Acoustic Pressure Pulsations Research Articles

A numerical model to investigate the irradiation effect on the dynamics of nuclear fuel bundles

The severe operation conditions in nuclear reactors, such as highly turbulent coolant flow, high temperatures and excessive irradiation doses, can compromise the structural integrity of nuclear fuel bundles. Specifically, the irradiation doses influence the microstructure of the material in terms of segregation and precipitation in addition to swelling. This leads to changes in the mechanical properties of the material and consequently, the dynamic characteristics will be altered. The current study presents a fully-coupled, three-dimensional, numerical, structural model that takes into account the irradiation effects on fuel bundle material. A constitutive model that describes the thermal and irradiation effects on the mechanical properties is utilized. This constitutive model is integrated in an in-house finite element code that is capable of predicting the dynamics of fuel bundles including the nonlinear material, contact dynamics, and various fluid and acoustic excitation forces. This model is utilized to predict the response of a CANDU fuel bundle under turbulence excitation, motion-dependent forces, and acoustic pressure pulsations generated by the heat transport pumps. The fuel-to-fuel and fuel-to-pressure tube contact dynamics are also included using the single point contact method (SPC). The dynamic response of the fuel bundle along with the associated impact forces and work rates are predicted over a range of flow velocities that are typical to those in an actual CANDU power plant. The results indicate that the location of the fuel channel inside the calandria tube may exacerbate the mechanical stresses on the fuel bundle endplates, which could compromise their structural integrity.

A Combined Delayed Detached Eddy Simulation and Linearized Navier–Stokes Equation Study on the Generation and Reduction of Aerodynamic Noises Inside Steam Turbine Control Valve With Acoustic Liner

Abstract This study was aimed at numerically investigating the source, generation mechanism, and strategy for reducing aerodynamic noises inside a steam turbine control valve. A delayed detached eddy simulation was performed to extract the three-dimensional unsteady turbulent flow structures formed within the serpentine flow passage of the turbine valve. Acoustic analogies, spatial Fourier transform, and spectral proper orthogonal decomposition on the delayed detached eddy simulation-simulated flow data were complementarily combined to clarify the generation mechanism of tonal and broadband aerodynamic noises. The results showed that broadband noises were produced by wall-attached jet flow and turbulent mixing flow between the annular wall jets and central reverse flow. High-intensity tonal noises were generated by the excitation of multi-order natural acoustic modes of the bell-shaped valve spindle. The intensive acoustic pressure pulsations concentrated inside the bell jar and propagated along the diffuser to the downstream turbine chamber. A novel ring acoustic liner was designed using the acoustic impedance model to reduce the valve noises without sacrificing the flow performance. The noise reduction effectiveness was evaluated by solving the linearized Navier–Stokes equations in the frequency domain.

Оценка частот акустических колебаний в выходном диффузоре газотурбинной установки

Calculated estimation of acoustic resonances in the flow part of gas turbines in the outlet diffusers is a current problem. Its solution will improve vibration reliability of essential elements of gas turbine plant (GTP) – the rear bearing housing support and the blade apparatus. At present there are only a limited number of calculated and experimental works devoted to the study of acoustic resonance effect in the output devices of gas turbines. The objective of this paper is to estimate frequencies of acoustic oscillations in the GTP output diffuser. It allows to avoid coincidence of the indicated frequencies with the frequencies of natural oscillations of GTP structural elements. The results of the analysis of frequencies of acoustic oscillations should be confirmed in further experimental studies of the specified output device, i.e., the output diffuser. The method to solve the problem is computational. The results of numerical calculations of acoustic resonances in the GTP outlet diffuser are used for the analysis. The calculations have been performed in the Modal Acoustics ANSYS Workbench program. The model is described and the computational program to calculate the acoustic modes in the output diffuser is specified. The boundary conditions to perform the specified numerical acoustic calculations are proposed. The modes and corresponding frequencies of acoustic oscillations that are possible in the GTP outlet diffuser are considered. Justification of validity of the results of numerical calculations is their partial comparison with analytical solution for the simplest acoustic model, as well as with the preliminary result of the experimental research. The results of the acoustic calculations of the model of the GTP outlet diffuser allow to determine the modes of acoustic oscillations, and to estimate the frequency range of these modes. To substantiate the calculated estimates of frequencies of acoustic pressure pulsations, as well as to clarify the amplitudes of these pulsations, experimental aerodynamic studies of the model of the outlet diffuser with a rotating turbine stage at the inlet are necessary. Refined calculation model of acoustic resonances in the GTP outlet diffuser will contribute to the offset of frequencies of acoustic gas vibrations from the natural frequencies of vibrations of the GTP structural elements, adjacent to the diffuser. The indicated frequency offset will improve the GTP vibration reliability at the design stage.

