scholarly journals Three-dimensional Floquet stability analysis of the wake in cylinder arrays

2007 ◽  
Vol 592 ◽  
pp. 79-88 ◽  
Author(s):  
N. K.-R. KEVLAHAN
Keyword(s):  
Reasonable Agreement ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Instability Mechanism ◽  
Cylinder Arrays ◽  
Spatial Periodicity ◽  
Wake Instability ◽  
Mode A ◽  
Three Dimensional Simulations

Three-dimensional stability of the periodic wake of tightly packed rotated and inline cylinder arrays is investigated for 60 ≤ Re ≤ 270. Results are compared with existing numerical and experimental studies for an isolated cylinder. Numerical Floquet analysis shows that the two-dimensional wakes of the rotated and inline arrays with spacing P/D = 1.5 become unstable at Rec = 64 ± 0.5 and Rec = 132 ± 1 respectively. Two-dimensional vortex shedding flow is unlikely in practice for such flows. The dominant spanwise wavelength is λ/D = 0.9 ± 0.1 for the rotated array at Re = 100 and λ/D = 3.0 ± 0.1 for the inline array at Re = 200. Three-dimensional simulations show excellent agreement with the Floquet analysis for the rotated case, and reasonable agreement for the inline case. The instability mechanism appears to be similar to Mode A for an isolated cylinder, although the structure of the three-dimensional vorticity is different due to the spatial periodicity of the flow. Unlike the isolated cylinder, both array flows are unstable as λ → ∞ (like a thin shear layer). This is the first investigation of three-dimensional wake instability in cylinder arrays, a problem of significant practical and theoretical interest.

Calculations of Fuel NO Formation in a Gas Turbine Combustor

1991 ◽  
Author(s):  
Thomas J. Overcamp ◽  
Ajay K. Agrawal ◽  
Wei-Seng Cheng ◽  
Tah-Teh Yang
Keyword(s):  
Gas Turbine ◽  
Coal Gasification ◽  
Nitrogen Concentration ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Gas Turbine Combustor ◽  
Nitrogen Inputs ◽  
Nitrogen Conversion ◽  
Three Dimensional Simulations

PCGC-2, a two-dimensional combustion code for pulverized coal gasification and combustion, and PHOENICS, a general purpose fluid dynamics code, were adapted for use in simulating the conversion of fuel nitrogen to nitric oxide, NO, in a gas turbine combustor using low-Btu fuel. A two-reaction global mechanism was used to describe the oxidation of fuel nitrogen. PCGC-2 is limited to two-dimensional, axisymmetric calculations. Both two- and three-dimensional simulations were made with PHOENICS. A parametric study was conducted to determine the variation of fuel nitrogen conversion with changes in the input variables including the inlet fuel nitrogen concentration and swirl numbers. The fuel nitrogen conversion predicted with both codes is similar to those reported in experimental studies on gaseous fuels. The conversion decreased with increasing fuel nitrogen inputs as shown in experimental data. The fuel conversion predicted in three-dimensional simulations for an industrial gas turbine was slightly higher than those in simplified two-dimensional simulations.

Bifurcation Characteristics of Flows in Rectangular Sudden Expansion Channels

2005 ◽  
Author(s):  
Francine Battaglia ◽  
George Papadopoulos
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Two Dimensional ◽  
Effective Expansion ◽  
Three Dimensional Simulations

The effect of three-dimensionality on low Reynolds number flows past a symmetric sudden expansion in a channel was investigated. The geometric expansion ratio of in the current study was 2:1 and the aspect ratio was 6:1. Both experimental velocity measurements and two- and three-dimensional simulations for the flow along the centerplane of the rectangular duct are presented for Reynolds numbers in the range of 150 to 600. Comparison of the two-dimensional simulations with the experiments revealed that the simulations fail to capture completely the total expansion effect on the flow, which couples both geometric and hydrodynamic effects. To properly do so requires the definition of an effective expansion ratio, which is the ratio of the downstream and upstream hydraulic diameters and is therefore a function of both the expansion and aspect ratios. When the two-dimensional geometry was consistent with the effective expansion ratio, the new results agreed well with the three-dimensional simulations and the experiments. Furthermore, in the range of Reynolds numbers investigated, the laminar flow through the expansion underwent a symmetry-breaking bifurcation. The critical Reynolds number evaluated from the experiments and the simulations was compared to other values reported in the literature. Overall, side-wall proximity was found to enhance flow stability, helping to sustain laminar flow symmetry to higher Reynolds numbers in comparison to nominally two-dimensional double-expansion geometries. Lastly, and most importantly, when the logarithm of the critical Reynolds number from all these studies was plotted against the reciprocal of the effective expansion ratio, a linear trend emerged that uniquely captured the bifurcation dynamics of all symmetric double-sided planar expansions.

