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 A24: Flow Instability: Nonlinear Dynamics and Control |
Hide Abstracts |
Chair: Qiong Liu, New Mexico State University Room: 251 B |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A24.00001: Flow Instabilities Induced by the Fluid-Structure Interaction of a Flexible Pipe Till Zeugin, Brandon Hilliard, Marius Neamtu-Halic, Markus Holzner The presence of turbulence in blood flow has been linked to cardiovascular diseases such as atherosclerosis, underlining the importance to understand how instabilities within pulsatile flows develop so that hemodynamic turbulence can be mitigated. Whereas transition of pulsatile flows in straight rigid pipes is governed by the Reynolds number (Re), the Womersley number (α), and the pulsation amplitude (A), hemodynamic flows are additionally subject to fluid-structure interactions (FSI) via compliant vessels, which may cause flow perturbations and potentially induce turbulence. In this study, we experimentally investigate the onset and development of instabilities in sinusoidal pulsatile flows through a straight flexible pipe with an inner diameter Di = 20 mm and a length Lel = 7.5Di. We systematically map out the transitional parameter space, as well as study the effect of system resonance on transition. We find that transition is strongly dependent on resonance regardless of A, though the underlying mechanism is the modulation of the effective amplitude (Ain). When Ain is controlled, resonance influences the transitional Reynolds number (ReT), i.e., the onset of a flow instability, and the slope of transition curves at large Ain. We observe three regimes where different types of instabilities occur. In the first regime, streaks appear for flows with small Ain, α < 8 and α > 20, which are typical precursors for turbulent puffs. A helical instability occurs in the second regime, with large Ain and 8 < α < 12. In the third regime, both streaks and helical structures are simultaneously present at large Ain and 12 < α < 20. This third regime has not yet been observed in rigid pipes. These findings show that system resonance is an additional parameter to consider when investigating FSI with compliant vessels, and that physiological in vitro studies should ensure proper flow conditions because certain flow regimes exhibit different turbulence characteristics. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A24.00002: Coherence resonance in an airfoil flow Xiangyu Zhai, Vikrant Gupta, Stephane Redonnet, Larry K.B. Li We present experimental evidence of coherence resonance in the flow around a prototypical low-Reynolds-number airfoil prior to stall. This flow undergoes a Hopf bifurcation at a critical Reynolds number, transitioning from a fixed point to a limit cycle characterized by self-excited low-frequency oscillations. We subject the flow to white noise of varying intensities, both before and after the Hopf point, and analyze the autocorrelation and spectral characteristics of the aerodynamic lift signal. Our findings reveal that the coherence factor reaches a maximum at an intermediate noise intensity, which is a signature of coherence resonance. To model the noise-induced dynamics, we use a stochastically forced Van der Pol oscillator, with its parameters determined through an output-only system identification procedure based on the Fokker–Planck equation. We find that the model predictions align well with our experimental results, underscoring the universality of coherence resonance in nonlinear dynamical systems near a Hopf bifurcation. This work establishes the potential for using the noise-induced dynamics arising from coherence resonance to develop early warning indicators of self-excited global instabilities in airfoil flows. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A24.00003: Nonlinear elongated structures in the entrance region of a circular pipe Pierre Ricco, Kaixin Zhu The nonlinear evolution of free-stream vortical disturbances entrained in the entrance region of a circular pipe is investigated using asymptotic and numerical methods. Attention is |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A24.00004: Dynamical system analysis of chaotic flow around two square cylinders Sidhartha Sahu, George Papadakis We investigate the chaotic dynamics of the irregular flow over two side-by-side square cylinders at a Reynolds number of 200 and a gap ratio of 1. For this set of parameters, the flow is chaotic. More specifically, the Navier-Stokes equations are linearized around the unsteady trajectory of the system, and the tangent space is analyzed. The Lyapunov exponents (LEs) and Covariant Lyapunov Vectors (CLVs) of the flow are identified using a periodic orthonormalization algorithm. The CLVs correspond to the eigenvalues and eigenvectors of typical linear stability analysis; however, the latter is performed on a steady base flow, whereas our analysis is performed on a time-varying base flow. For unsteady flows, the analysis of a time-varying tangent space is physically more meaningful and mathematically more rigorous than performing linear stability analysis on a time-averaged base flow. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A24.00005: Abstract Withdrawn
|
Sunday, November 24, 2024 9:05AM - 9:18AM |
