Secondary vortex dynamics in the cylinder wake during laminar-to-turbulent transition

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
Jeffrey McClure ◽  
Colin Pavan ◽  
Serhiy Yarusevych
Keyword(s):  
Vortex Dynamics ◽  
Secondary Vortex ◽  
Cylinder Wake ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition

Vortex dynamics for flow over a circular cylinder in proximity to a wall

2017 ◽  
Vol 812 ◽  
pp. 698-720 ◽  
Author(s):  
Guo-Sheng He ◽  
Jin-Jun Wang ◽  
Chong Pan ◽  
Li-Hao Feng ◽  
Qi Gao ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Shear Layer ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Vortex Dynamics ◽  
Wake Vortex ◽  
Secondary Vortex ◽  
Cylinder Wake ◽  
Gap Ratio ◽  
Shedding Frequency

The dynamics of vortical structures in flow over a circular cylinder in the vicinity of a flat plate is investigated using particle image velocimetry (PIV). The cylinder is placed above the flat plate with its axis parallel to the wall and normal to the flow direction. The Reynolds number $Re_{D}$ based on the cylinder diameter $D$ is 1072 and the gap $G$ between the cylinder and the flat plate is varied from gap-to-diameter ratio $G/D=0$ to $G/D=3.0$. The flow statistics and vortex dynamics are strongly dependent on the gap ratio $G/D$. Statistics show that as the cylinder comes close to the wall ($G/D\leqslant 2.0$), the cylinder wake becomes more and more asymmetric and a boundary layer separation is induced on the flat plate downstream of the cylinder. The wake vortex shedding frequency increases with decreasing $G/D$ until a critical gap ratio (about $G/D=0.25$) below which the vortex shedding is irregular. The deflection of the gap flow away from the wall and its following interaction with the upper shear layer may be the cause of the higher shedding frequency. The vortex dynamics is investigated based on the phase-averaged flow field and virtual dye visualization in the instantaneous PIV velocity field. It is revealed that when the cylinder is close to the wall ($G/D=2.0$), the cylinder wake vortices can periodically induce secondary spanwise vortices near the wall. As the cylinder approaches the wall ($G/D=1.0$) the secondary vortex can directly interact with the lower wake vortex, and a further approaching of the cylinder ($G/D=0.5$) can result in more complex interactions among the secondary vortex, the lower wake vortex and the upper wake vortex. The breakdown of vortices into filamentary debris during vortex interactions is clearly revealed by the coloured virtual dye visualizations. For $G/D<0.25$, the lower shear layer is strongly inhibited and only the upper shear layer can shed vortices. Investigation of the vortex formation, evolution and interaction in the flow promotes the understanding of the flow physics for different gap ratios.

Aspects of Flow Structure During a Cylinder Wake-Induced Laminar/Turbulent Transition

AIAA Journal ◽  
10.2514/2.613 ◽  
1999 ◽  
Vol 37 (10) ◽  
pp. 1197-1205 ◽  
Author(s):  
N. K. Kyriakides ◽  
E. G. Kastrinakis ◽  
S. G. Nychas ◽  
A. Goulas
Keyword(s):  
Flow Structure ◽  
Cylinder Wake ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

Laminar to turbulent transition in a finite length square duct subjected to inlet disturbance

2021 ◽  
Vol 33 (6) ◽  
pp. 065128
Author(s):  
Hamid Hassan Khan ◽  
Syed Fahad Anwer ◽  
Nadeem Hasan ◽  
Sanjeev Sanghi
Keyword(s):  
Finite Length ◽  
Square Duct ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition

Drag optimisation of a wing equipped with a morphing upper surface

2016 ◽  
Vol 120 (1225) ◽  
pp. 473-493 ◽  
Author(s):  
A. Koreanschi ◽  
O. Sugar-Gabor ◽  
R. M. Botez
Keyword(s):  
Genetic Algorithm ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Open Source ◽  
Experimental Testing ◽  
Shape Reconstruction ◽  
Laminar To Turbulent Transition ◽  
Wing Model ◽  
Turbulent Transition ◽  
Transition Delay

ABSTRACTThe drag coefficient and the laminar-to-turbulent transition for the aerofoil component of a wing model are optimised using an adaptive upper surface with two actuation points. The effects of the new shaped aerofoils on the global drag coefficient of the wing model are also studied. The aerofoil was optimised with an ‘in-house’ genetic algorithm program coupled with a cubic spline aerofoil shape reconstruction and XFoil 6.96 open-source aerodynamic solver. The wing model analysis was performed with the open-source solver XFLR5 and the 3D Panel Method was used for the aerodynamic calculation. The results of the aerofoil optimisation indicate improvements of both the drag coefficient and transition delay of 2% to 4%. These improvements in the aerofoil characteristics affect the global drag of the wing model, reducing it by up to 2%. The analyses were conducted for a single Reynolds number and speed over a range of angles of attack. The same cases will also be used in the experimental testing of the manufactured morphing wing model.

scholarly journals Experimental Analysis of Pressure Drop and Laminar to Turbulent Transition for Gas Flows in Smooth Microtubes

2007 ◽  
Vol 28 (8-9) ◽  
pp. 670-679 ◽  
Author(s):  
Gian Luca Morini ◽  
Marco Lorenzini ◽  
Stéphane Colin ◽  
Sandrine Geoffroy
Keyword(s):  
Pressure Drop ◽  
Experimental Analysis ◽  
Gas Flows ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition

Detecting Transition in Flat Plate Flow With Laser Interferometric Vibrometry (LIV)

2016 ◽  
Author(s):  
Pascal Bader ◽  
Wolfgang Sanz ◽  
Johannes Peterleithner ◽  
Jakob Woisetschläger ◽  
Franz Heitmeir ◽  
...  
Keyword(s):  
Flat Plate ◽  
Measurement Techniques ◽  
Transitional Zone ◽  
Transport Processes ◽  
Transitional Region ◽  
Test Cases ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Measurement Results ◽  
Laser Interferometric

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer. It is therefore vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition. Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results. An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques. Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.

Sign in / Sign up

Export Citation Format

Share Document