Spectral Response to Harmonic Excitation of Rods in a Confined Nuclear Fuel Mini-Bundle

2005 ◽  
Author(s):  
Radu O. Pomiˆrleanu
Keyword(s):  
Nuclear Fuel ◽  
Spectral Response ◽  
Variable Mass ◽  
Axial Flow ◽  
Harmonic Excitation ◽  
Viscous Effects ◽  
Rod Bundle ◽  
Fuel Bundle ◽  
Computational Fluid Dynamics Cfd ◽  
Euler Bernoulli Beam

In this paper, the effect of the confinement on the vibration of rods within nuclear fuel bundle is analyzed and discussed. Differential added damping of the rods depending on their position within the bundle adds to the classical development of modal and spectral analysis. This is accomplished by coupling the classical modeling of the variable-mass, Euler-Bernoulli beam on elastic supports with the two-dimensional computational fluid dynamics (CFD) estimation of motion-dependent effects, with the viscous effects integrally modeled. A 5×5 reduced-scale (shortened) rod bundle subject to room-temperature single-phase nominally axial flow within a square confinement is used to illustrate the response to a harmonically varying excitation. The harmonic analysis showed that there are significant differences in the response of the rods, depending on their position within the bundle.

Harmonic Analysis of a Cylinder Cluster in Square Confinement With Position-Dependent Fluid Damping

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Radu Pomirleanu
Keyword(s):  
Nuclear Fuel ◽  
Classical Method ◽  
Structural Characteristics ◽  
Variable Mass ◽  
Axial Flow ◽  
Dense Medium ◽  
Arbitrary Lagrangian Eulerian ◽  
Element Analysis ◽  
Fuel Rods ◽  
Nuclear Fuel Rods

The vibration of cylinder clusters in axial flow is a classical engineering problem, with applications to nuclear fuel rods and steam generator tubes. The classical method of solution to this problem consists in development of modal analysis of the entire cluster including structural characteristics and fluid-elastic effects due to the presence of the dense medium in the space between cylinders, followed by a forced-vibration analysis. It is shown here that the out-of-phase fluid-elastic effects (added damping) are dependent on the position of cylinders within the bundle, not unlike the already proven in-phase effects (added mass). A two-dimensional arbitrary Lagrangian Eulerian (ALE) finite-element analysis is used to compute the hydrodynamic coupling effects in a 5×5 rod cluster subject to single-phase parallel flow. These motion-dependent effects are subsequently embedded into the equations of motion for scaled-down array of nuclear fuel rods, which are structurally modeled as variable-mass Euler–Bernoulli beams on elastic supports. The modal and harmonic analyses developed on the basis of these equations shows that the rod response is affected by the rod position within the cluster, relative to the confinement.

Large-Scale Pulsation Detection by Means of Temperature Measurements

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
N. Silin ◽  
V. Masson ◽  
A. Rauschert
Keyword(s):  
Nuclear Fuel ◽  
Large Scale ◽  
Axial Flow ◽  
Temperature Measurements ◽  
Time Resolved ◽  
Structure Information ◽  
Rod Bundle ◽  
Nuclear Fuel Assembly ◽  
Large Scale Flow ◽  
Fuel Elements

In the present work we explore the potential of time-resolved temperature measurements to obtain information on large-scale pulsations in a rod bundle geometry with axial flow. Large-scale flow pulsation is the phenomenon that dominates the turbulent mixing between the subchannels of rod bundles, which explains why it is of great importance for the design or assessment of nuclear fuel elements. The objective of the present work is to determine the characteristics of large-scale pulsations that can be used for the verification or validation of computational fluid dynamics code results. The method proposed is to generate a temperature gradient across the location of flow pulsations and to measure the time-varying temperature field downstream. Pulsation characteristic times, lengths, and traveling speed have been obtained. This study has been performed in a rod bundle similar to a nuclear fuel assembly and the results obtained are in good agreement with previous works on similar geometries. The technique can be applied to obtain additional large-scale structure information in test sections designed for thermal measurements, in situations where convection is dominated by these structures.

