Turbulent wave attractors in large-aspect ratio domains.

2021 ◽  
Author(s):  
Ilias Sibgatullin ◽  
Stepan Elistratov ◽  
Eugeny Ermanyuk
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Large Scale ◽  
Global Scale ◽  
Large Aspect Ratio ◽  
Order Unity ◽  
Liquid Domain ◽  
Aspect Ratios ◽  
Energy Focusing ◽  
Mean Kinetic Energy

<div>Ocean abyss is an example of a system with continuous stratification subject to large-scale tidal forcing. Owing to specific dispersion relation of internal waves, the domains bounded by sloping boundaries may support wave patterns with wave rays converging to closed trajectories (geometric attractors) as result of iterative focusing reflections. Previously the behavior of kinetic energy in wave attractors has been investigated in domains with comparable scales of depth and horizontal length. As the geometric aspect ratio of the domain increases, the dynamic pattern of energy focusing may significantly evolve both in laminar and turbulent regimes. The present paper shows that the energy density in domains with large aspect ratio can significantly increase. In numerical simulations the input forcing has been introduced at global scale by prescribing small-amplitude deformations of the upper bound of the liquid domain. The evolution of internal wave motion in such system has been computed numerically for different values of the forcing amplitude. The behavior of the large-aspect-ratio system has been compared to the well-studied case of the system with depth-to-length ratio of order unity.  A number of most typical situations has been analyzed in terms of behavior of integral mechanical quantities such as total dissipation, mean kinetic energy and energy fluctuations in laminar and turbulent cases. The relative mean kinetic energy (normalized by the kinetic energy of the liquid domain undergoing rigid-body oscillations with the amplitude of the wavemaker), may increase by order of magnitude as compared to low-aspect-ratio system.<br>It was shown previously, that in the case of aspect ratio close to unity, the transition to wave turbulence regime is associated with a cascade of triadic wave-wave interactions. Now it is shown that for large aspect ratios the energy cascade in the system is due to generation of superharmonic waves corresponding to integer (including zero) multiples of the forcing frequency. As forcing amplitude increases beyond certain value, an abrupt change is observed in behavior of relative mean kinetic energy and spectra, accompanied with appearance of additional harmonic components corresponding to half-integer (including 1/2) and integer multiples of the forcing frequency.  </div><div> </div>

scholarly journals Numerical Smulation of Internal Waves and Effects of Accumulation of Kinetic Energy in Large Aspect Ratio Domains

2020 ◽  
Vol 32 (6) ◽  
pp. 200-212
Author(s):  
Stepan Alekseevich Elistratov ◽  
Kirill Alexandrovich Vatutin ◽  
Ilias Nailevich Sibgatullin ◽  
Evgeniy Valerievich Ermanyuk ◽  
Evgeny Aleksandrovich Mikhailov
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Internal Waves ◽  
Large Scale ◽  
Deep Ocean ◽  
Global Scale ◽  
Large Aspect Ratio ◽  
Order Unity ◽  
Wave Patterns ◽  
Energy Focusing

Tidal forcing excites internal waves in the bulk of the ocean. Deep ocean is an example of a system with continuous stratification subject to large-scale periodic forcing. Owing to specific dispersion relation of internal waves, the domains bounded by sloping boundaries may support wave patterns with wave rays converging to closed trajectories (geometric attractors) as result of iterative focusing reflections. Previously the behavior of kinetic energy in wave attractors has been investigated in two-dimensional domain with comparable depth and length. As the geometric aspect ratio of the domain increases, the dynamic pattern of energy focusing may significantly evolve both in laminar and turbulent regimes. The present paper shows that the energy density in domains with large aspect ratio can significantly increase. In numerical simulations the input forcing has been introduced at global scale by prescribing small-amplitude deformations of the upper bound of the liquid domain. The evolution of internal wave motion in such system has been computed numerically for different values of the forcing amplitude. The behavior of the large-aspect-ratio system has been compared to the well-studied case of the system with depth-to-length ratio of order unity. A number of most typical situations has been analysed in terms of behavior of integral mechanical quantities such as total dissipation, mean kinetic energy and energy fluctuations in laminar and turbulent cases.

Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratio

2012 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Large Aspect Ratio ◽  
Flow Method ◽  
Dynamic Coefficients ◽  
Aspect Ratios

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with large aspect ratio are calculated by means of a three dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor. For comparison, the dynamic coefficients were also calculated using two other codes: one developed on the bulk flow method and one based on finite difference method. These two sets of dynamic coefficients were compared with those obtained from CFD. Results show a reasonable correlation for the direct stiffness estimates, with largest value predicted by CFD. In terms of cross-coupled stiffness, which is known to be directly related to cross-coupled forces that contribute to rotor instability, the CFD predicts also the highest value; however a much larger discrepancy can be observed for this term (73% higher than value predicted by finite difference method and 79% higher than bulk flow code prediction). Similar large differences in predictions one can see in the estimates for damping and direct mass coefficients, where highest values are predicted by the bulk flow method. These large variations in damping and mass coefficients, and most importantly the large difference in the cross-coupled stiffness predictions, may be attributed to the large difference in seal geometry (i.e. the large aspect ratio AR>1.0 of this seal model vs. the short seal configuration the bulk flow code is usually calibrated for, using an empirical friction factor).

scholarly journals High resolution parameter study of the vertical shear instability

2020 ◽  
Vol 499 (2) ◽  
pp. 1841-1853
Author(s):  
Natascha Manger ◽  
Hubert Klahr ◽  
Wilhelm Kley ◽  
Mario Flock
Keyword(s):  
Aspect Ratio ◽  
Large Scale ◽  
Dead Zone ◽  
Pressure Ratio ◽  
Theoretical Models ◽  
Shear Instability ◽  
Vertical Shear ◽  
Parameter Study ◽  
Aspect Ratios ◽  
Strong Scaling

ABSTRACT Theoretical models of protoplanetary discs have shown the vertical shear instability (VSI) to be a prime candidate to explain turbulence in the dead zone of the disc. However, simulations of the VSI have yet to show consistent levels of key disc turbulence parameters like the stress-to-pressure ratio α. We aim to reconcile these different values by performing a parameter study on the VSI with focus on the disc density gradient p and aspect ratio h = H/R. We use full 2π 3D simulations of the disc for chosen set of both parameters. All simulations are evolved for 1000 reference orbits, at a resolution of 18 cells per h. We find that the saturated stress-to-pressure ratio in our simulations is dependent on the disc aspect ratio with a strong scaling of α∝h2.6, in contrast to the traditional α model, where viscosity scales as ν∝αh2 with a constant α. We also observe consistent formation of large scale vortices across all investigated parameters. The vortices show uniformly aspect ratios of χ ≈ 10 and radial widths of approximately 1.5H. With our findings we can reconcile the different values reported for the stress-to-pressure ratio from both isothermal and full radiation hydrodynamics models, and show long-term evolution effects of the VSI that could aide in the formation of planetesimals.

The Effect of Aspect-Ratio on the Development of the Large-Scale Structures in the Three-Dimensional Wall Jet

2005 ◽  
Author(s):  
Joseph W. Hall ◽  
Daniel Ewing
Keyword(s):  
Aspect Ratio ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Decomposition Analysis ◽  
Wall Pressure ◽  
Symmetric Mode ◽  
Large Scale Structures ◽  
Aspect Ratios ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets exiting rectangular nozzles with aspect-ratios of 1 and 4 was investigated using simultaneous measurements of the fluctuating wall pressure across the jet. The pressure fluctuations in the jets were asymmetric and caused the fluctuating wall pressure to be poorly correlated across the jet centerline. A Proper Orthogonal Decomposition analysis indicated that both the first and second modes make similar contributions to the variance of the fluctuating pressure, and were symmetric and antisymmetric, respectively, and the interplay between these modes caused the asymmetry in the instantaneous pressure fluctuations across the jet centreline. A wavelet analysis of the instantaneously reconstructed pressure fields indicated that the fluctuations were predominantly in two frequency bands near the jet centerline, but were only contained in one band on the outer lateral edges of the jet, indicating there were two different large-scale motions present. The development of large-scale structures in the two jets initially differed in the intermediate field with the antisymmetric mode being more prominent in the square jet and the symmetric mode being more prominent in the larger aspect-ratio jet. Further downstream, the symmetric mode was more prominent in both jets.

Baroclinic and Barotropic Annular Variability in the Northern Hemisphere

2015 ◽  
Vol 72 (3) ◽  
pp. 1117-1136 ◽  
Author(s):  
David W. J. Thompson ◽  
Ying Li
Keyword(s):  
Time Series ◽  
Kinetic Energy ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Spectral Power ◽  
Principal Component ◽  
Eddy Kinetic Energy ◽  
Annular Mode ◽  
Teleconnection Patterns ◽  
Mean Kinetic Energy

