Numerical simulation and analysis of multi-scale cavitating flows

Ghahramani, Ebrahim; Ström, Henrik; Bensow, Rickard

doi:10.1017/jfm.2021.424

Cited by 51 publications

(13 citation statements)

References 44 publications

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“…To overcome this limitation, some studies implemented a hybrid multiscale model that used the Eulerian mixture model to capture large cavity structures, and Lagrangian model to predict small sub-grid structures. 110,135 Recently, Ghahramani et al 110 investigated the capability of the hybrid model to capture the cavity dynamics in a multiscale problem. Their results exhibited a very good compatibility with the experiments, particularly in capturing the inception location and vapor packet volumes.…”

Section: ) Experimental and Numerical Methods Of Micro-scale Cavitati...mentioning

confidence: 99%

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

et al. 2022

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Section: ) Experimental and Numerical Methods Of Micro-scale Cavitati...mentioning

confidence: 99%

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

et al. 2022

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“…Given the more recent findings noted above, it is likely that any variation of free-stream nuclei populations with dissolved gas level, both within and between the three facilities, may have contributed to the variation in the results, although nuclei populations were not measured in these experiments. In simulating cavitating flows the incorporation of nuclei has resulted in the capture of a number of features of inception and developed cavity dynamics as reported by Hsiao, Ma & Chahine (2017) and Ghahramani, Ström & Bensow (2021). An aim of the current work is to provide a high quality data set which may be useful to further improve these nuclei models and increase the fidelity of the physics captured within simulations.…”

Section: Introductionmentioning

confidence: 95%

Nucleation effects on cavitation about a sphere

2022

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The influence of nucleation on cavitation about a sphere from inception through to supercavitation at a transcritical Reynolds number of $1.5\times 10^{6}$ is investigated experimentally. Two extreme free-stream nuclei populations, deplete and abundant, were investigated. Unsteady surface pressures from two sensors on opposing sides of the sphere were acquired simultaneous with high-resolution high-speed photography at cavitation numbers between 1.0 and 0.3. High-resolution spectrograms derived from these measurements reveal principally bi-modal shedding in attached and detached regimes. Correlations between unsteady pressure measurements show the high modes to be axisymmetric and low modes asymmetric. Modal topology is also discerned from the high-speed imaging. The bi-modal shedding for lower cavitation numbers is driven by coupled re-entrant jet formation and upstream shockwave propagation. The attached regime is shown to have two sub-regimes. For the abundant case, the continuous supply of activated nuclei around the sphere periphery in the first bi-modal regime has the effect of driving the high symmetric mode preferentially over the asymmetric low mode compared with the deplete case. For the first bi-modal regime, frequencies were unaffected by nucleation changes although peak responses were centred at a cavitation number of about 0.8 for the deplete and 0.825 for the abundant. For the second attached regime, where cavity lengths are of the order of the sphere size, changes in nucleation altered frequencies and amplitudes of peak unsteady pressures. For the abundant case, the continuous nuclei supply significantly reduced coherence with modal peak amplitudes reduced by an order compared with the deplete case. Continuous nuclei activation increased the probability of the high mode over the low compared with the deplete case but to a lesser extent than the first regime. Nuclei activations also significantly reduced inter-cavity and cavity durations, but not growth and collapse phases, which increased modal frequencies compared with the deplete case. The second regime asymmetric low mode topology, for both nucleation cases, is shown to be alternate shedding of oblique vortices from diametrically opposing sides of the sphere similar to low Reynolds number shedding about spheres and other axisymmetric bluff bodies in single-phase flows.

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“…This aspect can be revised and improved, for example by considering a reference time T re f obtained from laboratory tests or taking advantage of literature research. For example, in [9] the authors used a condensation coefficient smaller than the vaporization one, because of different time scales of the two processes. We calculate the coefficients C c and C v related to the three cavitation models (Kunz, Merkle and Saito) such that the transition from α = 0.9 to α = 0.1 takes place in the time interval T re f .…”

Section: Condensation/vaporization Coefficients Set Upmentioning

confidence: 99%

“…Among others, the Eulerian front-tracking techniques [7], and the Euler-Lagrangian methods [8], suitable for small-scale processes, where a countable number of bubbles is present. More recently, the Eulerian-Lagrangian method has been improved to treat multiscale processes characterized by the simultaneous presence of bubbles and sheet cavitation (see the very recent paper [9]). For engineering applications, homogeneous mixture methods are commonly employed, due to their practicality and adaptability to large-scale cavitation cases.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Performance of Cavitation Models with Analytically Calculated Coefficients

2021

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Cavitation is often simulated using a mixture model, which considers the transport of an active scalar, namely the vapor fraction αv. Source and sink terms of the transport equation of αv, namely vaporization and condensation terms, rule the dynamics of the cavity and are described through different models. These models contain empirical coefficients generally calibrated through optimization processes. The purpose of this paper is to propose an analytical approach for the calculation of the coefficients, based on the time scales of vaporization and condensation processes. Four different models are compared considering as a test-case a two-dimensional flow around a cylinder. Some relevant quantities are analyzed both for standard value of coefficients, as found in the literature, and the coefficients calculated through the analytical approach. The study shows that the analytical computation of the coefficients of the model substantially improve the results, and the models considered give similar results, both in terms of cavitation regime and mean vapor fraction produced.

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Numerical simulation and analysis of multi-scale cavitating flows

Abstract: Abstract

Cited by 51 publications

References 44 publications

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

Nucleation effects on cavitation about a sphere

Analysis of Performance of Cavitation Models with Analytically Calculated Coefficients

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