Data assimilation of flow-acoustic resonance.

A data assimilation (DA) strategy was developed for accurate prediction of the flow-acoustic resonant fields within a channel-branch system. The challenges of numerical simulation of such internal aeroacoustic systems are primarily associated with determination of the transfer loss between the acoustic waves and the shear layer vortices. Thus, a data-assimilated momentum loss model that comprises a viscous loss item and an inertial loss item was established and embedded into the Navier-Stokes equations. During the DA, the acoustic pressure pulsations measured from a dynamic pressure array served as the observational data, the ensemble Kalman filter served as the optimization algorithm, and a three-dimensional transient computational fluid dynamics method comprising an explicit algebraic Reynolds stress model (EARSM) served as the predictive model system. EARSM was used because its ability to predict internal flow-acoustic resonances was superior to that of other eddy viscosity models and Reynolds stress models. The data-assimilated flow-acoustic resonant fields were then comprehensively validated in terms of their acoustic fields, time-averaged flow fields, and phase-dependent flow fields. The time-averaged flow fields were obtained from planar particle-image velocimetry (PIV) measurements, and the phase-dependent flow fields were obtained from field programmable gate array-based phase-locking PIV measurements. The results demonstrate that the use of DA afforded an optimal simulation that efficiently decreased the numerical errors in the frequencies and amplitudes of the acoustic pressure pulsations, thereby achieving better agreement between time-averaged flow distributions and fluctuations. In addition, the data-assimilated numerical simulation completely reproduced the spatiotemporal evolution of the shear layer vortices, that is, their formation, developing, transport, and collapsing regions.

Phase-locking particle image velocimetry measurements of acoustic-driven flow interactions between tandem deep cavities

Acoustic-driven flow interactions between tandem deep cavities, which manifest as resonances between the natural acoustic standing-wave mode and the intrinsic shear-layer vortex structures, were experimentally investigated by using a pressure transducer array, the planar particle image velocimetry (PIV) technique, and phase-locking PIV measurements. Specifically, in the phase-locking PIV measurements, a field-programmable gate array-based phase-determination strategy was used to improve the phase-locking accuracy. The pressure measurement results demonstrated that under certain Reynolds numbers, significantly intensified acoustic pressure pulsations were excited once the magnitude of the acoustic resonance occurring inside the tandem deep cavities reached almost three times the magnitude of the dynamic pressure head at the channel inlet. Beyond that, the planar-PIV results illustrated the elevated turbulent flow quantities, such as the expanded velocity gradients, amplified shear-layer momentum thickness, intensified velocity fluctuations, and statistical Reynolds shear stresses. Subsequently, a proper orthogonal decomposition (POD) analysis was conducted to successfully extract the dominant flow modes underlying the acoustic-driven flow interactions, namely, the cavity-to-cavity flow mode and the counterrotating shedding vortex mode. The first POD mode gave rise to essential flow streaks that shuttled synchronously between the tandem deep cavities, while the second POD mode contributed to the streamwise vortex-shedding motions. Finally, the phase-locking PIV results comprehensively revealed the spatiotemporal evolutions of the coherent flow structures (the upper shedding vortices and the recirculation zones beneath) and their centroid trajectories. The findings of this study could be useful for revealing the flow–acoustic coupling mechanisms in related industrial facilities.

