Article
Mechanics
Anton Pershin, Cedric Beaume, Tom S. Eaves, Steven M. Tobias
Summary: This study examines the nonlinear robustness of laminar plane Couette flow under in-phase spanwise wall oscillations, by computing properties of the edge of chaos and using three measures to quantify the impact of the chosen control strategy on laminar-to-turbulent transition. A novel Bayesian approach is introduced to accurately calculate the laminarization probability, providing global information about the edge and allowing for the evaluation of control effectiveness.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Christopher J. Camobreco, Alban Potherat, Gregory J. Sheard
Summary: The transition to turbulence in conduits has been a long-standing problem in fluid mechanics, and understanding how to promote or suppress turbulence is crucial for energy production and conservation. While a global picture of three-dimensional (3-D) turbulence is emerging, subcritical turbulence in flows approaching two dimensions has not been observed. However, stability analysis and simulations have shown a subcritical quasi-two-dimensional (quasi-2-D) transition from laminar flow to turbulence, driven by nonlinear Tollmien-Schlichting waves. This alternative scenario calls for new thinking and strategies to control transition in rotating devices and nuclear fusion reactor blankets.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mathematics, Applied
Qi Chien, Dongyi Wei, Zhifei Zhang
Summary: In this paper, we prove the linear stability of pipe Poiseuille flow for general perturbations at high Reynolds number regime. This has been a long-standing problem and our work lays a foundation for the theoretical analysis of hydrodynamic stability of pipe flow.
COMMUNICATIONS ON PURE AND APPLIED MATHEMATICS
(2023)
Article
Mechanics
M. Cavelier, B-J Grea, A. Briard, L. Gostiaux
Summary: This study investigates the development and breaking process of standing waves at the interface between two miscible fluids with small density contrast. Experimental findings reveal that the wavelength of the standing waves is determined not only by linear processes and tank geometry, but also by nonlinear mode competition mechanism. Another destabilization process occurs at smaller scales as the standing wave amplitude grows, leading to turbulent mixing at the nodes. Various approaches using local and global stability analysis are proposed to predict the critical wave steepness.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ozge Ozcakir, Philip Hall
Summary: Families of exact coherent states in elliptical pipe flow, obtained from travelling-wave solutions in circular pipe flow using a continuation approach, suggest the possibility of two distinct classes of solutions at higher values. These include rotationally symmetric centre-mode states collapsing towards the pipe centre and rotationally asymmetric vortex-wave interaction states with additional mirror symmetry. These calculations represent the first instance of three-dimensional travelling waves in elliptical pipes and have the potential to provide fresh insight into coherent structures in Poiseuille flow in pipes and channels.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Zirui Liu, Vishnu R. Unni, Swetaprovo Chaudhuri, Ran Sui, Chung K. Law, Abhishek Saha
Summary: This study experimentally measured the flow characteristics of flame-generated 'turbulence' for expanding cellular laminar flames, analysing the energy spectra at different stages and indicating that the observed spectra are driven by the fractal topology of the cellularly unstable flamefront.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Duo Xu, Baofang Song, Marc Avila
Summary: The study reveals that in pulsatile and oscillatory flows through pipes, high pulsation amplitudes can lead to the replacement of classic stream-wise vortices by helical disturbances and the dominance of axisymmetric disturbances under high frequency and Reynolds number conditions. These optimal disturbances reach their peaks in a short time period and show exponential energy gain scaling with the Reynolds number of the oscillatory flow component.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Chang Liu, Colm-cille P. Caulfield, Dennice F. Gayme
Summary: In this study, a structured input-output analysis (SIOA) approach is employed to analyze the wavelengths of flow structures in stably stratified plane Couette flow. It is found that SIOA predicts high amplification in the low-Reynolds-number and low-bulk Richardson number spatially intermittent regime. Additionally, SIOA identifies quasi-horizontal flow structures resembling the turbulent-laminar layers observed in the high-Reynolds-number and high-bulk Richardson number intermittent regime. The study also suggests that the most amplified flow structures change with the Prandtl number, and a different quasi-horizontal flow structure is associated with density perturbations.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
