Interference Between Two Tandem Cylinders of Different Diameters

2006 ◽  
Author(s):  
Md. Mahbub Alam ◽  
Y. Zhou
Keyword(s):  
Low Frequency ◽  
Shear Layers ◽  
Diameter Ratio ◽  
The Other ◽  
Flow Structures ◽  
Incident Flow ◽  
Tandem Cylinders ◽  
Cylinder Diameter ◽  
Different Diameters ◽  
Dominant Frequencies

This paper presents a detailed investigation of Strouhal frequencies, forces and flow structures resulting from the interference between two tandem cylinders of different diameters. The upstream cylinder diameter (d) was varied from 25 mm to 6 mm, while the downstream cylinder diameter (D) of 25 mm was unchanged, the corresponding diameter ratio, d/D, being 1.0 ∼ 0.24. The spacing between the cylinders was 5.5d. At this spacing, the shear layers separated from the upstream cylinder roll up alternately, forming a vortex street in the gap between and behind the cylinders. Two dominant frequencies are detected behind the downstream cylinder at d/D = 1.0 ∼ 0.4. One is the same as detected between the cylinders, and the other is of relatively low frequency and is probably generated by the downstream cylinder. Whilst the former remains unchanged, the latter increases with decreasing d/D, due to an increase in the incident flow velocity of the downstream cylinder. The time-averaged drag on the downstream cylinder also increases with decreasing d/D, though the fluctuating forces drop because vortices impinging upon the downstream cylinder are impaired by decreasing d/D.

Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification

2008 ◽  
Vol 607 ◽  
pp. 51-80 ◽  
Author(s):  
J. C. HU ◽  
Y. ZHOU
Keyword(s):  
Initial Conditions ◽  
Shear Layers ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Incident Flow ◽  
Flow Topology ◽  
Single Vortex ◽  
Single Body ◽  
Image Velocimetry ◽  
Different Types

Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re=7000 using hot-wire, flow-visualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P, ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle (α) between the incident flow and the line through the cylinder centres is 0° ~ 90°. Four distinct flow structures are identified at x/d ≥ 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. S-Ia and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P/d ≤ 1.2. The pair of cylinders behaves like one single body, and shear layers separated from the free-stream sides of the cylinders roll up, forming one street of alternately arranged vortices. The street is comparable to that behind an isolated cylinder in terms of the topology and strength of vortices. Mode S-Ib occurs at α ≤ 10° and P/d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P/d=1.2~2.5 and α>20° or 1.5≤P/d≤4.0 and 10° < α≤20°, where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d≤5.0. The two streets interact vigorously, resulting in a single street of the lower-frequency vortices at x/d≥10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P/d≥2.5 and α=20°~88°; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d=10. At P/d≥2.5 and α≥88°, the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St≈0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed.

Lift Coefficients and Pressure Distribution Acting on Two Tandem Cylinders of Different Diameters

2014 ◽  
Vol 886 ◽  
pp. 417-421
Author(s):  
Yong Tao Wang ◽  
Zhong Min Yan ◽  
Hui Min Wang
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Flow Characteristics ◽  
Diameter Ratio ◽  
Tandem Arrangement ◽  
Tandem Cylinders ◽  
Gap Ratio ◽  
Different Diameters ◽  
Upstream Control ◽  
Control Cylinder

Flow characteristics of two different diameters cylinders in a tandem arrangement were investigated numerically in a uniform flow. The diameter of the downstream main cylinder was kept constant, and the diameter ratio between the upstream control cylinder and the downstream one was varied from 0.1 to 1.0. The studied Reynolds number based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder ranged from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on the lift coefficients and pressure distribution.

Drag Coefficients Acting on Two Tandem Cylinders of Different Diameters

2014 ◽  
Vol 886 ◽  
pp. 413-416
Author(s):  
Yong Tao Wang ◽  
Zhong Min Yan ◽  
Hui Min Wang
Keyword(s):  
Flow Characteristics ◽  
Diameter Ratio ◽  
Circular Cylinders ◽  
Drag Coefficients ◽  
Tandem Cylinders ◽  
Gap Ratio ◽  
Different Diameters ◽  
Volume Method ◽  
Upstream Control ◽  
Control Cylinder

The flow past two tandem circular cylinders of different diameters is simulated by using a finite volume method. The diameter of the downstream main cylinder is kept constant, and the diameter ratio between the upstream control cylinder and the downstream one is varied from 0.1 to 1.0. The Reynolds number based on the diameter of the downstream main cylinder is 100 and 150. The gap between the control cylinder and the main cylinder ranges from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on the drag coefficients and flow characteristics.

