scholarly journals Measuring Large Scale Flow Structures Behind a Bluff Body Using a Hot-wire Rake

2015 ◽  
Vol 126 ◽  
pp. 532-536 ◽  
Author(s):  
Nan Gao ◽  
Yaqing Li ◽  
Honglei Bai

This paper describes an investigation of the large-scale flow processes which occur in turbulent circular jet flows ( Re > 10 5 ). The existence of regular large-scale flow structures at low and moderate Reynolds numbers ( Re < 5 x 10 4 ) has clearly been demonstrated by flow-visualization experi­ments, but visual evidence for order in jet turbulence becomes ambiguous at a Reynolds number around 7 x 10 4 . A new time-domain technique for the study of two-dimensional large-scale flow structures has been developed by Bruun (1977). In this paper this technique is extended to the study of three-dimensional large-scale flow structures by the inclusion of X hot-wire and circumferential eductions. The evaluated large-scale structures in the turbulent jet ( Re = 2 x 10 5 ) are shown to deviate considerably from the axi-symmetric flow structures which occurs at low and moderate Reynolds numbers ( Re < 5 x 10 4 ). We observe a much smaller deformation rate of the semi-regular flow structure in the potential core in the turbulent jet case, and also the circumferential eductions reveal a rapid radial decrease in the circumferential coherence of the related large-scale flow structure in the mixing region. Further-­more, combining these results with the X hot-wire eductions in the mixing region proved that the major contributions to the shear stress uv is caused by circumferentially-narrow tongues of ‘fast moving ejected’ and ‘slow moving entrained ’fluid, similar to the ‘burst’ and ‘sweep’ events observed previously in turbulent wall boundary layers.


Author(s):  
Paulo Yu ◽  
Vibhav Durgesh

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.


Author(s):  
C. Resagk ◽  
R. du Puits ◽  
E. Lobutova ◽  
A. Maystrenko ◽  
A. Thess

2020 ◽  
Vol 184 ◽  
pp. 107224 ◽  
Author(s):  
Yongzhi Zhang ◽  
Jiayu Li ◽  
Mingxin Liu ◽  
Junjie Liu ◽  
Congcong Wang

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