Numerical Simulation of Flow Through Nuclear Fuel Bundles With Angular Misalignments

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
A. Bhattacharya ◽  
S. D. Yu
Keyword(s):  
Nuclear Fuel ◽  
Large Scale ◽  
Computational Models ◽  
Three Dimensional ◽  
Cross Flow ◽  
Eddy Simulation ◽  
Cfd Models ◽  
Fuel Bundle ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through

Comprehensive computational fluid dynamics (CFD) models are developed and analyzed in this paper to study the three-dimensional flow through simulated nuclear fuel bundles with angular misalignments inside a pressure tube. The large eddy simulation (LES) scheme is employed to solve the large scale complex computational models with an aim to understanding the effects of the bundle-to-bundle angular misalignments on unsteady flow and flow-induced excitations on the fuel bundle structures. The proposed numerical scheme is validated with both numerical and experimental work available in the literature. Numerical results obtained from the current computational models indicate the presence of significant lateral or cross-flow in the bundle-to-bundle interface region for bundles with angular misalignments. The mean and the rms values of the lateral fluid excitations on the first bundle are found to be sensitive with respect to the change in angular misalignments between bundles.

Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

2002 ◽  
Author(s):  
Wang Kee In ◽  
Dong Seok Oh ◽  
Tae Hyun Chun
Keyword(s):  
Turbulent Flow ◽  
Nuclear Fuel ◽  
Turbulence Models ◽  
Convective Transport ◽  
Stress Model ◽  
Convergence Criteria ◽  
Mean Flow ◽  
Numerical Predictions ◽  
Viscosity Models ◽  
Fuel Bundle

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

A Proposal for Passive Wall Treatment Applied in High Performance Axial Flow Compressors

2020 ◽  
Author(s):  
Rubén Bruno Díaz ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti ◽  
Francisco Carlos Elizio de Paula ◽  
Luiz Henrique Lindquist Whitacker
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Smooth Wall ◽  
Tip Leakage Flow ◽  
Viscous Effects ◽  
Stall Margin ◽  
Tip Leakage

Abstract Numerical simulations were carried out with the purpose of investigating the effect of applying circumferential grooves at axial compressor casing passive wall treatment to enhance the stall margin and change the tip leakage flow. The tip leakage flow is pointed out as one of the main contributors to stall inception in axial compressors. Hence, it is of major importance to treat appropriately the flow in this region. Circumferential grooves have shown a good performance in enhancing the stall margin in previous researches by changing the flow path in the tip clearance region. In this work, a passive wall treatment with four circumferential grooves was applied in the transonic axial compressor NASA Rotor 37. Its effect on the axial compressor performance and the flow in the tip clearance region was analyzed and set against the results attained for the smooth wall case. A 2.63% increase in the operational range of the axial compressor running at 100%N, was achieved, when compared with the original smooth wall casing configuration. The grooves installed at compressor casing, causes an increase in the flow entropy generation due to the high viscous effects in this gap region, between the rotor tip surface and casing with grooves. These viscous effects cause a drop in the turbomachine efficiency. For the grooves configurations used in this work, an efficiency drop of 0.7% was observed, compared with the original smooth wall. All the simulations were performed based on 3D turbulent flow calculations using Reynolds Averaged Navier-Stokes equations, and the flow eddy viscosity was determined using the two-equation SST turbulence model. The details of the grooves geometrical dimensions and its implementation are described in the paper.

scholarly journals Viscous effects in the absolute–convective instability of the Batchelor vortex

2002 ◽  
Vol 459 ◽  
pp. 371-396 ◽  
Author(s):  
C. OLENDRARU ◽  
A. SELLIER
Keyword(s):  
Reynolds Number ◽  
Convective Instability ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Absolute Instability ◽  
Viscous Effects ◽  
Swirling Jets ◽  
Bending Mode ◽  
Transitional Mode ◽  
The Absolute

