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 X27: Flow Instability: Rayleigh-Taylor Instability |
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Chair: Denis Aslangil, Colorado School of Mines Room: 251 E |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X27.00001: Experiments on the two- and three-layer Rayleigh-Taylor instability Ryan C Ahearn, Jeffrey W Jacobs Incompressible Rayleigh-Taylor instability experiments are presented in which two or three stratified miscible liquids having Atwood number of 0.3 at each interface are accelerated in a vertical linear induction motor driven drop tower. A test sled capable of only vertical motion contains the experiment tank and visualization equipment. The sled is positioned at the top of the tower within the linear motors, then is accelerated downward causing the initially stable interface or interfaces to become unstable and allowing the Rayleigh-Taylor instability to develop. Forced initial perturbations are produced by vertically oscillating the test sled prior to the start of acceleration. The experimental tank is illuminated with a white backlight. Video is recorded with a monochromatic high speed video camera allowing for the measurement of mixing layer growth rates for both the single- and two-interface cases. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X27.00002: Rayleigh-Taylor turbulence in its many shapes and sizes: understanding self-similar growth using statistically stationary minimal flow units Chian Yeh Goh, Guillaume Blanquart Self-similar Rayleigh-Taylor (RT) turbulence is studied using statistically stationary RT simulations of varying aspect ratios. Two key steps are taken to achieve flow stationarity. First, a coordinate transformation based on self-similar scaling is applied to the governing equations. Second, the transformed equations are evaluated at a specific mixing layer height. The resulting equations simulate statistically stationary RT (SRT) flow. In SRT flow, the mixing layer height, h, reaches a stationary value, and flow structures are observed to grow laterally until they reach the domain size, L. Leveraging these box-filling tendencies, the lateral domain length is varied at constant mixing layer height to generate SRT minimal flow units (MFUs) of different aspect ratios, h/L. Growth parameters, mixedness, correlation lengths, and planar-averaged statistics are presented as a function of aspect ratio and supported by theoretical scaling analyses. Finally, these SRT results are considered within the context of traditional temporally growing RT (TRT) flow. In TRT flow, observed values for the self-similar growth parameter, α, span a large range of values (0.02 - 0.12). This lack of agreement is commonly attributed to differences in initial conditions. We show that SRT MFUs can indeed reproduce flow dynamics with a similar range of α, establishing a possible relationship between the aspect ratio of a SRT flow with the initial conditions of a TRT flow. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X27.00003: Atwood number effects in statistically stationary Rayleigh Taylor turbulence Daniel Brito Matehuala, Chian Yeh Goh, Guillaume Blanquart The effect of Atwood number, A, on Rayleigh-Taylor (RT) turbulence is studied using a statistically stationary Rayleigh-Taylor (SRT) flow configuration. The SRT flow configuration represents the flow dynamics of late-time self-similar RT growth in the limit of small wavelength initial perturbations, and has been validated with the direct numerical simulation results of Cabot & Cook (2006) at A=0.5. Due to stationarity, SRT flow can be simulated over a long time at the same flow condition, leading to excellent statistical convergence. This is particularly useful for higher Atwood number cases that are challenging to simulate in the traditional temporally evolving RT configuration. We present justifications for the validity of the flow configuration beyond A = 0.5, and apply it to Atwood numbers in the range of 0.01 – 0.8. Results are validated against others in the literature. Scalings are proposed for ensemble-averaged quantities to obtain normalized profiles that are independent of the Atwood number, and analytical fits to these normalized profiles are examined. Finally, the consistency of the scaling analysis and model profiles are verified using the ensemble-averaged transport equations. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X27.00004: Investigation of the multilayer Rayleigh-Taylor instability with simultaneous velocity and three-layer volume fraction measurements Quinton Dzurny, Prasoon Suchandra, Samuel Petter, Devesh Ranjan The Rayleigh-Taylor instability (RTI) in a multi-layered environment is investigated through statistically stationary experiments conducted in a blown-down three-layer gas tunnel. The top and bottom layers of the gas tunnel are air, while an air-helium mixture is used for the lighter middle layer. This setup creates a three-layer stratification with an upper RTI unstable interface between the middle and top layers, and a lower RTI stable interface between the middle and bottom layers. Simultaneous particle image velocimetry (PIV) and two-tracer planar laser induced fluorescence (PLIF) are employed to resolve the velocity and volume fraction of each fluid layer. The two-tracer PLIF technique was developed to overcome the limitations of previous studies, which were limited by single-tracer PLIF measurements, only resolving the volume fraction of one fluid layer at a time. Velocity and volume-fraction profiles are presented for Atwood numbers ranging from 0.3 to 0.5. With two-tracer PLIF, the interactions and mixing between different fluid layers are examined using quantitative parameters such as molecular mixedness. The relationship between fluid layer interactions and the velocity field is also discussed. This work contributes to the understanding of RTI in a multilayer configuration, which is particularly significant for inertial confinement fusion (ICF) pellet design, as well as atmospheric and oceanic flows. Additionally, it provides measurements of parameters that aid in the development and validation of turbulence closure models for variable density flows. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X27.00005: Role of the magnetic fields on the evolution and dynamics of Rayleigh-Taylor instability Manohar Teja Kalluri, Andrew Hillier The magnetic Rayleigh Taylor instability (MRTI) is ubiquitous in a wide range of astrophysical and laboratory systems. However, the evolution and the dynamics of MRTI is not fully understood. Magnetic fields play a crucial role in the instability dynamics of these systems. Towards understanding the interplay between gravity and magnetic forces on the evolution of instability, we study MRTI under simplified setting using analytical and numerical techniques. Our study shows that the imposed magnetic field hinders the self-similarity of MRTI evolution. However, when sufficiently evolved, MRTI converges towards self-similar behaviour with the same temporal scaling as the HD instability. The study revealed various physical processes, like energy dissipation (ED), kinetic and magnetic energy partition, anisotropy that determine the non-linear growth of instability across a wide range of magnetic field strengths. A particularly interesting finding is the drastic increase in energy dissipation with marginal increase in field strength, with magnetic ED thrice the kinetic ED for all field strengths. To understand this surprising behaviour, we investigate the potential role of magnetic reconnection. Thus, the current study presents a comprehensive understanding on the influence of magnetic fields on the evolution and growth of non-linear MRTI, and the impact of magnetic reconnection on MRTI dynamics. The unspecialized configuration meant the results are applicable in a wide range of practical systems. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X27.00006: Atwood effects on nonlocality of mean scalar transport in three-dimensional Rayleigh-Taylor Instability Dana Lynn Lavacot, Brandon E Morgan, Ali Mani Previous work used the Macroscopic Forcing Method (MFM), a numerical method for determining closure operators, to show the importance of nonlocality in modeling mean scalar transport for the 2D low-Atwood (A=0.05) Rayleigh-Taylor (RT) instability (Lavacot et al., JFM, 2023). In this work, nonlocality of mean scalar transport in 3D variable density Rayleigh-Taylor instability is investigated. Three cases of different Atwood numbers (A=0.05, A=0.5, A=0.8) are studied, and MFM is extended to the variable density problem. In higher-Atwood cases (A>0.05), asymmetry of the eddy diffusivity moments is observed, and nonlocality is found to increase in importance as Atwood number increases. Implications of these results on modeling variable density RT mixing are discussed. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X27.00007: Numerical Study of Plasma Rayleigh-Taylor Instability with External Magnetic Field Zhaorui Li, Daniel Livescu In this study, we investigate the effects of externally imposed magnetic field, B0, on the suppression of Rayleigh-Taylor instability (RTI) under ICF deceleration stage conditions. The numerical results, using a two-fluid plasma model with full magnetic field dependent molecular transport, reveal that the rapid growth of self-generated magnetic field and current density in the early (linear) stage of RTI are primarily caused by the stretching or bending of B0. For simulations with weak B0 or large reference plasma beta β0, RTI can grow into nonlinear stage in which the peak value of self-generated magnetic field is about two order magnitude larger than that of B0. However, when β0 is below a critical value, the magnetic torque can completely offset the baroclinic torque in vortex generation, which fully inhibits RTI development beyond the linear stage. Our study also discovers that, for suppressing RTI development, imposing B0 in the horizontal direction is more effective than that in the vertical direction and the critical values of β0 found for B0 imposed in the horizontal and vertical directions are about 100 and 1, respectively. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X27.00008: RTI dynamics in various Knudsen - Mach parameter regimes. Swapnil Majumder, Daniel Livescu, Sharath S Girimaji Rayleigh-Taylor instability (RTI) is important in a variety of flows, including inertial confinement fusion (ICF). In ICF, RTI is known to occur over a range of Knudsen and Mach numbers. At low Knudsen numbers and high Mach numbers, RTI exhibits canonical growth on both bubble and spike sides. At high Knudsen and low Mach numbers, RTI xhibits diffusive growth on both bubble and spike sides. The objective of this study is to examine the transition from classical to diffusive behavior as Knudsen and Mach numbers are varied. Toward this end, we perform simulations using the Unified Gas Kinetic scheme (UGKS) to investigate RTI dynamics from the continuum regime to highly rarefied regime (Kn ~ 1). The simulation results reveal the various stages of transition from advective instability to diffusive transport. Additionally, the characteristics underlying the transitional advective-diffusive region in between are identified. The results of this study can lead to a more comprehensive understanding of RTI over a wide range of Mach and Knudsen numbers in practically relevant regimes. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X27.00009: Investigation of rarefaction wave driven Rayleigh-Taylor instability using particle image velocimetry Weston Meyers, Jeffrey W Jacobs Experiments are presented in which a diffuse interface between two gases of differing density is accelerated vertically using interaction with a rarefaction wave resulting in the Rayleigh-Taylor instability. Using equal volumetric flow rates of two unequal density gases, a flat interface is formed at the location of small exit holes in the test section. The interface is then given either a 2D or 3D initial perturbation by horizontal or vertical oscillation. A vacuum tank positioned below the test section and separated from it by a diaphragm is evacuated. The rupture of the diaphragm then creates a rarefaction wave resulting in a large (of order 1000 g), non-constant acceleration as it passes over the interface causing the Rayleigh-Taylor instability to develop. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X27.00010: Rayleigh-Taylor instability under sinusoidal acceleration profiles across a broad parameter range Nicholas Hyun Woo Pak, Elise Theriot, Denis Aslangil, Andrew Lawrie, Arindam Banerjee We study the dynamic properties of the Rayleigh-Taylor instability (RTI) that occurs at the interface between fluids of varying density, subjected to an external acceleration. Classical RTI occurs when the fluid is subjected to a constant gravity field. RTI subjected to time-dependent acceleration fields are less studied, although they are theorized to better represent hydrodynamic instabilities observed in high-energy-density processes. Previous studies have considered variable acceleration profiles in a piece-wise acceleration reversal. In this study, we consider smoother acceleration profiles that vary sinusoidally with time, as such reversals are conjectured to better represent the acceleration sign reversals that occur in most relevant engineering and astrophysical applications. We consider four acceleration profiles: constant acceleration, ADA, and two sinusoidal profiles, one matching the period of the ADA profiles, and the other matching the amplitude. We use the double-integral of acceleration as a relevant length scale to compare the sinusoidal cases; all results are compared to the constant gravity RTI case. This allows us to comment on the self-similar evolution of the RTI under variable acceleration profiles in terms of low-order parameters such as mixing layer width growth, mass flux, Reynold's stresses, anisotropy tensor, and molecular mixing. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X27.00011: On the arrested development of the Rayleigh Taylor instability with and without cabbeling Marek Stastna, Andrew P Grace Cabbeling, the phenomenon in which fluid parcels of the same density but different temperatures can mix to form a fluid parcel that is denser than its parents, commonly occurs in natural waters in late winter and early spring. We consider the classical Rayleigh Taylor instability in the cabbeling regime. Using three dimensional numerical simulations we track the instability into a mature quasi-turbulent regime. In the case of no cabbeling, the development of the Rayleigh Taylor instability is rapidly arrested by instability-induced mixing. In contrast, cabbeling allows the fluid to reach a self-sustaining regime in which cabbeling produces denser fluid that continues to drive further instability. By varying the proximity of the initially unstable interface to walls we demonstrate that very different regimes can be achieved in terms of the distribution of temperature and kinetic energy in the quasi-turbulent region. Finally, we discuss the distribution of the viscous dissipation, finding that while the flow regime is vortical, chaotic and efficiently mixing, no well-defined inertial subrange exists. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X27.00012: Spectral Analysis of Combined Kelvin-Helmholtz and Rayleigh-Taylor Instability Using SPOD and POD Hao Zhou, Hayden Baird, Zhongquan Zheng The flow field for 2D and 3D flow combining Kelvin-Helmholtz and Rayleigh-Taylor instabilities is simulated and analyzed using SPOD and POD on their frequency content. While SPOD results are already in the frequency domain, the POD frequency analysis is based on the corresponding spectra of POD time coefficients for each mode. The goal is to identify frequency interactions between KHI and RTI, such as RTI triggered inherent frequencies of KHI. Parameters that affect both KHI and RTI are studied, including shear strength, shear thickness, buoyancy strength, and density difference. Through the frequency analysis, it is found that the flow exhibits multiple characteristic regions of instability. Starting from the developing region, RTI causes the initial perturbation for KHI to develop. Then it progresses into the KHI-dominant region, where the characteristically periodic KHI vortex shedding occurs with distinct frequency peaks observed. Between the KHI- and RTI-dominant regions, there is a transitional region where the shed vortices begin to stretch and bubble due to RTI. In this region, the frequency peaks previously found are shifted and dampened. Lastly, the flow enters the RTI-dominant region, where RTI stretches and bubbles the shed vortices into the characteristic RTI plumes and mushroom structures. This last region loses the frequency peaks observed in the previous two regions. |
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