Sound Radiation From Two Side-by-Side Rectangular Cylinders With Slightly Different Aspect Ratios

2015 ◽  
Author(s):  
Ressa Octavianty ◽  
Masahito Asai
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Sound Radiation ◽  
Reynolds Numbers ◽  
Low Mach Number ◽  
Aspect Ratios ◽  
Square Cylinders ◽  
Vortex Streets ◽  
Rectangular Cylinders ◽  
Center Distance

Sound radiation from two side-by-side rectangular cylinders, one of which had a square cross-section and the other had a rectangular cross-section with aspect ratio AR = 1.2 to 1.5, was examined experimentally at Reynolds numbers Re = 1.0 × 104 - 3.3 × 104 in low Mach number flows. The center-to-center distance between two cylinders T/D was 3.6, 4.5 and 6.0. When the center-to-center distance was small, T/d = 3.6, vortex streets from two different cylinders were synchronized with the same frequency as that for a pair of identical square cylinders, even for the cylinder pair of ARs = 1.0 and 1.5. Sound radiation was dipole-like (planar-anti-symmetric), unlike in the case of square-cylinders-pair where sound radiation was in-phase. For larger cylinder spacing T/d = 6, highly modulated sound was radiated with two different frequencies due to non-synchronized vortex shedding from two cylinders.

scholarly journals Hydrodynamic Entrance Length for Laminar Flow in Microchannels with Rectangular Cross Section

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 240
Author(s):  
Germán Ferreira ◽  
Artur Sucena ◽  
Luís L. Ferrás ◽  
Fernando T. Pinho ◽  
Alexandre M. Afonso
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Creeping Flow ◽  
Low Reynolds Numbers ◽  
Viscous Forces ◽  
Aspect Ratios ◽  
Judicious Choice ◽  
Microsystem Design

This work presents a detailed numerical investigation on the required development length (L=L/B) in laminar Newtonian fluid flow in microchannels with rectangular cross section and different aspect ratios (AR). The advent of new microfluidic technologies shifted the practical Reynolds numbers (Re) to the range of unitary (and even lower) orders of magnitude, i.e., creeping flow conditions. Therefore, accurate estimations of L at Re≤O(1) are important for microsystem design. At such low Reynolds numbers, in which inertial forces are less dominant than viscous forces, flow characteristics become necessarily different from those at the macroscale where Re is typically much larger. A judicious choice of mesh refinement and adequate numerical methods allowed obtaining accurate results and a general correlation for estimating L, valid in the ranges 0≤Re≤2000 and 0.1≤AR≤1, thus covering applications in both macro and microfluidics.

Heat Transfer for Laminar Flow in Spiral Ducts of Rectangular Cross Section

2005 ◽  
Vol 127 (3) ◽  
pp. 352-356 ◽  
Author(s):  
Michael W. Egner ◽  
Louis C. Burmeister
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Aspect Ratios ◽  
Small Pitch

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined by making use of the FLUENT computational fluid dynamics program. The peripherally averaged Nusselt number is presented as a function of distance from the inlet and of the Dean number. Fully developed values of the Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in postentry regions. These results are applicable to spiral-plate heat exchangers.

Topology of vortex breakdown in closed polygonal containers

2017 ◽  
Vol 820 ◽  
pp. 263-283 ◽  
Author(s):  
Igor V. Naumov ◽  
Irina Yu. Podolskaya
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Cylindrical Container ◽  
Stagnation Points ◽  
Aspect Ratios ◽  
Particle Visualization ◽  
Cross Section Geometry

