When flexible pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In this paper, the pipe is subjected to internal flow and external flow at the same time. The dynamic stability of a double wall pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures for the development of a piping system in the field of ocean mining, and in the field of fluid energy generation, and so on. In this paper, the pipe structures are assumed to be composed of the cantilevered elastic tube structure. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence are added to are applied. Changing the flow direction and the fluid velocity as for the internal flow and the external flow, the dynamic stability of the double wall pipes is investigated and discussed. Moreover, changing the flow rate and the density of a fluid and a structure, these effects on the stability of double wall pipes are investigated.

When slender pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In the development of a piping system in the field of ocean mining, and in the field of fluid energy utilization, and so forth, the double walled pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures. In this paper, the pipe structures are assumed to be composed of the cantilevered beam structure which shows the complicated dynamic behavior than the other supported conditions. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence is added to are applied. Changing the flow direction and the fluid velocity of the internal flow and the external flow, and the specifications of modeling, the stability of the double walled pipes is investigated and discussed.

This paper presents a numerical methodology and simulation for three-dimensional transonic flow in Safety Relief Valves. Simulation of safety relief valve flows is very challenging due to complex flow paths, high pressure variation, supersonic flow with shock and expansion waves, boundary layers, etc. The 3D unsteady Reynolds averaged Navier-Stokes (URANS) equations with one-equation Spalart-Allmaras turbulence model is used. A fifth order WENO scheme for the inviscid flux and a second order central differencing for the viscous terms are employed to discretize the Navier-Stokes equations. The low diffusion E-CUSP scheme used as the approximate Riemann solver suggested by Zha et al. is utilized with the WENO scheme to evaluate the inviscid fluxes. Implicit time marching method with 2nd order temporal accuracy using Gauss-Seidel line relaxation is employed to achieve a fast convergence rate. Parallel computing is implemented to save wall clock simulation time. The valve flows with air under different inlet pressures and temperatures are successfully simulated for the full geometry with all the fine leakage channels. A 3D mesh topology is generated for the complex geometry. Detailed simulations of air flow are accomplished with inlet gauge pressure 0.5MPa and 2.1MPa. The simulated air mass flow rate agrees excellently with the experimental results with an error of 0.26% for the inlet pressure of 0.5Mpa, and an error of 2.5% for the inlet pressure of 2.1MPa. The shock waves and expansion waves downstream of the orifice are very well resolved.

Internal combustion method is widely used to reduce residual stress of large spherical tanks in China, when post weld heat treatment of the spherical tanks is required. During the heat treatment processes diversion umbrellas set in the spherical tanks can be utilized to drop the maximal difference of wall temperatures of the spherical tanks. Numerical simulation based on Fluent software was carried out to study the effect of an A-shaped diversion umbrella and three V-shaped diversion umbrellas with different angles on internal flow and wall temperatures of a 10000 m 3 spherical tank. The results show that the V-shaped diversion umbrellas have better performance than the A-shaped one, but the angles of the V-shaped diversion umbrellas from 100° to 140° have little effect on maximum wall temperature differences of the spherical tank during the heat preservation stage of the heat treatment processes.

High-amplitude acoustic pressure fluctuations associated with locked-on, resonant flow states frequently occur in engineering systems that involve internal cavities located in pipelines, such as components of gas transport systems, steam delivery pipelines and jet engines. This paper describes the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities. Effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). The internal flow was non-intrusively accessed by means of a borescope, which allowed illumination and optical recording of flow tracers inside the cavity. Instantaneous, phase- and time-averaged patterns of velocity and vorticity provided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity. Specifically, the introduction of the chamfers affected the phase and the location of formation of large-scale vortical structures in the shear layer, which is associated with a maximum of the vorticity thickness across the cavity opening. In turn, these changes in the flow structure affected the amplitude of acoustic pressure pulsations.

This paper focuses on the scalability of broadband turbulent noise in internal pipe flows. It discusses a universal scaling approach for broadband turbulent noise that is based on surface acoustic power modeled by ANSYS Fluent. This investigation proposes a strategy for amplitude scaling at frequencies above the onset frequency for non-planar acoustic waves, offering a generalized formulation for circular and rectangular pipes. Information based on the surface acoustic power, wall shear stress, kinetic energy and dynamic pressure is explored in view of improving the frequency scaling approach. For short, long and mitred bends, the reversed method is applied to reconstruct the broadband noise spectra, which compare well with the experimental ones. Finally, the noise spectra reconstruction is performed for T-joint and tees geometries.

