Turbulence in Small Air Jets at Exit Velocities Up to 705 Feet per Second

1957 ◽  
Vol 24 (3) ◽  
pp. 349-354
Author(s):  
L. W. Lassiter
Keyword(s):  
Turbulence Intensity ◽  
Broad Band ◽  
Axial Distance ◽  
Intensity Scale ◽  
Mean Velocity ◽  
Fully Developed Flow ◽  
Velocity Increase ◽  
The Core ◽  
Air Jets ◽  
Velocity Turbulence

Abstract Turbulence intensity, scale, and spectrum measurements were made on model jets of 1 in. and 2-in. diam at various mean velocities. The indications are that only in the fully developed flow is turbulence intensity invariant with mean velocity; intensity in the core, in the turbulent annulus, and in the transition region decreases in varying degrees with mean velocity increase. Longitudinal and radial scales of turbulence were found to increase in the annulus in proportion to about the square root of axial distance, and longitudinal scale is about 65 per cent greater than radial scale. Both radial and longitudinal scales seem to be essentially constant with mean velocity. Turbulence spectra were found to consist of a sharply peaked band of frequencies in the core, degenerating to a slightly peaked broad band at points in the mixing regions.

Flow structure of the free round turbulent jet in the initial region

1979 ◽  
Vol 90 (3) ◽  
pp. 531-539 ◽  
Author(s):  
L. Bogusławski ◽  
Cz. O. Popiel
Keyword(s):  
Kinetic Energy ◽  
Turbulent Shear ◽  
Axial Distance ◽  
Initial Region ◽  
Mean Velocity ◽  
The Core ◽  
Turbulent Shear Stress ◽  
Air Jet ◽  
The Mean ◽  
Good Agreement

This note presents measurements of radial and axial distributions of mean velocity, turbulent intensities and kinetic energy as well as radial distributions of the turbulent shear stress in the initial region of a turbulent air jet issuing from a long round pipe into still air. The pipe flow is transformed relatively smoothly into a jet flow. In the core subregion the mean centre-line velocity decreases slightly. The highest turbulence occurs at an axial distance of about 6d and radius of (0·7 to 0·8)d. On the axis the highest turbulent kinetic energy appears at a distance of (7·5 to 8·5)d. Normalized distributions of the turbulent quantities are in good agreement with known data on the developed region of jets issuing from short nozzles.

On the mechanism of wall turbulence

1982 ◽  
Vol 119 ◽  
pp. 173-217 ◽  
Author(s):  
A. E. Perry ◽  
M. S. Chong
Keyword(s):  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Scaling Laws ◽  
Heated Surface ◽  
Broad Band ◽  
Wall Turbulence ◽  
Mean Velocity ◽  
Quantitative Measurements ◽  
Temperature Distributions ◽  
The Mean

In this paper an attempt is made to formulate a model for the mechanism of wall turbulence that links recent flow-visualization observations with the various quantitative measurements and scaling laws established from anemometry studies. Various mechanisms are proposed, all of which use the concept of the horse-shoe, hairpin or ‘A’ vortex. It is shown that these models give a connection between the mean-velocity distribution, the broad-band turbulence-intensity distributions and the turbulence spectra. Temperature distributions above a heated surface are also considered. Although this aspect of the work is not yet complete, the analysis for this shows promise.

Effect of Freestream Turbulence and Flow Recovery in the Wake of a Flat Plate

2002 ◽  
Author(s):  
F. N. Krampa-Morlu ◽  
R. Balachandar
Keyword(s):  
Flat Plate ◽  
Turbulence Intensity ◽  
Flow Direction ◽  
Wake Region ◽  
Freestream Turbulence ◽  
Near Wake ◽  
Mean Velocity ◽  
Channel Boundary ◽  
The Mean ◽  
Velocity Turbulence

The study of the recovery of an open channel boundary flow in the presence of increased freestream turbulence (FST) generated in the wake region of a surface mounted flat plate is presented. Detailed LDA velocity measurements were obtained upstream and downstream of the flat plate, which is 3 mm in thickness and has a thickness-to-chord ratio of 0.12. The chord is placed parallel to the flow direction. The characteristics of the mean velocity, turbulence intensity, and the velocity skewness and flatness factors were investigated. The skin friction was increased while the strength of the boundary layer wake parameter decreased in the wake region. The turbulence intensity profiles in the wake region increasingly deviated significantly from the upstream profile. Generally, the increased FST noticed in the near-wake region was observed to decay with downstream distance. As a result, the mean velocity and turbulence intensity profiles showed a general sense of recovery towards the state of the approaching flow.

