Effects of small streamline curvature on turbulent duct flow

1979 ◽  
Vol 91 (4) ◽  
pp. 633-659 ◽  
Author(s):  
I. A. Hunt ◽  
P. N. Joubert
Keyword(s):  
Turbulence Intensity ◽  
Central Region ◽  
Flow Region ◽  
Energy Spectra ◽  
Turbulent Shear ◽  
Turbulence Energy ◽  
Wall Region ◽  
Mean Flow ◽  
Streamline Curvature ◽  
Central Flow

Mean velocity profiles, turbulence intensity distributions and streamwise energy spectra are presented for turbulent air flow in a smooth-walled, high aspect ratio rectangular duct with small streamwise curvature, and are compared with measurements taken in a similar straight duct.The results for the present curved flow are found to differ significantly from those for the more highly curved flows reported previously, and suggest the need to distinguish between ‘shear-dominated’ flows with small curvature and ‘inertia-dominated’ flows with high curvature. Velocity defect and angular-momentum defect hypotheses fail to correlate the central-region mean flow data, but the wall-region data are consistent with the conventional straight-wall similarity hypothesis. A secondary flow of Taylor–Goertler vortex pattern is found to occur in the central flow region.An examination of the flow equations yields a model for the mechanisms by which streamline curvature affects turbulent flow, in which a major effect is a direct change in the turbulent shear stress through a conservative reorientation of the turbulence intensity components. Data for the streamwise and transverse turbulence intensities show behaviour consistent with that expected from the equations, and the distribution of total turbulence energy in the central flow region is found to be nearly invariant with Reynolds number and wall curvature, in agreement with the model.Energy spectra for the streamwise component are examined in terms of a Townsend-type two-component turbulence model. They indicate that a universal, ‘active’ component exists in all flow regions, with an ‘inactive’ component which affects only the low wavenumber spectra intensities. This is taken to imply that the effects of streamline curvature are determined by the central-region flow structure alone.

scholarly journals Turbulence and Scale Measurements in a Square Channel with Transverse Square Ribs

1996 ◽  
Vol 2 (3) ◽  
pp. 209-218 ◽  
Author(s):  
Richard B. Rivir ◽  
Mingking K. Chyu ◽  
Paul K. Maciejewski
Keyword(s):  
Turbulence Intensity ◽  
Turbulent Shear ◽  
Mean Flow ◽  
Integral Scale ◽  
Square Channel ◽  
Turbulent Shear Layer ◽  
The Third ◽  
Mainstream Flow ◽  
The Mean ◽  
Flow Turbulence

Hot-wire measurements of the mean flow, turbulence characteristics, and integral scale in a square channel roughened with transverse ribs mounted on two opposing sidewalls are presented for three rib configurations: single rib, in-line multiple ribs, and staggered multiple ribs. Test conditions for multiple ribs use p/H = 10, H/D 0.17, andRe⁡D23,000. Measured results highlight the spatial distribution and evolution of turbulence intensity and integral scale from the flow entrance of the first period to the developed regime near the exit of the third period. The highly turbulent, shear layer initiated near the trailing upper-edge of a rib elevates the turbulence level in the mainstream of the channel. The magnitude of turbulence intensity in the channel core rises from 0.7% in the approaching flow to about 20–25% near the exit of the third period. The integral scale dominating the mainstream flow increases from approximately one-half the rib-height, 0.5H, in the approaching flow to 1.5-2.5H behind the first rib and further downstream.

Computational Fluid Dynamics Study of Separated Flow Over a Three-Dimensional Axisymmetric Hill

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Varun Chitta ◽  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Turbulent Shear ◽  
Turbulent Regime ◽  
Flow Transition ◽  
Mean Flow ◽  
Streamline Curvature

