scholarly journals Numerical Study of the Influence of the Inlet Turbulence Length Scale on the Turbulent Boundary Layer

2021 ◽  
Vol 11 (11) ◽  
pp. 5177
Author(s):  
Young-Tae Lee ◽  
Lokesh Kalyan Gutti ◽  
Hee-Chang Lim
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Numerical Study ◽  
Flow Simulation ◽  
Temporal Correlation ◽  
Spanwise Direction ◽  
Length Scale ◽  
Inlet Section ◽  
Length Scales ◽  
Turbulent Characteristics

In the past half century, large eddy simulations (LESs) have played an important role in turbulent flow simulation and improving the performance of computing technology. To generate a fully developed turbulent boundary layer in the channel domain using LES, suitable inflow conditions along with turbulent characteristics are required. This study aimed to clarify the effect of the integral length scale on the generation of turbulent boundary layers. To accomplish this, an artificially created boundary layer was imposed on the inlet section, which gradually evolved into a fully developed turbulent boundary layer flow inside the numerical domain. In this study, the synthetic inflow method, which is a commonly employed technique, was used by imposing the spatial and temporal correlation between two different points on the inlet section. In addition, we conducted parametric length scale studies on the inlet section and compared our results with existing data. The results showed that the larger length scales in the spanwise direction were not only effective in achieving the target shape of a fully developed turbulent boundary layer, but also developed it faster than the smaller length scales.

A Numerical Study of Turbulent Boundary Layer Flow Over a Flat Surface With a Single Dimple

2000 ◽  
Author(s):  
Mark E. Kithcart ◽  
David E. Klett
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Flat Surface ◽  
Numerical Study ◽  
Heat Transfer Augmentation ◽  
Study Results ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Abstract Turbulent boundary layer flow over a flat surface with a single dimple has been investigated numerically using the FLUENT CFD software package, and compared to an experiment by Ezerskii and Shekhov [1989], which studied the same configuration. The impetus for this work developed as a result of previous studies. Kithcart and Klett [1996], and Afanas’yev and Chudnovskiy [1992], showed that dimpled surfaces enhance heat transfer comparably to surfaces with protrusion roughness elements, but with a much lower drag penalty. However, the actual physical mechanisms involved in this phenomena were only partially known prior this study. Results obtained numerically are in good agreement with the experiment, most notably the confirmation of the existence of a region of enhanced heat transfer created by interaction of the flow with the dimple. In particular, the simulation indicates that heat transfer augmentation is a consequence of the development of a stagnation flow region within the dimple geometry, and the existence of coherent vortical structures which create a periodic flow-field within and immediately downstream of the dimple. This periodicity appears to govern the magnitude of the heat transfer augmentation.

A Parametric Numerical Study of the Effects of Freestream Turbulence Intensity and Length Scale on Anti-Vortex Film Cooling Design at High Blowing Ratio

2013 ◽  
Author(s):  
Timothy W. Repko ◽  
Andrew C. Nix ◽  
James D. Heidmann
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Numerical Study ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Length Scales ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Design

An advanced, high-effectiveness film-cooling design, the anti-vortex hole (AVH) has been investigated by several research groups and shown to mitigate or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low freestream turbulence levels. [1, 2] The effects of increased turbulence on the AVH geometry were previously investigated and presented by researchers at West Virginia University (WVU), in collaboration with NASA, in a preliminary CFD study [3] on the film effectiveness and net heat flux reduction (NHFR) at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. The current paper presents the results of an extended numerical parametric study, which attempts to separate the effects of turbulence intensity and length-scale on film cooling effectiveness of the AVH. In the extended study, higher freestream turbulence intensity and larger scale cases were investigated with turbulence intensities of 5, 10 and 20% and length scales based on cooling hole diameter of Λx/dm = 1, 3 and 6. Increasing turbulence intensity was shown to increase the centerline, span-averaged and area-averaged adiabatic film cooling effectiveness. Larger turbulent length scales were shown to have little to no effect on the centerline, span-averaged and area-averaged adiabatic film-cooling effectiveness at lower turbulence levels, but slightly increased effect at the highest turbulence levels investigated.

scholarly journals Spatial–spectral characteristics of momentum transport in a turbulent boundary layer

2017 ◽  
Vol 836 ◽  
pp. 599-634 ◽  
Author(s):  
D. Fiscaletti ◽  
R. de Kat ◽  
B. Ganapathisubramani
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Spatial Organization ◽  
Spectral Characteristics ◽  
Momentum Transport ◽  
Spectral Content ◽  
Length Scales ◽  
Wall Distance ◽  
Wave Velocities ◽  
Local Average

Spectral content and spatial organization of momentum transport events are investigated in a turbulent boundary layer at the Reynolds number $(Re_{\unicode[STIX]{x1D70F}})=2700$, with time-resolved planar particle image velocimetry. The spectral content of the Reynolds-shear-stress fluctuations reveals that the largest range of time and length scales can be observed in proximity to the wall, while this range becomes progressively more narrow when the wall distance increases. Farther from the wall, longer time and larger length scales exhibit an increasing spectral content. Wave velocities of transport events are estimated from wavenumber–frequency power spectra at different wall-normal locations. Wave velocities associated with ejection events (Q2) are lower than the local average streamwise velocity, while sweep events (Q4) are characterized by wave velocities larger than the local average velocity. These velocity deficits are almost insensitive to the wall distance, which is also confirmed from time tracking the intense transport events. The vertical advection velocities of the intense ejection and sweep events are on average a small fraction of the friction velocity $U_{\unicode[STIX]{x1D70F}}$, different from previous observations in a channel flow. In the range of wall-normal locations $60<y^{+}<600$, sweeps are considerably larger than ejections, which could be because the ejections are preferentially located in between the legs of hairpin packets. Finally, it is observed that negative quadrant events of the same type tend to appear in groups over a large spatial streamwise extent.

Numerical Study of Dual-Plume Interference in a Turbulent Boundary Layer

2017 ◽  
Vol 164 (3) ◽  
pp. 419-447 ◽  
Author(s):  
Shahin N. Oskouie ◽  
Bing-Chen Wang ◽  
Eugene Yee
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Numerical Study
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