A Counter-Rotating Pair of Turbulent Jets

1973 ◽  
Vol 95 (2) ◽  
pp. 207-213 ◽  
Author(s):  
B. D. Pratte ◽  
J. F. Keffer
Keyword(s):  
Turbulent Jets ◽  
Spreading Rate ◽  
Mean Flow ◽  
Linear Superposition ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Free Jet ◽  
Intensity Measurements ◽  
Limited Application ◽  
Sectional Shape

A study has been made of a pair of swirling jets having opposite rotation. Mean flow and turbulent intensity measurements were obtained and characteristics of the spreading rate determined. The swirling component of mean velocity decayed rapidly in the streamwise direction and by about 35 dia, the flow had most of the characteristics of the single, free jet without swirl. A linear superposition was found to be of limited application near the jet source but gave reasonable results in the developed flow downstream. It was observed that the major and minor axes of the flow, defining the asymmetrical cross-sectional shape, underwent a reversal of position as the flow progressed downstream.

scholarly journals Analytical Model of a Multi-Step Straightening Process for Linear Guideways Considering Neutral Axis Deviation

Symmetry ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 316 ◽  
Author(s):  
Yongquan Zhang ◽  
Hong Lu ◽  
He Ling ◽  
Yang Lian ◽  
Mingtian Ma
Keyword(s):  
Analytical Model ◽  
Cross Section ◽  
Predictive Accuracy ◽  
Neutral Axis ◽  
Longitudinal Stress ◽  
Linear Superposition ◽  
Element Analysis ◽  
Cross Sectional ◽  
The Cross ◽  
Sectional Shape

The cross-sectional shape of a linear guideway has been processed before the straightening process. The cross-section features influence not only the position of the neutral axis, but also the applied and residual stresses along the longitudinal direction, especially in a multi-step straightening process. This paper aims to present an analytical model based on elasto-plastic theory and three-point reverse bending theory to predict straightening stroke and longitudinal stress distribution during the multi-step straightening process of linear guideways. The deviation of the neutral axis is first analyzed considering the asymmetrical features of the cross-section. Owing to the cyclic loading during the multi-step straightening process, the longitudinal stress curves are then calculated using the linear superposition of stresses. Based on the cross-section features and the superposition of stresses, the bending moment is corrected to improve the predictive accuracy of the multi-step straightening process. Finite element analysis, as well as straightening experiments, have been performed to verify the applicability of the analytical model. The proposed approach can be implemented in the multi-step straightening process of linear guideways with similar cross-sectional shape to improve the straightening accuracy.

PIV measurements in a twin-jet STOVL fountain flow

2005 ◽  
Vol 109 (1100) ◽  
pp. 439-449 ◽  
Author(s):  
P. M. Cabrita ◽  
A. J. Saddington ◽  
K. Knowles
Keyword(s):  
Pressure Ratio ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Nozzle Pressure Ratio ◽  
Mean Velocity ◽  
Fountain Flow ◽  
Image Velocimetry ◽  
Nozzle Pressure

Abstract Mean velocity and first order turbulence measurements were obtained from a three-dimensional upwash fountain flow generated by the impingement of two compressible axisymmetric turbulent jets onto a normal plane. The jet impingement area and fountain formation regions were examined with data obtained through the use of particle image velocimetry. Seven configurations with different nozzle pressure ratios were considered to ascertain the influence of jet compressibility on the fountain development. Results indicate that the mixing of the fountain is dependent on the nozzle pressure ratio, leading to an increase in the fountain spreading rate with increase in nozzle pressure ratio.

