Bubble clustering and trapping in large vortices. Part 1: Triggered bubbly jets investigated by phase-averaging

2007 ◽  
Vol 33 (10) ◽  
pp. 1088-1110 ◽  
Author(s):  
Rade Ž. Milenković ◽  
Beat Sigg ◽  
George Yadigaroglu
Keyword(s):  
Phase Averaging ◽  
Bubbly Jets

scholarly journals Model Verification and Error Sensitivity of Turbulence-Related Tensor Characteristics in Pulsatile Blood Flow Simulations

Fluids ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 11
Author(s):  
Magnus Andersson ◽  
Matts Karlsson
Keyword(s):  
Blood Flow ◽  
Model Verification ◽  
Patient Specific ◽  
Flow Modeling ◽  
Spatiotemporal Resolution ◽  
Flow Simulations ◽  
Phase Averaging ◽  
Confidence Levels ◽  
Cardiovascular Flow ◽  
Computational Fluid Dynamics Cfd

Model verification, validation, and uncertainty quantification are essential procedures to estimate errors within cardiovascular flow modeling, where acceptable confidence levels are needed for clinical reliability. While more turbulent-like studies are frequently observed within the biofluid community, practical modeling guidelines are scarce. Verification procedures determine the agreement between the conceptual model and its numerical solution by comparing for example, discretization and phase-averaging-related errors of specific output parameters. This computational fluid dynamics (CFD) study presents a comprehensive and practical verification approach for pulsatile turbulent-like blood flow predictions by considering the amplitude and shape of the turbulence-related tensor field using anisotropic invariant mapping. These procedures were demonstrated by investigating the Reynolds stress tensor characteristics in a patient-specific aortic coarctation model, focusing on modeling-related errors associated with the spatiotemporal resolution and phase-averaging sampling size. Findings in this work suggest that attention should also be put on reducing phase-averaging related errors, as these could easily outweigh the errors associated with the spatiotemporal resolution when including too few cardiac cycles. Also, substantially more cycles are likely needed than typically reported for these flow regimes to sufficiently converge the phase-instant tensor characteristics. Here, higher degrees of active fluctuating directions, especially of lower amplitudes, appeared to be the most sensitive turbulence characteristics.

A Frequency-Domain Filtering Technique for Triple Decomposition of Unsteady Turbulent Flow

1992 ◽  
Vol 114 (1) ◽  
pp. 45-51 ◽  
Author(s):  
G. J. Brereton ◽  
A. Kodal
Keyword(s):  
Time Series ◽  
Turbulent Flow ◽  
Frequency Domain ◽  
Measurement Data ◽  
Averaging Technique ◽  
Phase Averaging ◽  
Spectral Estimates ◽  
Improved Performance ◽  
A New Technique ◽  
Flow Variables

A new technique is presented for decomposing unsteady turbulent flow variables into their organized unsteady and turbulent components, which appears to offer some significant advantages over existing ones. The technique uses power-spectral estimates of data to deduce the optimal frequency-domain filter for determining the organized and turbulent components of a time series of data. When contrasted with the phase-averaging technique, this method can be thought of as replacing the assumption that the organized motion is identically reproduced in successive cycles of known periodicity by a more general condition: the cross-correlation of the organized and turbulent components is minimized for a time series of measurement data, given the expected shape of the turbulence power spectrum. The method is significantly more general than the phase average in its applicability and makes more efficient use of available data. Performance evaluations for time series of unsteady turbulent velocity measurements attest to the accuracy of the technique and illustrate the improved performance of this method over the phase-averaging technique when cycle-to-cycle variations in organized motion are present.

Phase averaging in one-dimensional random systems

1982 ◽  
Vol 26 (8) ◽  
pp. 4742-4744 ◽  
Author(s):  
C. J. Lambert ◽  
M. F. Thorpe
Keyword(s):  
Random Systems ◽  
One Dimensional ◽  
Phase Averaging

Phase Averaging by Wavelet Transformation and the Application to Periodically Fluctuated Separation Flow

2002 ◽  
Author(s):  
Masaki Yamagishi ◽  
Tomoko Togano ◽  
Shinichi Tashiro
Keyword(s):  
Shear Layer ◽  
Wavelet Transformation ◽  
Dominant Frequency ◽  
Separation Flow ◽  
Mean Flow ◽  
Field Phase ◽  
Phase Averaging ◽  
Separated Shear Layer ◽  
The Mean ◽  
Almost All

The vortex structures in a separated region are generated by the motion of the separated shear layer caused by the introduction of periodic fluctuation. The main cause of the motion of the separated shear layer is the external fluctuation with the characteristic frequency. In order to investigate the principal motion of the velocity field, phase averaging was conducted to the velocity signals obtained by single hot-wire measurement. In phase averaging, wavelet analysis was applied to obtain the dominant frequency and the characteristic phase in the fluctuation. The profiles and the contours of the phase-averaged velocity could be found and discussed. The profiles vary dynamically at each phase and show the periodic motion of the shear layer. The separated shear layer flutters with the external fluctuation in the mean flow. If the suitable frequency is selected in the external fluctuation, the separated region disappears in almost all each phases owing to the depression of the shear layer near the wall.