scholarly journals CAD Tools and Computing in Architectural and Urban Acoustics

Buildings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 235
Author(s):  
Joanna Jablonska ◽  
Roman Czajka
Keyword(s):  
Computer Aided Design ◽  
Three Dimensional ◽  
Computing Methods ◽  
Building Industry ◽  
Two Dimensional ◽  
Cad Tools ◽  
Architectural Acoustics ◽  
Urban Level ◽  
Aided Design ◽  
Three Dimensional Simulations

Contemporary architectural and urban planning aims at optimal development of the environment, including in terms of acoustics. As such, support with computer-aided design (CAD) tools is, nowadays, obligatory. The authors present investigation outcomes of three different CAD and computing methods extracted for the study. The scope covers different scales of considerations from architectural acoustics to the urban level, which relates to the standard architect’s commissions field. The described approaches are applicable for both academics and professionals in the broadly understood building industry There were analysed and synthesized experiences from the use of two-dimensional and three-dimensional simulations, computing based on standardized formulas, and an acoustic meter (here: the SVAN 979 for RT60, LAeq measurement). The article concludes with an assessment, which shows possible uses of methods and confirmations of their usability.

Two- and Three-Dimensional Simulations of the Flow Around a Cylinder Fitted With Strakes

2012 ◽  
Author(s):  
Bruno S. Carmo ◽  
Rafael S. Gioria ◽  
Ivan Korkischko ◽  
Cesar M. Freire ◽  
Julio R. Meneghini
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Free Stream ◽  
Three Dimensional ◽  
The Body ◽  
Vortex Wake ◽  
Two Dimensional ◽  
Flow Around A Cylinder ◽  
Three Dimensional Simulations ◽  
Angle Of Rotation

Two- and three-dimensional simulations of the flow around straked cylinders are presented. For the two-dimensional simulations we used the Spectral/hp Element Method, and carried out simulations for five different angles of rotation of the cylinder with respect to the free stream. Fixed and elastically-mounted cylinders were tested, and the Reynolds number was kept constant and equal to 150. The results were compared to those obtained from the simulation of the flow around a bare cylinder under the same conditions. We observed that the two-dimensional strakes are not effective in suppressing the vibration of the cylinders, but also noticed that the responses were completely different even with a slight change in the angle of rotation of the body. The three-dimensional results showed that there are two mechanisms of suppression: the main one is the decrease in the vortex shedding correlation along the span, whilst a secondary one is the vortex wake formation farther downstream.

scholarly journals Theoretical and experimental studies of highly selective planar two-dimensional Bragg structures based on dielectric waveguides in the terahertz frequency range

2019 ◽  
Vol 30 ◽  
pp. 07009
Author(s):  
Naum Ginzburg ◽  
Nikolay Peskov ◽  
Vladislav Zaslavsky ◽  
Ekaterina Kocharovskaya ◽  
Andrey Malkin ◽  
...  
Keyword(s):  
Bragg Reflection ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Dielectric Waveguides ◽  
Two Dimensional ◽  
Terahertz Frequency ◽  
Frequency Range ◽  
Terahertz Frequency Range ◽  
Three Dimensional Modeling ◽  
Bragg Structures

Based on theoretical approach and three-dimensional modeling using the CST Microwave Studio code, planar dielectric two-dimensional Bragg structures in terahertz frequency range were developed and manufactured. Proof-of-principle electrodynamic experiments on the “cold” testing of these structures were carried out. It is shown that the experimental results are in good agreement with the theoretical predicts, including the existence of the highest Q mode inside the Bragg reflection band in the absence of periodicity defects.