scholarly journals Investigation of Low-Frequency Phenomena within Flow Pattern in Standard Mixing Vessel Induced by Pitched Blade Impeller

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 545
Author(s):  
Tomáš Brůha ◽  
Pavel Procházka ◽  
Václav Uruba
Keyword(s):  
Flow Pattern ◽  
Liquid Surface ◽  
Low Frequency ◽  
Flow Patterns ◽  
Flow Structures ◽  
Mean Flow ◽  
Main Plane ◽  
Piv Measurement ◽  
Significant Difference ◽  
Dominant Frequencies

An experimental study on the flow pattern dynamics in a standard mixing vessel with radial baffles filled with water and induced by a pitched blade impeller pumping downward is presented. Investigation is mainly focused on detection and analysis of quasi-periodical or periodical low-frequency phenomenon connected with time- and length-scales considerably exceeding the Blade Passage Frequency (hereinafter BPF) and common turbulent eddies. This phenomenon, which is expressed as large-scale mean-flow variations, is generally known as flow Macro-Instability (hereinafter MI). It could break-down just below the liquid surface, or it crashes to the liquid surface and causes its Macro-Swelling (hereinafter MS). Our investigation was based on classical two-dimensional (2D) Particle Image Velocimetry (hereinafter PIV) measurement within 3 selected vertical planes in the vessel and subsequent analysis of the velocity field. The dominant frequencies evaluated in the selected points and overall analysis of the quasi-periodical macro-flow pattern behavior is to be shown. Identification of the quasi-periodical substructures appeared within the flow pattern was performed using the Oscillation Pattern Decomposition (hereinafter OPD) method. Observation of the macro-flow patterns confirmed presence of the macro-flow structures detected within flow pattern at the identical mixing pilot plant setup by previous investigations of the MIs phenomenon, i.e., the primary circulation loop and strong impeller discharge jet located in the lower vessel segment and the strong ascending wall current at the baffle, which break-down below the surface very often. A further important contribution of the presented work is the investigation of both flow pattern within the baffles vicinity and in the middle of the sector far from the baffle, showing a significant difference. Low-frequency periodical (or quasi-periodical) behavior of the investigated macro-structures was qualitatively confirmed by the presented results and it was quantified using the velocity dominant frequencies evaluation, as noted below. This frequency analysis brings insight into the supposed and detected interconnections between dynamics of the adjacent flow structures. Detected different flow patterns within the main plane near the baffles and in the inclined plane reveal a strong influence of the baffle presence to the local vertical flow, especially within the upper part of the vessel. Quite a different flow pattern appears tangentially in front of and behind the baffle, where a wake is revealed, indicating significant influence of the baffle on the local tangential flow. The new findings represent a contribution to better understanding the physical phenomena behind the standard mixing process.

The Axis Feature: Illusionary Effects on Children's Judgments of Length

1982 ◽  
Vol 55 (3) ◽  
pp. 720-722
Author(s):  
Anat Scher
Keyword(s):  
Relative Length ◽  
The Other ◽  
Context Model ◽  
Structural Pattern ◽  
Perceptual Judgments ◽  
Length Estimation ◽  
Different Diameters

The effect of the position of lines on length estimation was investigated. 40 5-yr.-olds were asked to compare the two arms of an L-shaped figure presented inside circular frames of different diameters. For each figure one of the arms was on the axis, that is, the diameter, and the other arm was perpendicular to that axis. In making perceptual judgments about the relative length of two lines the children tended to describe the on-axis line as longer than the off-axis line. This illusion which, presumably, reflects a perceptual force induced by the characteristics of the structural pattern, supports the context model of visual anomalies.

scholarly journals Nucleotide Variation at theCHALCONE ISOMERASELocus inArabidopsis thaliana

Genetics ◽  
2000 ◽  
Vol 155 (2) ◽  
pp. 863-872 ◽  
Author(s):  
Helmi Kuittinen ◽  
Montserrat Aguadé
Keyword(s):  
Nucleotide Diversity ◽  
Direct Relationship ◽  
Selective Sweep ◽  
Balancing Selection ◽  
Neutral Theory ◽  
Low Frequency ◽  
The Other ◽  
Nucleotide Variation ◽  
Rapid Population Growth ◽  
History Of

