Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session A32: Environmental Flows |
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Chair: Jason Olsthoorn, Queen's University Room: 255 D |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A32.00001: Visual structures in laboratory generated buoyant plumes Blair Johnson, Biman Kalita, Luisa Florez Turbulent plumes are comprised of eddies and cauliform structures that visually highlight their dynamic nature as they develop in space and time. We present a series of laboratory experiments from which we analyze the visual signatures of turbulent buoyant plumes. We explore three different buoyancy conditions by mixing isopropyl alcohol into water released through a pipe at the base of a water tank, exploring Richardson numbers ranging from 1.4 to 2.0. By dyeing the plume mixture with fluorescein salt, with illumination provided by black lights, the plume exterior is visible for optical tracking. We capture the development of the starting plumes using continuous series of photographs collected at steady frame rates. A custom algorithm tracks the outline of the plume exterior, from which eddies and flow structures can be identified. We find the distribution of structure sizes follows a lognormal distribution. We find the plume spread angle to vary with initial buoyancy, and the front velocity to vary with buoyancy and Reynolds number. We perform spectral analysis on the edge signal of the plume from which we measure a slope of -2.2. We also explore the transition to turbulence as the plume begins to develop, with an interest in characterizing entrainment mechanisms and the dynamics of the interface between the turbulent plume fluid and quiescent ambient fluid. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A32.00002: Physics-informed and AI-supported Methane Plume Point-source Identification Julianne Chan, Ruo-Qian Wang
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Sunday, November 24, 2024 8:26AM - 8:39AM |
A32.00003: Turbulent Buoyant Plumes from Time-Varying Sources Zichuan Li, Alexis K Kaminski Turbulent buoyant plumes occur in a wide range of natural and industrial processes, including wildfires, volcanic eruptions, and methane leaks. As a plume rises, it expands due to the entrainment of ambient fluid at its edges. Previous research has explored the turbulent dynamics and corresponding entrainment of both steady plumes and starting plumes with steady source conditions via analytical, experimental, and numerical approaches. However, the behavior of turbulent buoyant plumes arising from time-varying sources has received comparatively less attention. In this study, we use direct numerical simulations to investigate the dynamics and entrainment processes of plumes driven by time-varying sources. We connect these processes to the structure of the overall plume and the turbulent features at the plume edge. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A32.00004: Experimental comparison of vertical buoyant plume dynamics produced by pre-mixed and diffusion flames and Aspen wood wool combustion Tyler Moore, Nathan Edward Murray A further understanding of turbulent plume dynamics produced from wood combustion is desirable to aid wildfire management and prevention and prescribed burn efficiency. Plume dynamics from Aspen wood wool combustion are compared to those created from pre-mixed and diffusion gas combustion. Multiple gas burner configurations are employed, allowing for varying plume structures. As wood combustion is transient, wood wool is packed into cylindrical shell geometries to encourage a steadier burn. Data is gathered via shadowgraph imaging utilizing a large-scale retroreflective screen at the USDA Forest Products Laboratory. Convective velocities are readily obtained by tracking the movement of density fluctuations and turbulent eddies in the plume. Analysis of the stability of these plumes is discussed. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A32.00005: Gravity currents under oscillatory forcing Herman Clercx, Cem Bingol, Rui Zhu, Eckart Heinz Meiburg, Matias Duran Matute We investigate the evolution of two-dimensional gravity currents, resulting from the well-known lock-exchange set-up, when they are affected by an external oscillatory forcing introduced by superimposing a horizontally uniform oscillating pressure gradient. We explore the effect of the velocity amplitude of the applied oscillating flow and its period of oscillations on the behavior of the evolving gravity currents. A key element introduced by the external forcing is the Stokes boundary layer near the no-slip bottom wall generating differential advection resulting in lifting of the gravity current. We have explored the effect of lifting on current propagation and the density structure of the current front. Our study shows the existence of significant effects of an oscillatory forcing on the dynamics, advection, and mixing properties of gravity currents. |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A32.00006: Gravity Currents Flowing Over an Array of Obstacles Craig McConnochie, Alex Meredith, Roger Nokes, Claudia Cenedese We experimentally investigate the density and velocity structure of a gravity current as it interacts with, and flows over, an array of closely spaced obstacles. Measurements of the fluid density and velocity are used to understand the transient response of the current as it interacts with the array of obstacles, with heights ranging from 18 - 50% of the fluid depth. As the current flows over the array, convective instabilities at the base of the current lead to mixing, in addition to that due to shear instabilities on the upper edge of the current. The additional mixing causes the front velocity of the current to reduce, as well as the density in the head of the current. Unlike when the obstacle array is sparsely packed, the current in maintains the head and tail structure of a smooth bed gravity current, despite the decreased density within the head. The velocity profiles are dependent on the obstacle height, which determines both the position of the current in relation to the obstacle array, and the strength of the return flow at the base of the tank. The experimental results provide a detailed understanding of the transient interaction of a gravity current with a closely spaced obstacle array, including the current structure, and the dominant mixing processes. