Three-Dimensional Processes in Laminar-Turbulent Transition

1985 ◽  
pp. 123-154 ◽  
Author(s):  
L. Kleiser
Keyword(s):  
Three Dimensional ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

An experimental study of the influence of riblets on transition

1996 ◽  
Vol 315 ◽  
pp. 31-49 ◽  
Author(s):  
G. R. Grek ◽  
V. V. Kozlov ◽  
S. V. Titarenko
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Negative Influence ◽  
Positive Influence ◽  
Linear Stage ◽  
Turbulent Transition ◽  
Transition Structures ◽  
Stage Transition ◽  
Tollmien Schlichting ◽  
Laminar Turbulent Transition

An experimental study of the effect of riblets on three-dimensional nonlinear structures, the so-called Λ-vortices on laminar-turbulent transition showed that riblets delay the transformation of the Λ-vortices into turbulent spots and shift the point of transition downstream. This result is opposite to the negative influence of such ribbed surfaces on two-dimensional linear Tollmien-Schlichting waves (the linear stage of transition). Thus, the ribbed surface influences laminar-turbulent transition structures differently: a negative influence on the linear-stage transition structures and a positive influence on the nonlinear-stage transition structures. It is demonstrated that transition control by means of riblets requires special attention to be paid to the choice of their location, taking into account the stage of transition.

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.

Coupling PSE and FLUENT to Predict Laminar-Turbulent Transition in Boundary Layers

2013 ◽  
Vol 432 ◽  
pp. 168-172
Author(s):  
Y. Zhou ◽  
Y.H. Fang
Keyword(s):  
Flat Plate ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Basic Flow ◽  
Two Dimensional ◽  
S Wave ◽  
S Waves ◽  
Turbulent Transition ◽  
Transition Criterion ◽  
Laminar Turbulent Transition

In this paper, the coupling method of PSE and FLUENT was experimented for predicting the laminar-turbulent transition. The software FLUENT was used to get the basic flow over a flat plate. A two-dimensional T-S wave and a pair of three-dimensional T-S waves were fed in at the entrance. The transition criterion was verified by DNS results. The availability of the coupling methodology has been evaluated.

The influence of Chine nose shapes on a slender body flight vehicle at high angles of attack

2011 ◽  
Vol 226 (2) ◽  
pp. 182-196 ◽  
Author(s):  
S Lim ◽  
S D Kim ◽  
D J Song
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Slender Body ◽  
Flight Vehicle ◽  
Side Force ◽  
Turbulent Transition ◽  
Flow Vortex ◽  
High Angles Of Attack ◽  
Laminar Turbulent Transition

The flow characteristics of asymmetric vortices and the side force of a slender body flight vehicle with chine nose at high angles of attack have been studied using a three-dimensional upwind Navier–Stokes method with the k– ω turbulence model and a simple laminar–turbulent transition model. Asymmetrically changing turbulent viscosities that arise from asymmetric laminar–turbulent transition conditions cause asymmetric cross-flow vortex structures and side forces at higher angles of attack. However, certain type of edges may cause fixed flow separations on these edges. In this study, the chine nose shape with chine edge on its both sides is considered for the method to reduce side force. The asymmetric flow control capacity of chine nose shapes at high angles of attack is studied.

scholarly journals Laminar–turbulent transition induced by a discrete roughness element in a supersonic boundary layer

2013 ◽  
Vol 735 ◽  
pp. 613-646 ◽  
Author(s):  
N. De Tullio ◽  
P. Paredes ◽  
N. D. Sandham ◽  
V. Theofilis
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Roughness Element ◽  
Three Dimensional ◽  
Supersonic Boundary Layer ◽  
Low Velocity ◽  
Adiabatic Wall ◽  
Turbulent Transition ◽  
Displacement Thickness ◽  
Laminar Turbulent Transition

AbstractThe linear instability and breakdown to turbulence induced by an isolated roughness element in a boundary layer at Mach $2. 5$, over an isothermal flat plate with laminar adiabatic wall temperature, have been analysed by means of direct numerical simulations, aided by spatial BiGlobal and three-dimensional parabolized (PSE-3D) stability analyses. It is important to understand transition in this flow regime since the process can be slower than in incompressible flow and is crucial to prediction of local heat loads on next-generation flight vehicles. The results show that the roughness element, with a height of the order of the boundary layer displacement thickness, generates a highly unstable wake, which is composed of a low-velocity streak surrounded by a three-dimensional high-shear layer and is able to sustain the rapid growth of a number of instability modes. The most unstable of these modes are associated with varicose or sinuous deformations of the low-velocity streak; they are a consequence of the instability developing in the three-dimensional shear layer as a whole (the varicose mode) or in the lateral shear layers (the sinuous mode). The most unstable wake mode is of the varicose type and grows on average ${\sim }17\hspace{0.167em} \% $ faster than the most unstable sinuous mode and ${\sim }30$ times faster than the most unstable boundary layer mode occurring in the absence of a roughness element. Due to the high growth-rates registered in the presence of the roughness element, an amplification factor of $N= 9$ is reached within ${\sim }50$ roughness heights from the roughness trailing edge. The independently performed Navier–Stokes, spatial BiGlobal and PSE-3D stability results are in excellent agreement with each other, validating the use of simplified theories for roughness-induced transition involving wake instabilities. Following the linear stages of the laminar–turbulent transition process, the roll-up of the three-dimensional shear layer leads to the formation of a wedge of turbulence, which spreads laterally at a rate similar to that observed in the case of compressible turbulent spots for the same Mach number.

The Effect of the Source Location on the Acoustic Excitation on Laminar-Turbulent Transition on Swept Wing Boundary Layer

2002 ◽  
Author(s):  
B. Gu¨lac¸ti ◽  
S. Aubrun ◽  
A. Seraudie ◽  
D. Arnal
Keyword(s):  
Wind Tunnel ◽  
Test Section ◽  
Three Dimensional ◽  
Source Location ◽  
Sound Level ◽  
Acoustic Excitation ◽  
Hot Wire ◽  
Swept Wing ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

The effect of the source location and the direction of the propagation on the laminar-turbulent transition on swept-wing three-dimensional boundary layers are investigated experimentally. Also the crossflow case is handled in detail. The source for the acoustic excitation is placed in four different locations: in front of the wing, on top of the test section, behind the wing and in front of the wind tunnel. Three different experimental cases (streamwise, crossflow and mixed cases) are examined for each location with two different excitation bands. For the most efficient frequency ranges and the highest sound pressure levels an upstream shift of transition motion between 20%–35% of chord length for streamwise case and between 5%–10% for the crossflow case are observed. While in front of the wing and behind the wing are the most efficient loudspeaker positions in the streamwise case, in the crossflow case the most efficient locations are observed to be in front of the wing and on top of the test section. It is concluded that acoustic sound level plays a more important role in the upstream shift of the transition than the source location and placing the loudspeaker in front of the wind tunnel is not an efficient position. For the crossflow instabilities dominated transition the stationary vortices are clearly seen from the velocity contours obtained by the hot-wire. Secondary instabilities couldn’t be observed in the hot-wire spectra. The surface roughness of the wing that is reduced to 0.25µm does not change the transition location in the crossflow case.

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