Three-dimensional stability analysis for a salt-finger convecting layer

2018 ◽  
Vol 841 ◽  
pp. 636-653
Author(s):  
Ting-Yueh Chang ◽  
Falin Chen ◽  
Min-Hsing Chang
Keyword(s):  
Stability Analysis ◽  
Three Dimensional ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Solute Diffusion ◽  
Two Dimensional ◽  
Grashof Number ◽  
Significant Difference ◽  
The Stability ◽  
Mode A

A three-dimensional linear stability analysis is carried out for a convecting layer in which both the temperature and solute distributions are linear in the horizontal direction. The three-dimensional results show that, for $Le=3$ and 100, the most unstable mode occurs invariably as the longitudinal mode, a vortex roll with its axis perpendicular to the longitudinal plane, suggesting that the two-dimensional results are sufficient to illustrate the stability characteristics of the convecting layer. Two-dimensional results show that the stability boundaries of the transverse mode (a vortex roll with its axis perpendicular to the transverse plane) and the longitudinal modes are virtually overlapped in the regime dominated by thermal diffusion and the regime dominated by solute diffusion, while these two modes hold a significant difference in the regime the salt-finger instability prevails. More precisely, the instability area in terms of thermal Grashof number $Gr$ and solute Grashof number $Gs$ is larger for the longitudinal mode than the transverse mode, implying that, under any circumstance, the longitudinal mode is always more unstable than the transverse mode.

Experimental and Theoretical Studies of Two-Dimensional Fixed-Type Cavities

1975 ◽  
Vol 97 (4) ◽  
pp. 515-521 ◽  
Author(s):  
R. A. Furness ◽  
S. P. Hutton
Keyword(s):  
Potential Flow ◽  
Reasonable Agreement ◽  
Experimental Studies ◽  
Liquid Jet ◽  
Theoretical Studies ◽  
Two Dimensional ◽  
Nozzle Throat ◽  
Jet Behavior ◽  
Fixed Type ◽  
Experimental And Theoretical Studies

Theoretical and experimental studies have been made of the growth and collapse of fixed cavities in a two-dimensional convergent-divergent nozzle. In this particular configuration an important feature was a re-entrant liquid jet which invaded the growing cavity from the downstream end, travelling upstream along the wall and interrupting the cavity when it reached the nozzle throat. A simple two-dimensional unsteady potential flow theory, developed to model the cycle, gave reasonable agreement with cinephotography and predicted the jet behavior. Because vaporization was neglected the theory overestimated the speed of the cycle.

Optimal Javelin Release

1995 ◽  
Vol 11 (4) ◽  
pp. 371-394 ◽  
Author(s):  
Russell J. Best ◽  
Roger M. Bartlett ◽  
Richard A. Sawyer
Keyword(s):  
Experimental Studies ◽  
Three Dimensional ◽  
High Standard ◽  
Flight Simulation ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Simulation Research ◽  
Simulation Evaluation ◽  
Model And Simulation ◽  
Two Dimensional Model

This paper reports a study of the optimal release of men's and women's new and old rule javelins involving modeling, simulation, optimization (including sensitivity analysis), and simulation evaluation. Because of the lack of repro-ducibility in earlier results of two-dimensional flight simulation research, the paper presents a continuation of the two-dimensional model used previously. As expected, each javelin was found to have a different optimal release for a given individual, and the optimal release varied with the thrower's nominal release speed. A limited degree of simulation evaluation was achieved by comparison of the model and simulation results with measured throws. Within the constraints of measurement error, this tended to support both the adequacy of the two-dimensional model and the results of the simulations for such high standard throws. However, further experimental studies to quantify the angle of yaw (sideslip) in measured wind conditions are recommended to assess any changes needed to the two-dimensional model of javelin throwing and to determine the advisability of including this three-dimensional aspect of javelin release in future simulations.

Simulation of Nonlinear Sloshing Behaviors under Dynamic Actions

2015 ◽  
Vol 772 ◽  
pp. 183-187
Author(s):  
Xiao Ye Yu ◽  
Alex To ◽  
Goman Ho
Keyword(s):  
Seismic Design ◽  
Reasonable Agreement ◽  
Three Dimensional ◽  
Structural Performance ◽  
Two Dimensional ◽  
Seismic Excitations ◽  
Structure Interaction ◽  
Ale Formulation ◽  
Steel Tank

This paper simulated the non-linear sloshing effects under typical dynamic actions. The sloshing simulation is realized with the Arbitrary Lagrangian Euleria (ALE) formulation plus bi-phase hydrodynamic biomaterial liquid gas materials. The study first investigated two dimensional (2D) sloshing problems under harmonic excitations. Through calibration studies in standard rectangular tanks, the case study demonstrated reasonable agreement with numerical results published by other researchers. The study was then extended to more complicated three dimensional (3D) sloshing problems, with the fluid-structure interaction (FSI) considered. The simulation well reflected the sloshing behaviours in a steel tank subject to given seismic excitations and provided available prediction for structural performance. The obtained results show that the used method is helpful for seismic design of liquid tanks.

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