Abstract Large-scale variability in the Northern Hemisphere (NH) circulation can be viewed in the context of three primary types of structures: 1) teleconnection patterns, 2) a barotropic annular mode, and 3) a baroclinic annular mode. The barotropic annular mode corresponds to the northern annular mode (NAM) and has been examined extensively in previous research. Here the authors examine the spatial structure and time-dependent behavior of the NH baroclinic annular mode (NBAM). The NAM and NBAM have very different signatures in large-scale NH climate variability. The NAM emerges as the leading principal component (PC) time series of the zonal-mean kinetic energy. It dominates the variance in the wave fluxes of momentum, projects weakly onto the eddy kinetic energy and wave fluxes of heat, and can be modeled as Gaussian red noise with a time scale of ~10 days. In contrast, the NBAM emerges as the leading PC time series of the eddy kinetic energy. It is most clearly identified when the planetary-scale waves are filtered from the data, dominates the variance in the synoptic-scale eddy kinetic energy and wave fluxes of heat, and has a relatively weak signature in the zonal-mean kinetic energy and the wave fluxes of momentum. The NBAM is marked by weak but significant enhanced spectral power on time scales of ~20–25 days. The NBAM is remarkably similar to its Southern Hemisphere counterpart despite the pronounced interhemispheric differences in orography and land–sea contrasts.

scholarly journals Learning Rotated Inscribed Ellipse for Oriented Object Detection in Remote Sensing Images

2021 ◽  
Vol 13 (18) ◽  
pp. 3622
Author(s):  
Xu He ◽  
Shiping Ma ◽  
Linyuan He ◽  
Le Ru ◽  
Chen Wang
Keyword(s):  
Remote Sensing ◽  
Aspect Ratio ◽  
Object Detection ◽  
Large Scale ◽  
Large Aspect Ratio ◽  
Remote Sensing Images ◽  
Orientation Error ◽  
Multi Scale ◽  
Half Axis ◽  
Oriented Object

Oriented object detection in remote sensing images (RSIs) is a significant yet challenging Earth Vision task, as the objects in RSIs usually emerge with complicated backgrounds, arbitrary orientations, multi-scale distributions, and dramatic aspect ratio variations. Existing oriented object detectors are mostly inherited from the anchor-based paradigm. However, the prominent performance of high-precision and real-time detection with anchor-based detectors is overshadowed by the design limitations of tediously rotated anchors. By using the simplicity and efficiency of keypoint-based detection, in this work, we extend a keypoint-based detector to the task of oriented object detection in RSIs. Specifically, we first simplify the oriented bounding box (OBB) as a center-based rotated inscribed ellipse (RIE), and then employ six parameters to represent the RIE inside each OBB: the center point position of the RIE, the offsets of the long half axis, the length of the short half axis, and an orientation label. In addition, to resolve the influence of complex backgrounds and large-scale variations, a high-resolution gated aggregation network (HRGANet) is designed to identify the targets of interest from complex backgrounds and fuse multi-scale features by using a gated aggregation model (GAM). Furthermore, by analyzing the influence of eccentricity on orientation error, eccentricity-wise orientation loss (ewoLoss) is proposed to assign the penalties on the orientation loss based on the eccentricity of the RIE, which effectively improves the accuracy of the detection of oriented objects with a large aspect ratio. Extensive experimental results on the DOTA and HRSC2016 datasets demonstrate the effectiveness of the proposed method.

scholarly journals An experimental study of the effect of the projection ratio and throat-aspect ratio on the efficiency and loss coefficient of a water jet pump

2021 ◽  
Vol 15 (3) ◽  
pp. 8277-8288
Author(s):  
Muhammad Penta Helios ◽  
Wanchai Asvapoositkul
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Water Jet ◽  
Loss Coefficient ◽  
Performance Parameters ◽  
Jet Pump ◽  
Pump System ◽  
Friction Process ◽  
Aspect Ratios

This study focuses on the influence of dimensionless geometry parameters on the performance and loss coefficient of the throat and diffuser of the water jet pump apparatus. A water jet pump system was designed for a total of nine experimental cases with three different projection ratios and three throat-aspect ratios . The volumetric and pressure ratios - performance parameters are measured at a constant motive pressure and under varying backpressure. The efficiencies of the water jet pump in each configuration were assessed and compared. It was found that increasing 2 or 3 times of projection ratio degrades efficiency about 2% to 5.5%, respectively. Higher projection ratio (   > 1) expands the water jet diameter, which clogs the secondary flow. Hence, the changes in  > 3 may have a significant impact on efficiency degradation. Shorter may cause the loss of kinetic energy in the diffuser, while longer  reduces momentum transfer on the secondary flow. Moreover, the changes in  and  influence friction loss coefficient in the throat and diffuser section, and it reduces with increasing of volumetric ratio. It can be concluded that the appropriate value of projection ratio and throat-aspect ratio plays a role in the kinetic energy dissipation. It is also responsible for the location friction process, at a different volumetric ratio. However, the experimental results denoted the best efficiency and loss coefficient was achieved at a low projection ratio ( = 1) and small throat-aspect ratios (  = 5). The best efficiency of the study was about 23.37%.

