Abstract
This paper provides new physical insight into the coupling between flow dynamics and cavitation bubble cloud behaviour at conditions relevant to both cavitation inception and the more complex phenomenon of flow “choking” using a multiphase compressible framework. Understanding the cavitation bubble cloud process and the parameters that determine its break-off frequency is important for control of phenomena such as structure vibration and erosion. Initially, the role of the pressure waves in the flow development is investigated. We highlight the differences between “physical” and “artificial” numerical waves by comparing cases with different boundary and differencing schemes. We analyse in detail the prediction of the coupling of flow and cavitation dynamics in a micro-channel 20 μm high containing Diesel at pressure differences 7 MPa and 8.5 MPa, corresponding to cavitation inception and "choking" conditions respectively. The results have a very good agreement with experimental data and demonstrate that pressure wave dynamics, rather than the “re-entrant jet dynamics” suggested by previous studies, determine the characteristics of the bubble cloud dynamics under “choking” conditions.
Highlights
Cavitation has been the subject of intensive research for decades due to its relevance to many engineering applications such as micro-channel flows, fuel injectors and propellants [1,2]
Based on the previous observations, in the first half of our paper we present a sensitivity analysis in order to further examine the effects that the boundary conditions and the differencing schemes have on the predictions of the cavitation dynamics in a micro-channel with emphasis on the cavitation bubble cloud behaviour
We initially discuss the sensitivity of the flow dynamics to the differencing schemes (i.e., Linear-upwind stabilised transport (LUST) and MUSCL) of the divergence terms and results are presented for two different outlet pressures, one representing the onset of cavitation and one representing the critical cavitation
Summary
Cavitation has been the subject of intensive research for decades due to its relevance to many engineering applications such as micro-channel flows, fuel injectors and propellants [1,2]. As the cavitation region evolves, and once a critical cavitation number is reached, cloud break-off occurs. During this process the cavity volume oscillates in either an intermittent or periodic manner. Understanding the mechanisms that govern the cloud break-off process, as well as the frequencies at which it occurs, is important since cloud break-off is linked to effects such as loss of lift in hydrofoil applications, and more generally to unwanted vibration and erosion. Lower values indicate a higher probability of cavitation [3]: P0 − Pv
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