On the vortex dynamics of shear-driven deep cavity flows with asymmetrical walls

2016 ◽  
Vol 94 (12) ◽  
pp. 1344-1352 ◽  
Author(s):  
D. Cornu ◽  
L. Keirsbulck ◽  
F. Kerhervé ◽  
F. Aloui ◽  
M. Lippert
Keyword(s):  
Physical Nature ◽  
Wall Pressure ◽  
Vortical Flow ◽  
Flow Structures ◽  
Cavity Flows ◽  
Convective Structures ◽  
Deep Cavity ◽  
Image Velocimetry ◽  
Flow Features ◽  
Deep Cavities

The influence of the length-to-depth aspect ratio and of wall asymmetry on the main vortical flow structures evolving in rectangular two-dimensional deep cavities is studied experimentally using wall-pressure and particle image velocimetry (PIV) measurements. Wall-pressure and cavity flow statistics have been analyzed and shown that the flow features are strongly affected especially by the asymmetry. An emphasis is given concerning the behavior of the shear layer oscillations that are compared to the analytical deep-cavity model prediction proposed by P.J.W. Block (NASA Tech. Note. 1976). The results show good agreement with Block’s model if the value of the convection velocity is properly adjusted. Stochastic estimation of the cavity flows demonstrates that convective structures are involved downstream of the cavity along the wall and highlights the physical nature of the pressure-producing flow structures.

Large Eddy Simulation of the Flow Around a Diffuser-Equipped Bluff Body in Ground Effect

2011 ◽  
Author(s):  
Lara Schembri Puglisevich ◽  
Gary Page
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Vortex Formation ◽  
Ground Effect ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

Unsteady Large Eddy Simulation (LES) is carried out for the flow around a bluff body equipped with an underbody rear diffuser in close proximity to the ground, representing an automotive diffuser. The goal is to demonstrate the ability of LES to model underbody vortical flow features at experimental Reynolds numbers (1.01 × 106 based on model height and incoming velocity). The scope of the time-dependent simulations is not to improve on Reynolds-Averaged Navier Stokes (RANS), but to give further insight into vortex formation and progression, allowing better understanding of the flow, hence allowing more control. Vortical flow structures in the diffuser region, along the sides and top surface of the bluff body are successfully modelled. Differences between instantaneous and time-averaged flow structures are presented and explained. Comparisons to pressure measurements from wind tunnel experiments on an identical bluff body model shows a good level of agreement.

scholarly journals Examining the Kinematic Structures within which Lightning Flashes are Initiated using a Cloud-Resolving Model

2021 ◽  
Author(s):  
Vicente Salinas ◽  
Eric C. Bruning ◽  
Edward R. Mansell
Keyword(s):  
Electric Fields ◽  
Careful Consideration ◽  
Vortical Flow ◽  
Flow Structures ◽  
Lightning Flash ◽  
Turbulent Eddies ◽  
Supercell Storms ◽  
Flow Features ◽  
Cloud Resolving Model ◽  
Eddy Flow

Abstract Lightning is frequently initiated within the convective regions of thunderstorms, and so flash rates tend to follow trends in updraft speed and volume. It has been suggested that lightning production is linked to the turbulent flow generated by updrafts as turbulent eddies organize charged hydrometeors into complex charge structures. These complex charge structures consist of local regions of increased charge magnitudes between which flash initiating electric fields may be generated. How turbulent kinematics influences lightning production, however, remains unclear. In this study, lightning flashes produced in a multi-cell and two supercell storms simulated using The Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) were examined to identify the kinematic flow structures within which they occurred. By relating the structures of updrafts to thermals, initiated lightning were expected to be located where the rate of strain and rotational flow are equal, or between updraft and eddy flow features. Results showed that the average lightning flash is initiated in kinematic flow structures dominated by vortical flow patterns, similar to those of thermals, and the structures’ kinematics are characterized by horizontal vorticity and vertical shearing. These kinematic features were common across all cases and demonstrated that where flash initiating electric fields are generated is along the periphery of updrafts where turbulent eddies are produced. Careful consideration of flow structures near initiated flashes is consistent with those of thermals rising through a storm.