This paper investigates the ability of computational fluid dynamics (CFD) simulations to accurately predict the turbulent flow separating from a three-dimensional (3D) axisymmetric hill using a recently developed four-equation eddy-viscosity model (EVM). The four-equation model, denoted as k–kL–ω–v2, was developed to demonstrate physically accurate responses to flow transition, streamline curvature, and system rotation effects. The model was previously tested on several two-dimensional cases with results showing improvement in predictions when compared to other popularly available EVMs. In this paper, we present a more complex 3D application of the model. The test case is turbulent boundary layer flow with thickness δ over a hill of height 2δ mounted in an enclosed channel. The flow Reynolds number based on the hill height (ReH) is 1.3 × 105. For validation purposes, CFD simulation results obtained using the k–kL–ω–v2 model are compared with two other Reynolds-averaged Navier–Stokes (RANS) models (fully turbulent shear stress transport k–ω and transition-sensitive k–kL–ω) and with experimental data. Results obtained from the simulations in terms of mean flow statistics, pressure distribution, and turbulence characteristics are presented and discussed in detail. The results indicate that both the complex physics of flow transition and streamline curvature should be taken into account to significantly improve RANS-based CFD predictions for applications involving blunt or curved bodies in a low Re turbulent regime.

scholarly journals An Unsteady Velocity Formulation for the Edge of the Near-Wall Region

1996 ◽  
Author(s):  
Dennis E. Wilson ◽  
Anthony J. Hanford
Keyword(s):  
Experimental Data ◽  
Turbulence Intensity ◽  
Surface Flux ◽  
Energy Spectra ◽  
Wall Region ◽  
Incoming Flow ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Stagnation Region ◽  
Near Wall

A phenomenological model is presented that relates freestream turbulence to the augmentation of stagnation-point surface flux quantities. The model requires the turbulence intensity, the longitudinal scale of the turbulence, and the energy spectra as inputs for the unsteady velocity at the edge of the near-wall viscous region. The form of the edge velocity contains both pulsations of the incoming flow and oscillations of the streamline. Incompressible results using a single fluctuating component are presented within the stagnation region of a two-dimensional cylinder. The time-averaged Froessling number is determined from the computations. These predictions are compared to existing incompressible experimental data. Additionally, the variations in the surface flux quantities with the longitudinal scale of the incoming freestream turbulence, the Reynolds number, and the freestream turbulence intensity are considered.

scholarly journals Compressible turbulent channel flows: DNS results and modelling

1995 ◽  
Vol 305 ◽  
pp. 185-218 ◽  
Author(s):  
P. G. Huang ◽  
G. N. Coleman ◽  
P. Bradshaw
Keyword(s):  
Turbulent Flows ◽  
Pressure Fluctuations ◽  
Channel Flows ◽  
Compressible Turbulence ◽  
Turbulent Shear ◽  
Turbulence Energy ◽  
Mean Flow ◽  
Reynolds Analogy ◽  
The Mean ◽  
Compressibility Effects

The present paper addresses some topical issues in modelling compressible turbulent shear flows. The work is based on direct numerical simulation (DNS) of two supersonic fully developed channel flows between very cold isothermal walls. Detailed decomposition and analysis of terms appearing in the mean momentum and energy equations are presented. The simulation results are used to provide insights into differences between conventional Reynolds and Favre averaging of the mean-flow and turbulent quantities. Study of the turbulence energy budget for the two cases shows that compressibility effects due to turbulent density and pressure fluctuations are insignificant. In particular, the dilatational dissipation and the mean product of the pressure and dilatation fluctuations are very small, contrary to the results of simulations for sheared homogeneous compressible turbulence and to recent proposals for models for general compressible turbulent flows. This provides a possible explanation of why the Van Driest density-weighted transformation (which ignores any true turbulent compressibility effects) is so successful in correlating compressible boundary-layer data. Finally, it is found that the DNS data do not support the strong Reynolds analogy. A more general representation of the analogy is analysed and shown to match the DNS data very well.

An Unsteady Velocity Formulation for the Edge of the Near-Wall Region

1998 ◽  
Vol 120 (2) ◽  
pp. 351-361 ◽  
Author(s):  
D. E. Wilson ◽  
A. J. Hanford
Keyword(s):  
Turbulence Intensity ◽  
Free Stream ◽  
Surface Flux ◽  
Energy Spectra ◽  
Wall Region ◽  
Incoming Flow ◽  
Two Dimensional ◽  
Stagnation Region ◽  
Free Stream Turbulence ◽  
Near Wall

A phenomenological model is presented that relates free-stream turbulence to the augmentation of stagnation-point surface flux quantities. The model requires the turbulence intensity, the longitudinal scale of the turbulence, and the energy spectra as inputs for the unsteady velocity at the edge of the near-wall viscous region. The form of the edge velocity contains both pulsations of the incoming flow and oscillations of the streamline. Incompressible results using a single fluctuating component are presented within the stagnation region of a two-dimensional cylinder. The time-averaged Froessling number is determined from the computations. These predictions are compared to existing incompressible experimental data. Additionally, the variations in the surface flux quantities with the longitudinal scale of the incoming free-stream turbulence, the Reynolds number, and the free-stream turbulence intensity are considered.

