Symmetry Breaking and Mode-Interaction in Vortex-Structure Interaction

2002 ◽  
Author(s):  
Njuki W. Mureithi ◽  
Hiroshi Kanki ◽  
Syuki Goda ◽  
Tomomichi Nakamura ◽  
Tomoharu Kashikura
Keyword(s):  
Vortex Structure ◽  
Frequency Ratio ◽  
Flow Direction ◽  
Temporal Structure ◽  
Experimental Tests ◽  
Mode Interaction ◽  
Structure Interaction ◽  
Shedding Frequency ◽  
Spatio Temporal ◽  
Temporal Symmetry

This paper presents some results of experiments and numerical computations on various aspects of vortex-structure interaction. Experimental tests were conducted in a small wind tunnel to investigate the effect of mechanical cylinder oscillation in the flow direction on the wake vortex structure. Depending on the excitation to Karman shedding frequency ratio, mode locked states, in the form of spatio-temporally repeatable patterns, could be observed. Symmetrical excitation leads to breaking of the Karman mode spatial-temporal symmetry. Depending on the excitation to Karman frequency ratio, modes lacking the usual Karman symmetry is observed. The existence of a stable spatio-temporal structure appears to be strongly dependent on the interaction (lock-in) between the near wake symmetrical shedding and the ‘established’ far wake Karman pattern. Preliminary work based on symmetry (group) theory is presented to support the foregoing experimental observations. By considering two oscillators having the Dm (κ,2π / m) inline shedding symmetry and the Karman wake having the spatio-temporal symmetry Z2 (κ,π), the possible symmetries of subsequent flow perturbations resulting from the modal interaction are determined. A mode having the reduced symmetry, Z2 (I,π2) was theoretically predicted and confirmed in the experiments. Finally, experimental tests show strong subharmonic lockin for forcing at rational ratios the vortex shedding frequency in the range 1 < m/n < 2. This phenomenon was also predicted theoretically.

scholarly journals Modulated waves in a periodically driven annular cavity

2010 ◽  
Vol 667 ◽  
pp. 336-357 ◽  
Author(s):  
H. M. BLACKBURN ◽  
J. M. LOPEZ
Keyword(s):  
Symmetry Group ◽  
Temporal Dynamics ◽  
Travelling Waves ◽  
Temporal Structure ◽  
Three Dimensional ◽  
Spanwise Direction ◽  
Two Dimensional ◽  
Periodically Driven ◽  
Spatio Temporal ◽  
Temporal Symmetry

Time-periodic flows with spatio-temporal symmetry Z2 × O(2) – invariance in the spanwise direction generating the O(2) symmetry group and a half-period-reflection symmetry in the streamwise direction generating a spatio-temporal Z2 symmetry group – are of interest largely because this is the symmetry group of periodic laminar two-dimensional wakes of symmetric bodies. Such flows are the base states for various three-dimensional instabilities; the periodically shedding two-dimensional circular cylinder wake with three-dimensional modes A and B being the generic example. However, it is not easy to physically realize the ideal flows owing to the presence of end effects and finite spanwise geometries. Flows past rings are sometimes advanced as providing a relevant idealization, but in fact these have symmetry group O(2) and only approach Z2 × O(2) symmetry in the infinite aspect ratio limit. The present work examines physically realizable periodically driven annular cavity flows that possess Z2 × O(2) spatio-temporal symmetry. The flows have three distinct codimension-1 instabilities: two synchronous modes (A and B), and two manifestations of a quasi-periodic (QP) mode, either as modulated standing waves or modulated travelling waves. It is found that the curvature of the system can determine which of these modes is the first to become unstable with increasing Reynolds number, and that even in the nonlinear regime near onset of three-dimensional instabilities the dynamics are dominated by mixed modes with complicated spatio-temporal structure. Supplementary movies illustrating the spatio-temporal dynamics are available at journals.cambridge.org/flm.

Dynamics of a Cylinder Wake Under Controlled Excitation

2003 ◽  
Author(s):  
Njuki W. Mureithi ◽  
Syuki Goda ◽  
Tomomichi Nakamura
Keyword(s):  
Frequency Ratio ◽  
Period Doubling ◽  
Experimental Tests ◽  
The Other ◽  
Mode Interaction ◽  
Theoretic Approach ◽  
Cylinder Wake ◽  
Strong Response ◽  
Asymmetric Mode ◽  
Other Hand

