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Summary This paper reports on two straightforward and versatile routes to functional doubly porous polymeric materials based on cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) via novel porogen templating methodologies. The quantitative removal of either CaCO3 particles or poly(methyl methacrylate) beads as macroporogens, in conjunction with either hydroxyapatite nanoparticles or a solvent as nanoporogens, led to the generation of macropores with dimensions in the 100 µm range, while the second porosity lied within the 1 µm order of magnitude, as evidenced by mercury intrusion porosimetry and scanning electron microscopy. The successful functionalization of such doubly porous PHEMA-based frameworks was implemented through a straightforward two-step chemical modification involving an activation stage, followed by the coupling of propargylamine as a model compound. Raman spectroscopy clearly indicated the occurrence of alkyne functionality within the biporous materials.

Functional doubly porous polymeric materials based on cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) were engineered via novel porogen templating methodologies. Two straightforward and versatile strategies were implemented through the use of either CaCO 3 microparticles or poly(methyl methacrylate) beads as macroporogens, in conjunction with either hydroxyapatite nanoparticles of around 200 nm average diameter or a porogenic solvent ( e.g ., ethanol) as nanoporogens. Upon porogen removal, macropores with dimensions in the 100 μm range were generated, while the second porosity lied within the 1 μm order of magnitude, as evidenced by mercury intrusion porosimetry and scanning electron microscopy. The possibility to further functionalize such biporous PHEMA-based frameworks was investigated through a two-step synthetic approach involving an activation stage, followed by the coupling of propargylamine as a model compound. The success of the functionalization procedure was clearly demonstrated by Raman spectroscopy that indicated the occurrence of alkyne functionality within the biporous materials.

The operators of electric power plants are interested in having at its disposal a rapid and reliable tool that provides condition monitoring as well as fault detection (unbalance, bow, cracks, etc.) and diagnostics for its rotating machinery. Monitoring machine vibrations is a major concern for any operator in order to ensure safety by preventing machine failure and scheduling any necessary maintenance. In the present paper a model based approach is used to balance a large steam turbo-generator unit experiencing high amplitude vibration levels. Such approach combines a finite element model for the shaft-bearing-support system and vibration measurement acquired on the real machine in order to identify the appropriate solution for balancing. Rotor lateral position is monitored using displacement probes mounted close to the bearings location combined to seismic transducers mounted on the bearing casing. Several vibration datasets, measured by the displacement probes and corresponding to different operating regimes of the machine, are used for fault detection. The results obtained from these analyzes are then used to balance the machine and thus reduce vibration levels.

The identification of the aero-acoustic scattering matrix of an orifice in a duct is achieved by computational fluid dynamics. The methodology first consists in performing a large eddy simulation of a turbulent compressible flow, with superimposed broadband acoustic excitations. After extracting time series of acoustic data with a specific filter, system identification techniques are applied. They allow us to determine the components of the acoustic scattering matrix of the orifice. Following the same procedure, a previous paper determines the scattering features of a sudden area expansion. In the present paper, the focus is on whistling orifices. The whistling ability of the tested orifice is evaluated by deriving the acoustic power balance from the scattering matrix. Comparisons with experiments at two different Mach numbers show a good agreement. The potential whistling frequency range is well predicted in terms of frequency and amplitude.

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.Copyright © 2013 by ASME

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.Copyright © 2013 by ASME

An experimental investigation of the parameters controlling the whistling frequency and amplitude of an orifice in a confined turbulent flow is undertaken. A circular single hole orifice with sharp edges, a hole diameter equal to 0.015 m and a thickness equal to 0.005 m, is arranged in an air test rig with an inner diameter equal to 0.03 m. The Mach number ranges around 0.02 and the Reynolds number around 10(4). Variable reflecting boundary conditions are arranged upstream and downstream, and several flow velocities are tested. It is found that the Bode-Nyquist criterion accurately predicts the conditions of self-sustained oscillation and the value of the whistling frequency. Furthermore, it is found that the acoustic velocity in whistling regime varies from 1% to 15% of the steady flow velocity, and that it depends on the overall acoustic reflection of the surrounding pipe and on the Strouhal number.

Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number, the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced.Copyright © 2011 by ASME

Whistling phenomena in pipe power plants have been observed in the past years. It occurs at pressure drop devices where vortex shedding is established. It generates high noise levels and excessive vibrations. Auregan and Starobinsky [1] have developed an experimental criterion to predict whistling frequencies of pressure drop devices submitted to plane propagating pressure waves. This criterion estimates the net acoustic power, an acoustic exergy generation indicating that the device behaves as an acoustic amplifier. The corresponding frequencies are potential whistling frequencies. The application of the criterion only requires the determination of the scattering matrix of the device. In previous works, this criterion was applied to different single hole orifices. The purpose of the present study is to apply the criterion to two orifices in series and to verify that the behavior of this system can be predicted from the scattering matrix of each individual orifice and of the straight pipe in-between. Measurements are done on an air test rig with an inner diameter of 3 cm, a Mach number of 2.6 × 10−2 and a Reynolds number of 104 . Different distances between orifices are characterized. The study of the influence of the second orifice on the whistling criterion shows an enhancement of the whistling potential and a shift of the main potential whistling frequency. A fair agreement is found between experimental and predicted results. Characterization of orifices in series is then possible from the coefficients of the scattering matrix of one orifice and an appropriate condition on the distance between the orifices.Copyright © 2009 by ASME

Strong tonal noise can be found on the main steam lines of power plants. The source of noise was identified to be located at the gate valves present on the steam lines. Analysis of on-site measurements showed that the source of noise was due to the cavity that forms the valve seat at the bottom of the valve body. The valve in its open position is then composed of this bottom cavity over which an unstable shear layer develops but also of the top cavity where the gate is stored in open position. The valve is of course also connected to the pipe. All these elements are good candidates for flow-acoustic phenomena. The development of the shear layer over the cavity gives rise to self-sustained flow oscillations and noise radiation. The vortices convected in the shear layer which develops from the upstream corner of the cavity interact with the downstream corner of the cavity. A pressure disturbance is then generated and acts as a feedback loop on the separation point at the upstream corner. Due to the phase relationship between the generation of the disturbance downstream and its influence upstream, this pressure feedback selection amplifies the shear layer and preferred modes of oscillation are then produced. It is also well known that at low Mach number these pressure oscillations in the cavity remain weak. However, in ducted configurations, powerful tones can be generated even at low Mach number when pressure oscillations in the shear layer couple with the acoustical response of the duct. In order to study these phenomena in configurations close to the industrial ones, both numerical and experimental approaches are carried out. A high-order numerical code has been developed in order to capture aeroacoustic interactions in turbulent flows. An experimental test rig has been built in order to study aeroacoustic phenomena in small scale models of control flow devices present on steam pipes of power plants. A vacuum pump is used instead of a ventilator for creating the flow through the test rig in order to study high pressure loss devices. The present paper aims at handling the flow-acoustic phenomena in the case of a fully 3D geometry of the gate valve. Both numerical and experimental investigation methods are used. In the second section of the paper, industrial problem and previous study are recalled. In the third section, the small scale model that is used for both numerical and experimental investigations is presented. In the fourth section, the numerical methods used in this paper are presented. In the fifth section, the experimental device and the measurements techniques are presented. In the sixth section, results of the acoustic modal analysis of the valve are analysed. In the seventh section, results of the flow-acoustic analysis of phenomena in the valve are analysed.