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 J21: Multiphase Turbulence |
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Chair: Marcus Herrmann, Arizona State University Room: 250 E |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J21.00001: On the coalescence of bubbles in highly turbulent flows Vivek Kumar, Ardalan Javadi, Suhas Jain, Cyrus K Aidun The coalescence of bubbles immediately downstream of bubble-generating systems, such as regenerative pumps, has not been studied despite broad applications in gas-liquid systems for optimizing industrial processes in chemical reactors, petroleum transport, and wastewater treatment. The flow field here consists of a coalescence-dominated bubbly flow regime in an extremely high Reynolds number turbulent flow decaying rapidly downstream. Understanding the impact of the turbulent intensity/Weber number and air content on the rate of coalescence is important for developing reliable predictive models for process design in these applications. In this study, we explore the bubble dynamics in a duct connected downstream of a side-channel |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J21.00002: Turbulent boundary layer relaxation over an air layer Ozgur Orun, Tyler W Furry, Simo A Makiharju The relaxation of turbulent boundary layers (TBLs) exposed to a free surface formed by a thin air layer is investigated. A backward facing step of height, h = 6.35 mm, is used to facilitate air layer formation and fix the flow separation downstream of which liquid TBL goes from a solid wall to a free surface. Experiments are conducted in a recirculating water tunnel with a 1830 mm long, (152.4 mm)2 cross-section test section and a gas-liquid separation tank. Laser Doppler Velocimetry (LDV) is employed to measure boundary layer relaxation and Reynolds stresses as a function of free stream velocity, U∞, and streamwise direction, x. Incoming TBL ranges between 200 < Reτ < 300, and nominal air layer thickness is kept constant at tAL/h = 1.5. Nearest to the air-water interface, TBL is found to relax more rapidly than in other regions, resulting in an inflection point that moves toward the centerline as the streamwise distance evolves from x/h = 1 to 74. Reynolds stress peaks are found to diffuse and move away from the interface, approaching the centerline with increasing streamwise distance. Time-resolved PIV is employed to quantify diffusion (ν∇2Ω) and stretching/tilting (Ω⋅∇V) evolution of initially wall-attached eddies. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J21.00003: Recovering resolvable small scales in hybrid LES-DNS AMR modeling of phase interfaces via spectral differential filtering Nihar Rameshbhai Thakkar, Marcus Herrmann In typical Large Eddy Simulations (LES) of turbulent two-phase flows involving immiscible fluids, terms arising due to the discontinuity in density and viscosity at the interface as well as the surface tension force are difficult to model using only filter scale information and are thus often simplified or ignored. An alternative to traditional LES modeling is to avoid the closure problem by using adaptive mesh refinement (AMR) to aggressively refine the mesh from the LES scale to a fully resolved DNS scale at the phase interface such that the interface does not appear in any LES filter. The resulting closure problem is then reduced to two standard single phase sub-grid momentum flux closure problems. However, abrupt mesh resolution and corresponding filter scale transitions in LES suffer from several shortcomings like commutative errors, energy pile-up at fine to coarse mesh transitions, and a slow fill-in of newly resolved small scales at coarse to fine mesh transitions (Piomelli et al., 2006). |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J21.00004: Energy transfer mechanisms in compressible two-phase turbulent flows Niccolò Tonicello, Suhas Jain, Luis Hatashita Compressible two-phase turbulent flows play a fundamental role in many different fields of engineering interest from aeronautical to marine applications. Within this regime, the inter-scale and inter-phase mechanisms to transfer kinetic energy through the cascade can be linked to the effects of compressibility and surface tension. We propose a simple benchmark problem based on decaying homogeneous isotropic turbulence which is used to study these different mechanisms of energy transfers. In particular, explicit filtering is applied to DNS data to investigate the different terms that appear in the filtered kinetic energy equation, namely the pressure-dilatation, resolved surface tension power, and sub-grid scale production. We seek correlations between sub-grid terms with resolved scale terms. Filter widths are varied to capture the contribution of different scales. For instance, at large filter widths, where full bubbles represent under-resolved features, backscatter is observed due to the effect of surface tension. This work not only proposes a benchmark case, but also provides useful scale-by-scale analyses with the goal of optimizing sub-grid scales closure models, to be ultimately tested in a-posteriori Large-Eddy Simulations. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J21.00005: Heat transfer behavior and turbulence flow statistics for subcooled pool boiling on earth and ISS gravity conditions based on CFD Direct Numerical Simulations. Sara Youssoufi, Amir Riaz, Elias Balaras Subcooled pool boiling defines a system where the temperature of the bulk liquid is lower than the saturation temperature of the considered fluid. In engineering applications, the effect of subcooled pool boiling on heat transfer nucleate boiling is generally considered to be negligible. However, some research emphasizes an impact in shifting the boiling curve. The present work is based on CFD high-fidelity computing results using an in-house DNS solver to solve the Navier-Stokes equations for incompressible flow, coupled to mass, momentum and energy equations. A level set technique is used to track the interface liquid-vapor. Time advancement is achieved using a fractional step method. Sharp jumps are implemented in velocity, temperature, and pressure. A dynamic contact angle is considered. Simulations have been conducted on both earth gravity and International Space Station (ISS) gravity for different subcooling levels. |
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