Vortex Dynamics in Near Wake Region Behind a Triangular Cylinder at Intermediate Reynolds Number

2021 ◽  
pp. 43-53
Author(s):  
Namit Agrawal ◽  
Maharshi Subhash
Keyword(s):  
Reynolds Number ◽  
Vortex Dynamics ◽  
Wake Region ◽  
Near Wake

scholarly journals Hyperbolicity, shadowing directions and sensitivity analysis of a turbulent three-dimensional flow

2019 ◽  
Vol 863 ◽  
pp. 644-669 ◽  
Author(s):  
Angxiu Ni
Keyword(s):  
Reynolds Number ◽  
Large Fraction ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Wake Region ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Long Time ◽  
Cylinder Flow ◽  
Far Wake

This paper uses compressible flow simulation to analyse the hyperbolicity, shadowing directions and sensitivities of a weakly turbulent three-dimensional cylinder flow at Reynolds number 525 and Mach number 0.1. By computing the first 40 covariant Lyapunov vectors (CLVs), we find that unstable CLVs are active in the near-wake region, whereas stable CLVs are active in the far-wake region. This phenomenon is related to hyperbolicity since it shows that CLVs point to different directions; it also suggests that for open flows there is a large fraction of CLVs that are stable. However, due to the extra neutral CLV and the occasional tangencies between CLVs, our system is not uniform hyperbolic. By the non-intrusive least-squares shadowing (NILSS) algorithm, we compute shadowing directions and sensitivities of long-time-averaged objectives. Our results suggest that shadowing methods may be valid for general chaotic fluid problems.

An Experimental Study on Flow Past an Equilateral Triangular Prism at Intermediate Reynolds Number and the Effect of its Orientation

2013 ◽  
Author(s):  
Namit Agrawal ◽  
Sushanta Dutta ◽  
B. K. Gandhi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flat Plate ◽  
Shear Layers ◽  
Apex Angle ◽  
Triangular Prism ◽  
Wake Region ◽  
Near Wake ◽  
Intermediate Regime ◽  
Free Shear Layers

This paper explores the effect of two orientations (0° and 180°) on near wake region of an equilateral triangular prism at intermediate Reynolds number. The paper also investigates the effect of Reynolds number on the near wake region at intermediate regime. Two orientations are defined such that the apex of the equilateral triangle is pointing upstream and downstream respectively. The flow field behind a triangular prism is different in these two orientations. When apex angle points upstream it corresponds to a fore-body attached to a flat plate while when apex angle points downstream the flat face acts like a flat plate with an after body attached to it. This after-body penetrates the recirculation zone formed behind the flat plate. These two effects are investigated for various Reynolds numbers in intermediate regime. Factors affecting drag coefficient and Strouhal number are different in both cases. In first case the fore-body changes the flow before it gets separated in two free shear layers. In other words, the fore-body affects the free shear layers formed and hence the drag. In the second case, the two shear layers are formed first then their interaction is modified by the after-body in the near wake region behind the prism. Particle Image Velocimetry (PIV) and Hotwire anemometry is being used in present study. Detailed flow field is investigated in terms of velocity magnitude, stream traces, vorticity contours, centerline recovery, power spectra, velocity profiles, Strouhal number and drag coefficient.

Wake of a Vibrating Cylinder at Re = 105

2011 ◽  
Author(s):  
R. D. Blevins ◽  
Jean-Franc¸ois Saint-Marcoux
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Flow Visualization ◽  
Vortex Dynamics ◽  
Velocity Profiles ◽  
Near Wake ◽  
Vortex Induced Vibration ◽  
Cylinder Flow

Measurements have been made of the wake of a circular cylinder at Reynolds number of 105 for a stationary cylinder and a cylinder vibrating +/− 1.25 diameters under natural vortex induced vibration. Wake velocity profiles were taken at 2, 4, 6, 12, 24 and 50 diameters downstream. The stationary cylinder profile reproduces the well known wake deficit law. The vibrating cylinder near wake is wider, deeper and flatter than that of the stationary cylinder. Flow visualization reveals the vortex dynamics in the wake. Correlation is shown with theory.

scholarly journals Measurements of Secondary Flows Within a Cascade of Curved Blades and in the Wake of the Cascade

1983 ◽  
Author(s):  
Ronald Lasser ◽  
Wilfred T. Rouleau
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Three Dimensional ◽  
Laser Doppler Anemometer ◽  
Secondary Flows ◽  
Wake Region ◽  
Near Wake ◽  
Primary Flow ◽  
Turning Angle ◽  
Blade Cascade

A laser-Doppler anemometer was used to measure the three-dimensional velocity field within a typical turbine blade cascade. The blades had a 12.7 cm chord, a turning angle of 104.8°, and a shape conforming to the camber line of a commercial turboexpander. The cascade was operated at a Reynolds number of 1.25×105. Strong secondary velocities, ranging up to 35 percent of the primary flow velocity, were found, resulting from the development of counter-rotating vortices within the blade passages. Large midspan velocity defects in the primary flow were coincident with these high secondary flows. The secondary flow persisted throughout the near wake region.

