This paper describes the work performed to study the shell mode vibration of a large cross-section flue gas duct. The work involved the collection of field vibration data, as well as predictive computational models associated with finite element analysis (FEA) and computational fluid dynamics (CFD). The goal of this work was to use predictive models to ascertain whether a proposed design change would reduce the vibration levels of the duct under similar operating conditions. The vibration observed in the duct was identified as a flow induced vibration (FIV) which excited the shell modes of the duct walls. This case study serves as an example of using predictive computational models (FEA and CFD), calibrated with vibration response data from field measurements, to represent the real world situation as closely as possible within specified budget and schedule constraints. Such calibrated models can be useful for forecasting the effectiveness of various proposed design changes.

Ancillary exhaust system structural design for turbines typically employs a separation of responsibilities between the design and installation functions. The design expectations must be implemented correctly during the installation phase to allow long-term serviceability and success of the turbine exhaust system. This paper will explore a case study reviewing bolt tightening of duct structural angle and plate flange joints using compressible high temperature fiberglass gasket material, as well as design suggestions for metal-on-metal duct sliding support joints to structural steel. Improper design and operation can lead to failure, downtime, warranty cost and reduced design life of the exhaust system. It is not uncommon for field installation personnel to modify key system design requirements during the installation phase; typically out of habit, perceived best practice, missed installation instructions and/or misunderstanding the system behavior. In addition, maintenance recommendations are often overlooked. Literature provides extensive background for bolting of stationary metal-to-metal plate joints, rigid gaskets and pressure vessel joints. There is a gap with respect to structural angle and plate flange joint bolt tensioning using compressible fiberglass gaskets at low pressures and high temperatures. Much of the industry standard tightening philosophy is useful, but has not been extensively studied and written about with respect to flanges under high exhaust temperatures or for sliding joints exposed to thermal expansion. This paper summarizes current industry practice, presents relevant test data and a case study, analyzes the effects of high thermal stresses, and recommends a tightening procedure for typical field applications of flange joints using high temperature gaskets, and the design of metal-to-metal sliding support joints.

The present study focuses on the analysis of the flow-induced vibration phenomenon typically encountered on piping systems containing an elbow. The correlation between the turbulent flow through the elbow and the dynamic forcing it yields on the piping walls was assessed experimentally. A closed water loop containing a transparent elbow was designed in order to develop fully turbulent duct flow condition. Particle Image Velocimetry (PIV) was applied in the transparent zone in order to provide unsteady data on the flow dynamics through the elbow; simultaneously, wall pressure fluctuations were measured on and around the elbow. Several flow configurations were tested in order to obtain a large coupled database linking the flow features to the resulting dynamic excitation on the walls. Finally, Partial Least Square Regression (PLSR) was applied in order to harvest the correlated information contained in multiple pressure signals at multiple time-delays and build a relationship capable of estimating the temporal evolution of the velocity field using a set of measured wall pressure signals.

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE is composed of Gasifier and Syngas cooler which are connected by Transfer duct. The support skirt of the Gasifier base is fixed, while the Syngas cooler side is supported by a constant hanger (floating support). In this paper, a FE model of the largest 2000-ton SKGE system in China is established by using ANSYS. The global dynamic response under the seismic load is simulated. In order to verify the correction of the calculation, the results are also compared with that by using ABAQUS. Compared to the traditional static analysis, it can be found that the deformation and stress distribution, the force and moment on several specified cross sections of SKGE change over time under seismic load based on the transient dynamic analysis. As the result of the seismic analysis is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), the seismic analysis is one of the most important analyses in the Gasification design, which will ensure the essential safety of SKGE system.

