High-flux synchrotron radiation has been employed in a time-resolved manner to characterise the distinct topology features and dynamics of different cavitation regimes arising in a throttle orifice with an abrupt flow-entry contraction. Radiographs obtained though both X-ray phasecontrast and absorption imaging have been captured at 67,890 frames per second. The flow lied in the turbulent regime (Re=35,500), while moderate (CN=2.0) to well-established (CN=6.0) cavitation conditions were examined encompassing the cloud and vortical cavitation regimes with pertinent transient features, such as cloud-cavity shedding. 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 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 have been obtained utilising absorption imaging, where beam attenuation is not associated with scattering and refraction events, and hence can be explicitly correlated with the projected vapour thickness in line-of-sight measurements. A combination of the two methods is proposed, as it has been found is capable of quantifying the vapour content arising in the complex nozzle flow, while also faithfully illustrating the dynamics of the highly-transient cavitation features.
Viscous oils flowing in the geometrically-complex hydraulic circuits of earth-moving machines are associated with extensive friction losses, thus reducing the fuel efficiency of the vehicles and increasing emissions. The present investigation examines the performance effectiveness of different hydraulic oils, in terms of secondary-flow suppression and pressure-drop reduction. The flow of two non-Newtonian oil compounds, containing poly(alkylmethacrylate) (PMA) and poly(ethylene-co-propylene) (OCP) polymers, respectively, have been comparatively investigated against a base, monograde liquid through Particle Image Velocimetry. An 180 o curved-tube layout and a check-valve replica have been selected as representative examples of the hydraulic components comprising the hydraulic circuit. The flow conditions prevailing in the experimental cases are characterised by Reynolds-number values in the range 76-1385. Precursor viscosity measurements with shear rate along with a theoretical analysis conducted using the FENE and PTT models have verified the influence of viscoelasticity and/or shearthinning on the liquid flow behaviour. PIV results have demonstrated that viscoelastic effects setting in due to the OCP additives tend to reduce the magnitude of the secondary flow pattern, commonly known as a Dean-vortex system, arising in the curved geometry by as much as 15% on average compared to the base liquid. A similar flow behaviour was also demonstrated in the valve replica layout with reference to the geometry-induced coherent vortical motion in the constriction region, where a vorticity decrease up to 38% was observed for the OCP sample. On the contrary, the flow behaviour of the primarily shearthinning PMA oil was found to be comparable to that of the base oil, hence not presenting significant flow-enhancement characteristics.
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