On the Development of Incompressible Round and Equilateral Triangular Jets Due to Reynolds Number Variation

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Reynolds Stresses ◽  
Turbulent Structures ◽  
Potential Core ◽  
Round Jets ◽  
Flat Side ◽  
Reynolds Number Effects ◽  
Velocity Decay ◽  
Number Variation

The aim of this study is to examine the effects of Reynolds number (Re = 6000–20,000) on mean and turbulent quantities as well as turbulent structures in the near and intermediate regions of equilateral triangular and round sharp contraction jets. The results show shorter potential core length, faster growth of turbulence intensity, and faster diffusion of turbulent structures to the centerline of the triangular jets, implying enhanced mixing in the near field of these jets. On the other hand, the velocity decay and jet spread rates are higher in the round jets. The obtained data in the round jets show that the jet at Re = 6000 has the most effective mixing, while an increase in Reynolds number reduces the mixing performance. In the triangular jets, however, no Reynolds number effects were observed on the measured quantities including the length of the potential core, the decay and spread rates, the axis-switching locations, and the value of the Reynolds number. In addition, the asymptotic values of the relative turbulence intensities on the jet centerline are almost independent of the Reynolds number and geometry. The ratios of transverse and spanwise Reynolds stresses are unity except close to the jet exit where the flow pattern in the major plane of the triangular jet deflects toward the flat side. Proper orthogonal decomposition (POD) analysis revealed that turbulent structures in minor and major planes have identical fractional kinetic energy. The integral length scales increased linearly with the streamwise distance with identical slope for all the test cases.

Experimental-Numerical Analysis of Turbulent Incompressible Isothermal Jets

2017 ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Turbulent Transport ◽  
Reynolds Numbers ◽  
Nozzle Geometry ◽  
System Response ◽  
Potential Core ◽  
Turbulence Structures ◽  
Round Jets ◽  
Core Length

An experimental investigation was conducted to study the effects of Reynolds number on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free equilateral triangular and round jets issuing from modified contoured nozzles (nozzles with sharp linear contractions). Detailed velocity measurements were made using a particle image velocimetry at Reynolds numbers of 6000, 10000, 13800 and 20000. Computational fluid dynamics (CFD) was also applied to understand the flow behaviors in different Reynolds numbers. We applied standard k-ε turbulence model in an axisymmetric domain to conduct the numerical simulation of the round jet cases. The potential core length was the system response quantity to evaluate our simulation against the experimental results. The geometrical comparative study shows enhanced mixing in the near field of the triangular jets compared to the round jets, regardless of Reynolds number. This conclusion is supported by shorter potential core length and faster growth of turbulence intensity on the centerline of the triangular jets. The obtained data in the round jets exhibit that the jet at the lowest Reynolds number has the most effective mixing with the ambient fluid, while increase in Reynolds number reduces the mixing performance. In the triangular jets almost there is no Reynolds number effect on the measured quantities including the length of the potential core, the decay rate and the axis-switching locations. The results revealed that the asymptotic values of the turbulence intensities on the jet centerline are not only independent of the Reynolds number but also they are the same for both the round and triangular jets. Due to the specific shape of the triangular nozzle, a skewed flow pattern is observed in the near field region in the major plane while the jet is absolutely symmetric in the minor plane. The turbulence structures in all the jets studied become larger as streamwise distance increases, while there is no considerable Reynolds number or nozzle geometry effects on the size of the structures on the jet centerline.

Experiments on the flow and acoustic properties of a moderate-Reynolds-number supersonic jet

1982 ◽  
Vol 116 ◽  
pp. 123-156 ◽  
Author(s):  
T. R. Troutt ◽  
D. K. Mclaughlin
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Near Field ◽  
Acoustic Properties ◽  
Generation Model ◽  
Initial Growth ◽  
Noise Generation ◽  
Mean Flow ◽  
Potential Core ◽  
Moderate Reynolds Number

An experimental investigation of the flow and acoustic properties of a moderate-Reynolds-number (Re = 70000), Mach number M = 2·1, axisymmetric jet has been performed. These measurements extended the experimental studies conducted previously in this laboratory to a higher-Reynolds-number regime where the flow and acoustic processes are considerably more complex. In fact, mean-flow and acoustic properties of this jet were determined to be closely comparable to published properties of high-Reynolds-number jets.The major results of the flow-field measurements demonstrate that the jet shear annulus is unstable over a broad frequency range. The initial growth rates and wavelengths of these instabilities as measured by a hot wire were found to be in reasonable agreement with linear stability theory predictions. Also, in agreement with subsonic-jet results, the potential core of the jet was found to be most responsive to excitation at frequencies near a Strouhal number of S = 0·3. The overall development of organized disturbances around S = 0·2 seems to agree in general with calculations performed using the instability theory originally developed by Morris and Tam.The acoustic near field was characterized in terms of sound-pressure level and directivity for both natural and excited (pure-tone) jets. In addition, propagation direction and azimuthal character of dominant spectral components were also measured. It was determined that the large-scale flow disturbances radiate noise in a directional pattern centred about 30° from the jet axis. The noise from these disturbances appears from simple ray tracing to be generated primarily near the region of the jet where the coherent fluctuations saturate in amplitude and begin to decay. It was also determined that the large-scale components of the near-field sound are made up predominately of axisymmetric (n = 0) and helical (n = ±1) modes. The dominant noise-generation mechanism appears to be a combination of Mach-wave generation and a process associated with the saturation and disintegration of the large-scale instability. Finally, the further development of a noise-generation model of the instability type appears to hold considerable promise.