Spent nuclear fuel generated at nuclear power plants must be safely stored during interim storage periods. A concrete storage cask developed for this purpose should be able to adequately emit the decay heat from the spent nuclear fuel. Moreover, the concrete storage cask must ensure that the temperatures of the spent nuclear fuel assemblies are maintained within the allowable values under normal and offnormal conditions and during an accident. However, the thermal conductivity of concrete is low and the allowable temperature of concrete is lower than that of steel. Therefore, the concrete storage cask must be designed to have heat removal capabilities with appropriate reliability. Accordingly, a passive heat removal system was designed to maintain the temperatures of the fuel assembly cladding material and concrete storage cask components within the allowable limits. The passive heat removal system consists of four air inlets and four air outlets with openings that are covered by mesh screens to prevent debris or wildlife from entering the ventilation ducts. The effect of each screen on the heat removal of the concrete storage cask depends on its mesh size. Therefore, thermal tests were performed to evaluate the heat removal performance in accordance with the mesh size of the screen. The screen mesh size was estimated to have an insignificant effect on the temperature rise of the canister surface and the over-pack surface, but it had a considerable effect on the temperature rise of the components of the over-pack body. As the screen mesh size decreased, the heat removal by the natural convection cooling through the passive heat-removal system was reduced, and the temperature of the concrete storage cask rose.

Hyper compressors are designed for LDPE production, compressing ethylene up to 3500bar with only two stages of compression, in order to reach conditions for the polymerization. The high operating and fluctuating pressure strongly impact design and life of all cylinder components. The packing cups are among the most stressed components of a hyper compressor cylinder. They are particularly subjected to very high pulsating pressures, thus fatigue and wear. Therefore, they are periodically replaced during maintenance and are critical for availability of the hyper compressor. A typical hyper compressor packing assembly contains 5 to 6 disc shaped packing cups that contain the plunger sealing rings at the internal diameter. The packing cups are provided with lube oil ducts to lubricate the sealing elements. Typically these ducts extend axially through the assembly to the injection points. For that purpose each packing cup could have a different number of lube oil passages. Moreover, at the external diameter are located passages for packing cooling oil. For these reasons each of the packing cups is a unique part with different machining features. In order to optimize the availability of spare parts and standardize the product, a new design of hyper compressor packing cups has been evaluated, called further “all-purpose packing cup”. The idea was to make the packing cups all equal to each other, and potentially to reduce manufacturing and warehousing costs. This idea has been realized by introducing in a single all-purpose cup, multiple sectors angularly offset with each other. Each sector contains the oil ducts required for a given cup position in the assembly. By rotating the cup about the plunger axis by e.g. 90° or 180° the desired sector can be activated (put in fluid communication with adjacent lube oil ducts). In this way the “all-purpose packing cup” can be mounted in each of the 5 to 6 different positions in the packing assembly. The all-purpose cup design has been analyzed by a well validated FEA approach on the high cycle fatigue and flaw propagation safety margins. The analysis was performed considering all multiple possible load combinations where, depending on the assembly configuration, different active lube oil holes (holes that deliver oil to the plunger) were pressurized while all remaining ducts were left unpressurized.

Unreinforced branch connections manufactured using elbow ducts can be occasionally encountered during the Fitness-For-Service evaluation of very old, low-service, carbon-steel pipelines. For these peculiar components, no Stress Intensification Factors (SIFs) are usually available in the international codes and standards used by practicioners for stress analysis purposes. In a previous work from the author [1], the SIFs for various elbow branch connections were determined via FEA and a formula was derived through a parametric analysis in order to calculate the SIF for the elbow tees using the codified SIF of the equivalent standard joints. The investigation was restricted to concentric elbow branches, i.e., tees where the elbow duct had the same principal axis of the run pipe. In this paper the case of non-concentric elbow branches was taken into account, considering the offset between elbow and run pipes and the rotation of the curved duct in the two main meridional planes, thus bringing into focus lateral and non-planar elbow tees. The SIFs were calculated using FEA for different configurations of reducing elbow branches with diameters ranging from 2” to 10” and thicknesses from Piping Schedule 10, 40 and 80. Lateral and non-planar joints were analyzed for one reference geometry and at various offsets and rotation angles. A parametric analysis was then carried out to evaluate the offset effect on the stress intensification both on run and branch side, for in-plane and out-of-plane bending. The results showed a significant impact only on the branch side where an increase in piping offset resulted in a reduction of the dominant out-of-plane bending SIF. The original formula devised for the concentric elbow branch connections was hence modified to include this offset effect. Finally, the combined role of offset and rotation angle was parametrically analyzed for the special geometry investigated. The results demonstrated a significative increment of the SIFs for non-planar tees, both on run and branch pipes, whilst in lateral joints the major SIF increased to a maximum only on the branch side.