Turbulent Flow Around Rectangular Cylinders with Different Streamwise Aspect Ratios

2021 ◽  
Author(s):  
Sedem Kumahor ◽  
Mark F. Tachie
Keyword(s):  
Aspect Ratio ◽  
High Speed ◽  
Second Harmonic ◽  
Cylinder Surface ◽  
Large Aspect Ratio ◽  
Reynolds Stresses ◽  
Square Cylinder ◽  
Mean Flow ◽  
Aspect Ratios ◽  
The Mean

Abstract Turbulent flows around a square cylinder and a rectangular cylinder with a streamwise aspect ratio of 5 in a uniform flow were investigated using time-resolved particle image velocimetry. The Reynolds number based on the cylinder height and oncoming flow velocity was 16200. Similarities and differences in the flow dynamics over the cylinders and in the near wake region were examined in terms of the mean flow, Reynolds stresses and triple velocity correlations. The budget of turbulent kinetic energy as well as temporal and spectral analyses were also performed. The results show that the primary, secondary and wake vortexes are smaller for the square cylinder compared to the large aspect ratio cylinder. There are regions of elevated Reynolds stresses and triple velocity correlations along the mean separating streamlines, and the magnitudes of these statistics are an order of magnitude higher over the square cylinder compared to the large aspect ratio cylinder. The topology of the triple velocity correlations shows low-speed ejection and high-speed sweep events, respectively, transporting instantaneous Reynolds normal stresses away from the mean separating streamline into the free-stream and toward the cylinder surface, regardless of aspect ratio. Near the leading and trailing edges of both cylinders, regions of negative turbulence production are observed and the dominant components contributing to this occurrence are discussed. Temporal autocorrelation coefficients of the streamwise and vertical velocity fluctuations show a periodic trend, with a periodicity that is directly linked to the Kármán shedding frequency and its second harmonic.

Large-Aspect-Ratio Structures in Simulated Ocean Surface Boundary Layer Turbulence under a Hurricane

2020 ◽  
Vol 50 (12) ◽  
pp. 3561-3584
Author(s):  
Clifford Watkins ◽  
Daniel B. Whitt
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Aspect Ratio ◽  
Prandtl Number ◽  
Ocean Surface ◽  
Surface Boundary ◽  
Large Aspect Ratio ◽  
Surface Boundary Layer ◽  
Velocity Magnitude ◽  
The Mean

AbstractA large-eddy simulation (LES) initialized and forced using observations is used to conduct a process study of ocean surface boundary layer (OSBL) turbulence in a 2-km box of ocean nominally under Hurricane Irene (2011) in 35 m of water on the New Jersey shelf. The LES captures the observed deepening, cooling, and persistent stratification of the OSBL as the storm approaches and passes. As the storm approaches, surface-intensified Ekman-layer rolls, with horizontal wavelengths of about 200 m and horizontal-to-vertical aspect and velocity magnitude ratios of about 20, dominate the kinetic energy and increase the turbulent Prandtl number from about 1 to 1.5 due partially to their restratifying vertical buoyancy flux. However, as the storm passes, these rolls are washed away in a few hours due to the rapid rotation of the wind. In the bulk OSBL, the gradient Richardson number of the mean profiles remains just above (just below) 1/4 as the storm approaches (passes). At the base of the OSBL, large-aspect-ratio Kelvin–Helmholtz billows, with Prandtl number below 1, intermittently dominate the kinetic energy. Overall, large-aspect-ratio covariance modifies the net vertical fluxes of buoyancy and momentum by about 10%, but these fluxes and the analogous diffusivity and viscosity still approximately collapse to time-independent dimensionless profiles, despite rapid changes in the forcing and the large structures. That is, the evolutions of the mean temperature and momentum profiles, which are driven by the net vertical flux convergences, mainly reflect the evolution of the wind and the initial ocean temperature profile.

Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratios

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Large Aspect Ratio ◽  
Flow Method ◽  
Dynamic Coefficients ◽  
Aspect Ratios

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with a large aspect ratio are calculated by means of a three-dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor. For comparison, the dynamic coefficients were also calculated using two other codes: one developed on the bulk flow method and one based on finite difference method. These two sets of dynamic coefficients were compared with those obtained from CFD. Results show a reasonable correlation for the direct stiffness estimates, with largest value predicted by CFD. In terms of cross-coupled stiffness, which is known to be directly related to cross-coupled forces that contribute to rotor instability, the CFD also predicts the highest value; however, a much larger discrepancy can be observed for this term (73% higher than the value predicted by the finite difference method and 79% higher than the bulk flow code prediction). One can see similar large differences in predictions in the estimates for damping and direct mass coefficients, where the highest values are predicted by the bulk flow method. These large variations in damping and mass coefficients, and most importantly the large difference in the cross-coupled stiffness predictions, may be attributed to the large difference in seal geometry (i.e., the large aspect ratio AR > 1.0 of this seal model versus the short seal configuration the bulk flow code is usually calibrated for using an empirical friction factor).

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