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 L14: General Fluid Dynamics: General II |
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Chair: Alberto Scotti, Arizona State University Room: 155 D |
Monday, November 25, 2024 8:00AM - 8:13AM |
L14.00001: A fully observer-covariant view of Fluid Mehanics with some applications. Alberto Scotti In this talk we present a formulation of the equations of motion of simple fluids that applies to generic observers. In this formulation, the state of the flow is described by sections of the cotangent bundle over the manifold that describes the space occupied by the fluid, whose evolution is given by the Lie derivative. Thus, we avoid the need to introduce an extra structure, the Levi-Civita connection. We initially formulate the equations for a class of observers that include the canonical inertial observers. Later, we invoke the principle of covariance to show how the formulation naturally extends to arbitrary observers. Time permitting, we will give consider a few applications, such as a generalized Orr-Sommerfeld equation and inertial equatorial waves on a wobbly planet. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L14.00002: Jacobian Eigenvalue Analysis for the Stability of Neural Autoregressive Models of Chaotic Dynamic Systems Conrad S Ainslie Neural network-based autoregressive methods for predicting complex multi-scale chaotic dynamical systems suffer from instability. Over long timeframes, compounding errors eventually result in a complete divergence from the training distribution. The lack of explainable dynamics inside the network itself makes it difficult to determine how quickly these autoregressive models would become unstable without exhaustive testing. Previous works have demonstrated that this divergence is caused by cascading errors that start in the small scale modes and propagate into the large scale modes, which result in eventual instability. The timeframe at which this process happens is currently not determinable without running to model until said divergence. Spectral analysis of the Jacobian of the model, with a focus on its largest eigenvalue in particular, gives a quantifiable metric to determine how quickly the model can become unstable. This work demonstrates this fact by analyzing the instabilities of multiple network architectures, and multiple numerical integration methods, on a canonical chaotic dynamical system. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L14.00003: On the Infinite-Reynolds number Limit of Navier-Stokes Solutions: Insights from the Principle of Minimum Pressure Haithem E Taha The convergence of Navier-Stokes solutions to one of Euler's solution as Reynolds number goes to infinity (i.e., viscosity goes to zero) is an open problem in mathematics. It is known that if such a convegence holds, it will be to a weak solution of Euler (i.e., a non-smooth solution which does not satisfy the PDE at every point, but satisfies an integral version of the equation). However, weak solutions of Euler are non-unique; and a selection criterion is needed. That is, which weak solution in Euler's family does match the limit of Navier-Stokes' solutions when viscosity goes to zero? |
Monday, November 25, 2024 8:39AM - 8:52AM |
L14.00004: Generation and Evolution of Singularities in Hydrodynamic Models of Wave Propagation Roberto Camassa, Dylan D Bruney Interesting phenomena in fluid dynamics, both from a mathematical and a physical perspective, stem from the interplay between fluids and their boundaries. Singularities can form in finite time when material surfaces are in smooth contact with boundaries of a fluid under gravity, and, conversely, certain regularity can be regained in the course of the evolution. These effects can be analytically and numerically predicted by simple mathematical models and observed in simple experimental setups. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L14.00005: Reduced Second Order Constitutive Theory of Fluids Samuel Paolucci A fully second order continuum theory of fluids has been previously developed (Continuum Mech. Thermodyn. (2022) 34:185-215). The constitutive equations depend on density, temperature and velocity, and their derivatives up to second order and satisfy the second law. These equations have been shown to be consistent but much more general than other known results. Since they contain a number of material derivatives terms of a number of quantities (e.g., strain rate and temperature gradient), we call this form of the equations as original. Here, using order of magnitude analysis in viscosity, we obtain reduced equations by replacing the material derivatives terms with the spatial gradients. This substitution maintains second order accuracy in viscosity. We also obtain corresponding simpler equations valid for simple fluids. The reduced constitutive equations equations are used to obtain results for the shock structure and thermal stress problems and compare the results with those from kinetic theory. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L14.00006: Leidenfrost spheres, projectiles, and speed model boats: assessing the superhydrophobic surfaces drag reduction Farrukh Kamoliddinov, Ivan U Vakarelski, Sigurdur T Thoroddsen Superhydrophobic surfaces are anticipated to lower the drag on bluff bodies moving through water by creating a thin air layer around the object, effectively providing a free-slip boundary condition. A proven method to assess the maximum possible drag reduction by such air layers involves the use of Leidenfrost vapor layers on heated metal bodies. Previously, this method was applied to calculate drag reduction on a free-falling heated sphere, primarily affected by form drag. We now apply this method to assess the impact of thin gas layers on the hydrodynamic drag of free-falling streamlined projectiles and towed model boats, where skin friction drag is predominant, and form drag is less significant [1]. Our comparisons of streamlined bodies, with and without these air layers, show only minor drag reductions at the sub-critical Reynolds numbers tested. This observation also applies to towed model boats. Both superhydrophobic surfaces and Leidenfrost vapor films yield similar results, indicating that skin friction drag is less affected by thin gas layers compared to form drag within the range of sub-critical Reynolds numbers studied [2]. These findings have considerable implications for the practical application of gas layers on superhydrophobic surfaces for energy conservation. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L14.00007: Drag Reduction in a Slanted Ahmed Body using Rod Inserts. James Kofi Arthur, Abdullah Nabi This work investigates the impact of the installation of rod inserts on the aerodynamic drag of a 1:30 scaled 25° slant angle Ahmed body (SAAB). The research was accomplished using planar particle image velocimetry measurements of a SAAB model in a water tunnel, complemented with finite element-based COMSOL Multiphysics simulations. For each methodology, the SAAB was tested at a Reynolds number (based on the SAAB length) of 5.61×104. At a deviation of 2%, the L-VEL Reynolds averaged Navier-Stokes turbulence model was found to best match the basic structural features of the experimental flow results. By modeling the placement of a single row of rods at porosities ranging from 60% to 95%, a proportional relationship between the midspan rear-end recirculation length and the drag coefficient (CD) was observed. Specifically, the CD trend was non-monotonic, with a drop of 5% reached when a 95% insert was installed. The results indicate the potential of implementing such rod arrangements in the automobile industry to offer substantive fuel consumption and environmental impact reduction. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L14.00008: The influence of γ-doses irradiation on structural and optical properties of NiO thinfilms prepared by Spin coating method Tesfaslasie Y Msgina We report a new green synthesized nanostructured thin films of Nickel oxide (NiO) prepared |
Monday, November 25, 2024 9:44AM - 9:57AM |
L14.00009: Experimental study on the correlation between ion rejection rate and ice growth rate in freeze desalination Dachuang SHI, Yixiang Wang, Shiji LIN, Zhigang Li Freshwater scarcity is one of the most urgent problems worldwide, and it is becoming severe due to global warming. Several seawater desalination methods have been developed to mitigate the water crisis. Among them, the freeze desalination method is a membrane-free approach, and thermodynamically, it consumes less energy than distillation methods because the latent heat of water crystallization is less than that of water evaporation. For freeze desalination methods, the ion rejection rate, which is the percentage of ions in the liquid phase, is an important parameter. It should be sufficiently high to generate portable water. However, due to the thermal motion of ions and the moving front of ice, ion trapping in ice reduces the ion rejection rate. To understand the ice growth rate on the ion rejection rate, we conduct experiments to study the quantitative correlation between the ion rejection and ice growth rates. Experiments show that when the ice growth rate exceeds the critical value of 0.283 mm/min, a linear relationship between the ice growth rate and the ion rejection rate is observed. Below this critical value, the ion rejection rate stabilizes at approximately 84.8%. This study provides helpful information for freeze desalination system design and parameter optimization. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L14.00010: Estimating Noise Induced by Turbulent Boundary Layers Using the Acoustic-Structural Reciprocity Technique HeeChang Lim, BonHeon Ku, YoungWoo Yi, ChinSuk Hong As the contribution of self-noise from flow has increased in aerodynamic applications, there is growing interest in numerically predicting the noise generated by wall pressure fluctuations in turbulent boundary layers [1-3]. In this study, we explored a prediction method for flow-induced noise in an aircraft wing cavity, using a simplified aerodynamic model. To capture the temporal and spatial randomness of wall pressure fluctuations, we adapted a random vibro-acoustics approach. The structural excitation by wall pressure fluctuations was modeled using the Corcos model and the Smol'yakov-Tkachenko model [4]. The acoustic-structural reciprocity technique was applied to efficiently calculate the transfer functions required for the random vibroacoustic model. This technique enables the effective computation of noise transfer functions at multiple points, facilitating the application of the random vibro-acoustics method [5]. To verify the acoustic-structural reciprocity technique, we compared the transfer functions in both direct and reciprocal directions, finding good agreement. In addition, we studied the effects of flow velocity on noise levels in the cavity and observed that the noise level increases with increasing flow velocity. We developed a prediction method for noise generated by flow over a structure, which has potential applications in estimating aircraft self-noise. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L14.00011: Flow Characteristics Inside a Circular Cylinder Under Vibrating and Rotating Conditions HeeChang Lim, YoungWoo Yi, ChinSuk Hong, BonHeon Ku Understanding the flow characteristics inside rotating structures is crucial not only for analyzing natural phenomena such as tornadoes and water circulations in oceans but also for modeling flow-induced vibrations generated within complex structures under vibrating conditions. This study aims to observe the flow characteristics, including velocity and pressure, under varying rotational and vibrational conditions over time in a closed cylindrical structures. To achieve this, we assumed various rotational and vibrational conditions and modeled the resulting flow characteristics using several computational fluid dynamics (CFD) techniques. Subsequently, we analyzed the changes in flow velocity and pressure within the cylindrical structures to understand the effect of vibration and rotational conditions. Based on these results, we modeled the flow-induced noise occurring within the cylindrical structures and proposed optimization directions to minimize the vibrations. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L14.00012: Numerical investigation of angular particle dynamics John Michael Tubije, Umberto Ciri, Sylvia Rodriguez-Abudo, Stefano Leonardi Suspended particles in fluid flows are typically modeled as spheres due to their isotropic properties, which simplify the resolution of particle shape, dynamics, and kinematics. While existing literature has extensively studied spheroidal particles that can either be prolate(rod-shaped) or oblate(disk-shaped), natural sediment grains often exhibit angularity. These edges as well as the non-isotropic shape can lead to different dynamic and kinematic behaviors compared to non-angular particles. In this study, we model angular particles as octahedrons using the Immersed Boundary Method. The first part of the study involves direct numerical simulations of oscillatory flow over a bed of angular particles to compare stress distributions with those over spherical beds. The second part examines the dynamic behavior differences among spherical, spheroidal, and octahedral particles in steady flow. Initial results indicate that octahedral particles exhibit more pronounced angular oscillations than spheroidal particles. Additionally, particle layout significantly influences rotation statistics, with upstream particle wakes affecting the torque on downstream particles. |
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