Spinning behavior of flow-acoustic resonant fields inside a cavity: Vortex-shedding modes and diametral acoustic modes

The spinning behavior of flow-acoustic resonant fields inside an axisymmetric cavity configuration was numerically investigated in four flow conditions containing different resonances between vortex-shedding modes and diametral acoustic modes. Zonal large-eddy simulations (ZLESs) were conducted to determine the aeroacoustic and aerodynamic fields simultaneously. In the ZLESs, a shear stress transport turbulence model was used to model the relatively steady flow field inside the inlet and outlet sections. Simultaneously, the wall-modeled LES formulation was used in the cavity section to resolve the highly complex flow-acoustic resonant fields. The ZLES results were well validated by the experimental results in the literature in terms of the frequency, amplitude, and spatial features of the acoustic pressure pulsations. Subsequently, the spinning behavior and mechanism of the excited diametral acoustic modes and the resonant vortex-shedding modes were comprehensively illustrated. The results showed that the excited diametral acoustic mode span anticlockwise along the cavity circumference, resulting in intense acoustic-pressure fluctuations several times greater than at the inlet dynamic-pressure head, together with longitudinal pressure propagations. Using proper orthogonal decomposition analysis, the spinning mechanism was found to be closely related to the interaction between the α-mode and the β-mode, which had fixed temporal and spatial phase lags. Thereafter, the first vortex-shedding mode gave rise to a strong spinning motion of the resonant flow field, while the second vortex-shedding mode created a slight spinning motion. The corresponding phase-dependent flow fields at consecutive planes along the cavity circumference revealed the spatiotemporal evolution of the velocity variations, surface streamlines, and vorticity variations of the shedding vortices. Large-scale helical vortex tubes were formed within the cavity volume due to the strong spinning behavior.

Influence of diametral acoustic mode on cavity flow dynamics: Zonal large eddy simulation and proper orthogonal decomposition

The influence of a diametral acoustic mode on the flow dynamics was numerically investigated for an axisymmetric cavity system with vortex-excited acoustic resonances occurring at high Reynolds numbers and low Mach numbers. The zonal large eddy simulation (ZLES) was conducted to simulate the flow-acoustic coupling fields by the first three diametral acoustic modes at their maximum resonance intensities, respectively. First, the ZLES-simulated acoustic pressure pulsations were well validated by a preliminary acoustic modal analysis and acoustic pressure measurements in the literature. Subsequently, the acoustic-driven cavity flow dynamics were comprehensively demonstrated in terms of the time-averaged flow quantities, shear layer quantities, and high-order turbulence quantities. The results demonstrated that the shear layer momentum thickness, velocity fluctuations, and Reynolds shear stresses were remarkably intensified by the strong resonances with the first and second diametral acoustic modes. Simultaneously, large-scale helical vortex tubes were formed within the cavity, yielding an intensified flow three-dimensionality. Thereafter, the dominant flow modes behind the acoustic-driven cavity flow dynamics were extracted using the data-driven proper orthogonal decomposition from the highly noisy ZLES database. It was found that the first diametral acoustic mode significantly enhanced the dominant positions of the vertical flow-oscillation mode, yielding a large-scale flapping behavior of the mainstream flow, while the second diametral acoustic mode would modulate the cavities to synchronously absorb/release the flow streaks, resulting in the alternating expansion and compression behaviors of the mainstream flow.