The topology of vortex breakdown in the confined flow generated by a rotating lid in a closed container with a polygonal cross-section geometry has been analysed experimentally and numerically for different height/radius aspect ratios $h$ from 0.5 to 3.0. The locations of stagnation points of the breakdown bubble emergence and corresponding Reynolds numbers were determined experimentally and numerically by STAR-CCM+ computational fluid dynamics software for square, pentagonal, hexagonal and octagonal cross-section configurations. The flow pattern and velocity were observed and measured by combining seeding particle visualization and laser Doppler anemometry. The vortex breakdown size and position on the container axis were identified for Reynolds numbers ranging from 500 to 2800 in steady flow conditions. The obtained results were compared with the flow structure in the closed cylindrical container. The results allowed revealing regularities of formation of the vortex breakdown bubble depending on $Re$ and $h$ and the cross-section geometry of the confined container. It was found in a diagram of $Re$ versus $h$ that reducing the number of cross-section angles from eight to four shifts the breakdown bubble location to higher Reynolds numbers and a smaller aspect ratio. The vortex breakdown bubble area for octagonal cross-section was detected to correspond to the one for the cylindrical container but these areas for square and cylindrical containers do not overlap in the entire range of aspect ratio.

Secondary Flow and Hydraulic Losses Within Sinuous Conduits of Rectangular Cross Section

1992 ◽  
Vol 114 (4) ◽  
pp. 593-600 ◽  
Author(s):  
Yukimaru Shimizu ◽  
Yoshiki Futaki ◽  
C. Samuel Martin
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Flow Patterns ◽  
Geometric Configuration ◽  
Hydraulic Losses ◽  
Aspect Ratios ◽  
Wide Range ◽  
The Relationship

This paper describes the relationship between hydraulic losses and secondary flow within sinuous conduits with complicated bends. It has been found that the nature of secondary flow present in the bends is quite sensitive to the geometric configuration of the bend and the actual aspect ratio of the conduit section. Indeed, many different secondary flow patterns have been found to exist as the bend geometry is altered. A wide range of experiments has been conducted for various aspect ratios of a rectangular conduit with different curvatures.

Linear stability of rectangular cavity flows driven by anti-parallel motion of two facing walls

2002 ◽  
Vol 458 ◽  
pp. 153-180 ◽  
Author(s):  
S. ALBENSOEDER ◽  
H. C. KUHLMANN
Keyword(s):  
Aspect Ratio ◽  
Linear Stability ◽  
Cross Section ◽  
Strain Field ◽  
Rectangular Cross Section ◽  
Small Range ◽  
Critical Mode ◽  
Plane Flow ◽  
Aspect Ratios ◽  
The Cross

The flow in an infinite slab of rectangular cross-section is investigated numerically by a finite volume method. Two facing walls which move parallel to each other with the same velocity, but in opposite directions, drive a plane flow in the cross-section of the slab. A linear stability analysis shows that the two-dimensional flow becomes unstable to different modes, depending on the cross-sectional aspect ratio, when the Reynolds number is increased. The critical mode is found to be stationary for all aspect ratios. When the separation of the moving walls is larger than approximately twice the height of the cavity, the basic flow forms two vortices, each close to one of the moving walls. The instability of this flow is of centrifugal type and similar to that in the classical lid-driven cavity problem with a single moving wall. When the moving walls are sufficiently close to each other (aspect ratio less than 2) the two vortices merge and form an elliptically strained vortex. Owing to the dipolar strain this flow becomes unstable through the elliptic instability. When both moving walls are very close, the finite-length plane-Couette flow becomes unstable by a similar elliptic mechanism near both turning zones. The critical mode produces wide streaks reaching far into the cavity. For a small range of aspect ratios near unity the flow consists of a single vortex. Here, the strain field is dominated by a four-fold symmetry. As a result the instability process is analogous to the instability of a Rankine vortex in an quadripolar strain field, resulting from vortex stretching into the four corners of the cavity.

scholarly journals Numerical Simulation of Turbulent Jets With Rectangular Cross-Section

1998 ◽  
Vol 120 (2) ◽  
pp. 285-290 ◽  
Author(s):  
R. V. Wilson ◽  
A. O. Demuren
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Stokes Equations ◽  
Rectangular Cross Section ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Reynolds Stresses ◽  
Spatial Discretization ◽  
Low Reynolds

Three-dimensional turbulent jets with rectangular cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at a low Reynolds number, whereas at a higher Reynolds number filtered forms of the equations are solved along with a sub-grid scale model to approximate effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Divergence-free velocity field is obtained by solving a Poisson equation for pressure with the same spatial discretization scheme for consistent accuracy. Computations are performed for different inlet conditions which represent different types of jet forcing within the shear layer. The phenomenon of axis-switching is observed in some cases. At low Reynolds numbers, it is based on self-induction of the vorticity field, whereas at higher Reynolds numbers, the turbulent structure becomes the dominant mechanism in natural jets. Budgets of the mean streamwise velocity show that convection is balanced by gradients of the Reynolds stresses and the pressure.

