scholarly journals An Observational Study of Vortex Spacing in Island Wake Vortex Streets

2006 ◽  
Vol 134 (8) ◽  
pp. 2285-2294 ◽  
Author(s):  
George S. Young ◽  
Jonathan Zawislak
Keyword(s):  
Aspect Ratio ◽  
Bluff Body ◽  
Three Dimensional ◽  
Width Ratio ◽  
Bluff Bodies ◽  
Von Karman ◽  
Vortex Streets ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Island Wake ◽  
Von Kármán

Abstract Vortex streets are a frequent occurrence in stratocumulus-topped flow downwind of mountainous islands. Theoretical studies dating back to von Kármán, supported by laboratory and numerical studies, have yielded similarity theories for the size and spacing of these vortices behind bluff bodies. Despite dynamical differences between such two-dimensional flows and the three-dimensional flow past isolated islands, satellite case studies suggest these geometric similarities may also hold for the atmospheric case. In this study, two of the resulting dimensionless ratios are measured using satellite imagery. One is the aspect ratio between cross-street and along-street spacing of the vortices. The second is the ratio of the cross-street spacing to the crosswind width of the island. A 30-image sample from the Aqua and Terra Moderate Resolution Imaging Spectroradiometer satellites is analyzed to obtain these ratios. The resulting set of values for the two dimensionless ratios is tested against the values found in bluff body studies. The aspect ratio is tested against the value of 0.28 resulting from von Kármán’s inviscid theory, and the dimensionless width ratio is tested against the value of 1.2 from Tyler’s laboratory study of flow around a bluff body. It is found that atmospheric vortex streets do indeed follow the geometric similarity theories, but with different values for the two ratios than those predicted by von Kármán and Tyler. The aspect ratio is larger than predicted as is the dimensionless width ratio. Both differences are consistent with the turbulent diffusion of vorticity in the wake of the island. The vortex streets more closely follow inviscid theory close to the island, with vortex expansion taking place a few vortex diameters downwind of the island.

Description of transient states of von Kármán vortex streets by low‐dimensional differential equations

1990 ◽  
Vol 2 (4) ◽  
pp. 479-481 ◽  
Author(s):  
F. Ohle ◽  
P. Lehmann ◽  
E. Roesch ◽  
H. Eckelmann ◽  
A. Hübler
Keyword(s):  
Differential Equations ◽  
Transient States ◽  
Von Karman ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Low Dimensional ◽  
Von Kármán

Instabilities of the von Kármán Boundary Layer

2015 ◽  
Vol 67 (3) ◽  
Author(s):  
R. J. Lingwood ◽  
P. Henrik Alfredsson
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Direct Numerical Simulations ◽  
Layer Model ◽  
Complex Flow ◽  
Von Karman ◽  
Dimensional Boundary ◽  
Flow Configurations ◽  
Von Kármán

Research on the von Kármán boundary layer extends back almost 100 years but remains a topic of active study, which continues to reveal new results; it is only now that fully nonlinear direct numerical simulations (DNS) have been conducted of the flow to compare with theoretical and experimental results. The von Kármán boundary layer, or rotating-disk boundary layer, provides, in some senses, a simple three-dimensional boundary-layer model with which to compare other more complex flow configurations but we will show that in fact the rotating-disk boundary layer itself exhibits a wealth of complex instability behaviors that are not yet fully understood.

Atmospheric Refractivity Anomalies Induced by Mesoscale von Kármán Vortex Streets

2013 ◽  
Author(s):  
Christopher G. Nunalee ◽  
Jean Minet ◽  
Sukanta Basu ◽  
Mikhail A. Vorontsov
Keyword(s):  
Von Karman ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Von Kármán

On the periodicity of atmospheric von Kármán vortex streets

2014 ◽  
Vol 14 (6) ◽  
pp. 1335-1355 ◽  
Author(s):  
Christopher G. Nunalee ◽  
Sukanta Basu
Keyword(s):  
Von Karman ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Von Kármán

Three-Dimensional Simulation of Gas Flow in Microducts

2005 ◽  
Author(s):  
Abhishek Agrawal ◽  
Amit Agrawal
Keyword(s):  
Aspect Ratio ◽  
Knudsen Number ◽  
Gas Flow ◽  
Flow Direction ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Theoretical Development ◽  
Width Ratio ◽  
Two Dimensional

