A model for flow-induced noise of Helmholtz resonator-like cavities

This paper presents a single prediction model for the noise generated by a turbulent boundry layer flow grazing on the opening of a Helmholtz-resonator like cavity. The prediction model is validated by comparison with an experimental study. The measured spectra inside the cavity are correctly predicted by the model

Flow-Induced Pulsations in Closed Side Branches With Wet Gas

In a recent paper it has been shown that the presence of liquid has an influence on Flow Induced Pulsations (FIPs) in closed side branches. Even larger effects of liquid in case of whistling in corrugated pipes were reported. For this experimental study, the “Tandem configuration” with two closed side branches along a main pipe is considered. It is characterized by the distance between the two closed side branches equal to the double of their acoustic length. The experiments reported in this paper aim at investigating the effect of the mixture water/gas on FIPs measured at the closed end of the two closed side branches. Different water flow rates are injected in the flow to obtain a mass factor rate in the range 0-10-4 m3/s. Furthermore, the relation between the multiphase flow pattern in the main pipe and the trend in the pulsation amplitude and Strouhal number is discussed, by comparison with the test for dry gas. To understand the effect of the type of flow, tests are performed with the injector far from and close to the upstream side branch. For the far configuration, at both low and high injection rates, pulsations decrease for increasing injection rates. However, in the intermediate region, an increase of pulsations is observed. These different ranges can be attributed to different (multiphase) flow regimes. Concerning the close configuration, only a decrease of the pulsations is observed over the full range. Furthermore, a decrease of the Strouhal number corresponding to the maximum pulsation level is observed

Whistling of short corrugated pipes: experimental investigation of the source locations

The goal of this study is to investigate the issue of the aeroacoustic source location within corrugated pipes. For this purpose, a configuration with a short pipe and well defined boundary conditions is chosen. These investigations have been carried out focusing on the first two whistling modes. This allows for a precise knowledge of the distribution of the acoustic velocity and pressure within the pipe. The methodological investigation of the source locations has been carried out by using straight pipe segments to replace the corrugated section near the acoustic velocity nodes and near the acoustic velocity antinodes. The sections of the corrugated pipe near the acoustic velocity antinodes has been identified as the main location of the sound sources. © 2010 by J. Golliard

Towards a Universal Scaling for Broadband Turbulent Noise in Internal Flow Devices

An investigation is performed on the scalability of broadband noise sources from separated flows in internal pipe systems. Broadband sources from for example wellhead chokes, bends and valves can potentially excite subsea manifolds through fluid acoustic coupling and fluid structural coupling. The focus of the current work is evaluation and improvement of scaling laws for collapse of sound power spectra. The approach proposed here is to use steady-state Computational Fluid Dynamics [CFD] to better estimate the properties of the flow in order to improve the scaling law and obtain a universal broadband spectrum. Steady Reynolds Averaged Navier-Stokes [RANS] simulations of several bend and orifice geometries have been performed. A surface acoustic power model based on modeled turbulent quantities is implemented. Based on the RANS data, more advanced models for scaling have been developed. Experimental sound power spectra from literature of the simulated geometries are scaled using different methodologies in both amplitude and frequency. When a new scaling based on CFD modeled surface acoustic power was used, a universal collapse among geometries occurred. Using CFD, the velocity in the high-speed sound-producing region is obtained, as well as a more accurate length scaling in order to improve the frequency scaling. A vast improvement in collapse over different geometries is achieved. The current work indicates that a universal collapse might indeed be present. The methodology does not require high fidelity calculations and is thus easy to implement. By comparing original and new scaling laws, it turns out that the ratio of fluctuating drag over steady drag can vary among geometries

Acoustic damping in smooth and corrugated pipes with and without liquid injection

From previous experiments, it was shown that small quantities of liquids reduce or eliminate the singing phenomenon in corrugated tubes. The singing mitigation was attributed to filling up of the corrugations, interference with the boundary layer or due to the increased acoustic damping. To evaluate the influence of the presence of liquids on the acoustic damping, this damping was measured in a smooth and a corrugated tube (internal diameter 49 mm). The damping was measured using an active source (loudspeaker) and measuring amplitude of sound waves on both sides of the pipe. This was done at different gas velocities (U = 0, 15, 30 m/s) and different liquid injection rates (0, 150, 250 350 ml/min) for a frequency range between 0-2200 Hz. The smooth pipe results compared well with literature models such as the Kirchhoff model. In the presence of liquid, the acoustic damping increased linearly with the liquid rate. This increase was higher than expected based on the assumptions of mist flow or overall pressure drop. In case of the corrugated tube, the measured damping is dominated by a large fluctuation due to the source behavior (negative damping) at flowing conditions. At low velocities a decrease in source strength was measured with increasing liquid. At higher gas velocities, it was observed that liquid has almost no effect on the damping. Copyright © 2013 by ASME