Turbulent boundary layer over a deep cavity: friction coefficient and streamwise velocity components

2007 ◽  
Vol 85 (12) ◽  
pp. 1447-1457 ◽  
Author(s):  
M El Hassan ◽  
L Labraga ◽  
L Keirsbulck
Keyword(s):  
Friction Coefficient ◽  
Streamwise Velocity ◽  
Skin Friction Coefficient ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Deep Cavity ◽  
Image Velocimetry ◽  
Skewness Coefficient ◽  
The Mean ◽  
Deep Cavities

Deep cavities are present in car vehicles in numerous forms. Although drag downstream cavities have interested many authors, this aspect was never treated for particularly deep cavities. The objective of the present investigation is to study the effect of a deep cavity, characterized by its length-to-depth ratio L/H = 0.2, on both the skin friction coefficient and the statistic components of the streamwise velocity. Laser Doppler velocimetry (LDV) was used for the mean velocity and its statistic components measurements. Results obtained by other authors allowed a comparison between shallow and deep cavity configurations. The main conclusion is that with the same flow conditions, the drag increase downstream from the cavity is less important compared to the square cavity. A localized skewness coefficient decrease and a flatness coefficient increase could be related to intermittence ejection of flow from the downstream part of the cavity. This hypothesis was confirmed thanks to particle image velocimetry (PIV) measurements. PACS No.: 47.27.nb

scholarly journals Vortical Flow Structures Induced by Red Blood Cells in Capillaries

2021 ◽  
Author(s):  
François Yaya ◽  
Johannes Römer ◽  
Achim Guckenberger ◽  
Thomas John ◽  
Stephan Gekle ◽  
...  
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Vortical Flow ◽  
Flow Structures

Aero-Acoustic Coupling Inside Large Deep Cavities at Low-Subsonic Speeds

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Mouhammad El Hassan ◽  
Laurent Keirsbulck ◽  
Larbi Labraga
Keyword(s):  
Wind Tunnel ◽  
Shear Layer ◽  
Convection Velocity ◽  
Pressure Amplitude ◽  
Hydrodynamic Mode ◽  
Freestream Velocity ◽  
Acoustic Coupling ◽  
Deep Cavity ◽  
Cross Correlations ◽  
Deep Cavities

Aero-acoustic coupling inside a deep cavity is present in many industrial processes. This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios (L/H=0.2 and 0.41), as a function of freestream velocities of a 2×2m2 wind tunnel. Convection velocity of instabilities was measured along the shear layer, using velocity cross-correlations. Experiments have shown that in deep cavity for low Mach numbers, oscillations of discrete frequencies can be produced. These oscillations appear when the freestream velocity becomes higher than a minimum value. Oscillations start at L/θ0=10 and 21 for L/H=0.2 and 0.41, respectively. The highest sound pressure level inside a deep cavity is localized at the cavity floor. A quite different behavior of the convection velocity was observed between oscillating and nonoscillating shear-layer modes. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model (1964, “Wind Tunnel Experiments on the Flow Over Rectangular Cavities at Subsonic and Transonic Speeds,” Aeronautical Research Council Reports and Memo No. 3438) when measured convection velocity is used and the empirical time delay is neglected. For L/H=0.2, only the first Rossiter mode is present. For L/H=0.41, both the first and the second modes are detected with the second mode being the strongest.

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

Experimental Study of Large-Scale Flow Structures in an Aneurysm

2018 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Large Scale ◽  
Flow Structures ◽  
Pump System ◽  
Vortical Structures ◽  
Abnormal Growth ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
The Impact ◽  
Inflow Conditions ◽  
Aneurysm Model

An aneurysm is an abnormal growth in the wall of a weakened blood vessel, and can often be fatal upon rupture. Studies have shown that aneurysm shape and hemodynamics, in conjunction with other parameters, play an important role in growth and rupture. The objective of this study was to investigate the impact of varying inflow conditions on flow structures in an aneurysm. An idealized rigid sidewall aneurysm model was prepared and the Womersley number (α) and Reynolds number (Re) values were varied from 2 to 5 and 50 to 250, respectively. A ViVitro Labs pump system was used for inflow control and Particle Image Velocimetry was used for conducting velocity measurements. The results showed that the primary vortex path varied with an increase in α, while an increase in Re was correlated to the vortex strength and formation of secondary vortical structures. The evolution and decay of vortical structures were also observed to be dependent on α and Re.

Sign in / Sign up

Export Citation Format

Share Document