Heat Transfer Mechanism and Associated Turbulence Structure in the Near-Wall Region of a Turbulent Boundary Layer

1985 ◽  
pp. 223-234 ◽  
Author(s):  
Yoichiro Iritani ◽  
Nobuhide Kasagi ◽  
Masaru Hirata
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Transfer Mechanism ◽  
Wall Region ◽  
Turbulence Structure ◽  
Heat Transfer Mechanism ◽  
Near Wall

Numerical Investigation of the Compressible Flat-Plate Turbulent Boundary Layer with Extended GAO-YONG Turbulence Model

2013 ◽  
Vol 444-445 ◽  
pp. 416-422
Author(s):  
Yang Yang Tang ◽  
Zhi Qiang Li ◽  
Yong Wang ◽  
Ya Chao Di ◽  
Huan Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Empirical Coefficients ◽  
Near Wall

The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.

Direct numerical simulation of turbulent flow and heat transfer in a spatially developing turbulent boundary layer laden with particles

2018 ◽  
Vol 845 ◽  
pp. 417-461 ◽  
Author(s):  
Dong Li ◽  
Kun Luo ◽  
Jianren Fan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flow ◽  
Solid Particles ◽  
Heated Wall ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Particle Laden Flows ◽  
Near Wall

Direct numerical simulations of particle-laden flows in a spatially developing turbulent thermal boundary layer over an isothermally heated wall have been performed with realistic fully developed turbulent inflow boundary conditions. To the authors’ best knowledge, this is the first time the effects of inertial solid particles on turbulent flow and heat transfer in a flat-plate turbulent boundary layer have been investigated, using a two-way coupled Eulerian–Lagrangian method. Results indicate that the presence of particles increases the mean streamwise velocity and temperature gradients of the fluid in the near-wall region. As a result, the skin-friction drag and heat transfer are significantly enhanced in the particle-laden flows with respect to the single-phase flow. The near-wall sweep and ejection motions are suppressed by the particles and hence the Reynolds shear stress and wall-normal turbulent heat flux are attenuated, which leads to reductions in the production of the turbulent kinetic energy and temperature fluctuations. In addition, the coherence and spacing of the near-wall velocity and temperature streaky structures are distinctly increased, while the turbulent vortical structures appear to be disorganized under the effect of the particles. Moreover, the intensity of the streamwise vortices decreases monotonically with increasing particle inertia.

scholarly journals Active control of multiscale features in wall-bounded turbulence

2019 ◽  
Vol 36 (1) ◽  
pp. 12-21 ◽  
Author(s):  
Xiaotong Cui ◽  
Nan Jiang ◽  
Xiaobo Zheng ◽  
Zhanqi Tang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Streamwise Velocity ◽  
Discrete Wavelet ◽  
Wall Region ◽  
Mean Velocity ◽  
Pzt Actuator ◽  
The Impact ◽  
Near Wall

Abstract This study experimentally investigates the impact of a single piezoelectric (PZT) actuator on a turbulent boundary layer from a statistical viewpoint. The working conditions of the actuator include a range of frequencies and amplitudes. The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer. The mean velocity profiles and other basic parameters are reported. Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region. The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy. The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales. Moreover, under the impact of the PZT actuator, the symmetry of vibration scales’ velocity signals is promoted and the structural composition appears in an orderly manner. Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency. Based on the flatness factor, the bursting process is also detected. The vibrations reduce the relative intensities of the burst events, indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

Development of the turbulent near wake of a tapered thick flat plate

1988 ◽  
Vol 189 ◽  
pp. 135-163 ◽  
Author(s):  
A. Haji-Haidari ◽  
C. R. Smith
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Wall Region ◽  
Turbulence Structure ◽  
Near Wake ◽  
Growth Region ◽  
Trailing Edge ◽  
Centreline Velocity ◽  
Hot Film