In this paper, the phenomenon of self-sustained pressure oscillations due to the flow past a deep, circular, axisymmetric cavity is investigated. In many engineering applications, such as flows through open gate valves, there exists potential for coupling between the vortex shedding from the upstream edge of the cavity and a diametral mode of the acoustic pressure fluctuations. In the present study, the unsteady pressure was measured at several azimuthal locations at the bottom of the cavity walls, and the associated acoustic mode shapes were calculated numerically for the four representative cases of the internal cavity geometry, which involved a reference case with sharp, 90°edges as well as several modifications that involved chamfers of various length of the upstream and the downstream edges of the cavity. In addition, the flow velocity in the vicinity of the cavity opening in selected cases was measured using digital particle image velocimetry (PIV). The optical access to the highly confined internal flow was provided by implementing an endoscope attached to the camera. This global, quantitative imaging approach yielded patterns of velocity, streamlines and out-of-plane vorticity component. Instantaneous and time-averaged flow patterns provided insight into the mechanism of the flow tone generation. Among the considered cavity geometries, the configuration that corresponded to the most efficient noise suppression was identified.

Internal two-phase flow is common in piping systems. Such flow may induce vibration that can lead to premature fatigue or wear of pipes. In the nuclear industry in particular, failure of piping components is critical and must be avoided. Two-phase damping is considered part of the solution, since it constitutes a dominant component of the total damping in piping with internal flow. However, the energy dissipation mechanisms in two-phase flow are yet to be fully understood. The purpose of this paper is to explore the relationships between two-phase damping and fluid properties. Simple experiments were carried out in a clear vertical clamped-clamped tube to verify the effects of fluid properties on two-phase damping. Various fluids, such as air, alcohol, pure water, sugared water, glycerol, and perfluorocarbon, were combined to obtain different controlled mixtures and to determine the effect of surface tension, density and viscosity on two-phase damping. Two-phase damping ratios were obtained from free transverse vibration measurements on the tube. Two sets of experiments with stagnant and moving continuous phase were conducted. Based on dimensional analysis, we obtained a semi-empirical model for two-phase damping in bubbly and slug flow. The Void fraction and Bond number are shown to be major parameters of two-phase damping, which is described as a kinetic energy transfer from the tube to the continuous phase through added mass of the dispersed phase.

Temperature gradients in the thermally stratified fluid flowing through a pipe may cause undesirable excessive thermal stresses at the pipe wall in the axial, circumferential, and radial directions, which can eventually lead to damages such as deformation, support failure, thermal fatigue, cracking, etc. to the piping systems. Several nuclear power plants have so far experienced such unwelcome mechanical damages to the pressurizer surge lines, feedwater nozzle, high pressure safety injection lines, or residual heat removal lines. In this regard, to determine the transient temperature distributions in the wall of a piping system subjected to internally thermal stratification with accuracy is the essential prerequisite for the assessment of the structural integrity of the piping system subjected to internally thermal stratification. In this study, to predict the transient temperature distributions in the wall of PWR pressurizer surge line with a complex geometry of 3-dimensionally bent piping realistically, 3-dimensional transient CFD calculations involving the conjugate heat transfer analysis are performed for the actual PWR pressurizer surge line subjected to stratified internal flows either during out-surge or in-surge operation using a commercial CFD code. In addition, the wall temperature distributions obtained by taking account of the existence of wall thickness as it is are compared with those by neglecting the existence of wall thickness to identify some requirements for a realistic and conservative thermal analysis.

Axial, radial and tangential structural oscillation of various propulsion system motor chamber walls is demonstrated to be able to produce substantial pressure wave amplitudes within the internal flow. Predicted resonant driving frequencies for forced rigid vibration may vary somewhat from the ideal acoustic estimate, depending on the grid density employed in the given numerical model. Similarly, predicted limiting pressure wave amplitudes may tend to asymptote somewhat higher in the case of radial and tangential structural motion, as the grid density is increased (and the corresponding time step decreased) for the numerical solver. Free dynamic structural deformation (in addition to any net rigid-body motion that might be involved) is illustrated to also have an appreciable influence on internal gasdynamic wave behavior.

Increasingly computational methods are being used for industrial problems in place of expensive or very difficult physical experiments. Attention needs to be given to all aspects of the input into these complex flow problems such as the inlet conditions as these may have a significant effect on the subsequent solution. High aspect ratio cross-sectional orifice (HAR) jets is one such field as such jets occur in many industrial situations. These can include gas dispersion within an enclosed space, within machinery and manufacturing processes. These will often be part of a more complex problem and previous work [1] has shown that it is crucial to model these jets numerically in as accurate and consistent way as possible given the limitations of turbulence models and computing power. The aim of this paper is to extend previous work [1] and to further analyse initial numerical results from simulations of the flow described in the experimental work of Meares [2]. The work here undertakes to do an initial assessment of the effect turbulence modelling has on the internal flow within the pipe and through the flange and gap in the gasket. The standard two-equation k-ε and the variant RNG and realisable models will be used with a standard wall law. Future work will look at time dependent simulations and also the use of Large Eddy Simulation. The effect of the length of pipe modeled and pipe pressure are also explored, consistent with the experimental work done by Meares [2] on HAR orifice jets for one gasket shape.

