Fluid Dynamics of a Conical Flame Stabilizer

1989 ◽  
Vol 111 (1) ◽  
pp. 97-102 ◽  
Author(s):  
D. R. Ballal ◽  
T. H. Chen ◽  
W. J. Schmoll
Keyword(s):  
Large Scale ◽  
Recirculation Zone ◽  
Axial Direction ◽  
Combustible Mixture ◽  
High Shear ◽  
Blockage Ratio ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Two Component ◽  
Skewness And Kurtosis

Turbulence measurements were performed on a 45 deg conical flame stabilizer with a 31 percent blockage ratio, mounted coaxially at the mouth of a circular pipe and supplied with a turbulent premixed methane-air mixture at a Reynolds number of 2.85 × 104. A two-component LDA system was used in the measurement of mean velocities, turbulence intensities, Reynolds stresses, skewness, and kurtosis. It was found that combustion accelerates mean-flow velocities but damps turbulence intensity via the processes of turbulent dilatation and viscous dissipation due to heat release. Measurements in the axial direction showed that the length of the recirculation zone was nearly doubled as a result of combustion. Also, the region around the downstream stagnation point where streamlines meet and velocities change direction was found to be highly turbulent. Skewness and kurtosis data indicated that large-scale eddies carrying fresh combustible mixture are entrained into the high-shear region surrounding the recirculation zone. Finally, a discussion of turbulence-combustion interaction is presented to explain these experimental results.

Study of the Standard k-ε Model for Tip Leakage Flow in an Axial Compressor Rotor

2016 ◽  
Vol 33 (4) ◽  
Author(s):  
Yanfei Gao ◽  
Yangwei Liu ◽  
Luyang Zhong ◽  
Jiexuan Hou ◽  
Lipeng Lu
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Axial Compressor ◽  
Leakage Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor

AbstractThe standard k-ε model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to “freeze” the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.

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

<div>Simulation results from a global <span>magnetohydrodynamic</span> model of the solar corona and the solar wind are compared with Parker Solar <span>Probe's</span> (<span>PSP</span>) observations during its first several orbits. The fully three-dimensional model (<span>Usmanov</span> <span>et</span> <span>al</span>., 2018, <span>ApJ</span>, 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 <span>helicity</span>, and correlation length are solved concurrently with the mean-flow equations. We specify boundary conditions at the coronal base using solar synoptic <span>magnetograms</span> and calculate plasma, magnetic field, and turbulence parameters along the <span>PSP</span> 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 <span>PSP</span> 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.</div>

scholarly journals Anisotropic source modelling for turbulent jet noise prediction

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190075 ◽  
Author(s):  
Xihai Xu ◽  
Xiaodong Li
Keyword(s):  
Large Scale ◽  
Noise Source ◽  
Jet Noise ◽  
Source Model ◽  
Noise Prediction ◽  
Reynolds Stresses ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Navier Stokes Equation ◽  
Anisotropic Source

An anisotropic component of the jet noise source model for the Reynolds-averaged Navier–Stokes equation-based jet noise prediction method is proposed. The modelling is based on Goldstein's generalized acoustic analogy, and both the fine-scale and large-scale turbulent noise sources are considered. To model the anisotropic characteristics of jet noise source, the Reynolds stress tensor is used in place of the turbulent kinetic energy. The Launder–Reece–Rodi model (LRR), combined with Menter's ω -equation for the length scale, with modified coefficients developed by the present authors, is used to calculate the mean flow velocities and Reynolds stresses accurately. Comparison between predicted results and acoustic data has been carried out to verify the accuracy of the new anisotropic source model. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

scholarly journals A Framework for Parameterizing Eddy Potential Vorticity Fluxes

2012 ◽  
Vol 42 (4) ◽  
pp. 539-557 ◽  
Author(s):  
David P. Marshall ◽  
James R. Maddison ◽  
Pavel S. Berloff
Keyword(s):  
Stress Tensor ◽  
Potential Vorticity ◽  
Large Scale ◽  
Eddy Diffusivity ◽  
Linear Instability ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Conservation Of Energy ◽  
The Mean ◽  
Energy And Momentum