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly & Ziada [1–3] investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross-section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.

Vortices occur when gas flow passes through a duct with a tube bank of heat exchangers, such as a gas heater and/or a boiler. Very high level noise called a “self-sustained tone” occurs due to the interference of the vortices and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions are vague. Then, perforated plates are used in both sides of the duct walls to suppress the self-sustained tones. Because we thought that the perforated plate might have acoustic damping and resonance mode of the duct perpendicular direction to the flow may be suppressed by its damping effect, when the self-sustained tone occurred. Some experiments were carried out to examine the suppression effect of the perforated plates installed. As a result, the suppression effect appeared in all cases. The purpose of this study is to clarify the effectiveness of the perforated plates for self-sustained tones.

When a rigid wall is replaced by a cavity covered by a flexible plate, the plate can cause broadband sound reflection in a duct. In this paper, analytical formulations in previous studies are extended to the plate with clamped-free boundary conditions. A set of static beam functions, which are a combination of sine series and third-order polynomial, is employed as the trial functions of the plate vibration velocity. Optimization is carried out in order to obtain the widest sound reflection bandwidth. Further studies with regard to the plate under several different classical boundary conditions based on the validated model show that, a clamped-free plate in the duct has the narrowest sound reflection bandwidth. In order to understand the precise mechanism of the spectra change, the behavior of each clamped-free plate mode is also analyzed. It is found that the weak first modal response in a clamped-free plate leads to its performance degradation.

The flow-excited acoustic resonance of single straight finned cylinder in cross-flow is investigated experimentally in this work. This phenomenon has been investigated in some detail for the case of bare cylinders; however, the effect of adding fins to the cylinders on the flow-sound interaction mechanism is not yet fully understood. During the experiments, the acoustic cross-modes of the duct housing the cylinder are self-excited due to the vortex shedding that emerges from the cylinder’s surface. In order to determine the effect of different fin parameters on the onset and intensity of acoustic resonance, fourteen different finned cylinders with fin thickness ranging from 0.35 to 1.5 mm and fin density ranging from 4 to 13.7 fin/inch are investigated for a Reynolds number ranging from 3.2×10 4 to 2.6×10 5 . The onset and intensity of the acoustic resonance generated from each finned cylinder are compared to those generated from an equivalent bare cylinder with the same effective diameter. It is observed that the finned cylinders experience an earlier acoustic resonance and higher levels of acoustic pressure compared to their equivalent bare cylinders. This suggests that adding fins to the cylinder enhances the flow coherence along the cylinder’s span and thus makes the flow more susceptible to acoustic excitation. Moreover, it is observed that for constant fin spacing the acoustic pressure amplitude increases and the acoustic resonance occurs at earlier velocities as the fin thickness increases. On the other hand, for constant fin thickness, as the fin spacing increases the amplitude of the acoustic pressure decreases, while the onset of the resonance is delayed. Finally, the effect of the cylinder’s aspect ratio is investigated in three different test sections. It is observed that the amplitude of the excited acoustic resonance depends on the cylinder’s aspect ratio. The acoustic resonance amplitude is weaker for finned cylinders with aspect ratio less than 5 compared to their equivalent bare cylinders. However, finned cylinders with aspect ratio higher than 6 produces stronger acoustic resonance compared to their equivalent bare cylinders.

High performance control valves may be subjected to noise problems especially when gas is the operating fluid. Depending on some geometric characteristics, the noise production can be characterized by broad band noise or tonal noise. When the latter condition occurs, the generated noise could overcome the limit of acceptance and the device does not respect the standard of usability. In a previous work, a dependency between the tonal noise and the main geometrical characteristics of a control rotary valve has been settled by experimental tests. Starting from these fluid dynamic observations in this work we coupled the modal analysis of the structure with experimental data to deeply understand this phenomenon. The natural frequencies of different perforated plates placed in a circular duct (configuration which mimics the full open control valve condition) are therefore considered to verify which of them are responsible of the tonal noise, generated by the interaction between the flow field and the acoustic one, observed in the experimental tests. To do this, the frequency modes consistent with the tonal noise generation, are numerically investigated by changing the geometrical characteristic of the device. By considering the rotary valve fully open, we especially investigated the effects of the plate thickness, the hole diameter and distribution.

