Effect of a Short Roughness Strip on the Near Wall Reynolds Stress Anisotropy Tensor in a Turbulent Boundary Layer

2007 ◽  
Vol 34 (3) ◽  
pp. 258-266
Author(s):  
M. O. Oyewola
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Reynolds Stress ◽  
Stress Anisotropy ◽  
Anisotropy Tensor ◽  
Roughness Strip ◽  
Near Wall

An experimental investigation of a three-dimensional turbulent boundary layer in an ‘S’-shaped duct

1999 ◽  
Vol 393 ◽  
pp. 175-213 ◽  
Author(s):  
J. M. BRUNS ◽  
H. H. FERNHOLZ ◽  
P. A. MONKEWITZ
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Reynolds Stress ◽  
Test Section ◽  
Three Dimensional ◽  
Hot Wire ◽  
Freestream Velocity ◽  
Wire Probe ◽  
The Mean ◽  
Near Wall

This paper describes the evolution of an incompressible turbulent boundary layer on the flat wall of an ‘S’-shaped wind tunnel test section under the influence of changing streamwise and spanwise pressure gradients. The unit Reynolds number based on the mean velocity at the entrance of the test section was fixed to 106 m−1, resulting in Reynolds numbers Reδ2, based on the streamwise momentum thickness and the local freestream velocity, between 3.9 and 11 × 103. The particular feature of the experiment is the succession of two opposite changes of core flow direction which causes a sign change of the spanwise pressure gradient accompanied by a reversal of the spanwise velocity component near the wall, i.e. by the formation of so-called cross-over velocity profiles. The aim of the study is to provide new insight into the development of the mean and fluctuating flow field in three-dimensional pressure-driven boundary layers, in particular of the turbulence structure of the near-wall and the cross-over region.Mean velocities, Reynolds stresses and all triple correlations were measured with a newly developed miniature triple-hot-wire probe and a near-wall hot-wire probe which could be rotated and traversed through the test plate. Skin friction measurements were mostly performed with a wall hot-wire probe. The data from single normal wires extend over wall distances of y+ [gsim ] 3 (in wall units), while the triple-wire probe covers the range y+ [gsim ] 30. The data show the behaviour of the mean flow angle near the wall to vary all the way to the wall. Then, to interpret the response of the turbulence to the pressure field, the relevant terms in the Reynolds stress transport equations are evaluated. Finally, an attempt is made to assess the departure of the Reynolds stress profiles from local equilibrium near the wall.

scholarly journals Reynolds averaged turbulence modelling using deep neural networks with embedded invariance

2016 ◽  
Vol 807 ◽  
pp. 155-166 ◽  
Author(s):  
Julia Ling ◽  
Andrew Kurzawski ◽  
Jeremy Templeton
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Reynolds Stress ◽  
Network Architecture ◽  
Eddy Viscosity ◽  
Deep Neural Networks ◽  
Test Cases ◽  
Neural Network Architecture ◽  
Stress Anisotropy ◽  
Anisotropy Tensor

There exists significant demand for improved Reynolds-averaged Navier–Stokes (RANS) turbulence models that are informed by and can represent a richer set of turbulence physics. This paper presents a method of using deep neural networks to learn a model for the Reynolds stress anisotropy tensor from high-fidelity simulation data. A novel neural network architecture is proposed which uses a multiplicative layer with an invariant tensor basis to embed Galilean invariance into the predicted anisotropy tensor. It is demonstrated that this neural network architecture provides improved prediction accuracy compared with a generic neural network architecture that does not embed this invariance property. The Reynolds stress anisotropy predictions of this invariant neural network are propagated through to the velocity field for two test cases. For both test cases, significant improvement versus baseline RANS linear eddy viscosity and nonlinear eddy viscosity models is demonstrated.

scholarly journals Influence of Surface Anisotropy on Turbulent Flow Over Irregular Roughness