Reynolds number effects in the near-field of a turbulent square jet

2015 ◽  
Vol 61 ◽  
pp. 249-258 ◽  
Author(s):  
A. Ghasemi ◽  
V. Roussinova ◽  
Ram Balachandar ◽  
R.M. Barron
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Reynolds Number Effects

Reynolds Number Effects on the Calibration of a Subminiature Four Hole Three Dimensional Wake Probe

2014 ◽  
Author(s):  
Gajanan Tatpatti ◽  
Sitaram Nekkanti
Keyword(s):  
Reynolds Number ◽  
Practical Importance ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Reynolds Number Effects ◽  
Number Variation ◽  
Yaw Angle ◽  
Nominal Dimension ◽  
Calibration Coefficients

A subminiature four-hole probe is designed and fabricated to be used specifically to measure wakes that occur in turbomachinery and its components. The probe has a nominal measuring area of 0.413 mm2 and has a nominal dimension of 0.254 mm in the direction across the wake downstream the trailing edge of a blade thus minimizing spatial and flow gradient errors in this direction. The non-nulling calibration of the probe is carried out in the pitch and yaw angle range of ±30° at 5° interval. The probe is calibrated at four different velocities, viz., 10 m/s, 20 m/s, 30 m/s and 50 m/s corresponding to the probe thickness Reynolds numbers in the range of 159 to 794 with objective of finding the effect of Reynolds number on the calibration coefficients. In addition to these, for practical importance the actual changes in yaw angle, pitch angle, static pressure, total pressure and velocity magnitude due to Reynolds number variation has been investigated. A method to incorporate the effect of Reynolds number for minimum interpolation errors is described.

Effects of Reynolds Number on Turbulent Characteristics of Surface Jet

2016 ◽  
Author(s):  
M. S. Rahman ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Reynolds Shear Stress ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
Potential Core ◽  
Turbulent Characteristics ◽  
Reynolds Number Effects ◽  
Surface Jet ◽  
Jet Characteristics

Experimental study was carried out to investigate the Reynolds number effects on surface jet characteristics. The surface jet was produced using orifice nozzle with offset height ratio of 2. Six different Reynolds numbers ranging from 2300 to 11900 were investigated. Potential core region of the jet decreased with Reynolds number up to the Reynolds number of 5500. Reattachment point was sensitive to Reynolds number within the range of the present study. The maximum velocity decay and jet spread were nearly independent of Reynolds number. The streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress distribution along surface-normal direction were affected by the free surface and showed Reynolds number independency at the Reynolds numbers beyond 5500.

Reynolds Number Effects on the Characteristics of Twin Jets Interacting With a Free Surface

2016 ◽  
Author(s):  
M. S. Rahman ◽  
E. M. Nabess ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
Free Jet ◽  
Turbulent Characteristics ◽  
Reynolds Number Effects ◽  
Velocity Decay ◽  
Twin Jets ◽  
Velocity Measuring

The effects of Reynolds number on the turbulent characteristics of surface attaching twin jet were investigated experimentally. Particle image velocimetry was used as the velocity measuring technique. Twin jets were produced using square orifice nozzle pair. The Reynolds numbers based on the jet exit velocity and the nozzle width were varied from 2620 to 7900. The offset height ratio was fixed at 2 during the experiments. The jet reattached to the free surface and the reattachment length decreased with increase of Reynolds number. Free surface showed significant effect on the maximum velocity decay, jet spread, streamwise mean velocity distribution, Reynolds shear and normal stresses in the upper jet. The decay and spread rate of the lower jet was comparable to free jet due to less confinement effect. The mean and turbulent quantities reported herein were nearly independent of Reynolds number. Proper orthogonal decomposition was performed to reveal the dynamic role of the energetic structures embedded within the flow.