DIFFRACTION OF MICROWAVES BY LONG METAL CYLINDERS

1955 ◽  
Vol 33 (8) ◽  
pp. 407-419 ◽  
Author(s):  
Albert W. Adey
Keyword(s):  
Plane Wave ◽  
Electric Field ◽  
Transmission Line ◽  
Cross Section ◽  
Parallel Plate ◽  
Rectangular Cross Section ◽  
Circular Cylinders ◽  
Wave Conditions ◽  
Rectangular Cylinders ◽  
Good Agreement

A parallel-plate transmission line has been applied to the study of the amplitude and phase of the diffracted electric field near metal cylinders of circular, square, and rectangular cross-section. The transverse dimensions of the cylinders are comparable with the wavelength (3.280 cm.). A travelling dipole probe inserted in the line through a slot in one of the plates permits investigation of the field. Absorbing wedges at the boundary of the line make the plates effectively infinite in extent. Essentially plane wave conditions exist in the region utilized in the measurements. Good agreement is obtained between calculation and experiment for circular cylinders. Measured results are given for square and rectangular cylinders. For one orientation of the rectangles the measured results are compared with approximate calculations.

Modeling and Numerical Simulation of Flow Resistance Characteristics in Slowly-Varying Rectangular Cross-Section Microchannel

2016 ◽  
Author(s):  
Shen Teng ◽  
Wang Jiong ◽  
Sun Dong ◽  
Liu Yafeng ◽  
Tian Zhouyu
Keyword(s):  
Numerical Simulation ◽  
Theoretical Calculation ◽  
Cross Section ◽  
Flow Resistance ◽  
Rectangular Cross Section ◽  
Flow Characteristics ◽  
Aspect Ratios ◽  
Good Accord ◽  
Simulation Results ◽  
Poiseuille Number

In this paper, flow characteristics in slowly-varying rectangular microchannels with different aspect ratios and Re numbers ranging from 7 to 200 are investigated. The obtained simulation results are compared with theoretics values based on the Bernoulli equations. The results show that the simulation results just hold an average discrepancy of 10% with the theoretical calculation value whichis presents a good accord. All the research of microchannel, the Poiseuille number of the flow is inconstant within the range of Re number, except when the contract angle is small where Poiseuille number is essentially unchanged.

Pressure Drop in Rectangular Microchannels as Compared With Theory Based on Arbitrary Cross Section

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Mohsen Akbari ◽  
David Sinton ◽  
Majid Bahrami
Keyword(s):  
Pressure Drop ◽  
Cross Section ◽  
Soft Lithography ◽  
Rectangular Cross Section ◽  
Streaming Potential ◽  
Arbitrary Cross Section ◽  
Working Fluid ◽  
Aspect Ratios ◽  
Flow Through ◽  
Developed Pressure

Pressure driven liquid flow through rectangular cross-section microchannels is investigated experimentally. Polydimethylsiloxane microchannels are fabricated using soft lithography. Pressure drop data are used to characterize the friction factor over a range of aspect ratios from 0.13 to 0.76 and Reynolds number from 1 to 35 with distilled water as working fluid. Results are compared with the general model developed to predict the fully developed pressure drop in arbitrary cross-section microchannels. Using available theories, effects of different losses, such as developing region, minor flow contraction and expansion, and streaming potential on the measured pressure drop, are investigated. Experimental results compare well with the theory based on the presure drop in channels of arbitrary cross section.

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