2019 ◽  
Vol 104 (2-3) ◽  
pp. 331-354 ◽  
Author(s):  
Angela Busse ◽  
Thomas O. Jelly
Keyword(s):  
Reynolds Stress ◽  
Surface Generation ◽  
Anisotropy Ratio ◽  
Surface Anisotropy ◽  
Outer Flow ◽  
Correlation Lengths ◽  
Stress Anisotropy ◽  
Dispersive Stress ◽  
The Mean ◽  
Near Wall

AbstractThe influence of surface anisotropy upon the near-wall region of a rough-wall turbulent channel flow is investigated using direct numerical simulation (DNS). A set of nine irregular rough surfaces with fixed mean peak-to-valley height, near-Gaussian height distributions and specified streamwise and spanwise correlation lengths were synthesised using a surface generation algorithm. By defining the surface anisotropy ratio (SAR) as the ratio of the streamwise and spanwise correlation lengths of the surface, we demonstrate that surfaces with a strong spanwise anisotropy (SAR < 1) can induce an over 200% increase in the roughness function ΔU+, compared to their streamwise anisotropic (SAR > 1) equivalent. Furthermore, we find that the relationship between the roughness function ΔU+ and the SAR parameter approximately follows an exponentially decaying function. The statistical response of the near-wall flow is studied using a “double-averaging” methodology in order to distinguish form-induced “dispersive” stresses from their turbulent counterparts. Outer-layer similarity is recovered for the mean velocity defect profile as well as the Reynolds stresses. The dispersive stresses all attain their maxima within the roughness canopy. Only the streamwise dispersive stress reaches levels that are comparable to the equivalent Reynolds stress, with surfaces of high SAR attaining the highest levels of streamwise dispersive stress. The Reynolds stress anisotropy also shows distinct differences between cases with strong streamwise anisotropy that stay close to an axisymmetric, rod-like state for all wall-normal locations, compared to cases with spanwise anisotropy where an axisymmetric, disk-like state of the Reynolds stress anisotropy tensor is observed around the roughness mean plane. Overall, the results from this study underline that the drag penalty incurred by a rough surface is strongly influenced by the surface topography and highlight its impact upon the mean momentum deficit in the outer flow as well as the Reynolds and dispersive stresses within the roughness layer.

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.

New perspectives on the impulsive roughness-perturbation of a turbulent boundary layer

2011 ◽  
Vol 677 ◽  
pp. 179-203 ◽  
Author(s):  
I. JACOBI ◽  
B. J. McKEON
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Spectral Energy ◽  
Internal Layers ◽  
Hot Wire ◽  
Mean Velocity ◽  
Composite Maps ◽  
Downstream Flow ◽  
Near Wall

The zero-pressure-gradient turbulent boundary layer over a flat plate was perturbed by a short strip of two-dimensional roughness elements, and the downstream response of the flow field was interrogated by hot-wire anemometry and particle image velocimetry. Two internal layers, marking the two transitions between rough and smooth boundary conditions, are shown to represent the edges of a ‘stress bore’ in the flow field. New scalings, based on the mean velocity gradient and the third moment of the streamwise fluctuating velocity component, are used to identify this ‘stress bore’ as the region of influence of the roughness impulse. Spectral composite maps reveal the redistribution of spectral energy by the impulsive perturbation – in particular, the region of the near-wall peak was reached by use of a single hot wire in order to identify the significant changes to the near-wall cycle. In addition, analysis of the distribution of vortex cores shows a distinct structural change in the flow associated with the perturbation. A short spatially impulsive patch of roughness is shown to provide a vehicle for modifying a large portion of the downstream flow field in a controlled and persistent way.

Effect of suction on the near‐wall anisotropy of a turbulent boundary layer

1994 ◽  
Vol 6 (1) ◽  
pp. 430-432 ◽  
Author(s):  
R. A. Antonia ◽  
P. R. Spalart ◽  
P. Mariani
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Near Wall
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