scholarly journals Direct numerical simulation of a wall jet: flow physics

2018 ◽  
Vol 852 ◽  
pp. 507-542 ◽  
Author(s):  
Iftekhar Z. Naqavi ◽  
James C. Tyacke ◽  
Paul G. Tucker
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Shear Stress ◽  
Direct Numerical Simulation ◽  
Outer Layer ◽  
Turbulent Diffusion ◽  
Reynolds Shear Stress ◽  
Wall Jet ◽  
Normal Stresses ◽  
Mean Flow

A direct numerical simulation (DNS) of a plane wall jet is performed at a Reynolds number of $Re_{j}=7500$. The streamwise length of the domain is long enough to achieve self-similarity for the mean flow and the Reynolds shear stress. This is the highest Reynolds number wall jet DNS for a large domain achieved to date. The high resolution simulation reveals the unsteady flow field in great detail and shows the transition process in the outer shear layer and inner boundary layer. Mean flow parameters of maximum velocity decay, wall shear stress, friction coefficient and jet spreading rate are consistent with several other studies reported in the literature. Mean flow, Reynolds normal and shear stress profiles are presented with various scalings, revealing the self-similar behaviour of the wall jet. The Reynolds normal stresses do not show complete similarity for the given Reynolds number and domain length. Previously published inner layer budgets based on LES are inaccurate and those that have been measured are only available in the outer layer. The current DNS provides fully balanced, explicitly calculated budgets for the turbulence kinetic energy, Reynolds normal stresses and Reynolds shear stress in both the inner and outer layers. The budgets are scaled with inner and outer variables. The inner-scaled budgets in the near wall region show great similarity with turbulent boundary layers. The only remarkable difference is for the turbulent diffusion in the wall-normal Reynolds stress and Reynolds shear stress budgets. The outer layer interacts with the inner layer through turbulent diffusion and the excess energy from the wall-normal direction is transferred to the spanwise direction.

scholarly journals Near-field flow structure of a confined wall jet on flat and concave rough walls

2008 ◽  
Vol 606 ◽  
pp. 27-49 ◽  
Author(s):  
I. ALBAYRAK ◽  
E. J. HOPFINGER ◽  
U. LEMMIN
Keyword(s):  
Shear Stress ◽  
Shear Layer ◽  
Outer Layer ◽  
Reynolds Shear Stress ◽  
Near Field ◽  
Wall Jet ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Free Jet ◽  
The Mean

Experimental results are presented of the mean flow and turbulence characteristics in the near field of a plane wall jet issuing from a nozzle onto flat and concave walls consisting of fixed sand beds. This is a flow configuration of interest for sediment erosion, also referred to as scouring. The measurements were made with an acoustic profiler that gives access to the three components of the instantaneous velocities. For the flat-wall flow, it is shown that the outer-layer spatial growth rate and the maxima of the Reynolds stresses approach the values accepted for the far field of a wall jet at a downstream distance x/b0 ≈ 8. These maxima are only about half the values of a plane free jet. This reduction in Reynolds stresses is also observed in the shear-layer region, x/b0 < 6, where the Reynolds shear stress is about half the value of a free shear layer. At distances x/b0 > 11, the maximum Reynolds shear stress approaches the value of a plane free jet. This change in Reynolds stresses is related to the mean vertical velocity that is negative for x/b0 < 8 and positive further downstream. The evolution of the inner region of the wall jet is found to be in good agreement with a previous model that explicitly includes the roughness length.On the concave wall, the mean flow and the Reynolds stresses are drastically changed by the adverse pressure gradient and especially by the development of Görtler vortices. On the downslope side of the scour hole, the flow is nearly separating with the wall shear stress tending to zero, whereas on the upslope side, the wall-friction coefficient is increased by a factor of about two by Görtler vortices. These vortices extend well into the outer layer and, just above the wall, cause a substantial increase in Reynolds shear stress.

Turbulent Vorticity Diffusion in the Stronger Wall Jet Managed by a Flat Plate Wing in the Outer Layer

2015 ◽  
Author(s):  
Takuma Katayama ◽  
Shinsuke Mochizuki
Keyword(s):  
Shear Stress ◽  
Flat Plate ◽  
Outer Layer ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Wall Jet ◽  
Mean Velocity ◽  
The Mean

The present experiment focuses on the vorticity diffusion in a stronger wall jet managed by a three-dimensional flat plate wing in the outer layer. Measurement of the fluctuating velocities and vorticity correlation has been carried out with 4-wire vorticity probe. The turbulent vorticity diffusion due to the large scale eddies in the outer layer is quantitatively examined by using the 4-wire vorticity probe. Quantitative relationship between vortex structure and Reynolds shear stress is revealed by means of directly measured experimental evidence which explains vorticity diffusion process and influence of the manipulating wing. It is expected that the three-dimensional outer layer manipulator contributes to keep convex profile of the mean velocity, namely, suppression of the turbulent diffusion and entrainment.