Assessment of the SSG Pressure-Strain Model in Free Turbulent Jets With and Without Swirl

1996 ◽  
Vol 118 (4) ◽  
pp. 800-809 ◽  
Author(s):  
B. A. Younis ◽  
T. B. Gatski ◽  
C. G. Speziale
Keyword(s):  
Linear Models ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Energy Dissipation Rate ◽  
Quadratic Model ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Plane Jet ◽  
Strain Model

Data from free turbulent jets both with and without swirl are used to assess the performance of the pressure-strain model of Speziale, Sarkar and Gatski, which is quadratic in the Reynolds stresses. Comparative predictions are also obtained with the two versions of the Launder, Reece and Rodi model, which are linear in the same terms. All models are used as part of a complete second-order closure based on the solution of differential transport equations for each nonzero component of uiuj together with an equation for the scalar energy dissipation rate. For nonswirling jets, the quadratic model underestimates the measured spreading rate of the plane jet but yields a better prediction for the axisymmetric case without resolving the plane jet/round jet anomaly. For the swirling axisymmetric jet, the same model accurately reproduces the effects of swirl on both the mean flow and the turbulence structure in sharp contrast with the linear models which yield results that are in serious error. The reasons for these differences are discussed.

Continuous monitoring of cardiac output in neonates using an intra-aortic Doppler probe

1999 ◽  
Vol 9 (1) ◽  
pp. 42-48 ◽  
Author(s):  
P Ewert ◽  
N Nagdyman ◽  
T Fischer ◽  
L Gortner ◽  
PE Lange
Keyword(s):  
Cardiac Output ◽  
Continuous Monitoring ◽  
Practical Method ◽  
Preterm Neonates ◽  
Mean Flow ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Descending Aorta ◽  
Doppler Probe ◽  
Considerable Benefit

AbstractContinuous monitoring of cardiac output in neonates would be of considerable benefit but, as yet, there is no practical method to achieve this aim. We have now evaluated the feasibility of using an intra-aortic Doppler probe. We introduced a pulsed Doppler probe of 0.46 mm diameter via the umbilical artery in two term and four preterm neonates. Indications in all patients for umbilical arterial catheter is always an unstable cardiopulmonary state. Body weights were between 770 and 3340 g. Velocities of blood flow in the thoracic aorta were continuously recorded to estimate cardiac output on-line for 12 h. No complications were encountered. It proved possible to derive high-quality Doppler curves. The received Doppler signal was stable but it proved sensitive to pathophysiologic changes in flow. Mean velocity of flow in the descending aorta was 16.4 cm/s (range 13.3_19.0 cm/s). We quantified flow by multiplying the mean velocity of the flow by the cross-sectional area of the descending aorta. Calculated mean flow was 135 ml/kg/min (range 111–179 ml/kg/min). These values are consistent with those measured by transcutaneous Doppler, and it should not be raised by left-to-right ductal shunts. This pilot study proved the feasibility of continuous monitoring of cardiac output. The technique should prove of great value in those infants with unstable circulatory conditions, and can be used even in infants with extremely low birth weights.

Compressibility Effects in Turbulent Subsonic Jets

2003 ◽  
Author(s):  
Zhexuan Wang ◽  
Yiannis Andreopoulos
Keyword(s):  
Mach Number ◽  
Pressure Fluctuations ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Jet Flows ◽  
Mean Velocity ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Mach Numbers ◽  
Response Pressure

The behavior of compressible turbulent jets issuing in still air in the absence of shock waves has been investigated at three different subsonic Mach numbers, 0.3, 0.6 and 0.9. Helium, nitrogen and krypton gases were used to generate the jet flows and investigate the density effects on the structure of turbulence. Particle Image Velocimetry and high-frequency response pressure transducers were used to obtain velocity, Mach number inside the flow field. The decay of the Mach number at the centerline of the axisymmetric jets increases with increasing the initial Mach number at the exit of the flow for all jets. The decay of mean velocity at the centerline of the jets is also higher at higher exit Mach numbers. However, the velocity non-dimensionalized by the exit velocity seems to decrease faster at low exit Mach numbers suggesting a reduced mixing with increasing the exit flow Mach numbers. Helium jets were found to have the largest spreading rate among the three different gas jets used in the present investigation, while krypton had the lowest spreading rate. Total pressure fluctuations appear to decrease with increasing exit flow Mach numbers. Unusually high turbulence intensities were measured in helium jets issuing in still air.