E. Parente, J-Ch Robinet, P. De Palma, S. Cherubini
Summary: Recently, the origin and growth of turbulent bands in shear flows have been investigated. Streaks and their inflectional instability play a significant role in the process. Linear and nonlinear energy optimisations reveal the mechanisms allowing the creation of a turbulent band in a tilted domain. Linear optimal perturbation generates oblique streaks, inducing turbulence in the whole domain. Spatially localised perturbations lead to the generation of a localised turbulent band.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Arghya Samanta
Summary: The aim of this study was to investigate the linear and nonlinear wave dynamics of a falling incompressible viscous fluid with the effect of odd viscosity. The study found that the odd viscosity coefficient can weaken surface and shear instabilities, as well as reduce the growth rate of the linear spatio-temporal response. Additionally, a nonlinear travelling wave solution of a two-equation model showed the attenuation of maximum amplitude and speed in the presence of an odd viscosity coefficient. This delayed the transition from a primary parallel flow with a flat surface to secondary flow generated through nonlinear wave interactions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Philip Hall
Summary: The study discusses the effect of small amplitude boundary forcing in the form of waves on high Reynolds number shear flows, considering both bounded and unbounded cases. The results show different instability characteristics and influencing factors in different scenarios.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
E. Parente, J. -Ch. Robinet, P. De Palma, S. Cherubini
Summary: In this study, nonlinear variational optimization is applied to find minimal seeds for the formation of turbulent bands in channel flow. The minimal energy threshold for obtaining spatially patterned turbulence is found to scale with the Reynolds number to the power of -8.5 for Reynolds numbers greater than 1000. The minimal seed exhibits spot-like structure and low-amplitude large-scale quadrupolar flow. Its evolution depends on the Reynolds number and initial energy, and two different formation mechanisms are observed.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Chih-Lun Liu, Alexis K. Kaminski, William D. Smyth
Summary: In a stably stratified shear layer, small changes in initial conditions have significant effects on instabilities and alter the path and level of turbulence, resulting in variations in the mixing efficiency.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Quang Duy Nguyen, Chengwang Lei
Summary: In this study, Particle Image Velocimetry (PIV) measurement was used to investigate the flow past a highly confined circular cylinder, revealing amplified characteristic frequency of separated shear layers and transition between different shedding modes. The theory of mixing layers was applied to predict the characteristics of separated shear layers with good agreement with experimental data, and vortex roll-up and merging locations were estimated based on energy contents of individual frequency modes.
Article
Mechanics
K. P. Sarath, K. V. Manu
Summary: This study investigates the stability and transition to turbulence in a diverging channel with a time-varying trapezoidal inflow boundary condition. Three categories of flow behavior are observed based on different Reynolds numbers and deceleration rates. The characteristics of primary instability, secondary instability, and streamwise vorticity generation are successfully captured using numerical simulations and dynamic mode decomposition algorithm.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Robert C. Houseago, Liu Hong, Shyuan Chen, James L. Best, Daniel R. Parsons, Leonardo P. Chamorro
Summary: This study experimentally investigated the distinct turbulence dynamics and transport modulated by a common seagrass species. The results showed that the flexible seagrass induced vortex shedding from the blade tips, unlike the rigid seagrass. The spatial and temporal characteristics of coherent flow structures revealed that Kelvin-Helmholtz-type vortices were the dominant flow structures associated with the waving motion of the seagrass.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Biochemical Research Methods
Liu Hong, Leonardo P. Chamorro
Summary: We propose a non-iterative ray tracing method with robust post-capture microlens array sensor alignment to reconstruct sparse particle concentration in light field particle image velocimetry and particle tracking velocimetry nearly instantaneously. The method utilizes kd-tree for storing voxels traversed by rays to reduce memory load and computational time, and employs a cloud point classification algorithm for particle identification and spatial reconstruction. Experimental results demonstrate the effectiveness of the proposed method, and its application in a microscope shows good agreement with theoretical solution.