The log behaviour of the Reynolds shear stress in accelerating turbulent boundary layers

2015 ◽  
Vol 775 ◽  
pp. 189-200 ◽  
Author(s):  
Guillermo Araya ◽  
Luciano Castillo ◽  
Fazle Hussain
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Direct Numerical Simulation ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Numerical Data ◽  
Turbulent Boundary Layers ◽  
Small Power ◽  
Streamwise Distance

Direct numerical simulation of highly accelerated turbulent boundary layers (TBLs) reveals that the Reynolds shear stress,$\overline{u^{\prime }v^{\prime }}^{+}$, monotonically decreases downstream and exhibits a logarithmic behaviour (e.g. $-\overline{u^{\prime }v^{\prime }}^{+}=-(1/A_{uv})\ln y^{+}+B_{uv}$) in the mesolayer region (e.g. $50\leqslant y^{+}\leqslant 170$). The thickness of the log layer of$\overline{u^{\prime }v^{\prime }}^{+}$increases with the streamwise distance and with the pressure gradient strength, extending over a large portion of the TBL thickness (up to 55 %). Simulations reveal that$V^{+}\,\partial U^{+}/\partial y^{+}\sim 1/y^{+}\sim \partial \overline{u^{\prime }v^{\prime }}^{+}/\partial y^{+}$, resulting in a logarithmic$\overline{u^{\prime }v^{\prime }}^{+}$profile. Also,$V^{+}\sim -y^{+}$is no longer negligible as in zero-pressure-gradient (ZPG) flows. Other experimental/numerical data at similar favourable-pressure-gradient (FPG) strengths also show the presence of a log region in$\overline{u^{\prime }v^{\prime }}^{+}$. This log region in$\overline{u^{\prime }v^{\prime }}^{+}$is larger in sink flows than in other spatially developing FPG flows. The latter flows exhibit the presence of a small power-law region in$\overline{u^{\prime }v^{\prime }}^{+}$, which is non-existent in sink flows.

Flow Characteristics of Three-Dimensional Curved Wall Jets on a Cylinder

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Mirae Kim ◽  
Hyun Dong Kim ◽  
Eunseop Yeom ◽  
Kyung Chun Kim
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Cylinder Surface ◽  
Cylinder Wall ◽  
Wall Jet ◽  
Wall Jets

Three-dimensional (3D) curved wall jets are a significant topic in various applications related to local heat and mass transfer. This study investigates the effects of the impinging angle and Reynolds number with a fixed distance from the nozzle to the surface of a cylinder. The particle image velocimetry (PIV) method was used to measure the mean streamwise velocity profiles, which were normalized by the maximum velocity along the centerline of the impinging jet onto the cylinder. After the impingement of the circular jet, a 3D curved wall jet develops on the cylinder surface due to the Coanda effect. At a given Reynolds number, the initial momentum of the wall jet increases, and flow separation occurs further downstream than in normal impingement as the impinging angle increases. At a given impinging angle, flow separation is delayed with increasing Reynolds number. A self-preserving wall jet profile was not attained in the 3D curved wall jet. The turbulence intensity and the Reynolds shear stress were obtained to analyze the turbulence characteristics. The radial turbulence intensity showed similar tendencies to a two-dimensional (2D) curved wall jet, but the streamwise turbulence intensity was dissimilar. The Reynolds shear stress decreases downstream of the cylinder wall due to the decreased velocity and centrifugal force.

Direct numerical simulation of a supersonic turbulent boundary layer at Mach 2.5

2000 ◽  
Vol 414 ◽  
pp. 1-33 ◽  
Author(s):  
STEPHEN E. GUARINI ◽  
ROBERT D. MOSER ◽  
KARIM SHARIFF ◽  
ALAN WRAY
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Incompressible Flow ◽  
Reynolds Shear Stress ◽  
Turbulent Heat ◽  
Adiabatic Wall ◽  
Momentum Integral