Fully resolved measurements of turbulent boundary layer flows up to

2018 ◽  
Vol 851 ◽  
pp. 391-415 ◽  
Author(s):  
M. Samie ◽  
I. Marusic ◽  
N. Hutchins ◽  
M. K. Fu ◽  
Y. Fan ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Turbulent Boundary Layers ◽  
Energy Spectra ◽  
Wall Region ◽  
Velocity Measurements ◽  
Number Range ◽  
High Reynolds

Fully resolved measurements of turbulent boundary layers are reported for the Reynolds number range $Re_{\unicode[STIX]{x1D70F}}=6000{-}20\,000$. Despite several decades of research in wall-bounded turbulence there is still controversy over the behaviour of streamwise turbulence intensities near the wall, especially at high Reynolds numbers. Much of it stems from the uncertainty in measurement due to finite spatial resolution. Conventional hot-wire anemometry is limited for high Reynolds number measurements due to limited spatial resolution issues that cause attenuation in the streamwise turbulence intensity profile near the wall. To address this issue we use the nano-scale thermal anemometry probe (NSTAP), developed at Princeton University to conduct velocity measurements in the high Reynolds number boundary layer facility at the University of Melbourne. The NSTAP has a sensing length almost one order of magnitude smaller than conventional hot-wires. This enables us to acquire fully resolved velocity measurements of turbulent boundary layers up to $Re_{\unicode[STIX]{x1D70F}}=20\,000$. Results show that in the near-wall region, the viscous-scaled streamwise turbulence intensity grows with $Re_{\unicode[STIX]{x1D70F}}$ in the Reynolds number range of the experiments. A second outer peak in the streamwise turbulence intensity is also shown to emerge at the highest Reynolds numbers. Moreover, the energy spectra in the near-wall region show excellent inner scaling over the small to moderate wavelength range, followed by a large-scale influence that increases with Reynolds number. Outer scaling in the outer region is found to collapse the energy spectra over high wavelengths across various Reynolds numbers.

scholarly journals Laser-Doppler Velocimetry Measurements Inside a Backward Curved Centrifugal Fan

2001 ◽  
Vol 7 (3) ◽  
pp. 173-181
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen
Keyword(s):  
Flow Rate ◽  
Turbulence Intensity ◽  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Flow Region ◽  
Design Flow ◽  
Laser Doppler ◽  
Centrifugal Fan ◽  
Doppler Velocimetry ◽  
Flow Rates

Laser-Doppler velocimetry (LDV) measurements are presented of relative mean velocity and turbulence intensity components inside the impeller passage of a centrifugal fan with twelve backward curved blades at design, under-design, and over-design flow rates. Additional LDV measurements were also performed at the volute outlet to examine the uniformity of the outlet flow for the three selected flow rates. Complementary flow visualization results in the tongue region are further presented. It is found that the number of characteristic flow regions and the average turbulence level increase with decreasing air flow rate. For the case of under-design flow rate, there are a through-flow region on the suction side, a reverse flow region on the pressure side, and a shear layer region in between. The corresponding average turbulence intensity is as high as 9.1% of blade tip velocity.

The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 2—Fluctuation Quantities

1996 ◽  
Vol 118 (4) ◽  
pp. 728-736 ◽  
Author(s):  
S. P. Mislevy ◽  
T. Wang
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transition Region ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Shear ◽  
Wall Region ◽  
Pressure Gradients ◽  
Baseline Case ◽  
Near Wall

The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. Boundary layer measurements were conducted for two constant-K cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The fluctuation quantities, u′, ν′, t′, the Reynolds shear stress (uν), and the Reynolds heat fluxes (νt and ut) were measured. In general, u′/U∞, ν′/U∞, and νt have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K = 0). The development of ν′ for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall region of high-turbulent shear generated at Y+ = 7. At stations farther downstream, this near-wall shear reduced in magnitude, while a second region of high-turbulent shear developed at Y+ = 70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y+ = 70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t′ in the near-wall region (Y+ < 20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/nonturbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large non turbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent fluctuations such that the production of turbulent spots was obscured. The turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Prt, are also presented.