Article
Energy & Fuels
Buen Zhang, Yaqing Jin, Shyuan Cheng, Yuan Zheng, Leonardo P. Chamorro
Summary: Laboratory experiments were conducted to study the effects of small-amplitude oscillations on a wind turbine. The study found that these oscillations had an impact on the turbine's motion, wake statistics, and power output. The results showed that rotational motion played a significant role in the turbine's behavior. A formulation for the turbine oscillation spectrum was derived, and it showed good agreement with measurements. Passive oscillations resulted in higher power output for a given yaw.
Article
Green & Sustainable Science & Technology
Yaqing Jin, Shyuan Cheng, Leonardo P. P. Chamorro
Summary: Laboratory experiments were conducted to investigate the effects of layout on the motions and power output fluctuations of wind turbines. The results showed that variations in flow channeling and turbine spacing can affect the turbine oscillations and power output.
JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY
(2022)
Article
Physics, Multidisciplinary
Y. Gao, J. E. Paul, M. Chen, L. Hong, L. P. Chamorro, N. R. Sottos, P. H. Geubelle
Summary: This study examines the interaction between a self-sustaining exothermic reaction front and buoyancy-driven convection flow during frontal polymerization. The thermal gradients generated by the polymerization front cause natural convection of the fluid, which in turn affects the reaction-diffusion dynamics and the front shape. Numerical analyses and experiments reveal the coupling between natural convection and frontal polymerization, showing that the frontal Rayleigh number influences the velocity field and front inclination. Higher Ra numbers lead to instability during polymerization, resulting in thermal-chemical patterns with tunable wavelengths and magnitudes.
PHYSICAL REVIEW LETTERS
(2023)
Article
Mechanics
Soohyeon Kang, Shyuan Cheng, Liu Hong, Jin-Tae Kim, Leonardo P. Chamorro
Summary: We studied the effect of single-sidewall cooling on Rayleigh-Benard (RB) convection experimentally and also analyzed the canonical RB to gain insight. The experiments were conducted at two canonical Rayleigh numbers and Prandtl number 5.4, with particle image velocimetry used to analyze the flow. The results showed that single-sidewall cooling led to pronounced changes in the flow structure and large-scale circulation (LSC), with lower buoyancy effects and different velocity spectra compared to the canonical case.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Tengfei Cai, Leonardo P. Chamorro, Fei Ma, Qiheng Zhu, Jian Han
Summary: This study experimentally investigates the impact of passive acoustic excitation modes from self-excited cavitating waterjet clouds on erosive patterns using high-speed imaging, scanning electron microscopy, and macroscopic three-dimensional scanning. The findings reveal that the fundamental excitation mode promotes the development of the primary cavitation cloud, while energy transfers from secondary to primary modes result in the maximum cavitation cloud volume inducing the best rock-breaking ability. The breaking mechanism involves a continuous peeling off of mineral grains under the cavitation cloud's impact, as observed through macroscopic and microscopic inspection of the rock coupons' topographies.
