scholarly journals An Experimental Study of Turbulent Boundary Layers Subjected to High Free-Stream Turbulence Effects

2005 ◽  
Author(s):  
Edgar Orsi ◽  
Roger L. Simpson
Keyword(s):  
Experimental Study ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulent Boundary Layers ◽  
Free Stream Turbulence ◽  
Turbulence Effects

scholarly journals Interactions of large-scale free-stream turbulence with turbulent boundary layers

2016 ◽  
Vol 802 ◽  
pp. 79-107 ◽  
Author(s):  
Eda Dogan ◽  
Ronald E. Hanson ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
Large Scale ◽  
Free Stream ◽  
Turbulent Boundary Layers ◽  
Scale Interactions ◽  
Free Stream Turbulence ◽  
Small Scales ◽  
Near Wall

The scale interactions occurring within a turbulent boundary layer are investigated in the presence of free-stream turbulence. The free-stream turbulence is generated by an active grid. The free stream is monitored by a single-component hot-wire probe, while a second probe is roved across the height of the boundary layer at the same streamwise location. Large-scale structures occurring in the free stream are shown to penetrate the boundary layer and increase the streamwise velocity fluctuations throughout. It is speculated that, depending on the extent of the penetration, i.e. based on the level of free-stream turbulence, the near-wall turbulence production peaks at different wall-normal locations than the expected location of $y^{+}\approx 15$ for a canonical turbulent boundary layer. It is shown that the large scales dominating the log region have a modulating effect on the small scales in the near-wall region; this effect becomes more significant with increasing turbulence in the free stream, i.e. similarly increasing $Re_{\unicode[STIX]{x1D706}_{0}}$. This modulating interaction and its Reynolds-number trend have similarities with canonical turbulent boundary layers at high Reynolds numbers where the interaction between the large scales and the envelope of the small scales exhibits a pure amplitude modulation (Hutchins & Marusic, Phil. Trans. R. Soc. Lond. A, vol. 365 (1852), 2007, pp. 647–664; Mathis et al., J. Fluid Mech., vol. 628, 2009, pp. 311–337). This similarity has encouraging implications towards generalising scale interactions in turbulent boundary layers.

366 Study on properties of turbulent boundary layers affected by large-scale free-stream turbulence

2011 ◽  
Vol 2011.60 (0) ◽  
pp. _366-1_-_366-2_
Author(s):  
Saori TSUKUDA ◽  
Hiroki SUZUKI ◽  
Kouji NAGATA ◽  
Tomoyuki KITAYAMA ◽  
Yasuhiko SAKAI ◽  
...  
Keyword(s):  
Boundary Layers ◽  
Large Scale ◽  
Free Stream ◽  
Turbulent Boundary Layers ◽  
Scale Free ◽  
Free Stream Turbulence

Heat Transfer In Turbulent Boundary Layers Subjected to Free-Stream Turbulence—Part II: Analysis and Correlation

2003 ◽  
Vol 125 (2) ◽  
pp. 242-251 ◽  
Author(s):  
Michael J. Barrett ◽  
D. Keith Hollingsworth
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulent Boundary Layers ◽  
Stanton Number ◽  
Length Scale ◽  
Free Stream Turbulence ◽  
New Correlation ◽  
Near Wall

A new heat transfer correlation for turbulent boundary layers subjected to free-stream turbulence was developed. The new correlation estimates dimensionless heat transfer coefficients without the use of conventional boundary-layer thickness measures and the associated Reynolds numbers. Using only free-stream parameters (mean velocity, turbulence intensity and length scale), the new correlation collected many authors’ elevated-turbulence, flat-plate Stanton number data to within ±11%. The level of scatter around the new correlation compared well to previous correlations that require additional flow information as input parameters. For a common subset of data, scatter using earlier correlation methods ranged from 5–10%; scatter around the new correlation varied from 6–9% over the same data subset. A length-scale dependence was identified in a Stanton number previously defined using a near-wall streamwise velocity fluctuation, St′. A new near-wall Stanton number was introduced; this parameter was regarded as a constant in a two-region boundary layer model on which the new correlation is based.

Spectral Measurements in Transitional Boundary Layers on a Concave Wall Under High and Low Free-Stream Turbulence Conditions

1997 ◽  
Vol 122 (3) ◽  
pp. 450-457 ◽  
Author(s):  
Ralph J. Volino ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Transfer Function ◽  
Boundary Layers ◽  
Free Stream ◽  
Low Frequency ◽  
Turbulent Boundary Layers ◽  
Spectral Measurements ◽  
Free Stream Turbulence ◽  
Concave Wall ◽  
Frequency Fluctuations

The relationship between free-stream turbulence and boundary layer behavior has been investigated using spectral measurements. The power spectral densities of turbulence quantities in transitional and fully turbulent boundary layers were computed and compared to the power spectra of the same quantities measured in the free stream. Comparisons were made using the “transfer function.” The transfer function is the ratio of two spectra at each frequency in the spectra. Comparisons were done in flows with low (0.6 percent) and high (8 percent) free-stream turbulence intensities. Evidence was gathered that suggests that relatively low-frequency, large-scale eddies in the free stream buffet the boundary layer, causing boundary layer unsteadiness at the same low frequencies. These fluctuations are present in both transitional and fully turbulent boundary layers. They are seen under both high and low free-stream turbulence conditions, although they are stronger in the high-turbulence case. Examination of the turbulent shear stress suggests that the low-frequency fluctuations enhance transport in the boundary layer but they are not so effective in promoting eddy transport as are turbulent eddies produced and residing within the boundary layer. In the fully-turbulent boundary layer, higher-frequency fluctuations are added to the low-frequency unsteadiness. These higher-frequency fluctuations, not seen in the transitional boundary layer, are associated with turbulence production in the boundary layer and appear not to be directly related to free-stream unsteadiness. [S0889-504X(00)00403-7]

Exponential Wake Structure of Heated Turbulent Boundary Layers at Elevated Levels of Free-Stream Turbulence

1987 ◽  
Vol 109 (2) ◽  
pp. 336-344
Author(s):  
P. Sepri
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Computer Code ◽  
Turbulent Boundary Layers ◽  
Wake Region ◽  
Predictive Tool ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Computational Capability

The wake region of a turbulent boundary layer is demonstrated to exhibit simple exponential behavior at elevated levels of free-stream turbulence. As a predictive tool, the computer code STANCOOL has been modified to include FST effects in heated turbulent boundary layers. Preliminary comparisons with experimental data indicate improvements in computational capability, although further development of the code is required. From these comparisons, three new results are offered: (1) At elevated levels of FST, several statistical profiles in the boundary layer wake region decay exponentially into the free stream; (2) v′T′ decays at half the rate of the mean velocity and temperature; (3) analytical expressions are provided for u′v′ and v′T′ in this case.

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