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE comprise the Gasifier and Syngas cooler connected by Transfer duct. The support skirt of the Gasifier base was fixed, while the Syngas cooler side was supported by a constant hanger (floating support). Therefore the design by rule is not applicable to the strength calculation of pressure vessels of the system. In this paper, a FE model of global analysis of the largest SKGE system in China to date was established which considered thirteen loads and twenty-four load combinations. In this model, FEA software ANSYS was used to calculate the global dynamic effect of this 2000-ton system. The whole structural deformation and stress distribution, force and moment on several specified cross sections of SKGE under different load combinations are also determined within this model, which is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), and essential safety of SKGE system.

Vortices occur when gas flow passes through a duct with a tube bank of heat exchangers, such as a gas heater and/or a boiler. Very high level noise called a “self-sustained tone” occurs due to the interference of the vortices and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions are vague. Then, rubber sheets as flexible walls are installed in both sides of the duct to suppress the self-sustained tone. The reasoning being that the resonant mode of the duct perpendicular to the flow may be suppressed by rubber sheet vibrations when the self-sustained tone occurred. Some experiments were carried out to examine the suppression effect of the installed rubber sheets. As a result, the suppression effect appeared at a certain condition. The purpose of this study is to clarify the effectiveness of the rubber sheet for self-sustained tones.

The flow-excited acoustic resonance of single and multiple cylinders in cross-flow is investigated experimentally. The effect of the cylinder(s) proximity to the acoustic particle velocity nodes of the first three acoustic cross-modes is presented. During the experiments, the acoustic cross-modes of the duct housing the cylinders are self-excited. For the case of a single cylinder, it is observed that although the cylinder’s location doesn’t significantly affect the vortex shedding process, it affects the mechanism of the flow-excited acoustic resonance and the levels of the generated acoustic pressure. When the cylinder is shifted away from the acoustic particle velocity anti-node of a specific acoustic cross-mode, a combination of cross-modes is excited with intensities that seem to be proportional to the ratio of the acoustic particle velocities of these modes at the cylinder’s location. For the case of two and three isolated cylinders positioned simultaneously side-by-side in the duct, it is observed that when the cylinders are positioned at different acoustic particle velocity anti-nodes of different cross-modes, the intensities of the excited acoustic resonance of these cross-modes are amplified compared to those with single cylinder. Nevertheless, when one cylinder is positioned at the acoustic particle velocity anti-node for a specific cross-mode and another cylinder is positioned at its acoustic particle velocity node, i.e. a cylinder that should excite the resonance and another one that should supress it, respectively; the excitation always takes over and the resonance occurs. Moreover, as the cylinder moves closer to the duct’s wall, the Strouhal number value decreases due to the interference between the wake of the cylinder and the wall. Therefore, the acoustic resonance for this case occurs at slightly higher flow velocities.

In the present paper the attention is focused on vortex shedding synchronization on acoustic resonance in in-line tube banks which occurred in the two-dimensional model of boiler. And we have examined the verification of proposed modeling method. We measured the characteristics of acoustic resonance, acoustic damping, the pressure fluctuation on the surface of tubes at the nodes of acoustic pressure and the acoustic pressure fluctuation on the side wall of the duct. As the acoustic mode number increased, the acoustic damping ratio decreased. As the tube pitch ratio in the flow direction decreased, the acoustic damping increased for all acoustic modes and the vortex shedding frequency became broad-band. The multiple resonance modes of lower acoustic damping were generated within the broad-band vortex shedding frequency. If the acoustic resonance occurred, the peak level of spectrum of surface pressure fluctuation and the coherence between vortex shedding and wall acoustic pressure in the tube banks also increased. The features of experimental results agree well with those obtained by using the proposed modeling method. We have discussed the characteristics of vortex shedding synchronization by using proposed the modeling method.

