3d Simulation of Turbulent and Cavitating Flow for the Analysis of Primary Breakup Mechanisms in Realistic Diesel Injection Processes

Numerical simulation of cavitating flow in maritime high-pressure direct fuel injection nozzles and assessment of cavitation-erosion damage

“…In fact, the spatial resolution of an LES was assessed 15 by the ratio of average cell size Δ x to Kolmogorov length scale η , which should amount to Δ x / η < 12 , according to Fröhlich et al 55 In the present study, we have Δ x ≈ 10 μ m and assuming the same dissipation rate as for the injector by Blume et al, 15 we obtain η ≈ 0 . 9 μ m and therefore Δ x / η ≈ 11 . Thus, we deem our resolution sufficient for a scale resolving simulation, keeping in mind that here a simplified turbulence treatment in terms of the omission of a sub-grid scale model is considered as discussed in the previous section.…”

“…In order to maintain a high grid quality during the complete injection cycle in the needle seat passage, the same grid motion methodology as described by Blume et al 15 is utilised. Thus, the grid movement is realised piecewise in five intermediate intervals for opening and closing each.…”

“…However, care must be taken when investigating fixed needle configurations, since important transient effects might not be captured if needle motion or the complete injection cycle is not taken into account in the simulation. 14,15 Entire injection cycles with moving needles have been investigated. 6,7,14,[16][17][18][19] For some of these studies, 6,7,16,17,19 erosion analysis was carried out as an integral over the entire period of the cycle by employing different quantities as erosion risk indicators: either Mean Depth of Penetration Rate (MDPR) 6,7,17 by a coupling of the CFD method with the ductile 1D erosion model by Franc 20 or acoustic pressure from single bubble collapses as well as mean and standard deviation of vapour volume fraction.…”

“…However, care must be taken when investigating fixed needle configurations, since important transient effects might not be captured if needle motion or the complete injection cycle is not taken into account in the simulation. 14,15…”

Combined visualisation of cavitation and vortical structures in a real-size optical diesel injector

“…Focusing on the internal flow of fuel injectors, refractive index gradients in all the aforementioned techniques set in due to the presence of liquid/vapour interfaces, hence the underlying velocity field cannot be assessed. Nevertheless, an illustration of the in-nozzle level of turbulence and coherent secondary-flow patterns is crucial for the evaluation of the device performance, since LES have highlighted their strong independence with cavitation and, consequently spray evolution (Ghiji et al 2017;Blume et al 2019;Koukouvinis et al 2020). It has to be noted that micro-PIV techniques which are, in principle, suitable for the flow-field illustration in microfluidics devices have scarcely been applied to optical injectors (Chaves et al 2010;Kolokotronis et al 2010;Hayashi et al 2012;Mamaikin et al 2020).…”