This paper presents some results of experimental tests as well as a group theoretic analysis of a 2D cylinder wake under forced excitation. The response of the Karman wake (K mode) to external perturbations is studied. Reflection-symmetric (S mode) perturbations and asymmetric (K1 mode) perturbations are considered. The perturbations are generated by mechanically oscillating the test cylinder. Tests were done in a small wind tunnel. Depending on the excitation to Karman shedding frequency ratio, mode locked states, in the form of spatio-temporally fixed patterns, could be observed. Harmonic asymmetric (mode K1=K) forcing at the Karman frequency strongly enhanced the Karman mode. Superharmonic forcing (with mode K1 ≠ K) had little effect on the Karman mode K. However, a detuning effect was observed. On the other hand, subharmonic (1/2, 1/3) K1 mode forcing significantly affected the K mode, with strong response at K1 mode harmonics. Subharmonic S mode excitation had a damping effect on the K mode. On the other hand harmonic and superharmonic forcing triggered a period-doubling instability, destroying the original K mode. Using a group theoretic approach, the general amplitude equations governing the interaction of the S/K1 modes with the K mode have been derived. A qualitative analysis of the equations helps explains some of the experimental results. For K1/K mode interactions, the symmetrical ‘compatibility’, via common subgroups, explains the strong resonances observed experimentally for 1/1 and 1/3 frequency ratios. For a frequency ratio 1/2, it is shown that K1 and K mode symmetries are incompatible; the two modes do not have a common symmetry subgroup. Consequently, traveling wave solutions, induced by total symmetry breaking, rather than standard steady state modes are expected to be more likely to occur. For S/K mode interaction, an earlier result is reiterated; thus, the Karman mode is shown, theoretically, to be destroyed via a period-doubling instability. This effect occurs for S mode frequencies as high as 3 times the Karman frequency.

scholarly journals Performance Characteristics in Runner of an Impulse Water Turbine with Splitter Blade

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 303
Author(s):  
Lingdi Tang ◽  
Shouqi Yuan ◽  
Yue Tang ◽  
Zhijun Gao
Keyword(s):  
Energy Conversion ◽  
Flow Direction ◽  
Mechanical Energy ◽  
Experimental Tests ◽  
High Energy ◽  
Negative Energy ◽  
Water Turbine ◽  
Conversion Performance ◽  
Water Turbines ◽  
Current Energy

The impulse water turbine is a promising energy conversion device that can be used as mechanical power or a micro hydro generator, and its application can effectively ease the current energy crisis. This paper aims to clarify the mechanism of liquid acting on runner blades, the hydraulic performance, and energy conversion characteristics in the runner domain of an impulse water turbine with a splitter blade by using experimental tests and numerical simulations. The runner was divided into seven areas along the flow direction, and the power variation in the runner domain was analyzed to reflect its energy conversion characteristics. The obtained results indicate that the critical area of the runner for doing the work is in the front half of the blades, while the rear area of the blades does relatively little work and even consumes the mechanical energy of the runner to produce negative work. The high energy area is concentrated in the flow passage facing the nozzle. The energy is gradually evenly distributed from the runner inlet to the runner outlet, and the negative energy caused by flow separation with high probability is gradually reduced. The clarification of the energy conversion performance is of great significance to improve the design of impulse water turbines.

scholarly journals Effect of Bottom Geometry on the Natural Sloshing Motion of Water Inside Tanks: An Experimental Analysis

2021 ◽  
Vol 11 (2) ◽  
pp. 605
Author(s):  
Antonio Agresta ◽  
Nicola Cavalagli ◽  
Chiara Biscarini ◽  
Filippo Ubertini
Keyword(s):  
Energy Dissipation ◽  
Water Depth ◽  
Shear Force ◽  
Experimental Tests ◽  
Shear Load ◽  
Damping Properties ◽  
Base Shear ◽  
Structure Interaction ◽  
Sloshing Phenomenon ◽  
Key Aspects

The present work aims at understanding and modelling some key aspects of the sloshing phenomenon, related to the motion of water inside a container and its effects on the substructure. In particular, the attention is focused on the effects of bottom shapes (flat, sloped and circular) and water depth ratio on the natural sloshing frequencies and damping properties of the inner fluid. To this aim, a series of experimental tests has been carried out on tanks characterised by different bottom shapes installed over a sliding table equipped with a shear load cell for the measurement of the dynamic base shear force. The results are useful for optimising the geometric characteristics of the tank and the fluid mass in order to obtain enhanced energy dissipation performances by exploiting fluid–structure interaction effects.

Evidence of soil-structure interaction from modular full-scale field experimental tests

2021 ◽  
Author(s):  
Athanasios Vratsikidis ◽  
Dimitris Pitilakis ◽  
Anastasios Anastasiadis ◽  
Anastasios Kapouniaris
Keyword(s):  
Soil Structure ◽  
Experimental Tests ◽  
Full Scale ◽  
Soil Structure Interaction ◽  
Structure Interaction ◽  
Scale Field

scholarly journals Disrupting the spatio-temporal symmetry of the electron dynamics in atmospheric pressure plasmas by voltage waveform tailoring

2019 ◽  
Vol 28 (1) ◽  
pp. 01LT01 ◽  
Author(s):  
Andrew R Gibson ◽  
Zoltán Donkó ◽  
Layla Alelyani ◽  
Lena Bischoff ◽  
Gerrit Hübner ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Electron Dynamics ◽  
Voltage Waveform ◽  
Atmospheric Pressure Plasmas ◽  
Spatio Temporal ◽  
Temporal Symmetry
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