Influence of Free-Stream Turbulence on Boundary Layer Transition in Favorable Pressure Gradients

1982 ◽  
Vol 104 (4) ◽  
pp. 743-750 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Wall Heat Transfer ◽  
Profile Data ◽  
Mean Velocity ◽  
Free Stream Turbulence

Results from an experimental study of large-scale, two-dimensional incompressible transitional boundary layer flows are presented. Tests were conducted on a heated flat wall with a zero pressure gradient and for two levels of “sink” streamwise acceleration; k = ν/U2 ∂U/∂x = 0.2 or 0.75 × 10−6. Free-stream turbulence intensity levels ranged from approximately 0.7 to 5 percent with limited data obtained outside these values. Convective heat-transfer distributions, laminar, transitional, and fully turbulent boundary layer mean velocity and temperature profile data, and free-stream turbulence intensity distributions are presented. Boundary layer integral quantities and shape factors are also given. Transition onset Reynolds number data obtained for this program agreed well with the results of other experimental and theoretical studies for both zero pressure gradient and accelerating flows. Comparisons of the profile data and wall heat-transfer distribution data indicated that fully turbulent mean velocity profiles were achieved upstream of fully turbulent wall heat-transfer rates.

Effects of Free-Stream Turbulence and Pressure Gradient on Flat-Plate Boundary-Layer Velocity Profiles and on Heat Transfer

1967 ◽  
Vol 89 (2) ◽  
pp. 169-175 ◽  
Author(s):  
G. H. Junkhan ◽  
G. K. Serovy
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Free Stream Turbulence ◽  
Favorable Pressure Gradient ◽  
Layer Velocity

Experimental data indicating some effects of free-stream turbulence intensity on time-average boundary-layer velocity profiles and on heat transfer from a constant-temperature flat plate with a favorable pressure gradient are presented for local Reynolds numbers ranging from 4 × 104 to 4 × 105 and for free-stream turbulence intensities from 0.4 to 8.3 percent. It is concluded that, for the range of variables covered by the experiments: (a) The effect of free-stream turbulence intensity on heat transfer through the laminar boundary layer with a zero pressure gradient is negligible; (b) for a given Reynolds number, the local Nusselt number increases with increasing free-stream turbulence intensity when a pressure gradient is present, the boundary-layer profiles for these conditions changing with a variation in free-stream turbulence intensity; and (c) no increase in Nusselt number with increase in free-stream turbulence intensity occurs for turbulent boundary layers with a favorable pressure gradient.

Boundary Layer Transition Under High Free-Stream Turbulence and Strong Acceleration Conditions: Part 1—Mean Flow Results

1997 ◽  
Vol 119 (3) ◽  
pp. 420-426 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Temperature Profiles ◽  
Mean Flow ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
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 roughly simulate those present on the downstream half of the pressure side of a gas turbine airfoil. Mean velocity and temperature profiles as well as skin friction and heat transfer coefficients are presented. The transition zone is of extended length in spite of the high free-stream turbulence level. Transitional values of skin friction coefficients and Stanton numbers drop below flat-plate, low-free-stream-turbulence, turbulent flow correlations, but remain well above laminar flow values. The mean velocity and temperature profiles exhibit clear changes in shape as the flow passes through transition. 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.

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 Comparison of k-ε Models in Predicting Heat Transfer and Skin Friction Under High Free Stream Turbulence

1996 ◽  
Author(s):  
Ganesh R. Iyer ◽  
Savash Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Empirical Correlations ◽  
Free Stream Turbulence ◽  
Boundary Layer Equations

Calculations of the effects of high free stream turbulence (FST) on heat transfer and skin friction in a flat plate turbulent boundary layer using different k-ε models (Launder-Sharma, K-Y Chien, Lam-Bremhorsi and Jones-Launder) are presented. This study was carried out in order to investigate the prediction capabilities of these models under high FST conditions. In doing so, TEXSTAN, a partial differential equation solver which is based on the ideas of Patankar and Spalding and solves steady-flow boundary layer equations, was used. Firstly, these models were compared as to how they predicted very low FST (≤ 1% turbulence intensity) cases. These baseline cases were tested by comparing predictions with both experimental data and empirical correlations. Then, these models were used in order to determine the effect of high FST (>5% turbulence intensity) on heat transfer and skin friction and compared with experimental data. Predictions for heat transfer and skin friction coefficient for all the turbulence intensities tested by all the models agreed well (within 1–8%) with experimental data. However, all these models predicted poorly the dissipation of turbulent kinetic energy (TKE) in the free stream and TKE profiles. Physical reasoning as to why the aforementioned models differ in their predictions and the probable cause of poor prediction of free-stream TKE and TKE profiles are given.

