An experimental cavitation tunnel to study hydraulic phenomena

Applications in which hydraulic phenomena arise are of great industrial and scientific interest. This is due to their inherent complexity in cases such as fluid-structure interaction and cavitation, and their effects on the energy performance of hydraulic machinery, which include the generation of instability, noise and vibrations.

Consequently, progress needs to be made in the understanding of all forms of hydraulic phenomena through experimental tests and numerical simulations. Their adverse effects must be controlled in all kinds of hydraulic machinery and the designs improved, and new technologies need to be developed that benefit industry and society in general, including environmental protection.

In this respect, the research group Barcelona Fluids & Energy Lab (IFLUIDS) at the Universitat Politècnica de Catalunya – BarcelonaTech (UPC) is making available to industry its experimental facilities for the study of hydraulic phenomena. These facilities have a closed hydraulic circuit through which fluid moves propelled by a centrifugal pump that feeds a test section where the test object can be situated (image 1). This hydrodynamic tunnel has a control system that enables the circulating flow and the reference pressure to be adapted independently during operation. The facility is instrumentalised with all kinds of sensors and a signal acquisition and recording system that can be used to monitor the operating variables in real time during the tests, including the flow, the pressure, the temperature or the vibrations. To enable the display and filming of fluid dynamic phenomena of interest, the test section is constructed with transparent walls.

Some of the studies that can be carried out in the experimental facilities of Barcelona Fluids & Energy Lab, taking advantage of all its computing capacity, are:

  • The effects of fluid-structure interaction in hydraulic machines
  • The emergence and cause of instability in hydraulic facilities
  • The turbulence generated by hydrodynamic profiles and other geometries
  • The fluid-dynamic forces generated on hydrodynamic profiles and other geometries
  • The load losses in components such as valves, filters, etc.
  • The origin of the generation of noise and vibration in hydraulic installations and new mitigation methods
  • The emergence of cavitation and the erosion caused by it in hydraulic profiles
  • The design and validation of hydraulic profiles that reduce the risk of cavitation
  • The effect of cavitation and other hydraulic phenomena in fluids with a special composition and chemical reactions
  • The development of sensors and instrumentation to measure flow
  • The validation of numerical models through ad hoc experimental tests
  • The effects of temperature on the performance and operation of hydraulic equipment

A case study: Study of the behaviour of a flowmeter in an operation with cavitation

Devices that measure flow by difference in pressure with geometries that restrict the section have high sensitivity to the formation and presence of cavitation. The cavitation tunnel has enabled the study of behaviour of this type of geometries in operations under cavitation conditions. For example, the load loss in Venturi tubes can be characterised depending on the flow and the operating temperature (video 1). At the same time, cavitation structures that form in the neck can be seen through images obtained with cameras that have high-speed filming and great sensitivity (video 2). The measures and the study of the results have enabled an increase in the range of operation and precision of this type of geometry to measure flows.

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