AbstractAn ~1.9-kb region encompassing the CHI gene, which encodes chalcone isomerase, was sequenced in 24 worldwide ecotypes of Arabidopsis thaliana (L.) Heynh. and in 1 ecotype of A. lyrata ssp. petraea. There was no evidence for dimorphism at the CHI region. A minimum of three recombination events was inferred in the history of the sampled ecotypes of the highly selfing A. thaliana. The estimated nucleotide diversity (θTOTAL = 0.004, θSIL = 0.005) was on the lower part of the range of the corresponding estimates for other gene regions. The skewness of the frequency spectrum toward an excess of low-frequency polymorphisms, together with the bell-shaped distribution of pairwise nucleotide differences at CHI, suggests that A. thaliana has recently experienced a rapid population growth. Although this pattern could also be explained by a recent selective sweep at the studied region, results from the other studied loci and from an AFLP survey seem to support the expansion hypothesis. Comparison of silent polymorphism and divergence at the CHI region and at the Adh1 and ChiA revealed in some cases a significant deviation of the direct relationship predicted by the neutral theory, which would be compatible with balancing selection acting at the latter regions.

Aerodynamics of Contra-Rotating Fans With Swept Blades

2015 ◽  
Author(s):  
K. Vijayraj ◽  
M. Govardhan
Keyword(s):  
Rotational Speed ◽  
Axial Flow ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
The Other ◽  
Flow Structures ◽  
Current Investigation ◽  
Rotating System ◽  
Stall Margin ◽  
Static Head

A Counter-Rotating System (CRS) is composed of a front rotor and a rear rotor which rotates in the opposite direction. Compared with traditional rotor-stator system, the rear rotor is used not only to recover the static head but also to supply energy to the fluid. Therefore, to achieve the same performance, the use of a CRS may lead to a reduction of the rotational speed and may generate better homogeneous flow downstream of the stage. On the other hand, the mixing area in between the two rotors induces complicated interacting flow structures. Blade sweep has attracted the turbomachinery blade designers owing to a variety of performance benefits it offers. However, the effect of blade sweep on the performance, stall margin improvements whether it is advantageous/disadvantageous to sweep one or both rotors has not been studied till now. In the current investigation blade sweep on the performance characteristics of contra rotating axial flow fans are studied. Two sweep schemes (axial sweeping and tip chord line sweeping) are studied for two sweep angles (20° and 30°). Effect of blade sweep on front rotor and rear rotor are dealt separately by sweeping one at a time. Both rotors are swept together and effect of such sweep scheme on the aerodynamic performance of the stage is also reported here. The performance of contra rotating fan is significantly affected by all these parameters. Blade sweep improved the pressure rise and stall margin of front rotors. Axially swept rotors are found to have higher pressure rise with reduced incidence losses near the tip for front rotors. Sweeping the rear rotor is not effective since the pressure rise is less than that of unswept rotor and also has less stall margin.

A periodic seismic isolation foundation with an extremely broad low-frequency attenuation zone: Theoretical analysis and experimental verification

2021 ◽  
pp. 136943322110646
Author(s):  
Peng Zhou ◽  
Shui Wan ◽  
Xiao Wang ◽  
Yingbo Zhu ◽  
Muyun Huang
Keyword(s):  
Seismic Isolation ◽  
Seismic Waves ◽  
Periodic Structures ◽  
Finite Size ◽  
Low Frequency ◽  
Bridge Structure ◽  
Engineering Structures ◽  
P Waves ◽  
New Type ◽  
Dominant Frequencies

The attenuation zones (AZs) of periodic structures can be used for seismic isolation design. To cover the dominant frequencies of more seismic waves, this paper proposes a new type of periodic isolation foundation (PIF) with an extremely wide low-frequency AZ of 3.31 Hz–17.01 Hz composed of optimized unit A with a wide AZ and optimized unit B with a low-frequency AZ. The two kinds of optimized units are obtained by topology optimization on the smallest periodic unit with the coupled finite element-genetic algorithm (GA) methodology. The transmission spectra of shear waves and P-waves through the proposed PIF of finite size are calculated, and the results show that the AZ of the PIF is approximately the superposition of the AZs of the two kinds of optimized units. Additionally, shake tests on a scale PIF specimen are performed to verify the attenuation performance for elastic waves within the designed AZs. Furthermore, numerical simulations show that the acceleration responses of the bridge structure with the proposed PIF are attenuated significantly compared to those with a concrete foundation under the action of different seismic waves. Therefore, the newly proposed PIF is a promising option for the reduction of seismic effects in engineering structures.

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