Measurements in a Transitional Boundary Layer With Görtler Vortices

1996 ◽  
Author(s):  
Ralph J. Volino ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Streamwise Velocity ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Görtler Vortices ◽  
Concave Wall ◽  
The Mean ◽  
Gortler Vortices

The laminar-turbulent transition process has been documented in a concave-wall boundary layer subject to low (0.6%) free-stream turbulence intensity. Transition began at a Reynolds number, Rex (based on distance from the leading edge of the test wall), of 3.5×105 and was completed by 4.7×105. The transition was strongly influenced by the presence of stationary, streamwise, Görtler vortices. Transition under similar conditions has been documented in previous studies, but because concave-wall transition tends to be rapid, measurements within the transition zone were sparse. In this study, emphasis is on measurements within the zone of intermittent flow. Twenty-five profiles of mean streamwise velocity, fluctuating streamwise velocity, and intermittency have been acquired at five values of Rex, and five spanwise locations relative to a Görtler vortex. The mean velocity profiles acquired near the vortex downwash sites exhibit inflection points and local minima. These minima, located in the outer part of the boundary layer, provide evidence of a “tilting” of the vortices in the spanwise direction. Profiles of fluctuating velocity and intermittency exhibit peaks near the locations of the minima in the mean velocity profiles. These peaks indicate that turbulence is generated in regions of high shear, which are relatively far from the wall. The transition mechanism in this flow is different from that on flat walls, where turbulence is produced in the near-wall region. The peak intermittency values in the profiles increase with Rex, but do not follow the “universal” distribution observed in most flat-wall, transitional boundary layers. The results have applications whenever strong concave curvature may result in the formation of Görtler vortices in otherwise 2-D flows. Because these cases were run with a low value of free-stream turbulence intensity, the flow is not a replication of a gas turbine flow. However, the results do provide a base case for further work on transition on the pressure side of gas turbine airfoils, where concave curvature effects are combined with the effects of high free-stream turbulence and strong streamwise pressure gradients, for they show the effects of embedded streamwise vorticity in a flow that is free of high-turbulence effects.

Importance of Boundary Layer Transition in a High-Pressure Turbine Cascade Using LES

2018 ◽  
Author(s):  
Luis M. Seguí ◽  
L. Y. M. Gicquel ◽  
F. Duchaine ◽  
J. de Laborderie
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Free Stream ◽  
Industrial Process ◽  
Great Difficulty ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Layer Flow

In the context of smooth surfaces where no industrial process modifies the flow and where no roughness affects the boundary layer flow, there are configurations today where the correct heat flux prediction is still unattained for certain operating points. This is the case of the LS89 configuration that has shown to be of great difficulty to accurately simulate the thermal fields for high Reynolds number flows even when performing wall-resolved Large Eddy Simulations (LES). The physics of the studied operating point (MUR235) are especially complex due to the interaction of a transitioning boundary layer, shock waves and free-stream turbulence injected at the inlet. In this paper, free-stream turbulent specifications are seen to be important towards the capture of the heat transfer profile on most regions of the blade. The boundary layer is found to be transitional when either artificially raising the level of turbulence at the inlet or by using a highly refined mesh that induces the generation of turbulent spots that increase the heat transfer. The important refinement done improves the heat flux predictions to the point it is approaching the experimental data.

Numerical Investigation of Three-Dimensional Separation in an Axial Flow Compressor: The Influence of Free-Stream Turbulence Intensity and Endwall Boundary Layer State

2016 ◽  
Author(s):  
Ashley D. Scillitoe ◽  
Paul G. Tucker ◽  
Paolo Adami
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Boundary Layer Transition ◽  
Surface Boundary ◽  
Suction Surface ◽  
Corner Separation ◽  
Free Stream Turbulence

Regions of three-dimensional separations are an inherent flow feature of the suction surface - endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor’s efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources. Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data is in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall. Increasing the free-stream turbulence intensity (FST) changes the suction surface boundary layer transition mode from separation induced to bypass. However, it doesn’t significantly alter the transition location and therefore the corner separation size. Additionally, the FST doesn’t noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST. The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear.

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