scholarly journals Studies on Wake-Disturbed Boundary Layers Under the Influences of Favorable Pressure Gradient and Free-Stream Turbulence: Part I — Experimetal Setup and Discussions on Transition Model

1997 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Takashi Kitazawa ◽  
Kazuyuki Koizumi ◽  
Tadashi Tanuma
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Test Model ◽  
Flat Plates ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Favorable Pressure Gradient

The objective of this study is to investigate effects of favorable pressure gradient as well as free-stream turbulence upon wake-induced boundary layer transition on a flat plate. Likewise in the previous study by Funazaki (1996), a spoked-wheel type wake generator is employed in this study. Two identical flat plates with sharp edge are used as test model. One of them is for measurement of boundary layers over the test plate by use of a single hot-wire probe, and the other is provided with thin stainless-steel foils on the surface to measure wake-affected heat transfer along the surface. Free-stream turbulence intensities are controlled with several types of turbulence grids. Pressure gradients over the test surface are adjusted by changing an inclination angle of the plate located opposite to the test model. In Part I, transition models proposed by Mayle and Dullenkopf (1990b) and Funazaki (1996a, 1996b) are compared with the experimental data obtained in this study to examine how such a model succeeds or fails in predicting the wake-induced boundary layer transition under the influences of favorable pressure gradient with a low free-stream turbulence.

Investigation of the Laminar-Turbulent Transition of Boundary Layers Disturbed by Wakes

1982 ◽  
Author(s):  
H. Pfeil ◽  
R. Herbst ◽  
T. Schröder
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbulent Spots ◽  
Turbulent Transition ◽  
Time Space ◽  
Favorable Pressure Gradient

The boundary layer transition under instationary afflux conditions as present in the stages of turbomachines is investigated. A model for the transition process is introduced by means of time-space distributions of the turbulent spots during transition and schematic drawings of the instantaneous boundary layer thicknesses. To confirm this model, measurements of the transition with zero and favorable pressure gradient are performed.

Boundary Layer Transition at High Levels of Free Stream Turbulence

1998 ◽  
Author(s):  
Masaharu Matsubara ◽  
P. Henrik Alfredsson ◽  
K. Johan A. Westin
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbine Blades ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Flow Visualisation ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence

Transition to turbulence in laminar boundary layers subjected to high levels of free stream turbulence (FST) can still not be reliably predicted, despite its technical importance, e.g. in the case of boundary layers developing on gas turbine blades. In a series of experiments in the MTL-wind tunnel at KTH the influence of grid-generated FST on boundary layer transition has been studied, with FST-levels up to 6%. It was shown from both flow visualisation and hot-wire measurements that the boundary layer develops unsteady streaky structures with high and low streamwise velocity. This leads to large amplitude low frequency fluctuations inside the boundary layer although the mean flow is still close to the laminar profile. Breakdown to turbulence occurs through an instability of the streaks which leads to the formation of turbulent spots. Accurate physical modelling of these processes seems to be needed in order to obtain a reliable prediction method.

scholarly journals Boundary Layer Transition of Strongly Concave Surfaces

1989 ◽  
Author(s):  
Stephen Riley ◽  
Mark W. Johnson ◽  
John C. Gibbings
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Radius Of Curvature ◽  
Pressure Gradients ◽  
Flat Plates ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Surface Data ◽  
Correlation Techniques

Boundary layer transition has been studied on two blades of constant 0.5 and 1 metre radius of curvature with free stream turbulence levels of 0.7%, 2.6% and 7.2%. Zero pressure gradients were used throughout. Strong Gortler vortices developed in the boundary layer which led to growth rates of up to ten times the flat plate rate. The boundary layer profile was also highly distorted by the vortices. Transition correlation techniques for flat plates proved totally inadequate for the concave surface data, but a method of obtaining correlations for these surfaces was suggested by considering the inner critical region of the boundary layer alone.