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A32.00007: The Cooling Box Problem: What does the water surface freeze? Jason Olsthoorn In environmental systems, such as lakes, the boundary condition at the air-water interface depends upon the atmospheric forcing and the induced convection. These processes are particularly important for seasonally ice-covered lakes, as they determine, in part, when the lake will freeze. To study this, we performed three-dimensional direct numerical simulations of surface-driven convection near the temperature of maximum density $\tilde T_{md}$. In this system with a nonlinear (quadratic) equation of state, we identified three convective regimes: (1) free convection when the water temperature is above $\tilde T_{md}$, (2) penetrative convection when the surface water temperature is below $\tilde T_{md}$ and the system is vigorously convecting, and (3) decaying convection when the system transitions to a laminar state. We discuss predictions for the regime transitions. Our hope is that this will lead to better estimates for the timing of ice-formation in lakes and other natural systems. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A32.00008: Bubble curtain dynamics in lock-exchange flows Shravan K.R. Raaghav, Ronald Driessen, Tom O'Mahoney, Robert Uittenbogaard, Herman Clercx, Matias Duran Matute Bubble curtains are commonly used in shipping locks to mitigate saltwater intrusion that occurs when the lock gate is opened for ships. The opening of the lock gate results in a lock-exchange flow where the denser salty water flows underneath the lighter freshwater in the form of a gravity current. The vertical momentum of the bubble curtain impedes the gravity current flow. We employed Euler-Euler large eddy simulations to model bubble curtains in a lock-exchange configuration and varied the problem’s parameters (water height – H , density difference – △ρ and air flow rate – qair) covering a wide range of Froude air number Frair = (gqair)1/3 (g'H)-1/2 values, with g the gravitational acceleration and g' the reduced gravity. The effectiveness of a bubble curtain is characterized by the amount of salt water that is blocked by it in comparison with the case without a bubble curtain. We compare the effectiveness as a function of Frair from simulations with recent experimental results (Bacot et al., JFM 941, A1, 2022) , showing a very good agreement. The results are further used to construct and test an analytical model for the effectiveness, and scaling relations for the typical velocity, length and mixing time scales of the recirculation cells present on each side of the bubble curtain. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A32.00009: Physics of large-scale subsea releases of CO2 Paal Skjetne, John C Morud, Jan E Olsen With offshore CCS projects gaining momentum, extensive research has focused on understanding chronic reservoir leaks (bubble trains and swarms) and their environmental impacts. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A32.00010: Turbulence and Pseudo-turbulence in Buoyancy-Driven Bubbly Flows: An Interface-Resolved DNS Approach Abbas Moradi Bilondi, Luca Brandt, Salar Zamani Salimi, Prasad Perlekar, Parisa Mirbod Bubbly flows affect mixing and mass transfer in chemical reactors, nuclear reactor cores, and wastewater treatment plants. By employing interface-resolved direct numerical simulations with a conservative diffusive interface method, this study explores bubble-induced turbulence, especially near-wall turbulence, and energy budgets in a flow with 2.7% volume fraction deformable air bubbles dispersed in water, and with density and viscosity ratios of 0.001 and 0.01, respectively. Our investigation focuses on how key dimensionless parameters such as Galilei number (ranging from 390 to 1100) and Eötvös number (ranging from 0.85 to 8.5) affect flow dynamics and energy budgets. Our findings reveal distinct bubble distribution patterns influenced by the Eötvös number. With lower bubble deformability (Eo = 0.85), bubbles predominantly accumulate near walls, while fewer bubbles are found in the center, exhibiting a more uniform central distribution. In contrast, higher deformability (Eo = 8.5) enhances breakup dynamics and causes bubbles to concentrate in the center, with fewer near the walls. This redistribution of bubbles significantly impacts the upward flow pattern, increasing the flow rate and fluctuations in the channel center and decreasing them near the walls. Furthermore, higher Galilei numbers lead to increased mean and fluctuation velocity statistics and elevated vorticity levels within the viscous sublayer, which in turn enhances the dissipation rate, particularly near the walls. |
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