Laminar boundary-layer transition on a heated underwater body

1984 ◽  
Vol 144 ◽  
pp. 79-101 ◽  
Author(s):  
Gerald C. Lauchle ◽  
G. B. Gurney
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Total Concentration ◽  
Heated Surface ◽  
Axisymmetric Body ◽  
The Body ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Maximum Heat

A large (3.05 m long × 0.32 m diameter) heated-surface, axisymmetric body, designed for transition research in a 1.22 m diameter water tunnel is described. Boundary-layer transition data are presented as functions of the heating power supplied to the body and the total concentration of free-stream particulate matter in the water. Body surface temperatures range from 0 to 25°C over the ambient water temperature, and the total heat supplied ranges from 0 to 93.3 kW. Transition-arclength Reynolds numbers are found to vary from 4.5 × 106 for the body operating cold to 3.64 × 107 for the maximum heat level considered. The concentration of free-stream particles is shown to affect the transition Reynolds number. These particles range in diameter from 10 to 70 μm and their concentration ranges from less than 5 to 198 particles per cm3. The decrease in transition Reynolds number due to to the higher concentration of particles is of order 30%.

Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 1—An Evaluation of Prediction Characteristics

1991 ◽  
Vol 113 (1) ◽  
pp. 10-17 ◽  
Author(s):  
R. C. Schmidt ◽  
S. V. Patankar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
External Boundary ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Low Reynolds

An analysis and evaluation of the capability of k–ε low-Reynolds-number turbulence models to predict transition in external boundary-layer flows subject to free-stream turbulence is presented. The similarities between the near-wall cross-stream regions in a fully turbulent boundary layer and the progressive stages through which developing boundary layers pass in the streamwise direction are used to describe the mechanisms by which the models simulate the transition process. Two representative models (Jones and Launder, 1972; Lam and Bremhorst, 1981) are employed in a series of computational tests designed to answer some specific practical questions about the ability of these models to yield accurate, reliable answers over a range of free-stream turbulence conditions.

An experimental study of boundary layer transition induced by a cylinder wake

2011 ◽  
Vol 684 ◽  
pp. 60-84 ◽  
Author(s):  
A. C. Mandal ◽  
J. Dey
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Late Stage ◽  
Free Stream ◽  
Experimental Studies ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence

AbstractBoundary layer transition induced by the wake of a circular cylinder in the free stream has been investigated using the particle image velocimetry technique. Some differences between simulation and experimental studies have been reported in the literature, and these have motivated the present study. The appearance of spanwise vortices in the early stage is further confirmed here. A spanwise vortex appears to evolve into a $ \mrm{\Lambda} $/hairpin vortex; the flow statistics also confirm such vortices. With increasing Reynolds number, based on the cylinder diameter, and with decreasing cylinder height from the plate, the physical size of these hairpin-like structures is found to decrease. Some mean flow characteristics, including the streamwise growth of the disturbance energy, in a wake-induced transition resemble those in bypass transition induced by free stream turbulence. Streamwise velocity streaks that are eventually generated in the late stage often undergo sinuous-type oscillations. Similar to other transitional flows, an inclined shear layer in the wall-normal plane is often seen to oscillate and shed vortices. The normalized shedding frequency of these vortices, estimated from the spatial spacing and the convection velocity of these vortices, is found to be independent of the Reynolds number, similar to that in ribbon-induced transition. Although the nature of free stream disturbance in a wake-induced transition and that in a bypass transition are different, the late-stage features including the flow breakdown characteristics of these two transitions appear to be similar.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

An Experimental Study of Heat Transfer on an Outlet Guide Vane

2014 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sundén ◽  
Valery Chernoray ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Guide Vane ◽  
Incidence Angle ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Layer Transition

In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and −25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminar-turbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.

Velocity and Pressure Measurements Along a Row of Confined Cylinders

2006 ◽  
Author(s):  
Barton L. Smith ◽  
Jack J. Stepan ◽  
Donald M. McEligot
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Symmetry Plane ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Recirculation Region ◽  
Pressure Measurements ◽  
Layer Transition ◽  
Flow Experiments

The results of flow experiments performed in a cylinder array designed to mimic a VHTR Nuclear Plant lower plenum design are presented. Pressure drop and velocity field measurements were made. Based on these measurements, five regimes of behavior are identified that are found to depend on Reynolds number. It is found that the recirculation region behind the cylinders is shorter than that of half cylinders placed on the wall representing the symmetry plane. Unlike a single cylinder, the separation point is found to always be on the rear of the cylinders, even at very low Reynolds number. Boundary layer transition is found to occur at much lower Reynolds numbers than previously reported.

