Mixing Enhancement by Using Turbulent Jets

2014 ◽  
Author(s):  
Hariyo P. S. Pratomo
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Axial Velocity ◽  
Radial Profile ◽  
Intermittent Flow ◽  
Pulsed Jets ◽  
Pulsed Jet ◽  
Air Jet ◽  
Radial Profiles ◽  
Lower Reynolds Number

Experimental results of a fully pulsed subsonic air jet issuing into the still surrounding air are reported in this paper. The intermittent flow containing a period of no flow between pulses due to the mechanically excitation was gauged by a single wire hot-wire anemometer operated in a constant temperature mode. A range of the Reynolds and Strouhal numbers of 1 × 104 < Re < 4 × 104 and 0.0064 < St < 0.0076 respectively was used to define the jets. Results of the traverse measurement agreed with earlier findings demonstrating strong effects of the excitation on the radial profiles of the mean axial velocity of the jet. Within the parameter ranges investigated, the pulsed jets were found to be significantly more spreading than steady jets. A less dispersive pulsed jet, however, appeared at a higher jet exit velocity. Strikingly, contradictory trends in the jet growth and entrainment at the higher and lower Reynolds number were seen as the lower Reynolds number does not produce a widening radial profile as a result of the increasing Strouhal number. From the axial measurements, the pulsed jets were characterized by the pulsed dominated- and high turbulence steady jet region in which their existences heavily relied on the magnitudes of the controlled parameters. A less fluctuating pulsed jet associated with the reduced magnitudes of aggregate turbulence intensity and relative turbulence energy however, appeared at an increased Strouhal number. Comparative studies with the existing results of non-circular orifice jets i.e cruciform, elliptic, and triangular jets are also reported to display the decay rates of centerline axial velocity and the spreading rates of the jets which benefit for the practical purposes.

scholarly journals The Dependence of Flue Pipe Airflow Parameters on the Proximity of an Obstacle to the Pipe’s Mouth

Sensors ◽  
2021 ◽  
Vol 22 (1) ◽  
pp. 10
Author(s):  
Damian Węgrzyn ◽  
Piotr Wrzeciono ◽  
Alicja Wieczorkowska
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Fundamental Frequency ◽  
Coming Out ◽  
Measuring Instruments ◽  
Air Jet ◽  
The Relationship

This paper describes the influence of the presence of an obstacle near the flue pipe’s mouth on the air jet, which directly affects the parameters of the sound generated by the flue pipe. Labial pipes of the most common types of mouth were tested. The method of interval calculus was used instead of invasive measuring instruments. The obtained results prove that the proximity of an obstacle affects the sound’s fundamental frequency, as the airflow speed coming out of the flue pipe’s mouth changes. The relationship between the airflow speed, the value of the Reynolds number, and the Strouhal number was also established. The thesis of the influence of the proximity of an obstacle on the fundamental frequency of the sound of a flue pipe was generalized, and formulas for calculating the untuning of the sound of the pipe were presented for various types of mouth.

An experimental study of an axisymmetric turbulent pulsed air jet

2009 ◽  
Vol 631 ◽  
pp. 23-63 ◽  
Author(s):  
I. CHOUTAPALLI ◽  
A. KROTHAPALLI ◽  
J. H. ARAKERI
Keyword(s):  
Experimental Study ◽  
Strouhal Number ◽  
Nozzle Exit ◽  
Momentum Flux ◽  
Vortex Rings ◽  
Distinct Region ◽  
Pulsed Jet ◽  
Air Jet ◽  
Random Components ◽  
High Reynolds

An experimental study is carried out to elucidate the structure of a high Reynolds number (~105) turbulent pulsed jet. Particle image velocimetry measurements showed that the near flow field is dominated by a series of vortex rings with jet-like flows in between. The data show that the vortex rings convect at nearly constant speed of 0.6Uj(Uj: mean jet exit velocity) and the spacing between the rings assumes a value of about 0.6/St(St: Strouhal number=fd/Uj, wherefis the pulsing frequency anddis the nozzle exit diameter). With increasing Strouhal number, the rings are closely spaced and the flow tends to assume a steady jet character at five diameters downstream of the nozzle exit. At lower Strouhal numbers there is a distinct region of jet flow in between the rings. Many of the global characteristics, entrainment, mass and momentum flux are essentially determined by the strength and spacing of the rings which, in turn, depend onSt. We show that the increase in momentum is due to both increased momentum flux and overpressure at the exit in accordance with Krueger & Gharib (AIAA J., vol. 43 (4), 2005, p. 792). This increase in momentum comes at the expense of higher energy required to produce the jet. We also present results of organized and random components of the fluctuations and production of the random turbulence in a pulsed jet. The two regions of dominant turbulence production are identified with the ring and the trailing jet shear layers.

