Predictive tools and Irradiation imaging of in-nozzle cavitating flows

by Prof. Manolis Gavaises (City University of London, School of Science and Technology, London, UK)

Monday 21 Nov 2022, 13:00 → 14:00 Europe/Berlin

E1.173 (XHQ / Schenefeld)

Prof Manolis Gavaises (MG) & Dr Ioannis Karathanassis (IK)

Abstract 1 (MG)

Cavitation is realised in many engineering applications as well as in ultrasound systems. Cavitation occurs when pressure falls suddenly below the fluid’s vapour (saturation) pressure. Depending on the pressure recovery process of the fluid towards pressures above the cavitation threshold, sudden vapour collapse during the condensation of the liquid results to radiated noise and catastrophic damage to nearby materials. Examples include hydraulic systems, fuel injectors and rotating fluid machinery (propellers, turbines, pumps) and even traumatic brain injury. On the other hand, ultrasound-induced cavitation is utilised in many applications such as ultrasound imaging, lithotripsy, histotripsy, drug delivery, cleaning and even microbial deactivation. The presentation gives an overview of such cases and the relevant computational models that have been developed. Emphasis is given on models that couple the compressible Navier-Stokes and energy conservation equations with a real-fluid thermodynamic closure approximation covering pressures from 0 to 4500bar and temperatures up to 3000K; these conditions expand from compressed liquid, vapor-liquid equilibrium to trans/supercritical mixing. The model assumes mechanical and thermal equilibrium between the liquid, vapour and air phases and thus, it avoids utilisation of case-dependent empirical phase-change models, typically employed for predicting such cases. 

Abstract 2 (IK)

X-ray imaging, especially using high-flux synchrotron radiation, has gained momentum recently as a technique capable of visualising cavitating flows in internal geometries. X-ray Phase-Contrast Imaging (XPCI), exploiting the shift in the X-ray wave phase during interactions with matter, offers sharp-refractive index gradients in the liquid/vapour interface region. Hence, it is suitable for capturing fine morphological fluctuations of transient cavitation structures. Nevertheless, the technique cannot provide information on the quantity of vapour within the orifice. Such data can be obtained utilising absorption imaging, where beam attenuation can be explicitly correlated with the projected vapour thickness in line-of-sight measurements. Different experimental campaigns at the Advanced Photon Source of the Argonne National Laboratory will be presented during which both XPCI and absorption imaging have been employed to capture the transient cavitating flow arising in a mm-sized orifice in a time resolved manner with spatial and temporal resolutions of 5 μm/pixel and 67,890 frames per second, respectively. A throttle orifice with an abrupt constriction in its flow layout, resembling a fuel injector, has been employed for the experiments. Recently obtained results from a separate campaign performed in the spallation source of the Paul Scherrer Institut will also be discussed. Neutron imaging has been demonstrated capable of producing quantitative data with respect to the extent of cavitation in the same orifice layout. Vapour-path length data were obtained in a time-averaged manner at a resolution of 16 μm/pixel with an increased active field of view compared to x-rays.  

Short Bios

Manolis Gavaises is Professor in Fluid Dynamics at City, University of London since 2009. He received his PhD from Imperial College London in 1997 (the 1998 Richard Way Prize for 'Most outstanding doctoral thesis in the area of IC engines in the UK'; the Arch T. Collwell Merit Award from the Society of Automotive Engineers (SAE)). MG started his academic career at City, University London in 2001. Between 2009-2012 he was holding the Delphi Diesel Systems (UK) Chair in Fuel Injection Equipment Fluid Dynamics. In 2012 he co-established and directs the International Institute for Cavitation Research (IICR); IICR now represents a wide network of Universities and industries looking into various aspects of cavitation and multiphase flows. 

https://orcid.org/0000-0003-0874-8534

https://scholar.google.com/citations?user=RnDOy8MAAAAJ

 

Dr Ioannis Karathanassis is currently a Senior Lecturer at City, University of London. He received his PhD from the NTUA in 2015 on heat-transfer enhancement techniques, which was awarded as the best Thesis in applied sciences by NCSR Demokritos, the largest research institution in Greece. During his appointment at City, he has worked closely with Caterpillar/Perkins Engines UK on thermal effects caused by the extreme fuel pressurisation in Diesel fuel systems. In 2018, he was promoted to Lecturer and since then his work on non-Newtonian flows of diesel fuels and hydraulic fluids has been supported by Lubrizol Corp. USA and Lubrizol Ltd. UK. In the same year, he was successful in his MSCA-GF (AHEAD GF Grant no.794831), which was submitted jointly with Sandia National Laboratories (US) on the development of laser diagnostic techniques for multiphase flows. 

https://www.city.ac.uk/people/academics/ioannis-karathanassis

 

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