukkumi bokkeum, a spicy stir-fried octopus dish. Using steaming and smoking methods, we made jjukkumi bokkeum home meal replacement (HMR) products. The response surface methodology (RSM) was employed to optimize the steam and smoke processes. Quick freezing was applied to freeze the test product at −35 °C. Then, the physicochemical, biological, nutritional characteristics, and shelf-life of the test HMR products were evaluated. The optimal conditions for steaming and smoking were 95 °C for 2 min and 70 °C for 11 min, respectively. The pH, volatile basic nitrogen content, and thiobarbituric acid-reactive substances content decreased after steaming and smoking, indicating that these processes maintained these parameters well. Sensory evaluation revealed that there were no changes in these characteristics after freezing and reheating. Further, the test HMR products contained the daily nutritional requirements of macro and micronutrients, as well as amino acids and fatty acids. The shelf-life of the HMR products was estimated to be 15 months. The findings of this study indicate that the application of steam and smoke processes to produce a jjukkumi bokkeum HMR product results in a high-quality product with a long shelf-life.