Vortex shedding from a ground tracking radar antenna and 3D tip flow characteristics

2013 ◽  
Vol 13 (5) ◽  
pp. 263
Author(s):  
Cengiz Camci ◽  
Baris Gumusel
Keyword(s):  
Vortex Shedding ◽  
Flow Characteristics ◽  
Radar Antenna ◽  
Tracking Radar

Channel-Confined Wake Structure Interactions Between Two Permeable Side-By-Side Bars of a Square Cross-Section

2021 ◽  
Author(s):  
Saqib Jamshed ◽  
Amit Dhiman
Keyword(s):  
Cross Section ◽  
Vortex Shedding ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Darcy Number ◽  
Drag Forces ◽  
Coefficient Distribution ◽  
Wake Patterns ◽  
Lower Permeability ◽  
The Impact

Abstract The current research focuses on the laminar flow through permeable side-by-side bars of a square cross-section in a channel-confined domain. Vorticity generation on the leeward sides of the permeable bodies further necessitates the study for a better understanding of underlying physics. Reynolds number Re and Darcy number Da are varied from 5 to 150 and 10-6 to 10-2, respectively, at transverse gap ratios s/d=2.5-10. In the perspective of periodic unsteady flow, critical Re for the onset of vortex shedding is analyzed. Streamlines, vorticity, pressure coefficient distribution, and velocity profiles are discussed to identify the wake patterns. In lower permeability level, vortex-shedding from the permeable square cylinders is observed either in synchronized anti-phase mode or a single large vortex street with a synchronized in-phase pattern in the near wake. A steady-state wake pattern symmetric and flocked towards the centerline is observed for all s/d at a higher permeability level regardless of Re. Wake patterns are not altered for Da=10-6-10-3; instead, prompt extermination of the two vortex streets downstream is observed at Da=10-3 as compared to Da=10-6. The impact of s/d, Re, and permeability on the drag is examined. A jump in the flow characteristics and drag forces is noticed at higher Re for the mid-range Da remarkably at lower s/d. For the extent of high permeability, the drag coefficient asymptotically gets closer to zero.

scholarly journals A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

2017 ◽  
Vol 813 ◽  
pp. 23-52 ◽  
Author(s):  
Rafael Pérez-Torró ◽  
Jae Wook Kim
Keyword(s):  
Vortex Shedding ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Domain Size ◽  
Aerodynamic Characteristics ◽  
Streamwise Vortices ◽  
Aerodynamic Forces ◽  
Laminar Separation ◽  
Eddy Simulation ◽  
Large Eddy

A numerical investigation on the stalled flow characteristics of a NACA0021 aerofoil with a sinusoidal wavy leading edge (WLE) at chord-based Reynolds number $Re_{\infty }=1.2\times 10^{5}$ and angle of attack $\unicode[STIX]{x1D6FC}=20^{\circ }$ is presented in this paper. It is observed that laminar separation bubbles (LSBs) form at the trough areas of the WLE in a collocated fashion rather than uniformly/periodically distributed over the span. It is found that the distribution of LSBs and their influence on the aerodynamic forces is strongly dependent on the spanwise domain size of the simulation, i.e. the wavenumber of the WLE used. The creation of a pair of counter-rotating streamwise vortices from the WLE and their evolution as an interface/buffer between the LSBs and the adjacent fully separated shear layers are discussed in detail. The current simulation results confirm that an increased lift and a decreased drag are achieved by using the WLEs compared to the straight leading edge (SLE) case, as observed in previous experiments. Additionally, the WLE cases exhibit a significantly reduced level of unsteady fluctuations in aerodynamic forces at the frequency of periodic vortex shedding. The beneficial aerodynamic characteristics of the WLE cases are attributed to the following three major events observed in the current simulations: (i) the appearance of a large low-pressure zone near the leading edge created by the LSBs; (ii) the reattachment of flow behind the LSBs resulting in a decreased volume of the rear wake; and, (iii) the deterioration of von-Kármán (periodic) vortex shedding due to the breakdown of spanwise coherent structures.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

scholarly journals Experimental and Numerical Research on Flow-Induced Vibration in Valves

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Asmaa Ali Hussein
Keyword(s):  
Finite Element ◽  
Flow Rate ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Operating Mode ◽  
Structural Vibration ◽  
Piping System ◽  
Flow Induced Vibration ◽  
Finite Element Software ◽  
Operation Conditions

Abstract   All central air conditioning systems contain piping system with various components, sizes, material, and layouts. If such systems in operating mode, the flow in piping system and its component such as valves can produce severe vibration due to some flow phenomenon’s. In this research, experimental measurements and numerical simulation are used to study the flow-induced vibration in valves. Computational fluid dynamics (CFD) concepts are included with one-way and two-way fluid-structure interaction concepts by using finite element software Package (ANSYS 14.57). Detection analysis is performed on flow characteristics under operation conditions and relations with structural vibration. Most of real geometrical, operational, and boundary conditions are simulated to obtain best similarity with real operation conditions. Comparisons performed between experimental data and numerical results (one-way and two-way simulation) to verify the results. The main conclusion was drawn from the study that the dominant source of vibration for valve is the water pulsation in addition to amount of water hammering. In addition, the main source of water pulsation in globe valve is the vortex shedding and pressure difference between upstream and downstream of valve. The vibration amplitude was increased with increasing flow rate until to be maximum when the flow rate around 30% and then decreased until flow rate reaches to around 85% and then trends to be constant. Keywords: Flow-induced vibration, vortex shedding, pressure pulsation, valve, finite element, ANSYS, fast Fourier transform (FFT).