Acoustics-driven vortex dynamics in channel branches with round intersections: Flow mode transition and three-dimensionality

A combined experimental and large eddy simulation study was conducted to investigate acoustics-driven vortex dynamics inside channel branches with round intersections. The underlying flow mode transition and intensified flow three-dimensionality, which are closely related to the Coanda effect at round intersections, were comprehensively demonstrated. A dynamic pressure transducer array was first used to establish the relationship of the excited acoustic pressure pulsations to the channel-branch intersection radius (r) and the mainstream Reynolds number. In complementary simulations, three configurations with r/D = 0, 0.2, and 0.4 (where D is the short edge of the side-branch) were selected for demonstration. First, the simulated results were well validated in terms of acoustic pressure pulsations and phase-dependent flow fields. Subsequent analysis of the time-averaged and statistical flow characteristics revealed the existence of significantly intensified flow fluctuations inside the round channel branches having r/D = 0.2 and 0.4. Next, the proper orthogonal decomposition analysis was conducted to extract the dominant flow modes and to identify the energy transition from the streamwise vortex-shedding mode to vertical flow-oscillation mode. To this end, the influence of flow-mode transition on the phase-dependent flow fields was further investigated. The intensified branch-flow streaks resulted in a channel flow transition from synchronous convection of co-rotating vortex pairs into alternating convection of a single large-scale vortex, yielding a stronger flapping motion of the mainstream flow. Finally, the intensified flow three-dimensionality, presented by the essential spanwise Reynolds shear stresses inside the round channel branches, was found to relate to the strong turbulent mixing process caused by the flapping mainstream flow and the vertical branch flow oscillation. These findings are of great significance for industrial pipeline design and optimization.

A passive damping device for suppressing acoustic pressure pulsations: The infinity tube.

Acoustic pressure pulsations in piping systems can cause detrimental damage and failure of industrial components. Both the acoustic resonance and the traveling wave phenomena are of concern for industrial piping systems and there is a need to study passive damping devices and their implementation into these systems. However, there is a challenge associated with manufacturing and installation of such devices as they may be cumbersome. Therefore, the infinity tube (IT) damping device has been presented here to provide a simplified device geometry which can be easily manufactured and implemented into piping systems. A theoretical equation for the transmission loss spectra of the IT device and the frequencies of resonance have been derived as a tool for designers. Additionally, the experimental investigation has shown a considerable increase in acoustic attenuation in comparison to the conventional Herschel-Quincke device due to the significantly shorter length which the IT device can be constructed from. Acoustic pressure and phase angle measurements have elucidated that the fundamental acoustic mode of an open-open pipe can be formed within the IT device. Moreover, a parametric study is presented which has clarified practical considerations required for implementation of the IT device into piping systems for suppressing pressure pulsation.

Experimental Study on Damping Acoustic Pressure Pulsations in Pipeline Systems Using Helmholtz Resonators

Abstract Acoustic pressure pulsations can be problematic in industrial pipelines, especially when the excitation frequency matches an acoustic resonance frequency of the pipeline. The objective of this paper is to investigate the effectiveness of Helmholtz resonators (HRs) in multiple arrangements on the attenuation of acoustic pressure pulsations in piping systems. In a resonant pipeline (i.e., an acoustic standing wave scenario), maximal attenuation is achieved when the HR is inserted at the acoustic pressure antinode. The insertion loss (IL) in an off-resonant system is found to be relatively consistent, unless there is a coupling between the HR and the downstream end termination in which case there is a decrease in attenuation. Multiple, small-volume HRs in various configurations can achieve the same level of damping as that of a single HR with the same total volume. Moreover, it is shown that the use of multiple HRs placed at strategic spacing intervals along the length of a pipeline can yield significant acoustic damping, without the need for characterizing the acoustic waves in the pipeline system. An axial spacing of a quarter wavelength of the frequency of interest between multiple HRs is shown to increase the peak attenuation, which is indicative of a favorable coupling between HRs. The effect of flow velocity and its directionality with respect to the sound source is also investigated. The results presented in this paper provide practical techniques that can be used for the implementation of HR in pipeline systems.

