Effects of Adverse Pressure Gradients on the Nature and Length of Boundary Layer Transition

1990 ◽  
Vol 112 (2) ◽  
pp. 196-205 ◽  
Author(s):  
G. J. Walker ◽  
J. P. Gostelow
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Basic Mechanism ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Instability Waves ◽  
Free Stream Turbulence ◽  
Transition Length ◽  
Tollmien Schlichting

Existing transition models are surveyed and deficiencies in previous predictions, which seriously overestimate transition length under an adverse pressure gradient, are discussed. A new model for transition in an adverse pressure gradient situation is proposed and experimental results are provided that confirm its validity. A correlation for transition length is advanced that incorporates both Reynolds number and pressure gradient effects. Under low free-stream turbulence conditions the basic mechanism of transition is laminar instability. There are, however, physical differences between zero and adverse pressure gradients. In the former case, transition occurs randomly, due to the breakdown of laminar instability waves in sets. For an adverse pressure gradient, the Tollmien–Schlichting waves appear more regularly with a well-defined spectral peak. As the adverse pressure gradient is increased from zero to the separation value the flow evolves continuously from random to periodic behavior and the dimensionless transition length progressively decreases.

Effects of Adverse Pressure Gradients on the Nature and Length of Boundary Layer Transition

1989 ◽  
Author(s):  
G. J. Walker ◽  
J. P. Gostelow
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Basic Mechanism ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Instability Waves ◽  
Free Stream Turbulence ◽  
Transition Length ◽  
Tollmien Schlichting

Existing transition models are surveyed and deficiencies in previous predictions, which seriously overestimate transition length under an adverse pressure gradient, are discussed. A new model for transition in an adverse pressure gradient situation is proposed and experimental results are provided which confirm its validity. A correlation for transition length is advanced which incorporates both Reynolds number and pressure gradient effects. Under low free-stream turbulence conditions the basic mechanism of transition is laminar instability. There are, however, physical differences between zero and adverse pressure gradients. In the former case transition occurs randomly, due to the breakdown of laminar instability waves in sets. For an adverse pressure gradient the Tollmien-Schlichting waves appear more regularly with a well-defined spectral peak. As the adverse pressure gradient is increased from zero to the separation value the flow evolves continuously from random to periodic behavior and the dimensionless transition length progressively decreases.

Measurements and Prediction of Free-Stream Turbulence and Pressure-Gradient Effects on Attached-Flow Boundary-Layer Transition

2003 ◽  
Author(s):  
S. K. Roberts ◽  
M. I. Yaras
Keyword(s):  
Reynolds Number ◽  
Free Stream ◽  
Turbine Blades ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Flow Reynolds Number ◽  
Attached Flow ◽  
Transition Length

This paper presents measurements of free-stream turbulence, streamwise pressure gradients and flow Reynolds number effects on attached-flow transition. The measurements were performed on a flat plate, at free-stream turbulence intensities ranging from 0.5% to 9.0%, four Reynolds numbers, and several streamwise pressure distributions, including ones that are typical of the suction side pressures of axial turbine blades. Based on the results, the extent of upstream movement of transition location with free-stream turbulence, the changes in transition length with variations in the streamwise pressure gradients, and the sensitivity of these trends to flow Reynolds number are quantified. Interpretation of the measurements is based primarily on streamwise and cross-stream intermittency distributions extracted from the velocity traces of hot-wire traverses. The measured transition inception locations and transition lengths are used to evaluate mathematical models available in the published literature. A modification is proposed to a transition length model to improve the prediction of the streamwise intermittency distribution.

Investigations of Boundary Layer Transition in an Adverse Pressure Gradient

1989 ◽  
Vol 111 (4) ◽  
pp. 366-374 ◽  
Author(s):  
J. P. Gostelow ◽  
A. R. Blunden
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Formation Rate ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Transition ◽  
Strong Increase ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Spot Formation

Boundary layer transition was measured on a flat plate for four different turbulence levels. A range of adverse pressure gradients was imposed for one of these. The zero pressure gradient results were in agreement with accepted data for transition inception, length, and turbulent spot formation rate. They were also well represented by Narasimha’s universal intermittency distribution. A surprisingly strong similarity was also exhibited by intermittency distributions under adverse pressure gradients. Dimensionless velocity profiles were reasonable for the zero pressure gradient cases but difficulties with skin-friction prediction were experienced under adverse pressure gradient conditions. For this moderate turbulence level the transition inception Reynolds number remained reasonably constant with pressure gradient. Transition lengths, however, were greatly reduced by the imposition of even a weak adverse pressure gradient. This was associated with a strong increase in turbulent spot formation rate.

