Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C02: Minisymposium: State of the Art in Naval Hydrodynamics |
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Chair: Thomas Fu, Office of Naval Research Room: 2B |
Sunday, November 24, 2019 8:00AM - 8:26AM |
C02.00001: Physics of Naval Flows Invited Speaker: Thomas Fu The flow past a ship operating in the ocean is one of our most challenging physics problems. Looking at a ship operating in waves, we see a fluid sheet separating off the bow, a multiphase contact line along the hull waterline, spray and bubbles from wave breaking, air wakes, and Kelvin ship waves. Below the waterline, we see turbulent boundary layers, 3-D flow separation and vortices, cavitation, and the rotational flow from the propeller. We also have the ocean itself adding a layer of complexity. A marine platform interacts with the world through environmental and hydrodynamic forcing. The environment (waves, wind, and buoyancy/gravity) acts on the platform, and it acts on the environment (propulsor, hull, and control surfaces). However, a naval platform's performance is characterized by more than just its performance as a ship, and in fact, it might be a submarine, planing craft, or amphibious vehicle, and the performance is also now characterized by its ability to perform military missions and survive. To the list of technical areas we have already mentioned, fluid dynamics and oceanography, we can now add acoustics, heat transfer, and meteorology. As we have noted the complexity of naval flows due to the range of physical phenomena (turbulence, waves, wave breaking, cavitation, boundary layers, etc.), we should also note the complexity due to the range of spatial and temporal time scales involved. For the phenomena already mentioned, we are interested in length scales ranging from Kolmogorov to Rossby. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:52AM |
C02.00002: Progress and Challenges for Computational Naval Hydrodynamics Invited Speaker: Pablo Carrica Flows around surface and underwater marine vehicles present challenges that are unique to computational naval hydrodynamics. Hydrodynamics phenomena of interest where considerable challenges remain to model and simulate include some problems that have been under study for decades due to their importance also in other fields. Boundary layer transition is important for small autonomous underwater vehicles, tests of model surface ships and submarines, and immersed sensors. A wide range of spatial and temporal scales that not always can be decoupled results in the need of models to make problems tractable. Bubbles are relevant in cavitation and wakes, and can affect propeller performance, coupling the large scale flow and dynamics of a maneuvering ship in waves with the small scale of sheet and cloud cavitation. For single-phase flow problems governed by the ship scale, including the classic naval architecture areas of resistance, propulsion, seakeeping and maneuvering, great progress has been made over the past 20 years, but considerable challenges related to turbulence modeling, separation, free surface modeling and waves, dynamic stability, and others. Two-phase flows of interest include bubble entrainment and transport, cavitation and bubble dynamics, air layer drag reduction, sprays and drops, and bubbly wake dynamics, among others. Larger and faster computers and progress on numerical techniques have enabled ever larger computations resolving more and modeling less, allowing researchers to reveal important physics that are then incorporated in models operating at larger space and time scales. However, even in the most optimistic scenarios computers are still decades away from resolving all the scales of interest for naval flows, making modeling still necessary. After an introduction to computational naval hydrodynamics problems, the presentation will focus on the progress and challenges involved in simulation of cavitating and bubbly flows on marine vehicles. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:18AM |
C02.00003: Physics of Surface Piercing Bodies Invited Speaker: Anne Fullerton Most Navy vehicles operate at or near the free surface in order to meet mission requirements. As such, it is important to be able to accurately model and understand the physics of surface piercing bodies to inform the Navy of the vehicle's performance during these operations. Continual advances in computing power and the ever-increasing availability of supercomputing resources have changed the way computational physics solvers are used in the Navy. However, even with modern High Performance Computing (HPC) resources, it is not currently feasible to directly simulate all of the relevant physics of Navy vehicles beneath, at, and above the free surface for necessary real-world time scales. Most modern computational physics codes address these shortcomings by resolving down to the smallest scales allowed by given computational resources and modeling phenomena that occur below the finest resolved scales. This work will discuss necessary physics of surface piercing bodies, current modeling techniques, and how they ultimately affect predictions which are used to inform the fleet. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:44AM |
C02.00004: Spray Root Propagation on a Deforming Plate: Applications in Vessel Slamming Invited Speaker: Christine Gilbert The wedge water entry experiment is used to model slamming of high-speed craft in waves when a vessel becomes partially airborne. This classic experiment in the field of Naval Engineering is well-known and predicted using simple models when the plates of the wedge are rigid. In the current work, flexible plates fabricated from aluminum and composites are examined. The experimental measurements include hydrodynamic pressure on the plate, rigid body motions, structural response, and spray root propagation. Using the information on the location of the spray root and existing theories (such as Wagner 1932 and Vorus 1996), on the 2-D body, it is possible to predict the pressure distribution on the plate using only the location of the spray root. That pressure distribution prediction agrees well with both experimental pressure measurements and a coupled numerical tool developed specifically for the water entry problem. Additionally, it was found that even with structural response, measurements scale very well except in the regime of low drop heights. A hydroelasticity factor, $R$, first proposed by Faltinsen 1999, is used to determine regimes when the structural response alters the hydrodynamic loads. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 10:10AM |
C02.00005: Super-hydrophobics Surface for Skin Friction Drag Reduction in High Reynolds Number Turbulent Flow Invited Speaker: Steven Ceccio Since Onda et al. (1996) reported the development of super-hydrophobic surfaces (SHS) with a fractal topology, there has been significant world-wide activity in research related to the physics, material science, and manufacture of a wide variety of SHS’s. Liquids undergoing laminar flow over SHS’s may develop a Cassie-Baxter state at the flow boundary, and the presence of the gas pockets between rough surface asperities leads to a reduction in the shear stress compared to that of a smooth solid boundary, especially in flow channels where the slip length is on the order of the channel dimension (e.g. micro-fluidic devices). Yet, SHS’s influence on fully developed turbulent boundary layers (TBL) is unclear. In order to develop SHS’s that will reduce skin friction drag at high Reynolds numbers ($Re \geq 10^5$), our multi-university research group conducted a five-year effort focusing on five areas: (1) creation of optimized SHS’s for high Reynolds number - we developed methodologies to manufacture specific SHS’s with the desired surface energy and topology for the experimental examination of TBL modification at high Reynolds numbers; (2) examination of the interaction of near-wall flows with micro-scale surface gas pockets; (3) examination of the turbulence modification of micro-structured SHS’s by TBL flow; (4) development of SHSs for passive and active gas replenishment to develop and maintain the Cassie-Baxter condition; and (5) experimental validation of SHS drag reduction at high Reynolds Numbers. This talk will present an overall summary of the efforts results and conclusions. [Preview Abstract] |
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