Direct numerical simulation has been performed to explore the turbulence near a freely deformable interface in a countercurrent air–water flow, at a shear Reynolds number Re� = 171. The deformations of the interface fall in the range of capillary waves of waveslope ak =0 .01, and very small phase speed-to-friction velocity ratio, c/u� .T heresults for the gas side are compared to open-channel flow data at the same shear Reynolds number, placing emphasis upon the influence of the waves in the interfacial viscosity-affected region, and away from it in the outer core flow. Comparison shows a similarity in the distribution of the turbulence intensities near the interface, confirming that for the range of flow conditions considered, the lighter phase perceives the interface like a flexible solid surface, at least in the limit of non-breaking waves. Overall, in a time-averaged sense, the interfacial motion affects the turbulence in the near-interface region; the most pertinent effect is a general dampening of the turbulent fluctuating field which, in turn, leads to a reduction in the interfacial dissipation. Furthermore, the turbulence is found to be less anisotropic at the interface than at the wall. This is confirmed by the analysis of the pressure– rate-of-strain tensor, where the effect of interfacial motion is shown to decrease the pressure strain correlation in the direction normal to the interface and in the spanwise direction. The analysis of the turbulent kinetic energy and Reynolds stress budgets reveals that the interface deformations mainly affect the so-called boundary term involving the redistribution of energy, i.e. by the action of pressure, turbulent fluctuations and molecular viscosity, and the dissipation terms, leaving the production terms almost unchanged. The non-zero value of the turbulent kinetic energy at the interface, together with the reduced dissipation, implies that the turbulent activity persists near the interface and contributes to accelerating the turbulent transfer mechanisms. Away from the interface, the decomposition of the fluctuating velocity gradient tensor demonstrates that the fluctuating rate-of-strain and rate-of-rotation at the interface influence the flow throughout the boundary layer more vigorously. The study also reveals the streaky structure over the deformable interface to be less organized than over a rigid wall. However, the elongation of the streaks does not seem to be much affected by the interfacial motion. A simple qualitative analysis of the quasi–streamwise vortices using different eduction techniques shows that the interfacial turbulent structures do not change with a change of boundary conditions.

Direct numerical simulation of turbulence in a sheared air-water flow with a deformable interface

Interface tracking towards the direct simulation of heat and mass transfer in multiphase flows

Surface divergence models for scalar exchange between turbulent streams

Heat transfer—A review of 2003 literature

The efficiency of transfer of gases and particles across the air-sea interface is controlled by several physical, biological and chemical processes in the atmosphere and water which are described here (including waves, large- and small-scale turbulence, bubbles, sea spray, rain and surface films). For a deeper understanding of relevant transport mechanisms, several models have been developed, ranging from conceptual models to numerical models. Most frequently the transfer is described by various functional dependencies of the wind speed, but more detailed descriptions need additional information. The study of gas transfer mechanisms uses a variety of experimental methods ranging from laboratory studies to carbon budgets, mass balance methods, micrometeorological techniques and thermographic techniques. Different methods resolve the transfer at different scales of time and space; this is important to take into account when comparing different results. Air-sea transfer is relevant in a wide range of applications, for example, local and regional fluxes, global models, remote sensing and computations of global inventories. The sensitivity of global models to the description of transfer velocity is limited; it is however likely that the formulations are more important when the resolution increases and other processes in models are improved. For global flux estimates using inventories or remote sensing products the accuracy of the transfer formulation as well as the accuracy of the wind field is crucial.

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Transfer Across the Air-Sea Interface

The impact of interfacial dynamics or turbulent heat transfer at a deformable, sheared gas-liquid interface is studied using Direct Numerical Simulation (DNS). The flow system comprises a gas and a liquid phase flowing in opposite directions. The governing equations for the two fluids are alternated solved in separate domains and then coupled at the interface by imposing continuity of velocity and stress. The deformations of the interface fall in the range of capillary waves of waveslope ak=0.01 (wave amplitude a times wavenumber k), and very small phase speed-to-friction velocity ratio, c/u*. The influence of low-to-moderate molecular Prandtl numbers (Pr) on the transport in the immediate vicinity of the interface is examined for the gas phase, and results are compared to existing will-bounded flow data. The shear-based Reynolds number Re* is 171 and Prandtl numbers of 1, 5, and 10 were studied. The effects induced by changes in Pr in both wall-bounded flow and over a gas-liquid interface were analyzed by comparing the relevant statistical flow properties, including the budgets for the temperature variance and the turbulent heat fluxes

Direct Numerical Simulation of turbulent heat transfer across a mobile, sheared gas-liquid interface

Simultaneous void fraction and wall temperature measurements were made during bottom-reflooding of a vertical Inconel tube under both constant and oscillatory injection rates. To support interpretation of these data, flow regime visualization experiments were also conducted by reflooding a heated quartz tube. With constant, high reflooding rates, inverted annular, transition, and dispersed flow regimes exist above the quench front, with typical chordal-average void fractions in the ranges of 10–30 percent, 30–70 percent, and 70–90 percent, respectively. Each regime exhibits different heat transfer rates. With lower injection rates or higher heating rates, annular droplet and dispersed flow regimes appear with void fractions above 80 percent. For reflooding with oscillatory inlet flow and high injection rates, large oscillations are seen in void fraction and wall temperature, indicating periodic changes in the flow regime near the quench front: The regime alternated between inverted annular (during an upstroke) and annular droplet flow (during a downstroke). These flow regimes were observed in the flow visualization experiments to be qualitatively similar to those for the constant injection cases. Heat transfer rates are substantially affected by the flow regime and increase (or decrease) as the void fraction falls (or rises). Compared to the constant-injection tests, increased rates of entrainment were observed during the forced-oscillation tests.

Reflooding With Steady and Oscillatory Injection: Part I—Flow Regimes, Void Fraction, and Heat Transfer

Reflooding With Steady and Oscillatory Coolant Injection: Part 2—Quench Front and Liquid Carryover Behavior

Direct numerical simulation of turbulence in a counter—current air—water flow with a free deformable interface has been performed. The data are compared to those obtained for an open channel flow. Comparison shows a similarity in the distribution of turbulence intensities. The analysis of the turbulent kinetic energy and of the Reynolds stresses also reveals insignificant differences, except in the direction normal to the interface, where both the pressure transport and the dissipation of the Reynolds stress are higher than in the wall flow. Looking at the shear stress \({u'_1}{u'_3}\) reveals that the interfacial motion promotes drag reduction in the vicinity of the interface.

Direct Numerical Simulation of Turbulence and Interfacial Dynamics in Counter—Current Air—Water Flows

Direct Numerical Simulation of Turbulent Heat Transfer Across a Mobile, Sheared Gas-Liquid Interface impact of interfacial dynamics on turbulent heat transfer at a deformable, sheared

G. Yadigaroglu

Papers

Direct Numerical Simulation of turbulent heat transfer across a mobile, sheared gas-liquid interface

Reflooding With Steady and Oscillatory Injection: Part I—Flow Regimes, Void Fraction, and Heat Transfer

Reflooding With Steady and Oscillatory Coolant Injection: Part 2—Quench Front and Liquid Carryover Behavior

Direct Numerical Simulation of Turbulence and Interfacial Dynamics in Counter—Current Air—Water Flows

Direct Numerical Simulation of Turbulent Heat Transfer Across a Mobile, Sheared Gas-Liquid Interface impact of interfacial dynamics on turbulent heat transfer at a deformable, sheared