scholarly journals Turbulence Characteristics in an Axisymmetric Sudden Expansion

1997 ◽  
Author(s):  
Saad A. Ahmed ◽  
Kamorudeen B. Abidogun
Keyword(s):  
Experimental Data ◽  
Shear Layer ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Reynolds Stresses ◽  
Central Difference ◽  
Dissipation Term ◽  
Layer Flow

Simultaneous two-component laser Doppler velocimeter measurements were made in an axisymmetric sudden expansion to measure the flow properties of a confined, isothermal flowfield of a research dump combustor. Measurements of mean velocities, Reynolds stresses, and triple products were carried out at axial distances ranging from 0.38H (H = step height) to 18H downstream of the dump plane. Detailed experimental data are provided to help in the understanding of the behavior of turbulent transport characteristics of a confined shear layer. In addition, the data from this study will be available for upgrading / or evaluating advanced numerical codes used to predict complex turbulent flows. The turbulent kinetic energy terms: convection, diffusion, and production terms were computed directly from the experimental data using central difference, while the viscous dissipation term was obtained from balance of energy equation. The results indicate that the shear layer flow created by the sudden expansion enhances the combustor performance by serving as a turbulence generator mechanism.

An isothermal experimental investigation of turbulence transport through an abrupt axisymmetric expansion

1998 ◽  
Vol 212 (1) ◽  
pp. 45-55
Author(s):  
S A Ahmed
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Swirling Flow ◽  
Energy Balance Equation ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Turbulence Energy ◽  
Reynolds Stresses ◽  
Dissipation Term ◽  
Flow Mixing

A non-intrusive, two-component laser Doppler velocimeter was employed to measure the flow properties of a confined, isothermal, swirling flowfield in an axisymmetric sudden expansion research combustor. A constant angle swirler was used to stir the flow at the inlet of the combustor. Measurements of mean velocities, Reynolds stresses and triple products were carried out at axial distances ranging from 0.38 H (step height) to 18 H downstream of the swirler. Detailed experimental data are provided to help in the understanding of the behaviour of swirling, recirculating, axisymmetric and turbulent flows. Also, these detailed experimental data will be available for upgrading advanced numerical codes. The turbulent kinetic energy terms, convection, diffusion and production, were computed directly from the experimental data using central differencing, while the dissipation term was obtained from an energy balance equation. The swirling flow data are compared with the simple dump flow in the same experimental arrangement and it is shown that swirl enhances the production and distribution of turbulence energy in the combustor which, in turn, indicates thorough flow mixing and earlier flow recovery.

Laser Velocimeter Measurements in Highly Turbulent Recirculating Flows

1984 ◽  
Vol 106 (2) ◽  
pp. 173-180 ◽  
Author(s):  
W. H. Stevenson ◽  
H. D. Thompson ◽  
R. R. Craig
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Quantitative Description ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Bias Error ◽  
Mean Velocity ◽  
One Dimensional ◽  
Numerical Predictions ◽  
Velocity Bias

This paper presents the results of an extensive study of subsonic separated flows using a laser Doppler velocimeter. Both a rectangular rearward facing step and cylindrical (axisymmetric) sudden expansion geometry were studied. The basic objectives were to resolve the question of whether a velocity bias error does, in fact, occur in LDV measurements in highly turbulent flows of this type and, if so, how it may be eliminated; map the velocity field (mean velocity, turbulence intensity, Reynolds stress, etc.) including the entire recirculation zone; and compare experimental results with numerical predictions based on the k-ε turbulence model. Measurements were carried out using a one-dimensional LDV operating in forward scatter with signal processing by means of a commercial counter-type processor. Results obtained show that velocity bias does occur in turbulent flows and that it can be overcome by proper data acquisition procedures. The results also indicate that the important mean velocity and turbulence quantities can be obtained with reasonable accuracy using a one-dimensional LDV system. Although the k-ε turbulence model provides a good qualitative picture of the flow field, it does not yield a completely adequate quantitative description. Results obtained here illustrate the discrepancies to be expected and provide a basis for further model development.

