Shadowgraph, Schlieren and interferometry in a 2D cavitating channel flow

Abstract

International audienceCavitation plays an important role in fuel atomization mechanisms but the physics of cavitation and its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required to support the development and the validation of numerical models and the design of tomorrow's injectors, in the context of pollutant and fuel consumption reduction. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test-oil (ISO 4113). Three different optical techniques are proposed to investigate the channel flow, with the pressure drop between upstream and downstream chambers as a parameter. A shadowgraph-like imaging technique allows the observation of cavitation inception and vapor cavities development throughout the channel. The technique also reveals the presence of density gradients (pressure or temperature) in the channel flow. However, this additional information is balanced by difficulties in image interpretation, which are discussed in the paper. In addition, a combination of Schlieren technique and interferometric imaging is used to measure the density fields inside the channel. The three techniques results are carefully analysed and confronted. These results reveal a wealth of information on the flow, with pressure waves generated by bubble collapses, turbulence in the wake of vapor cavities and bubble survival in flow regions of high pressure. Our results also show that cavitation inception is located in the shear layers between the recirculation zones and the main flow, relatively far from the inlet corner, where the pressure is minimum in average. To explain this behavior, we propose a scenario of cavitation inception based on the occurrence and the growing of instabilities in the shear layers

Numerical investigation of throttle flow under cavitating conditions

“…In any case, images from real-size nozzles do not have a good enough resolution to allow a detailed identification of flow structures. For that reason, several studies have been conducted in simplified nozzle geometries (Winklhofer et al, 2001;Mauger et al, 2012) that allow the use of experimental techniques such as Shadowgraph or Schlieren imaging. Experiments in these configurations have been used repeatedly for validation purposes of mathematical models for cavitation (Kärrholm et al, 2007;Som et al, 2010;Rakshit and Schmidt, 2012).…”

Near Nozzle Field Conditions in Diesel Fuel Injector Testing

“…In order to validate the choice of solver, several test cases were run and compared against the work of Mauger et al [21] (hereafter referred to simply as 'Mauger'). The Mauger experiment utilized a shadowgraph like optical setup with a narrow channel sandwiched between glass plates.…”

“…At the highest pressure drop the simulations at ΔP = 35 bar under predict the cavitation. [21] There may also be an effect from nominally small geometric differences between the nozzle inlet profile; in the calculations the model has 90° inlet while the Mauger test has a visibly larger angle with an inlet radius estimated to be up to 10μm.…”

Investigation of the effects of fluid properties representation and boundary condition selection in numerical simulations of micro scale flows with phase change

“…Nozzles are fundamental to a wide range of industrial processes such as spray painting, jet cutting and fuel injection systems. This application was chosen for a number of reasons: the geometry is simple and experiments for which measurements are available such as Winklhofer et al [31] or Mauger et al [18], the problem is of commercial interest (e.g. to support emissions regulations) and there exists a wide body of previous studies upon which to build.…”