The velocity field and turbulence structure in the near wake of a thick flat plate with a tapered trailing-edge geometry are examined using both hydrogen-bubble flow visualization and hot-film anemometry measurements. Tests were conducted for Re1 = 8.5 × 105 in the region 0 < x+ < 6400 behind the trailing edge. The probe and visualization results indicate a similarity between both (i) velocity and turbulence structure variations wih x+ in the near wake, and (ii) the corresponding changes in similar flow characteristics with y+ within a turbulent boundary layer. In particular, visualization data in the vicinity of the wake centreline reveal the existence of strong streamwise flow structures in the region close (x+ < 270) to the trailing edge. The streamwise orientation of the observed structures diminishes as x+ increases. From hot-film measurements, two separate regions along the wake centreline can be distinguished: (i) a linear growth region which extends over 0 < x+ < 100, wherein the centreline velocity varies linearly with x+; and (ii) a logarithmic growth region for x+ > 270, wherein the centreline velocity varies as log x+. The similarity in behaviour between these regions and the comparable wall region of a turbulent boundary layer suggests the existence of a common functionality. This similarity is demonstrated by a simple linear relationship of the form y+ = Kx+, which is shown to approximately collapse the velocity behaviour both across a turbulent boundary layer and along the wake centreline to a unified set of empirical relationships.

Experimental observation of hairpin auto-generation events in a turbulent boundary layer

2016 ◽  
Vol 795 ◽  
pp. 611-633 ◽  
Author(s):  
Y. Jodai ◽  
G. E. Elsinga
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Transition Process ◽  
Wall Region ◽  
Generation Model ◽  
Streamwise Vortices ◽  
Hairpin Vortices ◽  
Time Resolved ◽  
Near Wall

Time-resolved tomographic particle image velocimetry experiments show that new hairpin vortices are generated within a fully developed and unperturbed turbulent boundary layer. The measurements are taken at a Reynolds number based on the momentum thickness of 2038, and cover the near-wall region below $y^{+}=140$, where $y^{+}$ is the wall-normal distance in wall units. Instantaneous visualizations of the flow reveal near-wall low-speed streaks with associated quasi-streamwise vortices, retrograde inverted arch vortices, hairpin vortices and hairpin packets. The hairpin heads are observed as close to the wall as $y^{+}=30$. Examples of hairpin packet evolution reveal the development of new hairpin vortices, which are created upstream and close to the wall in a manner consistent with the auto-generation model (Zhou et al., J. Fluid Mech., vol. 387, 1999, pp. 353–396). The development of the new hairpin appears to be initiated by an approaching sweep event, which perturbs the shear layer associated with the initial packet. The shear layer rolls up, thereby forming the new hairpin head. The head subsequently connects to existing streamwise vortices and develops into a hairpin. The time scale associated with the hairpin auto-generation is 20–30 wall units of time. This demonstrates that hairpins can be created over short distances within a developed turbulent boundary layer, implying that they are not simply remnants of the laminar-to-turbulent transition process far upstream.

Modeling Interfacial Interactions and Turbulence in the Near-Wall Region of a Vertical Bubbly Boundary Layer

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Jamel Chahed ◽  
Lucien Masbernat
Keyword(s):  
Boundary Layer ◽  
Void Fraction ◽  
Fluid Model ◽  
Second Order ◽  
Turbulence Closure ◽  
Wall Region ◽  
Turbulence Structure ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Near Wall

Abstract A two-fluid model with second-order turbulence closure is used for the simulation of a turbulent bubbly boundary layer. The turbulence model is based on the decomposition of the Reynolds stress tensor in the liquid phase into two parts: a turbulent part and a pseudo-turbulent part. The reduction in second-order turbulence closure in the near-wall region is interpreted according to a modified wall logarithmic law. Numerical simulations of bubbly boundary layer developing on a vertical flat plate were performed in order to analyze the bubbles effect on the liquid turbulence structure and to evaluate the respective roles of turbulence and of interfacial forces in the near-wall distribution of the void fraction. The two-fluid model with the second-order turbulence closure succeeds in reproducing the diminution of the turbulent intensity observed in the near-wall region of bubbly boundary layer and the increase in turbulence outside the boundary layer. The analysis of the interfacial force in the near-wall zone has led to the development of relatively simple formulation of the lift-wall force in the logarithmic zone that depends on dimensionless distances to the wall. After appropriate adjustment, this formulation makes it possible to reproduce the shape of the near-wall void fraction peaking observed in bubbly boundary layer experiments.

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