Abstract A framework for parameterizing eddy potential vorticity fluxes is developed that is consistent with conservation of energy and momentum while retaining the symmetries of the original eddy flux. The framework involves rewriting the residual-mean eddy force, or equivalently the eddy potential vorticity flux, as the divergence of an eddy stress tensor. A norm of this tensor is bounded by the eddy energy, allowing the components of the stress tensor to be rewritten in terms of the eddy energy and nondimensional parameters describing the mean shape and orientation of the eddies. If a prognostic equation is solved for the eddy energy, the remaining unknowns are nondimensional and bounded in magnitude by unity. Moreover, these nondimensional geometric parameters have strong connections with classical stability theory. When applied to the Eady problem, it is shown that the new framework preserves the functional form of the Eady growth rate for linear instability. Moreover, in the limit in which Reynolds stresses are neglected, the framework reduces to a Gent and McWilliams type of eddy closure where the eddy diffusivity can be interpreted as the form proposed by Visbeck et al. Simulations of three-layer wind-driven gyres are used to diagnose the eddy shape and orientations in fully developed geostrophic turbulence. These fields are found to have large-scale structure that appears related to the structure of the mean flow. The eddy energy sets the magnitude of the eddy stress tensor and hence the eddy potential vorticity fluxes. Possible extensions of the framework to ensure potential vorticity is mixed on average are discussed.

Turbulence Structures of Leading Edge Film Cooling Jets

2000 ◽  
Author(s):  
Sabine Ardey ◽  
Stefan Wolff ◽  
Leonhard Fottner
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Suction Side ◽  
Pressure Side ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Turbulence Structures ◽  
Injection Zone

For a better understanding of the turbulence structures attached to film cooling jets, mean flow velocities and turbulent fluctuations were measured by means of 3D hot wire anemometry in the injection zone of a linear, large scale, high pressure turbine cascade with leading edge film cooling. Near the stagnation point, the blades are equipped with one row of film cooling holes each on the suction and pressure side. Two basically different coolant jet situations are compared: On the suction side the jet features the ordinary kidney vortex. On the pressure side, the jet separates completely from the blade surface since it is located above a large recirculation zone created by a locally adverse pressure gradient and a flow separation near the pressure side injection. The measured Reynolds stresses were analyzed with regard to turbulence production and diffusion. The Bousinesque Hypothesis was tested and could not be confirmed. It was found that the turbulence is highly anisotropic. In addition to the brief description of the experimental set up and the acquired data, given in this paper, the complete information are published as a test case (Ardey and Fottner, 1998) that is directly accessible via internet at: http://www.unibw-muenchen.de/campus/LRT12/welcome.html

Developing turbulent boundary layers with system rotation

1985 ◽  
Vol 157 ◽  
pp. 405-448 ◽  
Author(s):  
J. H. Watmuff ◽  
H. T. Witt ◽  
P. N. Joubert
Keyword(s):  
Skin Friction ◽  
Boundary Layers ◽  
Large Scale ◽  
Turbulent Boundary Layers ◽  
Momentum Balance ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Secondary Circulations ◽  
Spatially Periodic

Measurements are presented for low-Reynolds-number turbulent boundary layers developing in a zero pressure gradient on the sidewall of a duct. The effect of rotation on these layers is examined. The mean-velocity profiles affected by rotation are described in terms of a common universal sublayer and modified logarithmic and wake regions.The turbulence quantities follow an inner and outer scaling independent of rotation. The effect appears to be similar to that, of increased or decreased layer development. Streamwise-energy spectra indicate that, for a given non-dimensional wall distance, it is the low-wavenumber spectral components alone that are affected by rotation.Large spatially periodic spanwise variations of skin friction are observed in the destabilized layers. Mean-velocity vectors in the cross-stream plane clearly show an array of vortex-like structures which correlate strongly with the skin-friction pattern. Interesting properties of these mean-flow structures are shown and their effect on Reynolds stresses is revealed. Near the duct centreline, where we have measured detailed profiles, the variations are small and there is a reasonable momentum balance.Large-scale secondary circulations are also observed but the strength of the pattern is weak and it appears to be confined to the top and bottom regions of the duct. The evidence suggests that it has minimally affected the flow near the duct centreline where detailed profiles were measured.