A comprehensive dynamic model for analysing the vibrational behaviour of a CANDU fuel string

Inside a pressure tube, under a large drag load induced by the coolant flow, CANDU fuel bundles form a coherent structure called fuel string. The presence of a large number of unilateral frictional contact (UFC) constraints makes the dynamic behaviour of the fuel string very complex and highly nonlinear. In this paper, a comprehensive dynamic model for handling a large number of UFC constraints is presented. The complex fuel string problem is formulated to be a Linear Complementarity Problem (LCP). Use of the LCP eliminates the need for iteration and satisfies all the UFC constraints in the whole fuel string simultaneously. The computational power available these days allowed us to handle all the constraints among fuel rods, between rods and pressure tube and between neighbouring bundles. Finite element method was employed in order to discretize the fuel rods and endplates. The systems of equations of motion were then discretized in the time domain using Bozzak-Newmark integration scheme. This numerical model can be used to find the dynamic response of a fuel string to any given excitation including unsteady fluid forces or acoustic pressure pulsations. In this study, the response of a 12-bundle fuel string to gravity and harmonic excitations was found; all frictional contact forces everywhere along the string are obtained and can be used to predict fretting and material loss. The numerical model presented in this study can be used to improve new fuel designs, mitigate and decrease damage, develop new safety standards and handle other engineering problems where large numbers of UFC's is a challenge, like other types of nuclear fuel rods and heat exchanger tubes.

О возможности реализации режима слабой кавитации при ультразвуковой очистке РЭА

The procedure is described and results of the experimental investigation of unsteady cavitation phenomena at ultrasonic cleaning cavitation unstable products are presented. It is established that at certain correlations of parameters of a transmitter and liquid the short-term pulses of acoustic pressure in liquid and connected with them relaxation oscillations of feed electric current are possible. Short-term power pulses of acoustic pressure determine a possibility of damages in parts under cleaning. Maximum values of acoustic pressure are higher greatly than its averages. Acoustic pressure pulsations take place in a certain range of mean amplitudes of an amplitude speed common for any liquid. A possibility is shown for the realization of a weak cavitation mode at ultrasonic cleaning cavitation unstable products.

Research on the noise induced by cavitation under the asymmetric cavitation condition in a centrifugal pump

An experimental investigation has been carried out to research the noise induced by cavitation under the asymmetric cavitation (AC) condition in a centrifugal pump. The acoustic pressure signals at the pump inlet and outlet were measured respectively during the development of cavitation in a closed hydraulic test rig. It could be found that both the pump inlet and outlet acoustic pressures changed obviously with the development of cavitation. The time domain and the power spectrum density of the pump inlet and outlet acoustic pressure pulsations were analyzed. The broadband pulses of the acoustic pressure pulsations were found and the reasons for the phenomenon were given.

Modelling of fuel bundle vibration and the associated fretting wear in a CANDU fuel channel

In this paper a numerical model is developed to predict the vibration response of a CANDU11CANDU® is a registered trade-mark of Atomic Energy of Canada Limited (AECL). fuel bundle and the associated fretting wear in the surrounding pressure tube. Two excitation mechanisms are considered in this model: turbulence-induced excitation caused by coolant flow inside the fuel channel, and seismic excitation. For the seismic excitation, simulated accelerograms of a magnitude 6 earthquake for the eastern part of Canada are considered. These accelerograms are compatible with the 2005 national building code of Canada uniform hazard spectrum (UHS). The numerical model can be easily adapted to include the effects of fuel bundle impact during the refuelling and start-up of the reactor, and the acoustic pressure pulsations caused by the primary heat transport (PHT) pumps. The simulation is performed for a typical CANDU fuel bundle with 37 fuel elements using INDAP, which is an in-house general purpose finite element program capable of simulating the nonlinear dynamics of nuclear and power equipment subjected to fluid excitation. The clearances between the buttons of the inner fuel elements, and between the bearing pads of the outer fuel elements and the pressure tube, were measured from a typical CANDU fuel bundle. Some variability among the measured clearance values was observed. Therefore, probability density functions of the measured clearance values were established and the simulation was performed for the probabilistic distribution of the clearance values. The contact between the fuel bundle and the pressure tube is modelled using pseudo-force contact method. The results, along with the proposed modelling technique, can be used in future CANDU reactors to avoid fuel and pressure tube fretting damage due to the aforementioned excitation mechanisms.