Improved Prediction of Turbomachinery Flows Using Near-Wall Reynolds-Stress Model

2001 ◽  
Vol 124 (1) ◽  
pp. 86-99 ◽  
Author(s):  
G. A. Gerolymos ◽  
J. Neubauer ◽  
V. C. Sharma ◽  
I. Vallet
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Equations ◽  
Near Wall

In this paper an assessment of the improvement in the prediction of complex turbomachinery flows using a new near-wall Reynolds-stress model is attempted. The turbulence closure used is a near-wall low-turbulence-Reynolds-number Reynolds-stress model, that is independent of the distance-from-the-wall and of the normal-to-the-wall direction. The model takes into account the Coriolis redistribution effect on the Reynolds-stresses. The five mean flow equations and the seven turbulence model equations are solved using an implicit coupled OΔx3 upwind-biased solver. Results are compared with experimental data for three turbomachinery configurations: the NTUA high subsonic annular cascade, the NASA_37 rotor, and the RWTH 1 1/2 stage turbine. A detailed analysis of the flowfield is given. It is seen that the new model that takes into account the Reynolds-stress anisotropy substantially improves the agreement with experimental data, particularily for flows with large separation, while being only 30 percent more expensive than the k−ε model (thanks to an efficient implicit implementation). It is believed that further work on advanced turbulence models will substantially enhance the predictive capability of complex turbulent flows in turbomachinery.

Evaluation of Turbulence Models for Predicting Buoyant Flows

1990 ◽  
Vol 112 (4) ◽  
pp. 945-951 ◽  
Author(s):  
A. Shabbir ◽  
D. B. Taulbee
Keyword(s):  
Experimental Data ◽  
Kinetic Energy ◽  
Turbulent Transport ◽  
Turbulence Models ◽  
Heat Fluxes ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Buoyant Flows ◽  
Model Equations ◽  
Stress Models

Experimental data for the buoyant axisymmetric plume are used to validate certain closure hypotheses employed in turbulence model equations for calculating buoyant flows. Closure formulations for the turbulent transport of momentum, thermal energy, kinetic energy, and squared temperature used in the k–ε and algebraic stress models are investigated. Experimental data for the mean velocity, mean temperature, and kinetic energy are used in the closure formulation to obtain Reynolds stresses, heat fluxes, etc., which are then compared with their measured values.

An Investigation of two Turbulent Flows over Smooth and Rough Surfaces

1974 ◽  
Vol 16 (2) ◽  
pp. 71-78 ◽  
Author(s):  
W. K. Allan ◽  
V. Sharma
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Smooth Surface ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Experimental data for two-dimensional, low-speed, turbulent boundary layer flow has been used to verify the description of mean-velocity distributions proposed by Allan and to re-evaluate the entrainment function. The independence of pressure gradient and surface roughness as regards their effects on velocity profiles has been demonstrated. Boundary layer predictions agree with experimental data for a smooth surface, but further investigation is required for flow over a rough surface.

Analysis of Complex Flows From Experimental Data and Numerical Experiments

2010 ◽  
Author(s):  
Je´roˆme Ve´tel ◽  
Andre´ Garon ◽  
Dominique Pelletier
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Diagnostic Techniques ◽  
Complex Flows ◽  
Time Resolved ◽  
Taylor Hypothesis ◽  
The Rich ◽  
Passive Tracers ◽  
Advanced Post Processing

Fluid mechanics is considered to be a privileged field in physics because phenomena can be made visible. This is unfortunately not the case in turbulence where diffusion and mixing of passive tracers are enhanced by turbulent transport. Consequently, the analysis of the rich flow physics provided by direct numerical simulations (DNS) and by modern optical diagnostic techniques require advanced post-processing tools to extract fine flow details. In this context, this paper reviews most recent techniques used to reveal coherent structures and their dynamics in turbulent flows. In particular, results obtained with standard Eulerian techniques are compared to those obtained from a more recent Lagrangian technique. Even if this latter technique can provide finer details, it is found that the two methods are complementary. This is illustrated with DNS results and with experimental data including planar measurements as well as time-resolved measurements converted to quasi-instantaneous volumetric data by using the Taylor hypothesis.

