Free surface turbulence: Exploration and validation of multiphase CFD
Abstract
Multiphase turbulent flows are ubiquitous in surface ship hydrodynamics, contributing to the persistence of wakes with associated signatures. Field data have characterized bubble distribution in the wake and found that bubbles in the 100-200 ?m-diameter range persisted over several nautical miles. While bubble aging sets this end state, it is important for ONR to better understand the source of bubble formation (i.e. entrainment) as well as fragmentation mechanisms. Elucidating the entrainment and fragmentation processes has been an active field of study in naval hydrodynamics as well as physical oceanography and chemical engineering. The main fragmentation model is based on the seminal work of Hinze. While the main experimental dataset supports this model, recent work by an ONR supported group challenges this assumption and provides a more physical argument. Experimental data are necessary to confirm the new model. Air entrainment mechanisms are being continuously improved, but still suffer from much empiricism, due to lack of experimental evidence of the processes at play. Therefore, the temporal evolution of the distribution of bubbles as well as their source of entrainment still need to be answered fundamentally. While numerical models keep getting more sophisticated and refined, it is not possible to simulate a full wake with direct simulations. However, direct simulations can elucidate a subset of the processes at play and the results inform lower level models when bubble distributions are modeled. Furthermore, single phase flows can be simulated directly (if mass or heat transfers are not present); however, the introduction of a sharp discontinuity in the liquid-air interface forces a certain level of modeling in particular to capture break-up and coalescence. Thus, there is a need for experiments of adequate spatiotemporal resolution to gain fundamental knowledge, improve models, and provide validation datasets. It is expected that the joint experimental and numerical tools will improve prediction and mitigation of wakes. The main objectives of the proposed work are to conduct a detailed experimental campaign in multiphase flows to answer assumptions that challenge existing models, while providing comprehensive validation datasets. Specifically, two phenomena of importance to naval hydrodynamics will be explored: 1- Air entrainment from turbulent water flow 2- Bubble fragmentation The experimental objectives have been set in conjunction with numerical teams funded by ONR. Two experimental facilities will be used and state of the art diagnostics developed. Specifically, we will develop 3- Profilometry technique to resolve surface profiles in three dimension and time, coupled with velocity directly below, and 4- An imaging technique to resolve bubble distribution in high void fraction
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 20, 2020
- Source ID
- N000142012758
Entities
People
- Philippe Bardet
Organizations
- George Washington University
- Office of Naval Research
- United States Navy