Interaction of an Acoustic Disturbance and a Two-Dimensional Turbulent Jet: Experimental Data

1983 ◽  
Vol 105 (2) ◽  
pp. 134-139 ◽  
Author(s):  
F. O. Thomas ◽  
V. W. Goldschmidt
Keyword(s):  
Turbulent Jet ◽  
Vortical Flow ◽  
Energy Spectra ◽  
Flow Structures ◽  
Two Dimensional ◽  
Frequency Range ◽  
Initial Region ◽  
Acoustic Disturbance ◽  
Turbulent Flow Structure ◽  
The Mean

An experimental study was performed to determine the effects a periodic acoustic disturbance had upon a two-dimensional turbulent jet in both the initial and similarity regions. Correlation and energy spectra measurements in the initial region indicate that acoustic forcing within a certain frequency range is capable of restructuring the flow in this region. In particular, these measurements suggest the presence of vortical flow structures arranged symmetrically with respect to the jet centerline. Measurements of the mean and turbulent flow structure in the similarity region of the jet indicate strong acoustically induced effects. Evidence suggests that the interaction effects observed in the similarity region are intimately related to those in the initial region.

Acoustically Induced Enhancement of Widening and Fluctuation Intensity in a Two-Dimensional Turbulent Jet

1986 ◽  
Vol 108 (3) ◽  
pp. 331-337 ◽  
Author(s):  
F. O. Thomas ◽  
V. W. Goldschmidt
Keyword(s):  
Turbulent Jet ◽  
Flow Structures ◽  
Jet Flows ◽  
Underlying Structure ◽  
Detailed Data ◽  
Initial Region ◽  
Acoustic Disturbance ◽  
Fine Grained ◽  
Turbulent Plane ◽  
Plane Jet

The enhancement of widening rate and turbulence intensity in a turbulent plane jet, due to an acoustic disturbance are considered. Detailed data at a representative Strouhal number suggest a well organized symmetric structural array in the initial region of the flow. These highly organized flow structures act as efficient agents in the transport of energy to the fine-grained turbulence, leading to greater diffusivity, enhanced turbulence and an increase in widening. The data also suggest significant differences in the underlying structure of the natural and excited jet flows, hence putting in jeopardy any generalization of coherent motions especially excited to facilitate their study.

A vortex-street model of the flow in the similarity region of a two-dimensional free turbulent jet

1982 ◽  
Vol 123 ◽  
pp. 523-535 ◽  
Author(s):  
J. W. Oler ◽  
V. W. Goldschmidt
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Turbulent Jet ◽  
Vortex Street ◽  
Two Dimensional ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Core ◽  
The Mean ◽  
Similarity Relationships

The mean-velocity profiles and entrainment rates in the similarity region of a two-dimensional jet are generated by a simple superposition of Rankine vortices arranged to represent a vortex street. The spacings between the vortex centres, their two-dimensional offsets from the centreline, as well as the core radii and circulation strengths, are all governed by similarity relationships and based upon experimental data.Major details of the mean flow field such as the axial and lateral mean-velocity components and the magnitude of the Reynolds stress are properly determined by the model. The sign of the Reynolds stress is, however, not properly predicted.

Reattachment of a Two-Dimensional, Incompressible Jet to an Adjacent Flat Plate

1960 ◽  
Vol 11 (3) ◽  
pp. 201-232 ◽  
Author(s):  
C. Bourque ◽  
B. G. Newman
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Separation Bubble ◽  
Volume Flow ◽  
Turbulent Jet ◽  
Two Dimensional ◽  
General Investigation ◽  
Mean Pressure ◽  
The Mean ◽  
Coandǎ Effect

SummaryAs part of a general investigation into Coanda effect, a study has been made of the reattachment of a two-dimensional, incompressible, turbulent jet to an adjacent, inclined, flat plate. The jet separates from the boundaries at the slot lips and reattaches to the plate downstream, a phenomenon which is associated with the lowering of the pressure between the jet and the plate accompanying the entrainment of fluid there. It is found that the flow becomes independent of both the length of the plate and the Reynolds number when these parameters are sufficiently large: the flow, scaled with respect to the width of the slot, is then uniquely determined by the plate inclination. Two approximate theories are developed for the mean pressure within the separation bubble, the position of reattachment and the increase in volume flow from the slot: the agreement with experiment is fairly satisfactory. These theories are a development of Dodds's analysis for the reattachment of a jet to a plate offset from, and parallel to, the axis of the slot and, for the purpose of comparison, a limited study is also made of this flow.