Calculation of Fully-Developed Turbulent Flow in Rectangular Ducts With Nonuniform Wall Roughness

1997 ◽  
Vol 119 (3) ◽  
pp. 550-558 ◽  
Author(s):  
M. Naimi ◽  
F. B. Gessner
Keyword(s):  
Reynolds Stress ◽  
Turbulence Models ◽  
Equation Model ◽  
Mean Velocity ◽  
Fully Developed Flow ◽  
Square Duct ◽  
Fully Developed Turbulent Flow ◽  
Flow Situation ◽  
Velocity Turbulence ◽  
Transport Type

The predictive capabilities of four transport-type turbulence models are analyzed by comparing predictions with experimental data for fully-developed flow in (1) a rectangular duct with a step change in roughness on one wall (Case 1), and (2) a square duct with one rib-roughened wall (Case 2). The models include the Demuren-Rodi (DR) k-ε model, the Sugiyama et al. (S) k-ε model, the Launder-Li (LL) Reynolds stress transport equation model, and the differential stress (DS) model proposed recently by the authors. For the first flow situation (Case 1), the results show that the DS model yields improved agreement between predicted and measured primary and secondary mean velocity distributions in comparison to the DR and LL models. For the second flow situation (Case 2), the DS model is superior to the DR and S models for predicting experimentally observed mean velocity, turbulence kinetic energy, and Reynolds stress anisotropy behavior, especially in the vicinity of a corner formed by the juncture of adjacent smooth and rough walls. The results are analyzed in order to explain why the DR model leads to the formation of a spurious secondary flow cell near this corner that is not present in the experimental flow.

Turbulence suppression in combustion-driven magnetohydrodynamic channels

1988 ◽  
Vol 188 ◽  
pp. 147-157 ◽  
Author(s):  
J. C. Reis ◽  
C. H. Kruger
Keyword(s):  
Boundary Layer ◽  
Liquid Metal ◽  
Turbulence Intensity ◽  
Spectral Energy ◽  
Energy Distributions ◽  
Mean Velocity ◽  
Mhd Flows ◽  
The Core ◽  
Turbulence Suppression ◽  
The Mean

The effects of a magnetic field on core turbulence, mean-velocity boundary-layer profiles, turbulence-intensity boundary-layer profiles and turbulent spectral-energy distributions have been experimentally determined for combustion-driven magneto-hydrodynamic (MHD) flows. The turbulence suppression of the core was found to be similar to that of liquid-metal MHD flows, even though the turbulent structure was entirely different. The mean-velocity and turbulence-intensity boundary-layer profiles were affected much less than those of liquid-metal flows, primarily because the low-temperature thermal boundary layer reduced the electrical conductivity near the wall. No spectral dependence of turbulence suppression was observed in the core.

A Method of Measuring the Three-Dimensional Mean Flow and Turbulence Quantities Inside a Rotating Turbo-machinery Passage

1976 ◽  
Vol 98 (2) ◽  
pp. 137-144 ◽  
Author(s):  
C. A. Gorton ◽  
B. Lakshminarayana
Keyword(s):  
Turbulence Intensity ◽  
Three Dimensional ◽  
Hot Wire ◽  
Mean Flow ◽  
Mean Velocity ◽  
Hot Wire Anemometry ◽  
Turbo Machinery ◽  
Velocity Turbulence

A method of measuring the three-dimensional components of mean velocity and turbulence quantities within a rotating turbomachinery passage is developed through the use of hot wire anemometry techniques. Equations are derived which, when solved simultaneously and in conjunction with the data obtained from the hot wire anemometer measurements, will provide values for the radial, axial and tangential components of mean velocity, turbulence intensity and turbulence stress within the rotating turbomachinery passage. A three-bladed rocket pump inducer model, operating in air, was used in the experimentation. The method is very accurate and provides very useful information on the characteristics of the flow inside rotor passages hitherto unexplored.

