Large scale numerical modelling of slurry flow in horizontal pipelines has been carried out. A combination of analytical and commercial CFD modelling, with Eulerian two-phase flow models, has been used in the present investigation. The modelling results are validated with well-documented experimental data and are found to be in good agreement. Flow regime maps were developed and pressure drops calculated for a wide range of flow rates, particle sizes and solid concentrations. It was observed that flow regime maps calculated with analytical empirical correlations near the transition flow regimes are unreliable. It is concluded that the performance of this model at the presented scales allows for application at smaller scales that still feature turbulent flows.The Eulerian-granular multiphase flow model has been used in the present study. The Eulerian model solves momentum and continuity equations for each phase. Coupling between the phases is implemented through the pressure and interphase exchange coefficients. In this model, the different phases are treated as inter-

Gas transport in corrugated pipes often exhibit whistling behavior, due to periodic flow-induced pulsations generated in the pipe cavities. These aero-acoustic sources are strongly dependent on the geometrical dimensions and features of the cavities. As a result, uncertainties in the exact shape and geometry play a significant role in determining the singing behavior of corrugated pipes. While predictive modelling for idealized periodic structures is well established, this paper focusses on the sensitivity analysis and uncertainty quantification (UQ) of uncertain geometrical parameters using probabilistic models. The two most influential geometrical parameters varied within this study are the cavity width and downstream edge radius. Computational Fluid Dynamics (CFD) analysis was used to characterize the acoustic source. Stochastic collocation method was used for propagation of input parameter uncertainties. The analysis was performed with both full tensor product grid and sparse grid based on level-2 Clenshaw-Curtis points. The results show that uncertainties in the width and downstream edge radius of the cavity have an effect on the acoustic source power, peak Strouhal number and consequently the whistling onset velocity. Based on the assumed input parameters distribution functions, the confidence levels for the prediction of onset velocity were calculated. Finally, the results show the importance of performing uncertainty analysis to get more insights in the source of errors and consequently leading to a more robust design or risk-management oriented decision.

The integrity of compressors and pumps is of paramount importance for the gas and oil industry. Failures may result in serious production losses that are in no proportion with the cost of the equipment involved. Besides, the equipment may be inaccessible for maintenance for a long period of time due to unfavourable weather conditions. The requirements of compressors with respect to pressures, capacity, power and operating range, are increasing. The answer to this is innovative compressor concepts, advanced materials and manufacturing techniques. Unexpected phenomena, however, for instance due to fluid structure interactions, will occur that can lead to serious damage of the machine. In this paper such a phenomenon is discussed by presenting a case study. On the NAM L9 platform, a centrifugal compressor was operated for the transport of gas to shore. The compressor showed serious vibrations at certain conditions that finally led to failure. An analysis of the vibration measurements showed that extremely large vibrations could occur at the blade passing frequency. By means of modeling, an analysis could be made of the acoustic resonances that could possibly occur in the compressor. It was found that a likely cause of the failure was a resonance mode in the shroud cavity of the 3rd and 4th stage. The acoustic resonance modes could be excited by pulsation sources present in the machine. Especially, the sources at the low solidity vanes were suspected to contribute to the excitation of the resonance. Vortex shedding at the impeller edge was also suspected to contribute. The resonance in the cavity may exert large dynamic forces near the trailing edge of the impeller shroud. Due to a structural vibration modes of the shroud, a fatigue failure occurred. The paper describes the root cause analysis consisting of an analysis of the acoustic and structural vibration modes. The consequences for the design of similar compressors are subsequently reviewed. A future outlook is presented concerning dense gas compression systems for CO2 and high pressure reinjection.

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Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can be subject to Flow-Induced Pulsations when the flow velocities are higher than a certain onset velocity. The onset velocity for classical corrugated pipes can be predicted on basis of the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. A newly developed inner carcass design for flexible pipes features smaller corrugation cavities. The effect of narrow cavities on the whistling of corrugated cavities is evaluated. In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as deeper and narrower cavities. These tests were performed in order to evaluate the validity of a prediction model for the onset of pulsations, for corrugated pipes with these kinds of atypical variations. The experimental results show that the validity of the model remains reasonable, except when the cavities are very narrow. In this case, the model becomes overly conservative. The deviation is attributed to the momentum thickness of the boundary layer, which is too large compared to the cavity width. In this case, any instability of the shear layer is destroyed, which prevents whistling. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, are considered.