Phase Averaging Analysis of the Unsteady Velocity Profiles in a Separated Flow

2003 ◽  
Author(s):  
Masaki Yamagishi ◽  
Tomoko Togano ◽  
Shinichi Tashiro
Keyword(s):  
Phase Angle ◽  
Wavelet Transformation ◽  
Separated Flow ◽  
Time Dependent ◽  
Frequency Data ◽  
Two Phase ◽  
Averaging Technique ◽  
Phase Averaging ◽  
Dependent Signal ◽  
Averaging Techniques

By using phase averaging technique, turbulent structure in a flow was studied. For the phase angle of the time dependent signal modulated in frequency, data acquisition is difficult. This study proposed a new method of phase averaging by wavelet transformation. The purpose of the present study is to compare the results of the phase averaging by wavelet transformation with those by the traditional phase averaging technique. These two phase averaging techniques were applied to the experimental data of the velocities in a separated flow with periodical fluctuation. Between the results by these techniques, noticeable differences were shown. If the velocity signals include the frequency modulation, the profiles of phase-averaged velocity by the traditional technique will have nearly the same shapes and be similar to those of time-averaged velocity. On the other hand, the profiles by wavelet transformation showed the clear differences at each phase angle even for the velocity signals with modulated frequencies.

scholarly journals Benchmark Sea Trials on a 6-Meter Boat Powered by Kite

2020 ◽  
Vol 10 (18) ◽  
pp. 6148
Author(s):  
Kostia Roncin ◽  
Morgan Behrel ◽  
Paul Iachkine ◽  
Jean-Baptiste Leroux
Keyword(s):  
High Resolution ◽  
Power Law ◽  
Measurement System ◽  
Averaging Method ◽  
Wind Measurement ◽  
Phase Averaging

This paper presents sea trials on a 6-m boat specifically designed for kite propulsion. The kite control was automatic or manual, dynamic or static, depending on the point of sailing. The measurement system recorded boat motion and load generated by the kite. A particular attention was paid to wind measurement with several fixed and mobile locations directly on the kiteboat or in the vicinity. A high resolution weather modelling showed that a classical power law, describing the wind gradient, was not satisfactory to get the wind at kite location. 5-min measurement phases were systematically recorded. In the end, 101 runs were carried out. Data were processed with the phase-averaging method in order to produce reliable and accurate results.

The Phenomenon of Bubbles Negative Relative Velocity in Vertical Bubbly Jets

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Jamel Chahed ◽  
Aroua Aouadi ◽  
Mariem Rezig ◽  
Ghazi Bellakhal
Keyword(s):  
Slip Velocity ◽  
Added Mass ◽  
Mass Force ◽  
Relative Slip ◽  
Velocity Inversion ◽  
Injection Zone ◽  
Bubbly Jet ◽  
New Formulation ◽  
Interfacial Force ◽  
Bubbly Jets

Many experiments demonstrate that the bubble relative (slip) velocities in vertical turbulent sheared bubbly flows are significantly lower than those in quiescent infinite fluid. Moreover, vertical bubbly jet experiments performed by Sun and Faeth (1986, “Structure of Turbulent Bubbly Jets-1. Methods and Centerline Properties,” Int. J. Multiphase Flow, 12(1), pp. 99–114) indicate that bubble slip velocities have negative values in the high sheared zone near the injector. The present analysis shows that the phenomenon of the slip velocity inversion is associated with the effect of the turbulent part of the interfacial force. A new formulation of the turbulent contribution of the added mass force is proposed. This formulation is analyzed using the vertical bubbly jet experimental data. The results provide evidence that the turbulent contribution of the added mass force is at the origin of the slip velocity reduction and could explain the appearance of the negative values observed in bubbly jet experiments. As a whole, the turbulent contribution of the added mass force which comprises two terms (a nonlinear turbulent term and a convective acceleration term associated to the drift velocity) opposes the action of the gravity and their effect may be high enough to produce negative slip velocities. Taken separately, the two turbulent terms cannot explain the reversal and the reduction of slip through the entire section in the near injection zone of the bubbly jet. The combined effect of the two turbulent terms makes it possible to reproduce slip velocity profiles as observed in the near injection zone.

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