A24.00006: Thermoacoustic-hydrodynamic interactions in the wake of a cylinder embedded in a Rijke tube Christopher M Douglas, Jan O Pralits, Lutz Lesshafft In isolation, the Rijke tube and cylinder wake represent canonical, well-understood examples of thermoacoustic and hydrodynamic instabilities, respectively. However, many compressible flows, such as those found in high-enthalpy boundary layers and afterburners, feature thermoacoustic—hydrodynamic interactions that cannot be understood simply as a sum of these two elementary parts. This study analyzes the linear and nonlinear dynamics of a combined Rijke tube—cylinder wake system in order to elucidate how these basic instability modes interact to enrich the system behavior. Leveraging nonlinear time-domain simulations and numerical bifurcation analysis, we model the compressible flow over a heated cylinder embedded within a Rijke tube. We find independent neutral curves associated with both thermoacoustic and hydrodynamic instabilities that divide the parameter space into four regions characterized by the instability of neither, either, or both modes. These curves intersect at a double-Hopf point, where weakly-nonlinear analysis allows us to precisely extract the coupling strengths among the instabilities and their harmonics as well as infer the spatial structure of the components underpinning these couplings. Finally, the weakly-nonlinear structures are used as a basis on which to project the true nonlinear dynamics in the regime where both modes are unstable, enabling us to extract and interpret the underlying thermoacoustic—hydrodynamic interactions. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A24.00007: A Class of Instabilities Induced by Surface Vibrations Jerzy M Floryan, N N Haq Analysis of the Couette flow response to a bounding plate's vibrations has been carried out. Vibrations in the form of sinusoidal waves characterized by amplitude, wave number, and phase speed have been considered. It is shown that such vibrations can produce instability, giving rise to secondary flow in the form of streamwise vortices. This instability is driven by centrifugal forces created by wave-imposed changes in the direction of fluid movement. The waves cannot be too fast and too slow, too long and too short, and must have a sufficient amplitude to produce instability; relevant bounds have been given. Only subcritical waves, i.e., waves with phase speed smaller than the maximum flow velocity, can produce instability. An increase in the Reynolds number increases the range of vibration wave numbers and phase speeds capable of flow destabilization. A range of parameters has been found where vibrations decrease the flow resistance and, at the same time, produce streamwise vortices. Such vibrations represent an energy-efficient flow control tool for mixing intensification. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A24.00008: Avoiding explosive transient growth in laminar planar flows with optimal deceleration profiles Alec Linot, Kunihiko Taira Perturbations in decelerating laminar flows can exhibit massive growth not observed in either steady or accelerating flows. Some examples of deceleration profiles that exhibit this behavior include linear deceleration, exponentially decaying deceleration, and the decelerating segment of oscillatory flows. However, the Reynolds number at which this growth becomes substantial varies based on the deceleration profile, indicating that perturbations about some profiles are less prone to transient growth. As mitigating this growth is desirable to avoid turbulent transition, we seek the optimal deceleration profiles for minimizing the transient growth of perturbations in wall-driven channel flow. We perform this analysis by formulating a constrained optimization problem to minimize transient growth for wall motion that begins with a simple shear profile and decays to no flow. In this problem, we constrain the magnitude of the wall motion. When the wall motion is limited to positive values, we find that the optimal wall motion drastically reduces the growth of perturbations, compared to linear deceleration, by damping growth caused by the Orr mechanism (streamwise perturbations). When the wall motion is allowed to take on negative values, we find the optimal wall motion further reduces the growth of perturbations by damping growth from both the lift-up mechanism (spanwise perturbations) and the Orr mechanism. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A24.00009: Antagonistic effects of drag-reducing flow control on extreme events in turbulent flow Cesar A Leos, Jae Sung Park The effect of active flow control, such as external body forces in wall-bounded turbulent flows has been extensively studied, particularly for its role in reducing skin-friction drag. However, the impact of these forces on extreme events observed in various flow variables has received less attention. Despite numerous studies aimed at understanding and describing extreme events, there is lack of coherence in its definition across various fields. In this study, we introduce the definition based on wall shear stress and examine the evolution of extreme events using direct numerical simulations with the inclusion of external body forces up to a friction Reynolds number of 180. The results indicate that recurrent extreme wall-shear-stress events or very strong bursting phenomena are observed in both uncontrolled and controlled flows, as evidenced by high flatness values. Interestingly, in several cases, the magnitude of extreme events in drag-reducing flows exceeded the mean wall shear stress of the uncontrolled flow, indicating antagonistic or amplifying effects of flow control. A detailed analysis will be given to elucidate this amplifying effect by phase space dynamics. In addition, the dependence of Reynolds number on extreme events in drag-reducing flows will be explored. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700