Effects of high free-stream turbulence on a separated flow field over a two-dimensional hill

2012 ◽  
Author(s):  
T. Houra ◽  
K. Takano ◽  
M. Tagawa ◽  
Yasutaka Nagano
Keyword(s):  
Flow Field ◽  
Free Stream ◽  
Separated Flow ◽  
Two Dimensional ◽  
Free Stream Turbulence

Boundary layer development after a separated region

1998 ◽  
Vol 374 ◽  
pp. 91-116 ◽  
Author(s):  
IAN P. CASTRO ◽  
ELEANORA EPIK
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulence Models ◽  
Separated Flow ◽  
Leading Edge ◽  
Turbulence Structure ◽  
Outer Flow ◽  
Free Stream Turbulence ◽  
Layer Region

Measurements obtained in boundary layers developing downstream of the highly turbulent, separated flow generated at the leading edge of a blunt flat plate are presented. Two cases are considered: first, when there is only very low (wind tunnel) turbulence present in the free-stream flow and, second, when roughly isotropic, homogeneous turbulence is introduced. With conditions adjusted to ensure that the separated region was of the same length in both cases, the flow around reattachment was significantly different and subsequent differences in the development rate of the two boundary layers are identified. The paper complements, but is much more extensive than, the earlier presentation of some of the basic data (Castro & Epik 1996), confirming not only that the development process is very slow, but also that it is non-monotonic. Turbulence stress levels fall below those typical of zero-pressure-gradient boundary layers and, in many ways, the boundary layer has features similar to those found in standard boundary layers perturbed by free-stream turbulence. It is argued that, at least as far as the turbulence structure is concerned, the inner layer region develops no more quickly than does the outer flow and it is the latter which essentially determines the overall rate of development of the whole flow. Some numerical computations are used to assess the extent to which current turbulence models are adequate for such flows.

871 Effects of Free-Stream Turbulence on Heat Transfer over a Two-Dimensional Hill

2011 ◽  
Vol 2011.60 (0) ◽  
pp. _871-1_-_871-2_
Author(s):  
Kohei TAKANO ◽  
Tomoya HOURA ◽  
Masato TAGAWA ◽  
Yasutaka NAGANO
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Two Dimensional ◽  
Free Stream Turbulence

The Effect of Free-Stream Turbulence on Heat Transfer From a Rectangular Prism

1984 ◽  
Vol 106 (2) ◽  
pp. 268-275 ◽  
Author(s):  
D. C. McCormick ◽  
F. L. Test ◽  
R. C. Lessmann
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Transfer Rate ◽  
Free Stream ◽  
Two Dimensional ◽  
Free Stream Turbulence ◽  
Favorable Pressure Gradient ◽  
Temperature Heat ◽  
Predicted Values ◽  
Rectangular Body

This paper discussses the effect of free-stream turbulence on the constant temperature heat transfer rate from the surface of a two-dimensional rectangular body that is subject to a strongly favorable pressure gradient. Free-stream turbulence levels of 2 to 5 percent enhanced the heat transfer by 48 to 55 percent over predicted laminar values. Free-stream turbulence levels of 10 to 35 percent produced heat transfer results that behaved in some aspects as turbulent predictions, although considerably enhanced in magnitude over the predicted values.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jan Michálek ◽  
Michelangelo Monaldi ◽  
Tony Arts
Keyword(s):  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Flow Transition ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Very High

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a five-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

The Influence of Free Stream Turbulence on the Local Heat Transfer From Cylinders

1960 ◽  
Vol 82 (2) ◽  
pp. 101-107 ◽  
Author(s):  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Intensity ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients

Local heat-transfer coefficients and recovery factors are presented for three different cylinders in a two-dimensional subsonic air flow, with emphasis on the effect of screen-produced turbulence on these quantities. The increase in turbulent intensity so realized produced larger local heat-transfer coefficients, in a way dependent upon the location on the cylinders, through a direct increase in the heat transfer to the laminar boundary layer, through an earlier transition to turbulence, or through an alteration in the character of the separated flow. Alternatively, recovery factors were affected less, being invariant with respect to the turbulent intensity for attached boundary layer flow, but demonstrating large changes in those separated flow regions for which increased free stream turbulence produced substantial changes in the nature of the separated flow.

Evaluation of Turbulent Spot Production Rate in Boundary Layers Under Variable Pressure Gradients for Gas Turbine Applications

2019 ◽  
Author(s):  
M. Dellacasagrande ◽  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino
Keyword(s):  
Reynolds Number ◽  
Production Rate ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Free Stream Turbulence ◽  
Flow Parameters ◽  
Transition Length

Abstract The paper presents an experimental data base on transitional boundary layers developing on a flat plate installed within a variable area opening endwall channel. Measurements have been carried out by means of time-resolved PIV. The overall test matrix spans 3 Reynolds numbers, 4 free-stream turbulence intensity levels and 4 different flow adverse pressure gradients. For each condition, 16000 instantaneous flow fields have been acquired in order to obtain high statistical accuracy. The flow parameters have been varied in order to provide a gradual shift of the mode of transition from a bypass process occurring with mild adverse pressure gradients at high free-stream turbulence, to separated flow transition, occurring with low Reynolds number, low free-stream turbulence intensity and elevated adverse pressure gradient. In order to quantify the influence of the flow parameter variation on the boundary layer transition process, the transition onset and end positions, and the turbulent spot production rate have been evaluated with a wavelet based intermittency detection technique. This post-processing technique is in fact able to identify the vortical structures developing within the boundary layer, the intermittency function is then automatically evaluated for each tested condition counting the number of such structures and defining the cumulative probability function. The by-pass transition mode has the longest transition length that decreases with increasing the Reynolds number. The transition length of the separated flow case is smaller than the by-pass one, and the variation of the flow parameters has a similar impact. Similarly, the dimensionless turbulent spot production rate reduces when the Reynolds number is increasing. The variation of the inlet turbulence intensity has a small influence on this parameter except for the condition at the highest turbulence intensity, that always shows the lowest turbulent spot production rate because a by-pass type transition occurs. This large amount of data has been used to develop new correlations used to predict the spot production rate and the transition length in attached and separated flows.

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