A direct numerical simulation of a supersonic turbulent boundary layer has been performed. We take advantage of a technique developed by Spalart for incompressible flow. In this technique, it is assumed that the boundary layer grows so slowly in the streamwise direction that the turbulence can be treated as approximately homogeneous in this direction. The slow growth is accounted for by a coordinate transformation and a multiple-scale analysis. The result is a modified system of equations, in which the flow is homogeneous in both the streamwise and spanwise directions, and which represents the state of the boundary layer at a given streamwise location. The equations are solved using a mixed Fourier and B-spline Galerkin method.Results are presented for a case having an adiabatic wall, a Mach number of M = 2.5, and a Reynolds number, based on momentum integral thickness and wall viscosity, of Reθ′ = 849. The Reynolds number based on momentum integral thickness and free-stream viscosity is Reθ = 1577. The results indicate that the Van Driest transformed velocity satisfies the incompressible scalings and a small logarithmic region is obtained. Both turbulence intensities and the Reynolds shear stress compare well with the incompressible simulations of Spalart when scaled by mean density. Pressure fluctuations are higher than in incompressible flow. Morkovin's prediction that streamwise velocity and temperature fluctuations should be anti-correlated, which happens to be supported by compressible experiments, does not hold in the simulation. Instead, a relationship is found between the rates of turbulent heat and momentum transfer. The turbulent kinetic energy budget is computed and compared with the budgets from Spalart's incompressible simulations.

scholarly journals The Turbulent Flow over the BARC Rectangular Cylinder: A DNS Study

2021 ◽  
Author(s):  
Alessandro Chiarini ◽  
Maurizio Quadrio
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Finite Differences ◽  
Turbulence Models ◽  
Fine Tuning ◽  
Rectangular Cylinder ◽  
Budget Equation ◽  
Complete Set ◽  
First Time

AbstractA direct numerical simulation (DNS) of the incompressible flow around a rectangular cylinder with chord-to-thickness ratio 5:1 (also known as the BARC benchmark) is presented. The work replicates the first DNS of this kind recently presented by Cimarelli et al. (J Wind Eng Ind Aerodyn 174:39–495, 2018), and intends to contribute to a solid numerical benchmark, albeit at a relatively low value of the Reynolds number. The study differentiates from previous work by using an in-house finite-differences solver instead of the finite-volumes toolbox OpenFOAM, and by employing finer spatial discretization and longer temporal average. The main features of the flow are described, and quantitative differences with the existing results are highlighted. The complete set of terms appearing in the budget equation for the components of the Reynolds stress tensor is provided for the first time. The different regions of the flow where production, redistribution and dissipation of each component take place are identified, and the anisotropic and inhomogeneous nature of the flow is discussed. Such information is valuable for the verification and fine-tuning of turbulence models in this complex separating and reattaching flow.

scholarly journals Effects of Turbulent Reynolds Number on the Performance of Algebraic Flame Surface Density Models for Large Eddy Simulation in the Thin Reaction Zones Regime: A Direct Numerical Simulation Analysis

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Mohit Katragadda ◽  
Nilanjan Chakraborty ◽  
R. S. Cant
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Fractal Dimension ◽  
Direct Numerical Simulation ◽  
Surface Density ◽  
Flame Surface ◽  
Algebraic Models ◽  
Flame Surface Density ◽  
Turbulent Reynolds Number ◽  
Reaction Zones

A direct numerical simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different turbulent Reynolds numbers has been used to assess the performance of algebraic flame surface density (FSD) models based on a fractal representation of the flame wrinkling factor. The turbulent Reynolds number Rethas been varied by modifying the Karlovitz number Ka and the Damköhler number Da independently of each other in such a way that the flames remain within the thin reaction zones regime. It has been found that the turbulent Reynolds number and the Karlovitz number both have a significant influence on the fractal dimension, which is found to increase with increasing Retand Ka before reaching an asymptotic value for large values of Retand Ka. A parameterisation of the fractal dimension is presented in which the effects of the Reynolds and the Karlovitz numbers are explicitly taken into account. By contrast, the inner cut-off scale normalised by the Zel’dovich flame thicknessηi/δzdoes not exhibit any significant dependence on Retfor the cases considered here. The performance of several algebraic FSD models has been assessed based on various criteria. Most of the algebraic models show a deterioration in performance with increasing the LES filter width.

Effects of the Equivalence Ratio and Reynolds Number on Turbulence and Flame Front Interactions by Direct Numerical Simulation

2016 ◽  
Vol 30 (8) ◽  
pp. 6727-6737 ◽  
Author(s):  
Cong Xu ◽  
Zhihua Wang ◽  
Wubin Weng ◽  
Kaidi Wan ◽  
Ronald Whiddon ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Flame Front ◽  
Equivalence Ratio
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