The Effect of Pressure Gradients on Transition Zone Length in Hypersonic Boundary Layers

1997 ◽  
Vol 119 (1) ◽  
pp. 36-41 ◽  
Author(s):  
R. L. Kimmel
Keyword(s):  
Pressure Gradient ◽  
Transition Zone ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Zone Length ◽  
Hypersonic Boundary Layers ◽  
Favorable Pressure Gradient ◽  
Half Angle

Boundary layer transition was measured in zero, favorable, and adverse pressure gradients at Mach 8 using heat transfer. Models consisted of 7° half angle forecones 0.4826 m long, followed by flared or ogive aft bodies 0.5334 m long. The flares and ogives produced constant pressure gradients. For the cases examined, favorable pressure gradients delay transition and adverse pressure gradients promote transition, but transition zone lengths are shorter in favorable pressure gradient. Results of the effect of adverse pressure gradient on transition zone lengths were inconclusive.

Turbulent Spots in Strong Adverse Pressure Gradients: Part 2 — Spot Propagation and Spreading Rates

2001 ◽  
Author(s):  
A. D’Ovidio ◽  
J. A. Harkins ◽  
J. P. Gostelow
Keyword(s):  
Separation Bubble ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Flat Plates ◽  
Layer Transition ◽  
Turbulent Spots ◽  
Laminar Separation ◽  
Transition Length ◽  
Spreading Rates

The study of turbulent spots in strong adverse pressure gradients is of current interest in turbomachinery research. The aim of this investigation is to use information gathered from boundary layer transition and laminar separation, in wind tunnel tests on flat plates, to predict the equivalent phenomena occurring on turbomachinery blade surfaces. In Part 1 turbulent spot behavior was documented for two Reynolds numbers, corresponding to a laminar separation bubble (LSB) and an incipient separation condition (IS). In Part 2 further results are reported characterizing typical spot propagation and spreading rates and serving to validate or modify existing correlations for predicting transition length.

Effects of Free-Stream Turbulence and Adverse Pressure Gradients on Boundary Layer Transition

1994 ◽  
Vol 116 (3) ◽  
pp. 392-404 ◽  
Author(s):  
J. P. Gostelow ◽  
A. R. Blunden ◽  
G. J. Walker
Keyword(s):  
Pressure Gradient ◽  
Free Stream ◽  
Formation Rate ◽  
Transition Process ◽  
Pressure Gradients ◽  
Turbulence Level ◽  
Free Stream Turbulence ◽  
Exponential Decrease ◽  
Transition Length ◽  
Spot Formation

Boundary layer measurements are presented through transition for six different free-stream turbulence levels and a complete range of adverse pressure gradients for attached laminar flow. Measured intermittency distributions provide an excellent similarity basis for characterizing the transition process under all conditions tested when the Narasimha procedure for determining transition inception is used. This inception location procedure brings consistency to the data. Velocity profiles and integral parameters are influenced by turbulence level and pressure gradient and do not provide a consistent basis. Under strong adverse pressure gradients transition occurs rapidly and the velocity profile has not fully responded before the completion of transition. The starting turbulent layer does not attain an equilibrium velocity profile. A change in pressure gradient from zero to even a modest adverse level is accompanied by a severe reduction in transition length. Under diffusing conditions the physics of the transition process changes and the spot formation rate increases rapidly; instead of the “breakdown in sets” regime experienced in the absence of a pressure gradient, transition under strong adverse pressure gradients is more related to the amplification and subsequent instability of the Tollmien-Schlichting waves. Measurements reveal an exponential decrease in transition length with increasing adverse pressure gradient; a less severe exponential decrease is experienced with increasing turbulence level. Correlations of transition length are provided that facilitate its prediction in the form of suitable length parameters including spot formation rate.

Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)

2003 ◽  
Author(s):  
Jonathan H. Watmuff
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Distorted Waves ◽  
Thickness Variations

Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.

Free-Stream Turbulence and Pressure Gradient Effects on Heat Transfer and Boundary Layer Development on Highly Cooled Surfaces

1985 ◽  
Vol 107 (1) ◽  
pp. 54-59 ◽  
Author(s):  
K. Rued ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Boundary Layer Development ◽  
Gradient Effects ◽  
Layer Development

Heat transfer and boundary layer measurements were derived from flows over a cooled flat plate with various free-stream turbulence intensities (Tu = 1.6–11 percent), favorable pressure gradients (k = νe/ue2•due/dx = 0÷6•10−6) and cooling intensities (Tw/Te = 1.0–0.53). Special interest is directed towards the effects of the dominant parameters, including the influence on laminar to turbulent boundary layer transition. It is shown, that free-stream turbulence and pressure gradients are of primary importance. The increase of heat transfer due to wall cooling can be explained primarily by property variations as transition, and the influence of free-stream parameters are not affected.

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