Heat transfer of multi-slot nozzle air jet impingement with different Reynolds number

2020 ◽  
pp. 116470
Author(s):  
Jinqi Zhu ◽  
Ruifeng Dou ◽  
Ye Hu ◽  
Shixing Zhang ◽  
Xuyun Wang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Slot Nozzle ◽  
Air Jet

Mixing of an Acoustically Excited Air Jet With a Confined Hot Crossflow

1992 ◽  
Vol 114 (1) ◽  
pp. 46-54 ◽  
Author(s):  
P. J. Vermeulen ◽  
P. Grabinski ◽  
V. Ramesh
Keyword(s):  
Strouhal Number ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Mixing Zone ◽  
Wake Region ◽  
Mixing Processes ◽  
Jet Mixing ◽  
Air Jet ◽  
Percent Increase ◽  
Jet Structure

The mixing of an acoustically pulsed air jet with a confined hot crossflow has been assessed by temperature profile measurements. These novel experiments were designed to examine the effects of acoustic driver power and Strouhal number on jet structure, penetration, and mixing. The results showed that excitation produced strong changes in the measured temperature profiles. This resulted in significant increases in mixing zone size, penetration (at least 100 percent increase), and mixing, and the length to achieve a given mixed state was shortened by at least 70 percent. There was strong modification to the jet-wake region. The increase in jet penetration and mixing was saturating near 90 W, the largest driving power tested. The jet response as determined by penetration and mixing was optimum at a Strouhal number of 0.27. Overall, pulsating the jet flow significantly improved the jet mixing processes in a controllable manner.

Strouhal Number for VIV Excitation of Long Slender Structures

2018 ◽  
Author(s):  
Andrew E. Potts ◽  
Douglas A. Potts ◽  
Hayden Marcollo ◽  
Kanishka Jayasinghe
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Degrees Of Freedom ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Shedding Frequency ◽  
Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

Strouhal number of flat and flapped plates at moderate Reynolds number and different angles of attack: experimental data

2018 ◽  
Vol 230 (1) ◽  
pp. 333-349 ◽  
Author(s):  
Ali Bakhshandeh Rostami ◽  
Mohammad Mobasheramini ◽  
Antonio Carlos Fernandes
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Moderate Reynolds Number

scholarly journals Precessional instability of a fluid cylinder

2011 ◽  
Vol 666 ◽  
pp. 104-145 ◽  
Author(s):  
ROMAIN LAGRANGE ◽  
PATRICE MEUNIER ◽  
FRANÇOIS NADAL ◽  
CHRISTOPHE ELOY
Keyword(s):  
Reynolds Number ◽  
Nonlinear Effects ◽  
Intermittent Flow ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Weakly Nonlinear Theory ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Precessional Motion ◽  
Weakly Nonlinear Model

In this paper, the instability of a fluid inside a precessing cylinder is addressed theoretically and experimentally. The precessional motion forces Kelvin modes in the cylinder, which can become resonant for given precessional frequencies and cylinder aspect ratios. When the Reynolds number is large enough, these forced resonant Kelvin modes eventually become unstable. A linear stability analysis based on a triadic resonance between a forced Kelvin mode and two additional free Kelvin modes is carried out. This analysis allows us to predict the spatial structure of the instability and its threshold. These predictions are compared to the vorticity field measured by particle image velocimetry with an excellent agreement. When the Reynolds number is further increased, nonlinear effects appear. A weakly nonlinear theory is developed semi-empirically by introducing a geostrophic mode, which is triggered by the nonlinear interaction of a free Kelvin mode with itself in the presence of viscosity. Amplitude equations are obtained coupling the forced Kelvin mode, the two free Kelvin modes and the geostrophic mode. They show that the instability saturates to a fixed point just above threshold. Increasing the Reynolds number leads to a transition from a steady saturated regime to an intermittent flow in good agreement with experiments. Surprisingly, this weakly nonlinear model still gives a correct estimate of the mean flow inside the cylinder even far from the threshold when the flow is turbulent.

Jet-to-Plate Distance Effect on Heat Transfer From a Flat Plate to an Impinging Jet at Various Reynolds Numbers

2012 ◽  
Author(s):  
Patricia Streufert ◽  
Terry X. Yan ◽  
Mahdi G. Baygloo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Air Jet ◽  
Plate Distance

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.

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