The structure of a turbulent shear layer bounding a separation region

1987 ◽  
Vol 179 ◽  
pp. 439-468 ◽  
Author(s):  
I. P. Castro ◽  
A. Haque
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Large Scale ◽  
Turbulent Shear ◽  
Turbulence Structure ◽  
Similar Data ◽  
Reynolds Stresses ◽  
Plate Height ◽  
Separated Shear Layer ◽  
Wide Range

Detailed measurements within the separated shear layer behind a flat plate normal to an airflow are reported. A long, central splitter plate in the wake prevented vortex shedding and led to an extensive region of separated flow with mean reattachment some ten plate heights downstream. The Reynolds number based on plate height was in excess of 2 × 1044.Extensive use of pulsed-wire anemometry allowed measurements of all the Reynolds stresses throughout the flow, along with some velocity autocorrelations and integral timescale data. The latter help to substantiate the results of other workers obtained in separated flows of related geometry, particularly in the identification of a very low-frequency motion with a timescale much longer than that associated with the large eddies in the shear layer. Wall-skin-friction measurements are consistent with the few similar data previously published and indicate that the thin boundary layer developing beneath the separated region has some ‘laminar-like’ features.The Reynolds-stress measurements demonstrate that the turbulence structure of the separated shear layer differs from that of a plane mixing layer between two streams in a number of ways. In particular, the normal stresses all rise monotonically as reattachment is approached, are always considerably higher than the plane layer values and develop in quite different ways. Flow similarity is not a useful concept. A major conclusion is that any effects of stabilizing streamline curvature are weak compared with the effects of the re-entrainment at the low-velocity edge of the shear layer of turbulent fluid returned around reattachment. It is argued that the general features of the flow are likely to be similar to those that occur in a wide range of complex turbulent flows dominated by a shear layer bounding a large-scale recirculating region.

Improved Prediction of Turbomachinery Flows Using Near-Wall Reynolds-Stress Model

2001 ◽  
Author(s):  
G. A. Gerolymos ◽  
J. Neubauer ◽  
V. C. Sharma ◽  
I. Vallet
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Equations ◽  
Near Wall

In this paper an assessment of the improvement in the prediction of complex turbomachinery flows using a new near-wall Reynolds-stress model is attempted. The turbulence closure used is a near-wall low-turbulence-Reynolds-number Reynolds-stress model, that is independent of the distance-from-the-wall and of the normal-to-the-wall direction. The model takes into account the Coriolis redistribution effect on the Reynolds-stresses. The 5 mean flow equations and the 7 turbulence model equations are solved using an implicit coupled O(Δx3) upwind-biased solver. Results are compared with experimental data for 3 turbomachinery configurations: the ntua high subsonic annular cascade, the nasa_37 rotor, and the rwth 1½ stage turbine. A detailed analysis of the flowfield is given. It is seen that the new model that takes into account the Reynolds-stress anisotropy substantially improves the agreement with experimental data, particularly for flows with large separation, while being only 30% more expensive than the k – ε model (thanks to an efficient implicit implementation). It is believed that further work on advanced turbulence models will substantially enhance the predictive capability of complex turbulent flows in turbomachinery.

Recirculating Turbulent Flows of Thixotropic Fluids

2001 ◽  
Author(s):  
Américo S. Pereira ◽  
Fernando T. Pinho
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Aqueous Suspension ◽  
Flow Characteristics ◽  
Shear Thinning ◽  
Sudden Expansion ◽  
Reynolds Stresses ◽  
Hydrodynamic Behaviour ◽  
Inlet Conditions ◽  
High Reynolds

Abstract An aqueous suspension of 1% by weight laponite was investigated in terms of its rheology and hydrodynamic behaviour in a sudden expansion flow. The fluid was shear-thinning, thixotropic and had an yield stress which was measured by direct and indirect methods. The oscillatory tests showed that the elasticity of the 1% Laponite suspension was very small. The high Reynolds number turbulent flow downstream of a sudden expansion, with fully-developed inlet conditions, showed no major difference in relation to the flow of water. There were no differences between the laponite and water mean and turbulent flow characteristics upstream and downstream of the expansion plane, except for a small anticipation of the loci of maximum Reynolds stresses with the suspension, but this had no further consequence. In conclusion, although the laponite suspension was thixotropic, shear-thinning and viscoplastic, its hydrodynamic behaviour in a sudden expansion was akin to that of water, a result which could not be anticipated.

Computation of two-phase shear-layer flow using an Eulerian-Lagrangian analysis

1988 ◽  
Author(s):  
JAYANT SABNIS ◽  
SANG-KEUN CHOI ◽  
RICHARD BUGGELN ◽  
HOWARD GIBELING
Keyword(s):  
Shear Layer ◽  
Lagrangian Analysis ◽  
Two Phase ◽  
Layer Flow
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