scholarly journals Flow Turbulence Characteristics and Mass Transport in the Near-Wake Region of an Aquaculture Cage Net Panel

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 294
Author(s):  
Dongdong Shao ◽  
Li Huang ◽  
Ruo-Qian Wang ◽  
Carlo Gualtieri ◽  
Alan Cuthbertson
Keyword(s):  
Mass Transport ◽  
Near Field ◽  
Lateral Spreading ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Turbulence Characteristics ◽  
Macro Scale ◽  
Flow Turbulence ◽  
Fish Cages

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal embayments or fjords, significantly affecting flow and mass transport in the surrounding waters. Existing studies have focused primarily on the macro-scale flow blockage effects of fish cages, and the complex wake flow and associated near-field mass transport in the presence of the cages remain largely unclear. As a first step toward resolving this knowledge gap, this study employed the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) flow imaging technique to measure turbulence characteristics and associated mass transport in the near wake of a steady current through an aquaculture cage net panel in parametric flume experiments. In the near-wake region, defined as ~3M (mesh size) downstream of the net, the flow turbulence was observed to be highly inhomogeneous and anisotropic in nature. Further downstream, the turbulent intensity followed a power-law decay after the turbulence production region, albeit with a decay exponent much smaller than reported values for analogous grid-generated turbulence. Overall, the presence of the net panel slightly enhanced the lateral spreading of the scalar plume, but the lateral distribution of the scalar concentration, concentration fluctuation and transverse turbulent scalar flux exhibited self-similarity from the near-wake region where the flow was still strongly inhomogeneous. The apparent turbulent diffusivity estimated from the gross plume parameters was found to be in reasonable agreement with the Taylor diffusivity calculated as the product of the transverse velocity fluctuation and integral length scale, even when the plume development was still transitioning from a turbulent-convective to turbulent-diffusive regime. The findings of this study provide references to the near-field scalar transport of fish cages, which has important implications in the assessment of the environmental impacts and environmental carrying capacity of cage-based aquaculture.

Study of the Laminar Free-Convection Wake Above an Isothermal Vertical Plate

1973 ◽  
Vol 95 (3) ◽  
pp. 289-294 ◽  
Author(s):  
N. E. Hardwick ◽  
E. K. Levy
Keyword(s):  
Free Convection ◽  
Vertical Plate ◽  
Fluid Motion ◽  
Heated Plate ◽  
Two Dimensional ◽  
Wake Region ◽  
Hot Wire ◽  
Near Wake ◽  
Steady Laminar ◽  
Finite Difference Techniques

The steady, laminar, two-dimensional wake above a thin vertical isothermal heated plate cooled by free convection was investigated theoretically and experimentally. The system of partial differential equations governing the fluid motion and heat transfer in the vicinity of the plate and in the near wake region was formulated and solved using finite difference techniques. Using air, the temperature and velocity profiles in the wake region were measured experimentally using a laser holographic interferometer and a constant temperature hot wire anemometer.

scholarly journals Flow past a square-section cylinder with a wavy stagnation face

2001 ◽  
Vol 426 ◽  
pp. 263-295 ◽  
Author(s):  
RUPAD M. DAREKAR ◽  
SPENCER J. SHERWIN
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Physical Structure ◽  
Near Wake ◽  
Hairpin Vortices ◽  
Independent State ◽  
Flow Past ◽  
Edge Surface

Numerical investigations have been performed for the flow past square-section cylinders with a spanwise geometric deformation leading to a stagnation face with a sinusoidal waviness. The computations were performed using a spectral/hp element solver over a range of Reynolds numbers from 10 to 150.Starting from fully developed shedding past a straight cylinder at a Reynolds number of 100, a sufficiently high waviness is impulsively introduced resulting in the stabilization of the near wake to a time-independent state. It is shown that the spanwise waviness sets up a cross-flow within the growing boundary layer on the leading-edge surface thereby generating streamwise and vertical components of vorticity. These additional components of vorticity appear in regions close to the inflection points of the wavy stagnation face where the spanwise vorticity is weakened. This redistribution of vorticity leads to the breakdown of the unsteady and staggered Kármán vortex wake into a steady and symmetric near-wake structure. The steady nature of the near wake is associated with a reduction in total drag of about 16% at a Reynolds number of 100 compared with the straight, non-wavy cylinder.Further increases in the amplitude of the waviness lead to the emergence of hairpin vortices from the near-wake region. This wake topology has similarities to the wake of a sphere at low Reynolds numbers. The physical structure of the wake due to the variation of the amplitude of the waviness is identified with five distinct regimes. Furthermore, the introduction of a waviness at a wavelength close to the mode A wavelength and the primary wavelength of the straight square-section cylinder leads to the suppression of the Kármán street at a minimal waviness amplitude.

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