One of the research topics of most interest by the FluidLab group is the analysis of hydraulic systems and devices working in heavy-duty conditions. Particularly, four main sub-topics can be distinguished, related with cavitation, slurry flows, impact erosion, and fluid-dynamic noise. The synergy of laboratory experiments and theoretical/computational modeling drives our research in these areas.

 

Cavitation	Slurry flows	Impact erosion	Fluid-dynamic noise

 

 

 

Cavitation

Cavitation can be roughly considered as the rapid vaporization and condensation of a liquid, caused by a pressure reduction in the fluid. This is a serious concern in several applications, a significant example being hydraulic machinery and flow control devices. Cavitation, in fact, can produce severe consequences such as performance deterioration, high vibration and noise levels, and lifetime reduction of equipment.

The research of the FluidLab group on this topic.

 

 

Slurry flows

 A slurry is a solid-liquid mixture with solid content ranging from few percent by volume up to about 50% by volume. Slurry flows are frequently encountered in the mining industry, where slurry pipelines are used to transport the mineral concentrate to a mining processing plant near a mine. Other applications involving these flows include the oil sands transportation in the petroleum industry, the production of chemicals, and so on.

The modeling of slurry flows is particularly complex as it must account properly for the interactions between the fluid and the particles, between the particles and the solid walls, and among the particles themselves. The FluidLab group developed a two-fluid model for the simulation of slurry flows which, by comparison to experimental data reported in the literature, proved capable in efficiently predicting the features of most engineering interest. The research involved also CHAM Limited, and the two-fluid model was implemented in the PHOENICS code. The numerical activities carried out by the FluidLab group could take advantage of the recently established cooperation with Prof. Vaclav Matoušek from the Czech Technical University in Prague and the Institute of Hydrodynamics of the Czech Academy of Sciences, who is a widely recognized experimentalist in the field of slurry flows.

 

 

 

Impact erosion

Impact erosion is the removal of material from a surface subjected to the impingements of solid particles dragged by a fluid. This is a very serious issue in several engineering fields, such as the hydrotransport of mining tailings and the oil and gas extraction processes.

Being capable of predicting the vulnerability to erosion of pipelines and hydraulic equipment would be of great help to improve the design and the management of the processes and, even if the latest releases of the most widely used CFD codes are equipped with utilities for erosion calculation, this is still a challenging task for a number of reasons. Firstly, the computational cost of the numerical simulations is high and become prohibitive as soon as the particle concentration exceeds about few percent by volume. Secondly, the erosion damage produced by the impinging particles is typically estimated using simple formulas without a strong physical foundation, thereby limiting the predictive capacity of of the model. Finally, and related to the above, the solution of CFD-based erosion prediction models are subject to a high degree of uncertainty due to the considerable number of sub-models and parameters of ambiguous nature and difficult to quantify. The FluidLab group looks at the erosion phenomenon from a fluid dynamic point of view, and it aims at improving the applicability and reliability of the CFD approach by developing more accurate and effective models to describe the particle-laden flow, especially in the near-wall region. The collaborations with important realities, such as ENI S.p.A., as well as the availability of experimental facilities for slurry erosion testing of materials and real-scale hydraulic devices add considerable value to the research.   

 

• Abrasive jet impingement test

 It is the most widely used method to impact erosion study. Basic setup is shown in the sketch below.

 

 

• Gate valve

Gate valve is a very common hydraulic device for flow regulation. It inevitably suffers from impact erosion when deployed in the field with sand production.

 

 

Fluid-Dynamic noise

The fluid-dynamic noise is produced by a gas or a liquid because of its turbulent motion, because of the variating flow or because of its interaction with the structure that surrounds it. Different generation mechanisms coexist in creating a phenomenon whose impact on the noise emissions of industrial plants may be very concerning.

Especially in gas plants, the acoustic emissions far from industrial machineries are induced by the flow. The associated noise is referred to as aero-dynamic noise. These acoustic emissions are particularly intense close to control valves inside the pipe that perturb the air-flow and let it interact with the rigid walls of the valve. The study performed by the FluidLab group focused on the prediction of the noise emitted by control devices in different flow conditions. Numerical studies have been performed through an in-house code developed in the Open-Foam library for the investigation of the dynamic of noise production and propagation inside pipelines. The analysis helps to identify the nature of the noise produced by the flow close to control devices and suggests new hint for the optimization of noise reduction at the outlet valves’ body.

                                           

                                                     

The effective noise that propagates inside the pipeline and outside of it has been then investigated in order to provide useful information in the industrial framework where the international standards set the rules to be respected by the valves’ manufacturers. Numerical computations have been performed again in order to collect the fluid-dynamic quantities of interest for the application of acoustic models that describe the main features of the acoustic source. The international standards description of the acoustic source has been than compared for the evaluation of the parameter that most influences the external noise prediction.