Passive Control of the Two-Dimensional Jet Using a Rectangular Notch

2002 ◽  
Author(s):  
Shigetaka Fujita ◽  
Takashi Harima ◽  
Hideo Osaka
Keyword(s):  
Passive Control ◽  
Core Region ◽  
Turbulent Jet ◽  
Upstream Region ◽  
Entrainment Rate ◽  
Two Dimensional ◽  
Flow Properties ◽  
Potential Core ◽  
The Mean ◽  
Rectangular Notch

The mean and turbulent flow properties of turbulent jet issuing from a quasi two-dimensional (2-D) nozzle with a rectangular notch (aspect ratio: AR=12.5) perpendicular to the two-dimensional nozzle at the midspan, have been measured. The exit Reynolds number was kept constant 13000. The aim of this study is to examine the effects of the rectangular notch on the mean and turbulent flowfields of the two-dimensional jet, and to clarify a possibility of a passive control of the two-dimensional jet using a rectangular notch. From the experiments, it was revealed that the potential core region existed until the section of x/d=25. In the upstream region, the entrainment rate was smaller than that of the two-dimensional jet due to the inward secondary flow on the y and z axes. Furthermore, the streamwise development of the turbulent intensity was delayed.

Self-sustained double-diffusive interleaving

2010 ◽  
Vol 662 ◽  
pp. 384-397
Author(s):  
ALESSANDRO STOCCHINO
Keyword(s):  
Convective Flow ◽  
Vector Fields ◽  
Flow Fields ◽  
Flow Structures ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Particle Image Velocimetry Technique ◽  
The Mean ◽  
Double Diffusive

The formation and evolution of double-diffusive interleaving is experimentally investigated with the purpose of analysing the influence of the convective flow structures, at different scales, on the mean flow. Recently, Krishnamurti (J. Fluid Mech., vol. 558, 2006, p. 113) has shown that, in the case of a continuous stratification experiment, the Reynolds stresses, due to convective flow patches, are able to vertically transport horizontal momentum, maintaining the mean flow. This mechanism is similar to the turbulent wind observed in thermal convection. In this study, the interleaving is produced using the classical set-up of Ruddick & Turner (Deep-Sea Res., vol. 558, 1979, p. 903). The dam-break experiments better resemble the case of oceanic fronts, where interleaving is commonly observed. The flow structures are investigated by measuring the two-dimensional flow fields using the particle image velocimetry technique. The resulting two-dimensional vector fields reveal complex fine-scale flow structures, and convective patterns are observed inside the finger-favourable layers. Vortical structures at scales comparable with the layer thickness are embedded in these regions and seem to be responsible for sustaining the horizontal mean flow against the viscous dissipations, especially in a region close to the layer nose. A spectral analysis of the flow fields suggest that the energy balance is governed by an inverse energy cascade, which implies a transfer of energy from the smaller scales to the larger scales (mean flow).

Directional Surface Roughness Influence on Turbulent Flow Structure

2019 ◽  
Author(s):  
Zambri Harun ◽  
Ashraf A. Abbas ◽  
Bagus Nugroho
Keyword(s):  
Surface Roughness ◽  
Turbulent Flow ◽  
Surface Pattern ◽  
Flow Structures ◽  
Mean Velocity ◽  
Turbulent Flow Structure ◽  
Series Of Experiments ◽  
The Mean ◽  
Turbulence Production ◽  
Current Report

Abstract A series of experiments have been conducted to investigate turbulent flow structures when it is exposed to a highly directional riblet-type surfaces roughness (converging-diverging/herringbone pattern) at a relatively low Reynolds number (Reτ). These experiments show that even at a low Reτ, the surface pattern is able to modify the turbulent boundary layer. Over the diverging region, we observe a decrease in drag penalty, while over the converging region there is an increase of drag penalty, which is indicated by the shift in the mean velocity profiles. The surface roughness also influences the turbulence production, indicated by the elevated turbulence intensities profiles for both the converging and diverging regions. The result seems to deviate from early investigations that show an increase in turbulence intensities above the converging region and a lowered turbulence intensities above the diverging region. The discrepancy may be caused by the lower Reτ Ret in the current report. Other important statistics such as skewness and flatness are also reported.