Reynolds Number Effects in Cascades and Axial Flow Compressors

1964 ◽  
Vol 86 (3) ◽  
pp. 236-242
Author(s):  
J. H. Horlock ◽  
R. Shaw ◽  
D. Pollard ◽  
A. Lewkowicz
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Guide Vane ◽  
Axial Flow ◽  
Compressor Cascade ◽  
Compressor Blades ◽  
Laminar Separation ◽  
Reynolds Number Effects ◽  
Number Variation ◽  
Flow Compressor

A series of tests on guide vane and compressor cascades is reported. The Reynolds number was varied in the guide vane cascade tests, and the Reynolds number and the cascade aspect ratio were varied in the compressor cascade tests. The substantial laminar separation observed in the compressor cascades at high aspect ratio (and low Reynolds number) was suppressed in the cascade tests at low aspect ratio, 2:1. Effects of Reynolds number variation on the performance of a single stage axial flow compressor are also given, and compared with predictions of performance using the cascade tests. Calculations of laminar separation points agree quite well with the experimental observations. It appears that transition due to laminar boundary layer instability is unlikely to occur on compressor blades, in the normal operating range of Reynolds number.

LES of an Isothermal High Reynolds Number Turbulent Round Jet

2014 ◽  
Author(s):  
Sasan Salkhordeh ◽  
Sagnik Mazumdar ◽  
D. Tyler Landfried ◽  
Anirban Jana ◽  
Mark L. Kimber
Keyword(s):  
Reynolds Number ◽  
Computational Model ◽  
Order Statistics ◽  
High Reynolds Number ◽  
Flow Profile ◽  
Reynolds Stresses ◽  
Potential Core ◽  
Turbulent Fluctuations ◽  
Eddy Simulation ◽  
High Reynolds

Round turbulent jets have fundamental relevance in various engineering applications and are also of practical interest in the lower plenum of the High Temperature Gas-Cooled Reactors (HTGR). In the direction of developing an experimentally validated computational model for the lower plenum flow, a Large Eddy Simulation (LES) of an isothermal high Reynolds number confined jet has been studied. The enclosure within which the jet is confined has been selected large enough so that the results can be compared with well-known experimental studies available in the literature. The Sub-Grid Scale (SGS) model chosen within the LES framework is a variant of the dynamic Smagorinsky model. The effect of inlet flow profile and turbulent fluctuations on the evolution of the jet have been analyzed in detail. The mesh distribution was found to play a vital role in the magnitude and profile of the Reynolds stresses throughout the computational domain. Additionally, it is critically important to properly specify the turbulent fluctuations at the jet inlet in order to accurately predict key near field characteristics such as the potential core length. We perform a separate discrete eddy simulation of the flow in the nozzle upstream of the jet inlet to accurately determine the inlet turbulent fluctuations. The LES results of this study include both first order statistics (mean velocity field) and second order statistics (components of the Reynolds stresses). For each of these quantities, excellent agreement is obtained between our LES predictions and experimental measurements. This research lays the groundwork needed to develop a high-fidelity computational model of the complex mixing flow in the HTGR lower plenum.

scholarly journals On noise generation in low Reynolds number temporal round jets at a Mach number of 0.9

2018 ◽  
Vol 859 ◽  
pp. 1022-1056 ◽  
Author(s):  
Christophe Bogey
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Acoustic Waves ◽  
Mixing Layer ◽  
Noise Generation ◽  
Noise Component ◽  
Potential Core ◽  
Lower Velocity ◽  
Round Jets ◽  
Jet Axis

Two temporally developing isothermal round jets at a Mach number of 0.9 and Reynolds numbers of 3125 and 12 500 are simulated in order to investigate noise generation in high-subsonic jet flows. Snapshots and statistical properties of the flow and sound fields, including mean, root-mean-square and skewness values, spectra and auto- and cross-correlations of velocity and pressure, are presented. The jet at a Reynolds number of 12 500 develops more rapidly, exhibits more fine turbulent scales and generates more high-frequency acoustic waves than the other. In both cases, however, when the jet potential core closes, mixing-layer turbulent structures intermittently intrude on the jet axis and strong low-frequency acoustic waves are emitted in the downstream direction. These waves are dominated by the axisymmetric mode and are significantly correlated with centreline flow fluctuations. These results are similar to those obtained at the end of the potential core of spatially developing jets. They suggest that the mechanism responsible for the downstream noise component of these jets also occurs in temporal jets, regardless of the Reynolds number. This mechanism is revealed by averaging the flow and pressure fields of the present jets using a sample synchronization with the minimum values of centreline velocity at potential-core closing. A spot characterized by a lower velocity and a higher level of vorticity relative to the background flow field is found to develop in the interfacial region between the mixing layer and the potential core, to strengthen rapidly and reach a peak intensity when arriving on the jet axis, and then to break down. This is accompanied by the growth and decay of a hydrodynamic pressure wave, propagating at a velocity which, initially, is close to 65 per cent of the jet velocity and slightly increases, but quickly decreases after the collapse of the high-vorticity spot in the flow. During that process, sound waves are radiated in the downstream direction.

Sign in / Sign up

Export Citation Format

Share Document