Investigation of the Laminar-Turbulent Transition of Boundary Layers Disturbed by Wakes

1983 ◽  
Vol 105 (1) ◽  
pp. 130-137 ◽  
Author(s):  
H. Pfeil ◽  
R. Herbst ◽  
T. Schro¨der
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbulent Spots ◽  
Turbulent Transition ◽  
Time Space ◽  
Favorable Pressure Gradient

The boundary layer transition under instationary afflux conditions as present in the stages of turbomachines is investigated. A model for the transition process is introduced by means of time-space distributions of the turbulent spots during transition and schematic drawings of the instantaneous boundary layer thicknesses. To confirm this model, measurements of the transition with zero and favorable pressure gradient are performed.

scholarly journals Influence of Free Stream Turbulence and Blade Pressure Gradient on Boundary Layer and Loss Behaviour of Turbine Cascades

1986 ◽  
Author(s):  
H. Hoheisel ◽  
R. Kiock ◽  
H. J. Lichtfuß ◽  
L. Fottner
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Surface Velocity ◽  
Experimental Investigations ◽  
Layer Transition ◽  
Blade Loading ◽  
Free Stream Turbulence ◽  
Turbine Cascades

The optimization of the blade surface velocity distribution is promising a reduction of turbine cascade losses. Theoretical and experimental investigations on three turbine cascades with the same blade loading show the important influence of the blade pressure gradient and the free stream turbulence on the loss behaviour. The results presented demonstrate that it is the boundary layer transition behaviour that determines the losses on turbine cascades. An enormous effort in measuring technique is required in order to define the location of transition from cascade experiments very accurately.

Boundary Layer Transition Under High Free-Stream Turbulence and Strong Acceleration Conditions: Part 2—Turbulent Transport Results

1997 ◽  
Vol 119 (3) ◽  
pp. 427-432 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulent Transport ◽  
Turbulent Heat Flux ◽  
Boundary Layer Transition ◽  
Turbulent Shear ◽  
Turbulent Heat ◽  
Layer Transition ◽  
Free Stream Turbulence

Measurements from heated boundary layers along a concave-curved test wall subject to high (initially 8 percent) free-stream turbulence intensity and strong (K = (ν/U∞2 dU∞/dx, as high as 9 × 10−6) acceleration are presented and discussed. Conditions for the experiments were chosen to simulate those present on the downstream half of the pressure side of a gas turbine airfoil. Turbulence statistics, including the turbulent shear stress, the turbulent heat flux, and the turbulent Prandtl number are presented. The transition zone is of extended length in spite of the high free-stream turbulence level. Turbulence quantities are strongly suppressed below values in unaccelerated turbulent boundary layers. Turbulent transport quantities rise with the intermittency, as the boundary layer proceeds through transition. Octant analysis shows a similar eddy structure in the present flow as was observed in transitional flows under low free-stream turbulence conditions. To the authors’ knowledge, this is the first detailed documentation of a high-free-stream-turbulence boundary layer flow in such a strong acceleration field.

Influence of Free-Stream Turbulence and Blade Pressure Gradient on Boundary Layer and Loss Behavior of Turbine Cascades

1987 ◽  
Vol 109 (2) ◽  
pp. 210-219 ◽  
Author(s):  
H. Hoheisel ◽  
R. Kiock ◽  
H. J. Lichtfuss ◽  
L. Fottner
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Surface Velocity ◽  
Experimental Investigations ◽  
Layer Transition ◽  
Blade Loading ◽  
Free Stream Turbulence ◽  
Turbine Cascades

The optimization of the blade surface velocity distribution is promising for a reduction of turbine cascade losses. Theoretical and experimental investigations on three turbine cascades with the same blade loading show the important influence of the blade pressure gradient and the free-stream turbulence on the loss behavior. The results presented demonstrate that it is the boundary layer transition behavior that determines the losses on turbine cascades. An enormous effort in measuring technique is required in order to define the location of transition from cascade experiments very accurately.

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.

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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