The fluidelastic instability behaviour of flexible cylinders subjected to internal single-phase (liquid or gas) flows is now reasonably well understood. Although many piping systems operate in two-phase flows, so far very little work has been done to study their dynamic behaviour under such flows. This paper presents the results of a series of experiments to study the fluidelastic instability behaviour of flexible tubular cylinders subjected to two-phase internal flow. Several flexible cylinders of different diameters, lengths and flexural rigidities were tested over a broad range of flow velocities and void fractions in an air-water loop to simulate two-phase flows. Well-defined fluidelastic instabilities were observed in two-phase flows. The existing theory to formulate the fluidelastic behaviour under internal flow was developed further to take into account two-phase flow. The agreement between the experimental results and the modified theory is remarkably good. However, it depends on using an appropriate model to formulate the characteristics of the two-phase flows.

Centrifugal pump is a typical turbomachinery, which transfers mechanical energy to hydraulic energy through the rotational motion of impeller blades. It is commonly used and generally operated at a very high efficiency. Therefore, it would seem that theoretical discussion of performance and experimental observations of internal flow conditions inside the pump should be fully understood by now. However, it appears that neither the basic expressions nor the theoretical design methods are that clear. For example, the most fundamental definition of pump head, which is the most important equation in pump textbooks, is not often well explained. The purpose of this oral presentation is to share preliminary results of on-going studies on the energy transfer in centrifugal pumps.

This paper is aimed at presenting recent advances in modeling and simulation of vibrating structures in presence of external as well as of internal fluid flows using methods based on symmetric variational BEM formulation coupled with the FE. The structural weak form is coupled with a novel boundary element variational formulation of a compressible viscous fluid. The proposed formulation has distinct advantages: ( i ) over the classical FE, it avoids the discretisation of the fluid domain; ( ii ) over the collocation BEM formulation, it avoids the explicit calculation of the finite part of hypersingular integrals. Also, the discretisation, by the boundary finite element procedure, of the resulting mixed variational functional leads to a symmetric algebraic system. A computer code based on these concepts has been developed and applied to calculate 3D vibroacoustic behavior of various coupled mechanical systems.

Improved computing power has increased the capacity of numerical modellers to simulate real-life situations with the expectation that results will be useable and accurate. It is easy when modelling physically large geometries to over simplify aspects of the model, usually because of mesh restrictions, that could be to the detriment of the results. For many years Computational Fluid Dynamics has been used to simulate leaks of hydrocarbons with the production areas of offshore superstructures, [1, 2]. Many simplifications are required, one of which is modelling these leaks as axisymmetric jets. Previous work, [3, 4] has shown that this is not a good simplification and could have serious safety implications. A more accurate model of the jet is needed for the full consequences of a gas leak to be ascertained. Having established that a leak from a flange or crack in a pipe needs to be modelled as a high aspect ratio cross-sectional orifice jet there are also other considerations. Work on the turbulence model and inlet conditions that are best suited for these simulations has been done, [5, 6]. This paper investigates the flow within the pipe and up through the gasket before release into the air as a jet. Different idealised shapes of gaskets are used and the flow at the jet exit are investigated. It is hoped that a range of conditions can be established that set criteria for such modelling in the future.

Two-phase flow is common in the nuclear industry. It is a potential source of vibration in piping systems. In this paper, two-phase damping in the bubbly flow regime is related to the interface surface area between phases and, therefore, to flow configuration. Two sets of experiments were performed with a vertical tube clamped at both ends. First, gas bubbles of controlled geometry were simulated with glass spheres let to settle in stagnant water. Second, air was injected in stagnant alcohol to generate a uniform and measurable bubble flow. In both cases, the two-phase damping ratio is correlated to the number of bubbles (or spheres). Two-phase damping is directly related to the interface surface area, based on a spherical bubble model. Further experiments were carried out on tubes with internal two-phase air-water flows. A strong dependence of two-phase damping on flow configuration in bubbly flow regime is observed. A series of photographs attests to the fact that two-phase damping increases for a larger number of bubbles, and for smaller bubbles. It is highest immediately prior to the transition from bubbly flow to slug or churn flow regimes. Beyond the transition, damping decreases. An analytical model is proposed to predict two-phase flow damping in bubbly flow, based on a spherical bubble model. The results also reveal that the transition between bubbly flow and slug/churn flow depends on tube diameter. Consequently, the tube diameter also has an effect on two-phase damping. The above results could lead to some modifications of existing flow regime maps for small diameter tubes.

Two-phase internal flow is present in many piping system components. Although two-phase damping is known to be a significant constituent of the total damping, the energy dissipation mechanisms that govern two-phase damping are not well understood. In this paper, damping of vertical clamped-clamped tubes subjected to two-phase air-water internal flow is investigated. Experimental data is reported, showing no dependence of two-phase damping on tube natural frequency, and a strong dependence on void fraction, flow velocity and flow regime. Two-phase damping increases with void fraction, reaches a maximum, and decreases beyond that point. The maximum damping ratio is roughly 3% for all flow velocities. It is reached at around 50% void fraction for high velocities, and 25% void fraction for low velocities. Data points plotted on two-phase flow pattern maps indicate that damping is greater in a bubbly flow regime than it is in a slug or churn regime. The maximum two-phase damping is reached at the highest void fraction before the transition to a slug or churn flow regime. It appears that two-phase damping may depend on the interface surface area between phases.