Effects of Streamwise Pressure Gradient on Turbulent Spot Development

1996 ◽  
Vol 118 (4) ◽  
pp. 737-743 ◽  
Author(s):  
J. P. Gostelow ◽  
N. Melwani ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Pressure Distribution ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Turbulent Layer ◽  
Wide Range

A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet, which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition and the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution, strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the centerline and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot, which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

scholarly journals Effects of Streamwise Pressure Gradient on Turbulent Spot Development

1995 ◽  
Author(s):  
J. P. Gostelow ◽  
N. Melwani ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Pressure Distribution ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Turbulent Layer ◽  
Wide Range

A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition aad the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the center line and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

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.

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.

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.

Premature boundary layer transition caused by surface static pressure tappings

1988 ◽  
Vol 92 (912) ◽  
pp. 63-68 ◽  
Author(s):  
P. E. Roach ◽  
J. T. Turner
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Static Pressure ◽  
Cross Flow ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Wide Range ◽  
Boundary Layer Interaction

Summary Experiments have been performed to study the influence of multiple surface static pressure tappings on transition of the boundary layer on a circular cylinder in cross-flow. A wide range of tapping and cylinder dimensions have been examined to demonstrate that the tappings can act in the same way as trip wires or other surface roughness to reduce the Reynolds number at which transition occurs. Hence, the pressure distribution around the cylinder may be influenced by the presence of the tappings, leading to incorrect measurements. Examination of the data has resulted in a correlation which should make it possible to avoid this tapping/boundary layer interaction in future experiments involving similar cylindrical bodies.

Transition in a Separation Bubble

1996 ◽  
Vol 118 (4) ◽  
pp. 752-759 ◽  
Author(s):  
E. Malkiel ◽  
R. E. Mayle
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Lateral Direction ◽  
Intensity Measurements ◽  
Separated Shear Layer ◽  
Laminar Shear

In the interest of being able to predict separating–reattaching flows, it is necessary to have an accurate model of transition in separation bubbles. An experimental investigation of the process of turbulence development in a separation bubble shows that transition occurs within the separated shear layer. A comparison of simultaneous velocity traces from comparison of simultaneous velocity traces from probes separated in the lateral direction suggests that Kelvin–Helmholtz waves, which originate in the laminar shear layer, do not break down to turbulence simultaneously across their span when they proceed to agglomerate. The streamwise development of intermittency in this region can be characterized by turbulent spot theory with a high dimensionless spot production rate. Moreover, the progression of intermittency along the centerline of the shear layer is similar to that in attached boundary layer transition. The transverse development of intermittency is also remarkably similar to that in attached boundary layers. The parameters obtained from these measurements agree with correlations previously deduced from turbulence intensity measurements.

scholarly journals Modeling of Boundary Layer Transition in Turbulent Flows by Linear Combination Integral Method

1994 ◽  
Author(s):  
J. P. Gostelow ◽  
G. Hong ◽  
G. J. Walker ◽  
J. Dey
Keyword(s):  
Boundary Layer ◽  
Velocity Profile ◽  
Linear Combination ◽  
Integral Method ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Turbulent Layer ◽  
Free Stream Turbulence ◽  
Turbulence Effects

Transitional boundary layer parameters in zero and variable pressure gradient flows, typical of turbomachinery applications, are predicted using an integral method of the linear combination type. The code used is that of Dey and Narasimha and the turbulent layer is calculated by a lag-entrainment method. The predictions of test data represent an improvement upon earlier methods; although reasonable agreement is obtained for these low Reynolds number test cases further refinement of predictive correlations to account for free-stream turbulence effects on laminar boundary layers and transition inception is indicated. The transitional parameters are found to be particularly sensitive to the initial conditions selected for the turbulent layer. Techniques are identified for overcoming this sensitivity and for adequately representing the transition region. Free-stream turbulence effects are quite strong, particularly on the velocity profile of the laminar layer. Modifications to laminar methods are advocated to account for the strong effects on the velocity profile and the early formation of turbulent spots.

Bypass Transition Modelling: A New Method Which Accounts for Free-Stream Turbulence Intensity and Length Scale

2000 ◽  
Author(s):  
Paul E. Roach ◽  
David H. Brierley
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Length Scale ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Free Stream Turbulence

The publication of the present authors’ boundary layer transition data in 1992 (now widely known as the ERCOFTAC test case T3) has led to a spate of new experimental and modelling efforts aimed at improving our understanding of this problem. This paper describes a new method of determining boundary layer transition with zero mean pressure gradient. The approach examines the development of a laminar boundary layer to the start of transition, accounting for the influences of free-stream turbulence and test surface geometry. It is presented as a “proof of concept”, requiring a significant amount of work before it can be considered as a practically applicable model for transition prediction. The method is based upon one first put forward by G.I. Taylor in the 1930’s, and accounts for the action of local, instantaneous pressure gradients on the developing laminar boundary layer. These pressure gradients are related to the intensity and length scale of turbulence in the free-stream using Taylor’s simple isotropic model. The findings demonstrate the need to account for the separate influences of free-stream turbulence intensity and length scale when considering the transition process. Although the length scale has less of an effect than the intensity, its influence is, nevertheless, significant and must not be overlooked. This fact goes a long way towards explaining the large scatter to be found in simple correlations which involve only the turbulence intensity. Intriguingly, it is demonstrated that it is the free-stream turbulence at the leading edge of the test surface which is important, not that found locally outside the boundary layer. The additional influence of leading edge geometry is also shown to play a major role in fixing the point at which transition begins. It is suggested that the leading edge geometry will distort the incident turbulent eddies, modifying the effective “free-stream” turbulence properties. Consequently, it is shown that the scale of the eddies relative to the leading edge thickness is a further important parameter, and helps bring together a large number of test cases.

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