The Critical Height of Distributed Roughness to Cause Boundary Layer Transition

1959 ◽  
Vol 63 (588) ◽  
pp. 722-722
Author(s):  
R. L. Dommett
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Laminar Boundary Layer ◽  
Boundary Layer Transition ◽  
Critical Height ◽  
Layer Transition ◽  
Local Conditions ◽  
Additional Advantage ◽  
Boundary Layer Equations ◽  
General Method

It has been found that there is a critical height for “sandpaper” type roughness below which no measurable disturbances are introduced into a laminar boundary layer and above which transition is initiated at the roughness. Braslow and Knox have proposed a method of predicting this height, for flow over a flat plate or a cone, using exact solutions of the laminar boundary layer equations combined with a correlation of experimental results in terms of a Reynolds number based on roughness height, k, and local conditions at the top of the elements. A simpler, yet more general, method can be constructed by taking additional advantage of the linearity of the velocity profile near the wall in a laminar boundary layer.

The flow structure in the lee of an inclined 6:1 prolate spheroid

1994 ◽  
Vol 269 ◽  
pp. 79-106 ◽  
Author(s):  
T. C. Fu ◽  
A. Shekarriz ◽  
J. Katz ◽  
T. T. Huang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Incidence Angle ◽  
Prolate Spheroid ◽  
The Body ◽  
Boundary Layer Transition ◽  
Primary Vortex ◽  
Vortex Sheets ◽  
Vorticity Distribution

Particle displacement velocimetry is used to measure the velocity and vorticity distributions around an inclined 6: 1 prolate spheroid. The objective is to determine the effects of boundary-layer tripping, incidence angle, and Reynolds number on the flow structure. The vorticity distributions are also used for computing the lateral forces and rolling moments that occur when the flow is asymmetric. The computed forces agree with results of direct measurements. It is shown that when the flow is not tripped, separation causes the formation of a pair of vortex sheets. The size of these sheets increases with increasing incidence angle and axial location. Their orientation and internal vorticity distribution also depend on incidence. Rollup into distinct vortices occurs in some cases, and the primary vortex contains between 20 % and 50 % of the overall circulation. The entire flow is unsteady and there are considerable variations in the instantaneous vorticity distributions. The remainder of the lee side, excluding these vortex sheets, remains almost vorticity free, providing clear evidence that the flow can be characterized as open separation. Boundary-layer tripping causes earlier separation on part of the model, brings the primary vortex closer to the body, and spreads the vorticity over a larger region. The increased variability in the vorticity distribution causes considerable force fluctuations, but the mean loads remain unchanged. Trends with increasing Reynolds number are conflicting, probably because of boundary-layer transition. The separation point moves towards the leeward meridian and the normal force decreases when the Reynolds number is increased from 0.42 × 106 to 1.3 × 106. Further increase in the Reynolds number to 2.1 × 106 and tripping cause an increase in forces and earlier separation.

Effects of Concave Curvature on Boundary Layer Transition Under High Free-Stream Turbulence Conditions

2001 ◽  
Author(s):  
Michael P. Schultz ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Turbulent Transport ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Turbulent Shear ◽  
Radius Of Curvature ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbulent Shear Stress

An experimental investigation has been carried out on a transitional boundary layer subject to high (initially 9%) free-stream turbulence, strong acceleration K=ν/Uw2dUw/dxas high as9×10-6, and strong concave curvature (boundary layer thickness between 2% and 5% of the wall radius of curvature). Mean and fluctuating velocity as well as turbulent shear stress are documented and compared to results from equivalent cases on a flat wall and a wall with milder concave curvature. The data show that curvature does have a significant effect, moving the transition location upstream, increasing turbulent transport, and causing skin friction to rise by as much as 40%. Conditional sampling results are presented which show that the curvature effect is present in both the turbulent and non-turbulent zones of the transitional flow.

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