The effects of viscosity on the instability properties of the Batchelor vortex are investigated. The characteristics of spatially amplified branches are first documented in the convectively unstable regime for different values of the swirl parameter q and the co-flow parameter a at several Reynolds numbers Re. The absolute–convective instability transition curves, determined by the Briggs–Bers zero-group velocity criterion, are delineated in the (a, q)-parameter plane as a function of Re. The azimuthal wavenumber m of the critical transitional mode is found to depend on the magnitude of the swirl q and on the jet (a > −0.5) or wake (a < −0.5) nature of the axial flow. At large Reynolds numbers, the inviscid results of Olendraru et al. (1999) are recovered. As the Reynolds number decreases, the pocket of absolute instability in the (a, q)-plane is found to shrink gradually. At Re = 667; the critical transitional modes for swirling jets are m = −2 or m = −3 and absolute instability prevails at moderate swirl values even in the absence of counterflow. For higher swirl levels, the bending mode m = −1 becomes critical. The results are in good overall agreement with those obtained by Delbende et al. (1998) at the same Reynolds number. However, a bending (m = +1) viscous mode is found to partake in the outer absolute–convective instability transition for jets at very low positive levels of swirl. This asymmetric branch is the spatial counterpart of the temporal viscous mode isolated by Khorrami (1991) and Mayer & Powell (1992). At Re = 100, the critical transitional mode for swirling jets is m = −2 at moderate and high swirl values and, in order to trigger an absolute instability, a slight counterflow is always required. A bending (m = +1) viscous mode again becomes critical at very low swirl values. For wakes (a < −0.5) the critical transitional mode is always found to be the bending mode m = −1, whatever the Reynolds number. However, above q = 1.5, near-neutral centre modes are found to define a tongue of weak absolute instability in the (a, q)-plane. Such modes had been analytically predicted by Stewartson & Brown (1985) in a strictly temporal inviscid framework.

scholarly journals Numerical and Experimental Estimation of the Efficiency of a Quadcopter Rotor Operating at Hover

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 261 ◽  
Author(s):  
Andres G. ◽  
Juan S. ◽  
Omar López ◽  
Laura Suárez C, ◽  
Jaime A. Escobar
Keyword(s):  
Pressure Coefficient ◽  
Tip Vortex ◽  
Small Scale ◽  
Viscous Effects ◽  
Lattice Method ◽  
Vortex Lattice Method ◽  
Computational Fluid Dynamics Cfd ◽  
Experimental Values ◽  
Thrust And Torque

Globalization has led to an increase in the use of small copters for different activities such as geo-referencing, agricultural fields monitoring, survillance, among others. This is the main reason why there is a strong interest in the performance of small-scale propellers used in unmanned aerial vehicles. The flow developed by rotors is complex and the estimation of its aerodynamic performance is not a trivial process. In addition, viscous effects, when the rotor operates at low Reynolds, affect its performance. In the present paper, two different computational methods, Computational Fluid Dynamics (CFD) and the Unsteady Vortex Lattice Method (UVLM) with a viscous correction, were used to study the performance of an isolated rotor of a quadcopter flying at hover. The Multi Reference Frame model and transition S S T κ - ω turbulence model were used in the CFD simulations. The tip vortex core growth was used to account for the viscous effects in the UVLM. The wake structure, pressure coefficient, thrust and torque predictions from both methods are compared. Thrust and torque results from simulations were validated by means of experimental results of a characterization of a single rotor. Finally, figure of merit of the rotor is evaluated showing that UVLM overestimates the efficiency of the rotor; meanwhile, CFD predictions are close to experimental values.