Hydrodynamics in Indo-Pacific seagrasses with a focus on short canopies

2018 ◽  
Vol 61 (1) ◽  
pp. 1-8
Author(s):  
Mahatma Lanuru ◽  
Rohani Ambo-Rappe ◽  
Khairul Amri ◽  
Susan L. Williams
Keyword(s):  
Water Flow ◽  
Turbulence Intensity ◽  
Physical Stability ◽  
Shear Velocity ◽  
Thalassia Hemprichii ◽  
Mean Velocity ◽  
Environmental Threats ◽  
Cymodocea Rotundata ◽  
Syringodium Isoetifolium ◽  
Velocity Turbulence

Abstract Seagrass hydrodynamic regimes are important to understand and also to guide seagrass restoration, which is of great interest in Indonesia because of environmental threats to the exceptionally high seagrass species richness. Hydrodynamic regimes influence the physical stability of seagrass beds, sedimentation rates, and the advection of nutrients and food to seagrasses and associated organisms. In a flume, we determined the effect of canopies of Cymodocea rotundata, Enhalus acoroides, Halodule uninervis, Syringodium isoetifolium and Thalassia hemprichii on water velocity, turbulence, turbulence intensity and shear velocity. The taller canopies of Enhalus and Cymodocea slowed water flow, but the shorter canopies (<5 cm) had little effect. Seagrasses did not influence turbulence and turbulence intensity (turbulence normalized to mean velocity) but they reduced shear velocity U*. Our results indicate that Enhalus is a good candidate for transplantation in terms of reducing mean water flow and shear velocities, but that Halodule should also be considered as it also reduced shear velocities and it spreads quickly after transplantation. Our results extend the understanding of seagrass-hydrodynamic relationships to include very short canopies, unlike the taller canopies studied to date.

Characteristics of the wake behind a cascade of airfoils

1973 ◽  
Vol 61 (4) ◽  
pp. 707-730 ◽  
Author(s):  
R. Raj ◽  
B. Lakshminarayana
Keyword(s):  
Experimental Investigation ◽  
Decay Rate ◽  
Flat Plate ◽  
Reynolds Stress ◽  
Turbulence Intensity ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Velocity Defect ◽  
Velocity Turbulence ◽  
Far Wake

An analytical and experimental investigation of the near and far wake characteristics of a cascade of airfoils is reported in this paper. The measurement of mean velocity, turbulence intensity and Reynolds stress across the wake at several distances downstream of the cascade indicates that the wake is asymmetrical and this asymmetry is maintained even up to 3/4 chord length. Experiments carried out at three incidences reveal that the decay of the wake defect is strongly dependent on the downstream variation of the wake edge velocity. For a cascade, the decay rate of the wake defect is found to be slower than that of a flat plate, cylinder or symmetrical airfoil (at zero incidence). The level of turbulence and Reynolds stresses are found to be high and some comments are made regarding self-preservation and structure of the flow. Semi-theoretical expressions are given for the wake profile, and decay of the velocity defect, turbulence intensity and Reynolds stress.

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different atmospheric inflow conditions

2016 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Blind Test ◽  
The Mean ◽  
Inlet Conditions ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth Blind test workshop which was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at NTNU's wind tunnel. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within Computational Fluid Dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development up until 9 rotor diameters downstream at three different atmospheric inflow conditions. Besides a spatially uniform inflow field of very low turbulence intensity (TI = 0.23 %) as well as high turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated atmospheric shear flow (TI = 10.1 %). Five different research groups contributed with their predictions using a variety of simulation models, ranging from fully resolved Reynolds Averaged Navier Stokes (RANS) models to Large Eddy Simulations (LES). For the three inlet conditions the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. The prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (Improved Delayed Detached Eddy Simulation) model, however, are consistently managing to provide fairly accurate predictions of the wake turbulence.

Fully-Developed Laminar Flow in Sinusoidal Grooves

2001 ◽  
Vol 123 (3) ◽  
pp. 656-661 ◽  
Author(s):  
Scott K. Thomas ◽  
Richard C. Lykins ◽  
Kirk L. Yerkes
Keyword(s):  
Contact Angle ◽  
Shear Stress ◽  
Volumetric Flow Rate ◽  
Numerical Data ◽  
Mean Velocity ◽  
Constant Property ◽  
Fully Developed Flow ◽  
Vapor Interface ◽  
The Mean ◽  
Poiseuille Number

The flow of a constant property fluid through a sinusoidal groove has been analyzed. A numerical solution of the conservation of mass and momentum equations for fully developed flow is presented. The mean velocity, volumetric flow rate, and Poiseuille number are presented as functions of the groove geometry, meniscus contact angle, and shear stress at the liquid-vapor interface. In addition, a semi-analytical solution for the normalized mean velocity in terms of the normalized shear stress at the meniscus is shown to agree with the numerical data quite well.

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