Three-dimensional lattice Boltzmann method based simulations of a microduct have been undertaken in this paper. The objective is to understand the different physical phenomena occurring at these small scales and to investigate when the flow can be treated as two-dimensional. Towards this end, the Knudsen number and aspect ratio (depth to width ratio) are varied for a fixed pressure ratio. The pressure in the microduct is non-linear with the non-linearity in pressure reducing with an increase in Knudsen number. The pressure and velocity behaves somewhat similar to two-dimensional microchannels even when the aspect ratio is unity. The slip velocity at the impenetrable wall has two components: along and perpendicular to the flow. Our results show that the streamwise velocity near the centerline is relatively invariant along the depth for aspect ratio more than three, suggesting that the microduct can be modeled as a two-dimensional microchannel. However, the velocity component along the depth is never identically zero, implying that the flow is not truly two-dimensional. A curious change in vector direction in a plane normal to the flow direction is observed around aspect ratio of four. These first set of three-dimensional results are significant because they will help in theoretical development and flow modeling at micro scales.

Numerical characterization of three-dimensional bluff body shear layer behaviour

2016 ◽  
Vol 799 ◽  
pp. 1-26 ◽  
Author(s):  
Daniel T. Prosser ◽  
Marilyn J. Smith
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Bluff Body ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Time Averaging ◽  
Bluff Bodies ◽  
Face Shape

Three-dimensional bluff body aerodynamics are pertinent across a broad range of engineering disciplines. In three-dimensional bluff body flows, shear layer behaviour has a primary influence on the surface pressure distributions and, therefore, the integrated forces and moments. There currently exists a significant gap in understanding of the flow around canonical three-dimensional bluff bodies such as rectangular prisms and short circular cylinders. High-fidelity numerical experiments using a hybrid turbulence closure that resolves large eddies in separated wakes close this gap and provide new insights into the unsteady behaviour of these bodies. A time-averaging technique that captures the mean shear layer behaviours in these unsteady turbulent flows is developed, and empirical characterizations are developed for important quantities, including the shear layer reattachment distance, the separation bubble pressure, the maximum reattachment pressure, and the stagnation point location. Many of these quantities are found to exhibit a universal behaviour that varies only with the incidence angle and face shape (flat or curved) when an appropriate normalization is applied.

scholarly journals On the recirculating flow of three-dimensional asymmetric bluff bodies

2020 ◽  
Vol 61 (12) ◽  
Author(s):  
Antoine Legeai ◽  
Olivier Cadot
Keyword(s):  
Bluff Body ◽  
Reference Model ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Recirculating Flow ◽  
Bistable Dynamics ◽  
Geometrical Variation ◽  
Static Instability ◽  
State Selection

Abstract The paper investigates the role of geometrical asymmetric modifications of a rectangular flat-backed body on the properties of the recirculating flow at a Reynolds number $$Re=1.8\times 10^5$$ R e = 1.8 × 10 5 . The reference model has two reflectional symmetries denoted $$s_y$$ s y and $$s_z$$ s z in both spanwise directions. The flow is subjected to the static instability that leads to two mirrored wake states breaking the symmetry $$s_y$$ s y . Two families of geometrical variation of the fore-body and after-body are studied, each breaking one of the reflectional symmetries of the reference model. Geometrical modifications that preserve $$s_y$$ s y evidence possibilities of bistable dynamics suppression although the static instability persists. Geometrical modifications that do not preserve $$s_y$$ s y produces a large unbalance of both wake states in accordance to recent observations on real cars (Bonnavion et al. in J Wind Eng Ind Aerodyn 184:77–89, 2019). Results offer perspectives for potential drag reduction induced by appropriate coupling of bluff body geometry and wake state selection. Graphic abstract

scholarly journals von Kármán–Howarth equation for three-dimensional two-fluid plasmas

2016 ◽  
Vol 93 (6) ◽  
Author(s):  
N. Andrés ◽  
P. D. Mininni ◽  
P. Dmitruk ◽  
D. O. Gómez
Keyword(s):  
Three Dimensional ◽  
Von Karman ◽  
Von Kármán ◽  
Two Fluid

Optical Wave Propagation through von Kármán Vortex Streets

2013 ◽  
Author(s):  
Jean Minet ◽  
Christopher G. Nunalee ◽  
Mikhail A. Vorontsov ◽  
Sukanta Basu
Keyword(s):  
Wave Propagation ◽  
Optical Wave ◽  
Optical Wave Propagation ◽  
Von Karman ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Von Kármán

The theory of quasi-geostrophic von Kármán vortex streets in two-layer fluids on a beta-plane

2004 ◽  
Vol 505 ◽  
pp. 23-57 ◽  
Author(s):  
VLADIMIR M. GRYANIK ◽  
HARTMUT BORTH ◽  
DIRK OLBERS
Keyword(s):  
Von Karman ◽  
Beta Plane ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Von Kármán
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