Orifice impedance under grazing flow measured with a single microphone method

The effect of one-sided grazing mean ow on the acoustical impedance of rectangular orifices is measured at low Mach number and low Helmholtz number by means of a single microphone method. The results are fairly consistent with previous experimental results obtained by means of a two-microphone impedance tube. Furthermore no significant in- uence of the aperture aspect ratio and aperture wall thickness on the non-dimensional scaled impedance is found, at least for the qualitative trend. Comparison with an existing theoretical model shows reasonable agreement for the resistance, provided that the exper- imental results are tentatively corrected for boundary layer- and induced ow effects. For the reactance no agreement is found

Singing mitigation in corrugated tubes with liquid injection

Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can generate a high amplitude tonal sound (singing). Small quantities of liquid can result in a significant amplitude reduction or total mitigation of this sound production. To evaluate different potential mechanisms, liquid injection tests were done in both a horizontal and vertical small scale (49 mm) setup including high speed camera recordings using a transparent corrugated section. The singing amplitude decreased linearly with the liquid injection rate for both orientations, although the effect in the vertical setup was even faster. Liquid injection resulted also in higher onset velocities. The video recordings showed partially filled corrugations. For horizontal corrugations, liquid crept upward in the corrugations. In the vertical test, liquid accumulated at the upward edge with intermitted liquid spill over to downstream corrugations. The liquid fill up did not change significantly with higher liquid loads. Taking the fill-up grade and additional damping into account, a match could be made between the measured singing amplitude and a predicted singing amplitude as function of liquid rate. However, no model has been found to predict the liquid fill-up yet. Copyright © 2013 by ASME

On the effect of water film on flow-induced pulsations in closed side branches in tandem configuration

Previous studies demonstrate that the presence of liquid strongly influences the pressure pulsation amplitudes of flow induced pulsations. In particular, in case of annular flow (thin liquid film on the walls) the pulsations can be eliminated. The present study aims at evaluating the contribution of the liquid film to the pulsation reduction. Experiments have been performed in a tandem configuration with two side branches upward oriented. The side branches have the same diameter as the main pipe. A first set of experiments has been conducted with the injection point located far upstream the upstream side branch. To isolate the sole effect of the film, a second and a third set of experiments have been performed with the injection point located close upstream the T-junction with the injection such that a thin film only was generated. In the first configuration (far upstream), the pulsation level decreases with increasing liquid rate. The reduction in amplitude compares well with the assumption of added damping in the length between the two side branches. A similar decrease in pulsation amplitude was obtained in the second configuration. However, the amplitude reduction depends on the local liquid flow pattern at the (upstream) side branch and in particular on whether liquid bypasses the side branch or it interferes with the shear layer. This indicates that acoustical damping is the main effect and small amounts of liquid do not significantly interfere with the shear layer

Qualification of new design of flexible pipe against singing: testing at multiple scales

Flexible pipes for production of oil and gas typically present a corrugated inner surface. This has been identified as the cause of "singing risers": Flow-Induced Pulsations due to the interaction of sound waves with the shear layers at the small cavities present at each of the multiple corrugations. The new flexible technology discussed in this paper, called K-carcass, is made of shaped wires and presents a very different bore profile compared to other folded-strip flexibles. In a preliminary study based on small scale testing, it was showed that the new inner profile geometry of this technology was more robust for Flow-Induced Pulsations compared to the folded strip carcass. A qualification program was initiated to address the different risks associated with the introduction of a new pipe technology. A primary goals of this qualification program was to extend the results of the preliminary study to the actual carcass at field conditions (natural gas at production pressure). In this paper, the method followed to qualify the singing behavior of the new flexible technology as installed in the field at operational conditions is considered. The testing program and the scaling approach used to extrapolate results obtained at different scales towards full-scale pipes are described. The program includes a combination of small-scale and large-scale testing. The small scale singing testing consists of blow-through tests of 2" and 3" pipes with corrugated inner bore with air at low pressures on a setup with well-defined acoustic boundary conditions. The large-scale singing testing consists of similar tests on 3" and 5" pipes with natural gas at close-to-operational pressures. These tests are completed with full-scale tests, where a reference riser and a prototype of new-technology riser are tested with natural gas at high pressure. The combination of scales and gas properties at which the tests are done, and the continuity between the different tests conditions, will allow the validation of theoretical and empirical scaling laws used in the qualification of the new riser in operational conditions. The blow-through tests with the prototype pipe with the new K-carcass tested with natural gas at close-to-operational pressure did not show any singing. In contrast, the reference pipe (with folded-strip carcass) started singing even at low velocities. The test results can be extended to an allowable production envelope for a pipe in field conditions. Such a qualification of new technology has to rely on existing prediction tools. As these tools were developed to analyze the singing behavior of the existing technologies, this combined theoretical and experimental approach reduces the risks associated with the introduction of a new technology