CFD Simulations of Helical Strakes Reducing Vortex Induced Motion of a Semi-Submersible

2018 ◽  
Author(s):  
Jiawei He ◽  
Decheng Wan ◽  
Zhiqiang Hu
Keyword(s):  
Vortex Shedding ◽  
Flow Characteristics ◽  
Boundary Region ◽  
Detached Eddy Simulation ◽  
Cfd Simulations ◽  
Mooring Lines ◽  
Boundary Area ◽  
Eddy Simulation ◽  
Helical Strakes ◽  
Induced Motion

This paper describes a set of VIM CFD simulations for a semi-submersible with and without helical strakes. The numerical investigations are conducted under low Reynolds number (Re) using naoe-FOAM-SJTU, a solver developed based on the open source framework OpenFOAM. The self-developed six degree-of-freedom (6DoF) motion module and mooring system module are applied to model motions of semi-submersible and the constraint of mooring lines, respectively. To carry out the calculations, turbulence closure has been chosen the Shear Stress Transport (SST) based Delay Detached eddy simulation (DDES), which uses the RANS model inside the boundary region and LES model outside the boundary area. This allows a realistic simulation within the boundary region where the vortex shedding is taking place, while not using unnecessary amounts of computational power. The Vortex Induced Motion (VIM) of semi-submersible with and without helical strakes was compared against each other for different reduced velocities (Ur). The flow characteristics of the semi-submersible platform is studied based on the characteristics of vortex shedding. For different current incident angles, time histories, trajectories and vorticity of the semi-submersible at different reduced velocities are reported. The result shows our CFD solver naoe-FOAM-SJTU is applicable and reliable to study VIM of semi-submersibles.

Square-Cylinder Flow Characteristics Modulated Using Upstream Control Rod

2012 ◽  
Vol 28 (2) ◽  
pp. 279-289 ◽  
Author(s):  
S. C. Yen ◽  
S. F. Wu
Keyword(s):  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Square Cylinder ◽  
Control Rod ◽  
Pressure Profiles ◽  
Spacing Ratio ◽  
Cylinder Flow ◽  
Upstream Control

AbstractThe flow patterns, vortex-shedding frequency and aerodynamic performance of the square-cylinder flow were modulated using an upstream control rod. Additionally, the flow behaviors were examined using various Reynolds numbers, rotation angles, and spacing ratios. The flow patterns were visualized using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow modes were characterized based on the kinematics theory. Moreover, the vortex-shedding frequencies behind upstream control rod and the square cylinder were detected using two hot-wire anemometers. The surface pressure on square cylinder was determined using a linear pressure scanner. Then, the aerodynamic parameters were calculated using the surface-pressure profiles. Three characteristic flow modes — single, attached, and bi-vortex-street — were categorized by varying the Reynolds number and spacing ratio. In the attached mode, the position of upstream control rod determined the flow characteristics. Furthermore, in the attached mode, the mean drag force of the square cylinder is about 57% lower than of single-square cylinder.

Unsteady Pressure Measurement of an Axial Fan

2001 ◽  
Author(s):  
C. Xu ◽  
R. S. Amano
Keyword(s):  
Vortex Shedding ◽  
Pressure Measurement ◽  
Flow Characteristics ◽  
Rotational Frequency ◽  
Time Dependent ◽  
Pressure Measurements ◽  
Axial Fan ◽  
Unsteady Pressure ◽  
Pressure Distributions ◽  
Start Up

Abstract An unsteady pressure measurement system was developed to measure the unsteady pressure field of an axial fan. The fan unsteady pressure fields of an inlet and outlet were obtained at three axial positions for seven-radial directions. The results showed that there is a relatively long response time for pressure drop both in inlet and outlet sections during the fan start-up. The measurements also showed that, due to the vortex shedding from the trailing edge of each fan blade, the fan outlet unsteady pressure distributions have a primary frequency related to the fan operating frequency. The time-dependent pressure measurements showed that pressure distributions of inlet and outlet during the fan start-up were severely unsteady and the main variation frequency of the pressure is much smaller than the fan rotational frequency. The pressure measurement on the fan blades showed that the pressure oscillations were mainly dominated by the vortex shedding from the fen blades. A flow visualization study was also performed to validate the flow characteristics near the blade surface. A complete set of time-dependent pressure measurements along the blade fan surfaces, fan inlet and outlet are suitable for an axial fan database for an industrial use as well as CFD code validation.

An experimental study of steady and pulsating cross-flow over a semi-staggered tube bundle

2005 ◽  
Vol 219 (3) ◽  
pp. 283-298 ◽  
Author(s):  
E Konstantinidis ◽  
D Castiglia ◽  
S Balabani
Keyword(s):  
Experimental Study ◽  
Vortex Shedding ◽  
Considerable Increase ◽  
Tube Bundle ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Velocity Fluctuations ◽  
The Mean

This paper describes an experimental study of the cross-flow characteristics in a semi-staggered tube bundle for Reynolds numbers in the range 1100-12 900. It is shown that by displacing transversely the tubes in the even rows of an in-line bundle by one diameter the vortex-shedding mechanism is suppressed. Vortex shedding is re-established and reinforced by pulsations superimposed on to the approaching flow and a considerable increase in the power of the associated velocity fluctuations is observed in the bundle. Two cases of pulsating flow are examined with different effects on the flow structure of the bundle. Detailed measurements of the mean and fluctuating velocity fields in the semi-staggered tube bundle together with flow visualization images are also reported in the paper in order to examine in depth the effects of tube displacement and flow pulsations. Comparisons with in-line and staggered configurations having the same spacing-to-diameter ratios are made.

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