Offset Turbulent Jets in Low-Aspect Ratio Cavities

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
C. Nath ◽  
S. I. Voropayev ◽  
D. Lord ◽  
H. J. S. Fernando
Keyword(s):  
Aspect Ratio ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Optimal Operation ◽  
Mean Velocity ◽  
Mixing Depth ◽  
Low Aspect Ratio ◽  
Image Velocimetry ◽  
D Values ◽  
Petroleum Reserves

The flow induced by a round turbulent offset jet in a low-aspect ratio cylinder is investigated experimentally, with applications to degassing of U.S. Strategic Petroleum Reserves (SPR). Particle image velocimetry and flow visualization are used for flow diagnostics. The measurements include the jet penetration (mixing) depth l, jet spreading rate, and the mean velocity/vorticity fields for different offset positions Δ. With the introduction of offset, the flow patterns change drastically. For 0 < Δ/D < 0.2 the jet deflects toward the wall while precessing (as in the axisymmetric case), for 0.2 < Δ/D < 0.4 the jet hugs the wall but with an oscillating tail, and for 0.45 < Δ/D the jet appears as a wall jet. In all cases, the jet is destroyed at a certain distance (mixing or penetration depth) from the origin. This mixing depth takes its lowest value for 0 < Δ/D < 0.2, with l ≈ (3.2–3.6)D, becomes maximum at Δ/D = 0.4 with l ≈ 5.2D, and drops to l ≈ 4.5D when the jet is close to the wall. Recommendations are made for suitable Δ/D values for optimal operation of SPR degassing.

On the cross-sectional shape of the cellulose crystallites in the tunicate Halocynthia papillosa

1990 ◽  
Vol 48 (3) ◽  
pp. 566-567
Author(s):  
J.-F. Revol ◽  
Y. Van Daele ◽  
F. Gaill
Keyword(s):  
Contrast Imaging ◽  
Animal Kingdom ◽  
Bright Field ◽  
Field Mode ◽  
Cross Sectional ◽  
Ultrathin Sections ◽  
The Cross ◽  
Sectional Shape ◽  
Valonia Ventricosa ◽  
C Nmr

The only form of cellulose which could unequivocally be ascribed to the animal kingdom is the tunicin that occurs in the tests of the tunicates. Recently, high-resolution solid-state l3C NMR revealed that tunicin belongs to the Iβ form of cellulose as opposed to the Iα form found in Valonia and bacterial celluloses. The high perfection of the tunicin crystallites led us to study its crosssectional shape and to compare it with the shape of those in Valonia ventricosa (V.v.), the goal being to relate the cross-section of cellulose crystallites with the two allomorphs Iα and Iβ.In the present work the source of tunicin was the test of the ascidian Halocvnthia papillosa (H.p.). Diffraction contrast imaging in the bright field mode was applied on ultrathin sections of the V.v. cell wall and H.p. test with cellulose crystallites perpendicular to the plane of the sections. The electron microscope, a Philips 400T, was operated at 120 kV in a low intensity beam condition.

Automated 3D measurement of fiber cross section morphology in handsheets

2012 ◽  
Vol 27 (2) ◽  
pp. 264-269 ◽  
Author(s):  
Christian Lorbach ◽  
Ulrich Hirn ◽  
Johannes Kritzinger ◽  
Wolfgang Bauer
Keyword(s):  
Image Analysis ◽  
Cross Section ◽  
Cross Sections ◽  
Image Plane ◽  
3D Measurement ◽  
Cross Sectional ◽  
Fiber Cross Section ◽  
Fiber Wall ◽  
Sectional Shape ◽  
Cross Section Geometry

Abstract We present a method for 3D measurement of fiber cross sectional morphology from handsheets. An automated procedure is used to acquire 3D datasets of fiber cross sectional images using an automated microtome and light microscopy. The fiber cross section geometry is extracted using digital image analysis. Simple sample preparation and highly automated image acquisition and image analysis are providing an efficient tool to analyze large samples. It is demonstrated that if fibers are tilted towards the image plane the images of fiber cross sections are always larger than the true fiber cross section geometry. In our analysis the tilting angles of the fibers to the image plane are measured. The resulting fiber cross sectional images are distorted to compensate the error due to fiber tilt, restoring the true fiber cross sectional shape. We use an approximated correction, the paper provides error estimates of the approximation. Measurement results for fiber wall thickness, fiber coarseness and fiber collapse are presented for one hardwood and one softwood pulp.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

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