Article
Physics, Fluids & Plasmas
Ali M. Hamed, Christopher T. O'Brien, Adam J. Hall, Ryan M. Gallary, Joshua J. DaRosa, Quinlan L. Goddard, Bailey R. McAtee
Summary: Planar particle image velocimetry and volumetric particle tracking velocimetry were used to study the flow over 2D bar roughness elements in a turbulent boundary layer. The effects of spacing and height ratio on the flow field and turbulence past the downstream bar were investigated. Results showed that sheltering by an upstream bar reduced the reattachment length and velocity deficit past the downstream bar, and also reduced the Reynolds shear stress. The vortical structures past the isolated bar were visualized, and the three-dimensionality of the vortical structures in the wake of the downstream bar was enhanced by sheltering.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Energy & Fuels
Esmail Mahmoodi, Mohammad Khezri, Arash Ebrahimi, Uwe Ritschel, Leonardo P. Chamorro, Ali Khanjari
Summary: The aerodynamic interactions between wind turbines in wind farms cause significant energy losses. Optimizing the flow between turbines is a promising solution to minimize these losses. This study proposes a simplified analytical model combining the Gaussian wake model and the cylindrical vortex induction model to evaluate the interaction between wake and induction zones in 3.5 MW wind turbines with 328 m spacing.
Article
Mechanics
Shyuan Cheng, Stefano Olivieri, Marco E. Rosti, Leonardo P. Chamorro
Summary: The effect of single perforations and their location on the drag and reconfiguration of flexible plates was studied through experiments and simulations. The results showed that the perforated plates exhibited distinct jets in the wake, significantly affecting the aerodynamic force and plate deformation. The velocity and position of the jets were influenced by both the incoming flow and the location of the perforations. A simple formulation was developed to predict the change in drag for different perforated plates.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Marine
Tengfei Cai, Leonardo P. Chamorro, Fei Ma, Jian Han
Summary: The impact of nozzle lip geometry on the characteristics of cavitation cloud induced by self-excited cavitating waterjets (SECJ) is investigated experimentally. The results show that a nozzle lip with a short throat and a whistle can increase the volume of cavitation cloud, reduce the shedding frequency, extend the effective standoff distance, and enhance the cavitation erosive ability.
Article
Mechanics
Diego Siguenza-Alvarado, Venkatesh Pulletikurthi, Jhon J. Quinones, Clarice Nelson, Shyuan Cheng, Ali Doosttalab, Leonardo P. Chamorro, Luciano Castillo
Summary: An experimental investigation was conducted to explore the interaction and wake statistics of model wind turbines operating over two-dimensional hills. The results indicate that the advection terms play a more significant role than turbulence in the wake recovery mechanism with steeper hill slopes.
Article
Mechanics
Soohyeon Kang, Liu Hong, Shyuan Cheng, James L. Best, Leonardo P. Chamorro
Summary: In this study, we experimentally investigated the settling behavior of spherical particles in different quiescent media and at different release frequencies. The results showed that the particle trajectories exhibited preferential in-plane motions in water and ethanol, while they displayed nearly vertical paths in the G60 mixture and oil media. Varying degrees of particle separation resulted in higher terminal velocities and reduced particle drag. The vertical and lateral pair dispersions exhibited ballistic scaling with dependences on the initial separation and the type of medium.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Biochemical Research Methods
M. Hannah Choi, Liu Hong, Leonardo P. Chamorro, Boyd Edwards, Aaron T. Timperman
Summary: The ability to measure the charge and size of single particles is crucial for understanding particle adhesion and interaction with the environment. The new technique called TrACE combines particle tracking velocimetry (PTV) and AC electrophoresis to accurately measure the charge and size of particles. This technique shows promise in studying the physical properties of cells and has potential applications in various fields.
Article
Green & Sustainable Science & Technology
Humberto Bocanegra Evans, Ali Doosttalab, Diego Siguenza-Alvarado, Shyuan Cheng, Leonardo P. Chamorro, Luciano Castillo
Summary: The experiments investigated the effect of the relative height of low-level-jet (LLJ) peak velocity on the wake and power output fluctuations of wind turbines. The results showed that the LLJ peak velocity coinciding with the turbine top tip had a significant impact on the wake and fluctuations. The strong mean shear above the wake promoted vertical transport and generation of coherent motions. The wake velocity spectra exhibited a distinct local signature, while the power output fluctuations were not significantly affected. The large-scale velocity fluctuations may affect wind turbines in arrays.
JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY
(2022)