Investigation of the Flow Field in a Rectangular Vessel Equipped With a Side-Entering Agitator

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
C. Gómez ◽  
C. P. J. Bennington ◽  
F. Taghipour
Keyword(s):  
Axial Flow ◽  
Limited Attention ◽  
Pulp Fiber ◽  
Fiber Suspensions ◽  
Process Industries ◽  
Piv Measurements ◽  
Stirred Vessels ◽  
Paper Manufacturing ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd

The hydrodynamics of stirred vessels with side-entering impellers, which are used in numerous process industries including petroleum, foods, and pulp and paper manufacturing, have received limited attention. In the present work, the flow in a reduced size rectangular tank equipped with a side-entering axial flow impeller, scaled down from the industrial agitation of low consistency pulp fiber suspensions, was investigated using particle image velocimetry (PIV) and computational fluid dynamics (CFD), in the laminar regime (18≤Re≤120). Tuning of the PIV measuring parameters for an optimum capture of valid velocity vectors within a representative portion of the vessel is described. A detailed description of the construction and refinement of the grid and quantification of the discretization error in the CFD results is also presented. The simulation predictions were extensively evaluated by comparing the measured planar flow patterns and velocity fields at various locations in the mixing vessel. Very good agreement was found between PIV measurements and computed velocities confirming the efficiency of CFD in the analysis of mixing systems. The prediction of global mixing parameters was also evaluated. The computed impeller torque and impeller power number agreed very well with experimental measurements over the range of Re studied.

Pressure Drop and Flow Pulsation in Tight-Lattice Rod Bundle

2012 ◽  
Author(s):  
Chi Young Lee ◽  
Chang Hwan Shin ◽  
Ju Yong Park ◽  
Dong Seok Oh ◽  
Tae Hyun Chun ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Fuel Assembly ◽  
Nuclear Reactor ◽  
Power Reactor ◽  
Reactor Power ◽  
Flow Pulsation ◽  
Rod Bundle ◽  
Fuel Bundle ◽  
Cylindrical Solid ◽  
Tight Lattice

In order to ensure the compactness and high-power density of a nuclear power reactor, the research on tight-lattice fuel bundle, with a narrow gap distance between fuels, has been highlighted. Recently, KAERI (Korea Atomic Energy Research Institute) has been developing dual-cooled annular fuel to increase a significant amount of the reactor power in OPR1000 (Optimized Power Reactor), a PWR (Pressurized Water Reactor) optimized in the Republic of Korea. The dual-cooled annular fuel is configured to allow a coolant flow through the inner channel as well as the outer channel. To introduce the dual-cooled annular fuel to OPR1000 is aiming at increasing the reactor power by 20% and reducing the fuel-pellet temperature by 30%, as compared to the cylindrical solid fuel, without a change in reactor components. In such a case, due to larger outer diameter of a dual-cooled annular fuel, the dual-cooled annular fuel assembly exhibits a smaller P/D (Pitch-to-Diameter ratio) than the conventional cylindrical solid fuel assembly. In other words, the dual-cooled annular fuel array becomes the tight-lattice fuel bundle configuration, and such a change in P/D can significantly affect the thermal-hydraulic characteristics in nuclear reactor core. In this paper, the pressure drop and flow pulsation in tight-lattice rod bundle were investigated. As the test sections, the tight-lattice rod bundle of P/D = 1.08 was prepared with the regular rod bundle of P/D = 1.35. The friction factors in P/D = 1.08 appeared smaller than those in P/D = 1.35. For P/D = 1.08, the twist-vane spacer grid became the larger pressure loss coefficients than the plain spacer grid. In P/D = 1.08, the flow pulsation, quasi-periodic oscillating flow motion, was visualized successfully by PIV (Particle Image Velocimetry) and MIR (Matching Index of Refraction) techniques. The peak frequency and power spectral density of flow pulsation increased with increasing the Reynolds number. Our belief is that this work can contribute to a design of nuclear reactor with tight-lattice fuel bundle for compactness and power-uprate and a further understanding of the coolant mixing phenomena in a nuclear fuel assembly.

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