Effects of pitching rotation on aerodynamics of tandem flapping wing sections of a hovering dragonfly

2010 ◽  
Vol 114 (1161) ◽  
pp. 699-710 ◽  
Author(s):  
E. M. Elarbi ◽  
N. Qin
Keyword(s):  
Small Difference ◽  
Flapping Wing ◽  
Flow Structures ◽  
Vertical Force ◽  
Horizontal Force ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Dragonfly Wing ◽  
Simple Supports ◽  
The Mean

AbstractThis paper studies hovering capability of flapping two-dimensional tandem wing sections inspired by a real dragonfly wing configuration and kinematics. Based on unsteady numerical simulations, the dragonfly corrugated wings have been benchmarked against a flat wing in terms of the aerodynamic forces and flow structures generated during a flapping cycle. The timing of rotation at each stroke is studied by pitch rotation at three different rates, i.e., 80%, 60% and 40% of a flapping period. The results suggest that the longer time pitch rotation with the period of 80% of the overall flapping period is closer to the force calculations obtained of a balanced flight, that is, the mean vertical forcesupports the dragonfly weight of 0.754 g with a small difference of 0.92% and the mean horizontal forceindicates negligible thrust. However, the corrugated wing performs aerodynamically differently from the flat plate with differences inand inby ±2.06% for the corrugated shape. The vorticity flow field for both wings have been recorded at some instants of flapping motions which give more explanation of such dissimilarity.

Study of the Turbulent Flow Structure around a Standard Rushton Impeller

2014 ◽  
Vol 35 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Bohuš Kysela ◽  
Jiří Konfršt ◽  
Ivan Fořt ◽  
Michal Kotek ◽  
Zdeněk Chára
Keyword(s):  
Particle Image ◽  
Laser Doppler Anemometry ◽  
Turbulent Jet ◽  
Piv Measurements ◽  
Rushton Turbine ◽  
Image Velocimetry ◽  
Validity Range ◽  
Turbulent Flow Structure ◽  
The Mean ◽  
Rushton Impeller

Abstract The velocity field around the standard Rushton turbine was investigated by the Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) measurements. The mean ensembleaveraged velocity profiles and root mean square values of fluctuations were evaluated at two different regions. The first one was in the discharge stream in the radial direction from the impeller where the radial flow is dominant and it is commonly modelled as a swirling turbulent jet. The validity range of the turbulent jet model was studied. The second evaluated region is under the impeller where flow seems to be at first sight rather rigorous but obtained results show nonnegligible values of fluctuation velocity.

A one-dimensional self-gravitating stellar gas

1966 ◽  
Vol 25 ◽  
pp. 46-48 ◽  
Author(s):  
M. Lecar
Keyword(s):  
Gravitational Field ◽  
Phase Space ◽  
Motion Picture ◽  
Space Distribution ◽  
Two Dimensional ◽  
One Dimensional ◽  
Phase Space Distribution ◽  
Dimensional Phase Space ◽  
The Mean

“Dynamical mixing”, i.e. relaxation of a stellar phase space distribution through interaction with the mean gravitational field, is numerically investigated for a one-dimensional self-gravitating stellar gas. Qualitative results are presented in the form of a motion picture of the flow of phase points (representing homogeneous slabs of stars) in two-dimensional phase space.

The Influence of Blade Wakes on the Performance of Interturbine Diffusers

1996 ◽  
Vol 118 (2) ◽  
pp. 347-352 ◽  
Author(s):  
R. G. Dominy ◽  
D. A. Kirkham
Keyword(s):  
Performance Modeling ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Two Dimensional ◽  
Correct Performance ◽  
Analysis Methods ◽  
Flow Factor ◽  
The Mean ◽  
Lp Turbine

Interturbine diffusers provide continuity between HP and LP turbines while diffusing the flow upstream of the LP turbine. Increasing the mean turbine diameter offers the potential advantage of reducing the flow factor in the following stages, leading to increased efficiency. The flows associated with these interturbine diffusers differ from those in simple annular diffusers both as a consequence of their high-curvature S-shaped geometry and of the presence of wakes created by the upstream turbine. It is shown that even the simplest two-dimensional wakes result in significantly modified flows through such ducts. These introduce strong secondary flows demonstrating that fully three-dimensional, viscous analysis methods are essential for correct performance modeling.

Sign in / Sign up

Export Citation Format

Share Document