scholarly journals The flow structure of submerged round jets at low Re numbers

2019 ◽  
Vol 196 ◽  
pp. 00046
Author(s):  
Vadim Lemanov ◽  
Konstantin Sharov ◽  
Vitaly Matyunin
Keyword(s):  
Experimental Investigation ◽  
Transition Zone ◽  
Initial Conditions ◽  
Longitudinal Velocity ◽  
Cylindrical Tube ◽  
Reynolds Numbers ◽  
Submerged Jet ◽  
Round Jets ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

An experimental investigation of a laminar-turbulent transition in a round jet flowing from a cylindrical tube with a diameter of 3.2 mm have been carried out. The range of Reynolds numbers in the experiments Re = Ud / v were of 700-12000. The measurements have been carried out via the PIV system. The profiles of average velocities and their pulsations in the laminar-turbulent transition zone have been obtained, as well as axial distributions of the longitudinal velocity and longitudinal velocity pulsations. Based on a comparison with the data of other authors, the effect of the initial conditions on the laminar-turbulent transition in a submerged jet has been shown.

On the Effects of Turbulence Modeling on the Fluid-Structure Interaction of a Rigid Cylinder

2016 ◽  
Author(s):  
Guilherme Feitosa Rosetti ◽  
Guilherme Vaz ◽  
André Luís Condino Fujarra
Keyword(s):  
Turbulence Modeling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Turbulent Transition ◽  
Moving Cylinder ◽  
Wide Range ◽  
Cylinder Flow ◽  
Laminar Turbulent Transition

The cylinder flow is a canonical problem for Computational Fluid Dynamics (CFD), as it can display several of the most relevant issues for a wide class of flows, such as boundary layer separation, vortex shedding, flow instabilities, laminar-turbulent transition and others. Several applications also display these features justifying the amount of energy invested in studying this problem in a wide range of Reynolds numbers. The Unsteady Reynolds Averaged Navier Stokes (URANS) equations combined with simplifying assumptions for turbulence have been shown inappropriate for the captive cylinder flow in an important range of Reynolds numbers. For that reason, recent improvements in turbulence modeling has been one of the most important lines of research within that issue, aiming at better prediction of flow and loads, mainly targeting the three-dimensional effects and laminar-turbulent transition, which are so important for blunt bodies. In contrast, a much smaller amount of work is observed concerning the investigation of turbulent effects when the cylinder moves with driven or free motions. Evidently, larger understanding of the contribution of turbulence in those situations can lead to more precise mathematical and numerical modeling of the flow around a moving cylinder. In this paper, we present CFD calculations in a range of moderate Reynolds numbers with different turbulence models and considering a cylinder in captive condition, in driven and in free motions. The results corroborate an intuitive notion that the inertial effects indeed play very important role in determining loads and motions. The flow also seems to adapt to the motions in such a way that vortices are more correlated and less influenced by turbulence effects. Due to good comparison of the numerical and experimental results for the moving-cylinder cases, it is observed that the choice of turbulence model for driven and free motions calculations is markedly less decisive than for the captive cylinder case.

On Methods of Experimental Investigation of the Laminar-Turbulent Transition at Transonic Velocities

1997 ◽  
Vol 32 (6) ◽  
pp. 793-797 ◽  
Author(s):  
V. I. Biryukov ◽  
V. D. Bokser ◽  
V. G. Mikeladze ◽  
G. K. Shapovalov
Keyword(s):  
Experimental Investigation ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

scholarly journals Laminar–turbulent transition in channel flow with superhydrophobic surfaces modelled as a partial slip wall

2019 ◽  
Vol 881 ◽  
pp. 462-497 ◽  
Author(s):  
Francesco Picella ◽  
J.-Ch. Robinet ◽  
S. Cherubini
Keyword(s):  
Channel Flow ◽  
Initial Conditions ◽  
Slip Length ◽  
Low Noise ◽  
Superhydrophobic Surfaces ◽  
Partial Slip ◽  
Turbulent Transition ◽  
Onset Of Turbulence ◽  
Fully Developed Turbulent Flow ◽  
Laminar Turbulent Transition

Superhydrophobic surfaces are capable of trapping gas pockets within the micro-roughnesses on their surfaces when submerged in a liquid, with the overall effect of lubricating the flow on top of them. These bio-inspired surfaces have proven to be capable of dramatically reducing skin friction of the overlying flow in both laminar and turbulent regimes. However, their effect in transitional conditions, in which the flow evolution strongly depends on the initial conditions, has still not been deeply investigated. In this work the influence of superhydrophobic surfaces on several scenarios of laminar–turbulent transition in channel flow is studied by means of direct numerical simulations. A single phase incompressible flow has been considered and the effect of the micro-structured superhydrophobic surfaces has been modelled imposing a slip condition with given slip length at both walls. The evolution from laminar, to transitional, to fully developed turbulent flow has been followed starting from several different initial conditions. When modal disturbances issued from linear stability analyses are used for perturbing the laminar flow, as in supercritical conditions or in the classical K-type transition scenario, superhydrophobic surfaces are able to delay or even avoid the onset of turbulence, leading to a considerable drag reduction. Whereas, when transition is triggered by non-modal mechanisms, as in the optimal or uncontrolled transition scenarios, which are currently observed in noisy environments, these surfaces are totally ineffective for controlling transition. Superhydrophobic surfaces can thus be considered effective for delaying transition only in low-noise environments, where transition is triggered mostly by modal mechanisms.

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