Free Surface Flow Phenomena Effects on MHD flow

Free Surface Flow Phenomena: Effects on MHD flow control and interfacial transport Mohamed Abdou DOE Budget Meeting, Germantown March 13, 2001

What is a truly “free” surface? • Constant pressure, moving boundary unable to support an applied pressure gradient or shear stress. • Term is often used for any gas/void to liquid interface where material properties change dramatically and surface tension or wave phenomena is observed. Bubble rising and coalescence - Kunugi Calculation Shear layer instability at water surface - Dabari data

Important free surface flow phenomena affecting flow control and interfacial transport • Modification of turbulence and secondary flows by free surface • MHD interactions with turbulence, bulk flow, and surface stability • Turbulence production and movement in complex geometries • Variation of physical properties with scalar temperature/concentration Turbulence structures generated at the liquidsolid interface heavily effect heat and mass transfer across interface (Illustration from Rashidi)

Free surfaces flow phenomena are critical in many industrial and scientific processes • Liquid Jet and Film Stability and Dynamics: fuel injection, combustion processes, water jet cutting, ink jet printers, continuous rod/sheet/ribbon/sphere casting, flood/jet soldering, ocean waves, boat hull design, ocean/river structure engineering, surfing, liquid walls for fusion • Liquid MHD / free surface interactions: melt/mold stirring and heating, liquid jet/flow control and shaping, crystal growth, astrophysical phenomena, liquid metal walls for particle accelerators and fusion reactors • Liquid MHD / turbulence interactions: microstructure control in casting, boundary layer control, astrophysical dynamos and plasmas, liquid walls for particle • Free surface heat and mass transfer: oceanography, meteorology, global climate change, wetted-wall absorbers/chemical reactor, condensers, vertical tube evaporator, film cooling of turbine blades, impurity control in casting, liquid walls for particle accelerators and fusion reactors Turbulent flow effect on dendrite formation in casting - Juric simulation

Temperature Rise (K) What is Global Warming? Increasing Green House Gases: Humidity, CO 2, Methane, NOx, Sox etc. Infra Red Absorption into Green House Gases and on the Earth surface I. R. Absorption Sun Earth I. R. Radiatio n Preserving Heat in the Air Temperature Rise in the Air I. R. : Infra Red Year

Free surface mass transport is affecting CO 2 concentrations Missing Sink Problem over past 30 years Measured atmospheric CO 2 increase (34 ppm) - Spent Fossile Fuel emissions (61 ppm) = Missing Sink(-27 ppm) ? Turbulent Heat and Mass transfer across Free Surface ? Wind flow Free surface contour wind-driven calculation CO 2 absorption at the turbulent free-surface deformed by the shear wind, by means of direct numerical solution procedure for a coupled gas-liquid flow

Coherent Structures in Wind-driven Turbulent Free Surface Flow Wind Water Atmospheric Pressure Contour Surface (Green) High Speed Gas Side Regions (Brown) High Speed Water-Side Regions (Blue) Streamwise Instantaneous Velocity (Color Section)

Some Common Aspects between Global Warming Problem and Fusion Science Thermofluid Research Similar Phenomena • High Pr flow with radiation heating at free surface from plasma • High Sc flow with CO 2 absorption at free surface of sea Similar Flow Characteristics • Re is high, both have the similar turbulence characteristics. • MHD (fusion) and Coriollis (global warming) forces can influence the average velocity Heat and Mass Transfer Similarity • High Pr, very low thermal diffusivity->very thin thermal boundary layer->large temperature gradient at interface • High Sc, very low molecular diffusivity->very thin concentration boundary layer->large concentration gradient at interface.

Liquid Jet Stability and Breakup commercial Injet Printer quality is hampered by formation of “satellite” droplets Micro-injector increases relative importance of surface tension by decreasing size eliminates satellite droplets and improves precision micro Simulation of commercial inkjet by Rider, Kothe, et al. Data from Ho

Vertical B field effects on Liquid Metal Film Flows Continuous sheet casting can achieve smoothly increasing film thickness control via MHD forces Film thickness profiles for various Hartmann Numbers Simulation by Lofgren, et al.

Liquid Jet Research for IFE Chambers High-velocity, oscillating jets for liquid “pocket” • flow trajectory and jet deformation • primary breakup / droplet formation • dissembly processes • liquid debris interaction / clearance • partial head recovery High-velocity, low surface-ripple jets for liquid “grid” • surface smoothness control • pointing accuracy / vibration • primary breakup / droplet ejection Graphics from UCB

Oscillating jet experiments and simulations • Single jet water experiments and numerical simulations show proper trajectory at near prototypic Re • Turbulent eddy effect on droplet ejection is accurately modeled in either experiment or simulation Data from UCB Simulations from UCLA Regions flattened by interaction with neighboring jet

Modeling of Stationary Jet Deformation • Initially rectangular jets deform due to surface tension and corner region pressurization in nozzle • Capillary wave fans from corner regions propagate across jet face - largest source of surface roughness • Numerical simulations with integral turbulence models are being used to redesign nozzle shape and exit cross-section to avoid these effects.

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