Characterization of Time-Averaged Turbulence Statistics for Shear Thinning Fluid in Horizontal Concentric Annulus Using RANS Based CFD Simulation

2016 ◽  
Author(s):  
Xiao Xiong ◽  
Mohammad Azizur Rahman ◽  
Yan Zhang
Keyword(s):  
Cfd Simulation ◽  
Model Simulation ◽  
Polymer Concentration ◽  
Shear Thinning ◽  
Turbulent Shear ◽  
Wall Region ◽  
Turbulence Statistics ◽  
Concentric Annulus ◽  
Sst Model ◽  
Shear Thinning Fluid

A RANS based shear stress transportation (SST) model was employed in this study to validate experimental results from a recent literature, which investigated the fully developed turbulent flow for a non-Newtonian shear thinning fluid, containing drag reduction polymer additives in a horizontal concentric annulus (inner to outer radio θ = 0.4). The polymer concentration varied from 0.07% V/V to 0.12% V/V and three mass flow rates from 3.92 kg/s to 5.95 kg/s were analyzed. The viscous property of the fluid was modeled by the power-law model. Simulation performed with the commercial code of ANSYS-CFX indicated that the SST model with default model constants overestimated the turbulence statistics of shear thinning flow in the near wall region where y+<60. As an effort to improve simulation accuracy, one of the model constants α1 was tuned in this study for the first time. Simulation results obtained from the modified model showed better agreement with experimental data compared to those from the default one. The present study represents a successful benchmark task for simulating turbulent shear thinning flow in concentric annuli with modified turbulence model constants.

Large-scale Structure and Turbulence Transport in the Young Solar Wind – Comparison of Parker Solar Probe Observations with a Global 3D Reynolds-averaged MHD Model

2021 ◽  
Author(s):  
Rohit Chhiber ◽  
Arcadi Usmanov ◽  
William Matthaeus ◽  
Melvyn Goldstein ◽  
Riddhi Bandyopadhyay
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Transport Equations ◽  
Turbulence Energy ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Coulomb Collisions ◽  
Flow Equations ◽  
Simulation Results ◽  
Turbulence Transport

&lt;div&gt;Simulation results from a global &lt;span&gt;magnetohydrodynamic&lt;/span&gt; model of the solar corona and the solar wind are compared with Parker Solar &lt;span&gt;Probe's&lt;/span&gt; (&lt;span&gt;PSP&lt;/span&gt;) observations during its first several orbits. The fully three-dimensional model (&lt;span&gt;Usmanov&lt;/span&gt; &lt;span&gt;et&lt;/span&gt; &lt;span&gt;al&lt;/span&gt;., 2018, &lt;span&gt;ApJ&lt;/span&gt;, 865, 25) is based on Reynolds-averaged mean-flow equations coupled with turbulence transport equations. The model accounts for effects of electron heat conduction, Coulomb collisions, Reynolds stresses, and heating of protons and electrons via nonlinear turbulent cascade. Turbulence transport equations for turbulence energy, cross &lt;span&gt;helicity&lt;/span&gt;, and correlation length are solved concurrently with the mean-flow equations. We specify boundary conditions at the coronal base using solar synoptic &lt;span&gt;magnetograms&lt;/span&gt; and calculate plasma, magnetic field, and turbulence parameters along the &lt;span&gt;PSP&lt;/span&gt; trajectory. We also accumulate data from all orbits considered, to obtain the trends observed as a function of heliocentric distance. Comparison of simulation results with &lt;span&gt;PSP&lt;/span&gt; data show general agreement. Finally, we generate synthetic fluctuations constrained by the local rms turbulence amplitude given by the model, and compare properties of this synthetic turbulence with PSP observations.&lt;/div&gt;

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