Near-wall turbulence statistics and flow structures over three-dimensional roughness in a turbulent channel flow

2011 ◽  
Vol 667 ◽  
pp. 1-37 ◽  
Author(s):  
JIARONG HONG ◽  
JOSEPH KATZ ◽  
MICHAEL P. SCHULTZ
Keyword(s):  
Channel Flow ◽  
Outer Layer ◽  
Large Scale ◽  
Wall Turbulence ◽  
Small Scale ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Dissipation Rates ◽  
Near Wall Turbulence ◽  
Near Wall

Utilizing an optically index-matched facility and high-resolution particle image velocimetry measurements, this paper examines flow structure and turbulence in a rough-wall channel flow for Reτ in the 3520–5360 range. The scales of pyramidal roughness elements satisfy the ‘well-characterized’ flow conditions, with h/k ≈ 50 and k+ = 60 ~ 100, where h is half height of the channel and k is the roughness height. The near-wall turbulence measurements are sensitive to spatial resolution, and vary with Reynolds number. Spatial variations in the mean flow, Reynolds stresses, as well as the turbulent kinetic energy (TKE) production and dissipation rates are confined to y < 2k. All the Reynolds stress components have local maxima at slightly higher elevations, but the streamwise-normal component increases rapidly at y < k, peaking at the top of the pyramids. The TKE production and dissipation rates along with turbulence transport also peak near the wall. The spatial energy and shear spectra show an increasing contribution of large-scale motions and a diminishing role of small motions with increasing distance from the wall. As the spectra steepen at low wavenumbers, they flatten and develop bumps in wavenumbers corresponding to k − 3k, which fall in the dissipation range. Instantaneous realizations show that roughness-scale eddies are generated near the wall, and lifted up rapidly by large-scale structures that populate the outer layer. A linear stochastic estimation-based analysis shows that the latter share common features with hairpin packets. This process floods the outer layer with roughness-scale eddies, in addition to those generated by the energy-cascading process. Consequently, although the imprints of roughness diminish in the outer-layer Reynolds stresses, consistent with the wall similarity hypothesis, the small-scale turbulence contains a clear roughness signature across the entire channel.

scholarly journals Self-sustaining processes at all scales in wall-bounded turbulent shear flows

2017 ◽  
Vol 375 (2089) ◽  
pp. 20160088 ◽  
Author(s):  
Carlo Cossu ◽  
Yongyun Hwang
Keyword(s):  
Large Scale ◽  
Shear Flows ◽  
Stokes Equations ◽  
Wall Turbulence ◽  
Turbulent Shear ◽  
Large Reynolds Number ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Full Account ◽  
Turbulent Shear Flows

We collect and discuss the results of our recent studies which show evidence of the existence of a whole family of self-sustaining motions in wall-bounded turbulent shear flows with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. The statistical and dynamical features of this family of self-sustaining motions, which are associated with streaks and quasi-streamwise vortices, are consistent with those of Townsend’s attached eddies. Motions at each relevant scale are able to sustain themselves in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect. The coherent self-sustaining process is embedded in a set of invariant solutions of the filtered Navier–Stokes equations which take into full account the Reynolds stresses associated with the residual smaller-scale motions. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

Numerical and Experimental Investigation of an Annular Jet Flow With Large Blockage

2004 ◽  
Vol 126 (3) ◽  
pp. 375-384 ◽  
Author(s):  
Christian Del Taglia ◽  
Lars Blum ◽  
Ju¨rg Gass ◽  
Yiannis Ventikos ◽  
Dimos Poulikakos
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Large Scale ◽  
Recirculation Zone ◽  
Blockage Ratio ◽  
Flow Conditions ◽  
Preferential Direction ◽  
Vortical Structures ◽  
Annular Jet ◽  
Unsteady Simulation

Unsteady 3-D numerical simulations and 3-D LDA measurements of an annular jet with a blockage ratio of 0.89 and Reynolds number 4400 are presented. At these flow conditions, the flow inside of the recirculation zone is asymmetric, with a preferential direction. Very good predictions of the velocity fluctuation values are achieved with the unsteady simulation technique in the same region, as the fluctuations are mainly large scale, structure dominated. A frequency near to 10 Hz is identified in the simulations, which is attributed to the principal shedding behavior of the vortical structures.

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