A pure tone phenomenon has been observed at 460 Hz on a piping steam line of a power plant. The source has been identified to be generated in a gate valve and to be of cavity noise type. This paper presents the investigations carried out on experimental models in order to analyze the problem. 2D and 3D axisymmetric models are used and lock-in situations between shear layer modes and acoustic duct modes are proven to give rise to powerful tones. Some counter measures are also tested with the objective of lowering the amplitude of pressure oscillations.

Duct flows of solid-liquid slurries are frequently encountered in many engineering applications. The literature about the behaviour of such mixtures in correspondence to hydraulic singularities — such as sudden variation of duct section, perforated plates and bar screens — is rather poor, despite they are integral part of the plants. The technical difficulties faced whilst performing experimental tests made CFD almost the only possible way to study the flow field in detail. In the present work the flow of sand-water mixtures through a sudden expansion in a rectangular horizontal duct is investigated by means of a two-fluid model. Due to the lack of experimental data available, a sensitivity analysis is performed to quantify the influence of the terms of the two-fluid model which proved negligible in the horizontal pipe case, topic of previous investigations. Computations were performed for either dilute or dense mixtures, in order to study the effect of the mean solids concentration on the flow field. Moreover, the effect of channel width is investigated to assess the validity of the hypothesis of two-dimensionality of the flow.

The phenomenon of flow-excited acoustic resonance is a design concern in many engineering applications, especially when wakes of bluff bodies are encountered in ducts, piping systems, heat exchangers, and other confined systems. In this article, the case of self-excited acoustic resonance of two side-by-side cylinders in a duct with cross-flow is investigated both numerically and experimentally. A single spacing ratio between the cylinders, T/D = 2.5, is investigated, where D is the diameter of the cylinders and T is the center-to-center distance between them. The numerical investigation is performed using a finite-volume method at a Reynolds number of 30,000 to simulate the unsteady flow field, which is then coupled with a finite element simulation of the resonant sound field. The experimental investigation is performed using phase-locked Particle Image Velocimetry (PIV) during the occurrence of flow-excited acoustic resonance. The results of both methods reveal that the flow-excited acoustic resonance produces a strong oscillatory flow pattern in the cylinder wakes with strong in-phase vortex shedding being synchronized by the excited acoustic resonance. The distribution and strength of the aeroacoustic sources and sinks within the flow field have been computed by means of Howe’s theory of aerodynamic sound for both the experimental and numerical cases, with the results of the two methods comparing favorably, showing similar trends in the oscillating flow fields, and very similar trends in the distribution of net acoustic power.

Piping systems conveying gases at high pressure often generate high level of vibration and noise. These phenomena, in many cases, are initiated by the coupling between an unstable separated flow and an acoustic mode of the piping system. Various types of cavities in pipe flow are among the flow geometries which are known to be liable to the generation of tonal noise. Flow over cavities in ducts and piping systems has been investigated extensively for two and three dimensional situations. In this case, the feedback loop which generates the tonal noise is caused by the coupling between the instability of the shear layer forming at the cavity opening and an acoustic mode. This paper presents a study of tonal noise generation by subsonic pipe flows over a cavity formed inside a fully open gate valve. Previous 2D and 3D studies, presented in a companion paper, have shown that the presence of the valve-seat cavity is responsible for the generation of acoustic tonal noise. In this paper, the full 3D geometry of the valve, on a small scale model, is studied with experiments and using an unsteady compressible flow solver developed at EDF. Experimentally, the evolution of the fluid acoustic coupling in term of frequency and amplitude with the flow velocity is studied. Also, a modal analysis have been done to identify the frequency of acoustic mode of the valve. Numerically, the complex 3D geometry is meshed and computation is performed. The results show an acoustic tonal noise in a frequency range compatible with that experimentally. The study is underway, future analysis of the velocity and acoustic fields in the simulation may help to identify the shear layer and acoustic modes and to identify how they couple together.