Reynolds Number Effect on the Flow Demeanorin a Vertical Circular Free Turbulent Jet with Cross Flow

2021 ◽  
Vol 409 ◽  
pp. 158-178
Author(s):  
Abdelkader Feddal ◽  
Abbes Azzi ◽  
Ahmed Zineddine Dellil
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Turbulence Models ◽  
Turbulent Jets ◽  
Turbulent Jet ◽  
Low Velocity ◽  
Transverse Current ◽  
Ansys Cfx ◽  
The Cross ◽  
Two Jets

This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 104, 10 104 and 20 104 .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.

Passive scalar dispersion and mixing in a turbulent jet

1995 ◽  
Vol 292 ◽  
pp. 1-38 ◽  
Author(s):  
Chenning Tong ◽  
Z. Warhaft
Keyword(s):  
Reynolds Number ◽  
Cross Correlation ◽  
Thermal Field ◽  
Temperature Fluctuations ◽  
Passive Scalar ◽  
Turbulent Jet ◽  
Grid Turbulence ◽  
Far Field ◽  
The Cross ◽  
Heated Jet

The dispersion and mixing of passive scalar (temperature) fluctuations is studied in a turbulent jet. The temperature fluctuations were produced by heated fine wire rings placed axisymmetrically in the flow. Typically the ring diameters were of the same order as the jet, Dj, and they were placed in the self-similar region. However, other initial conditions were studied, including a very small diameter ring used to approximate a point source. Using a single ring to study dispersion (which is analogous to placing a line source in a planar flow such as grid turbulence), it was found that the intense local thermal field close to the ring disperses and fills the whole jet in approximately 1.5 eddy turnover times. Thereafter the thermal field evolves in the same way as for the traditional heated jet experiments. Two heated rings were used to study the mixing of two independently introduced scalar fields. Here an inference method (invoking the principle of superposition) was used to determine the evolution of the cross-correlation coefficient, ρ, and the segregation parameter, α, as well as the coherence and co-spectrum. While initially strongly dependent on ring locations and spacing, ρ and α reached asymptotic values of 1 and 0.04, respectively, also in about 1.5 eddy turnover times. These results are contrasted with mixing and dispersion in grid turbulence where the evolution is slower. Measurements in the far field of the jet (where ρ = 1) of the square of the scalar derivative conditioned on the scalar fluctuation itself, as well as other conditional statistics, showed strong dependence on the measurement location, as well as the direction in which the derivative was determined. The cross-correlation between the square of the scalar derivative and the signal showed a clear Reynolds-number trend, decreasing as the jet Reynolds number was varied from 2800 to 18 000. The far-field measurements, using the heated rings, were corroborated by new heated jet experiments.

Double Wall Cooling of an Effusion Plate With Simultaneous Cross Flow and Impingement Jet Array Internal Cooling

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
David Ritchie ◽  
Austin Click ◽  
Phillip M. Ligrani ◽  
Federico Liberatore ◽  
Rajeshriben Patel ◽  
...  
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Stream Flow ◽  
Cross Flow ◽  
Main Stream ◽  
Streamwise Location ◽  
Net Heat Flux ◽  
Contraction Ratio ◽  
The Cross ◽  
Double Wall

Considered is double wall cooling, with full-coverage effusion-cooling on the hot side of the effusion plate, and a combination of impingement cooling and cross flow cooling, employed together on the cold side of the effusion plate. Data are given for a main stream flow passage with a contraction ratio (CR) of 4 for main stream Reynolds numbers Rems and Rems,avg of 157,000–161,000 and 233,000–244,000, respectively. Hot-side measurements (on the main stream flow or hot side of the effusion plate) are presented, which are measured using infrared thermography. Using a transient thermal measurement approach, measured are spatially resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficient. For the same Reynolds number, initial blowing ratio (BR), and streamwise location, increased thermal protection is often provided when the effusion coolant is provided by the cross flow/impingement combination configuration, compared to the cross flow only supply arrangement. In general, higher adiabatic effectiveness values are provided by the impingement only arrangement, relative to the impingement/cross flow combination configuration, when compared at the same Reynolds number, initial BR, and x/de location. Data for one streamwise location of x/de = 60 show that the highest net heat flux reduction line-averaged net heat flux reduction (NHFR) values are produced either by the impingement/cross flow combination configuration or by the impingement only arrangement, depending upon the particular magnitude of BR, which is considered.

scholarly journals Effect of Jet Inclination Angle and Hole Exit Shape on Vortical Flow Structures in Low-Reynolds Number Jet in Cross-Flow

2012 ◽  
Vol 2012 ◽  
pp. 1-7
Author(s):  
Yufeng Yao ◽  
Mohamad Maidi ◽  
Jun Yao
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Inclination Angle ◽  
Qualitative Agreement ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Vortical Flow ◽  
Flow Structures ◽  
Good Qualitative Agreement ◽  
The Cross

Numerical studies have been performed to visualize vortical flow structures emerged from jet cross-flow interactions. A single square jet issuing perpendicularly into a cross-flow was simulated first, followed by two additional scenarios, that is, inclined square jet at angles of 30° and 60° and round and elliptic jets at an angle of 90°, respectively. The simulation considers a jet to cross-flow velocity ratio of 2.5 and a Reynolds number of 225, based on the free-stream flow quantities and the jet exit width in case of square jet or minor axis length in case of elliptic jet. For the single square jet, the vortical flow structures simulated are in good qualitative agreement with the findings by other researchers. Further analysis reveals that the jet penetrates deeper into the cross-flow field for the normal jet, and the decrease of the jet inclination angle weakens the cross-flow entrainment in the near-wake region. For both noncircular and circular jet hole shapes, the flow field in the vicinity of the jet exit has been dominated by large-scale dynamic flow structures and it was found that the elliptic jet hole geometry has maximum “lifted-off” effect among three hole configurations studied. This finding is also in good qualitative agreement with existing experimental observations.

Resonance in Flow-Induced Cable Vibration: Analytical Prediction and Numerical Simulation

2005 ◽  
Author(s):  
M. K. Kwan ◽  
R. R. Hwang ◽  
C. T. Hsu
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Cross Section ◽  
Flow Direction ◽  
Cross Flow ◽  
Transverse Cross Section ◽  
Analytical Prediction ◽  
Water Flows ◽  
Flow Displacement ◽  
The Cross

Flow-induced resonance for a two-end hinged cable under uniform incoming flows is investigated using analytical prediction and numerical simulation. In this study, the fundamental mode is analyzed for simplicity. First, based on a series of physical judgments, the approximate cable trajectory is predicted — the whole cable vibrates as a standing wave, with its locus on the transverse cross-section having a convex “8”-like shape. To find the exact path, however, experiment or numerical simulation is necessary. Hence, a bronze cable at aspect ratio (length/diameter) of 100 under water flows at Reynolds number (based on cable diameter and incoming velocity) of 200 is computed. The result confirms our predictions. Moreover, it is found that the amplitude of the cross-flow displacement is much higher than that of the streamwise displacement, despite the higher streamwise fluid force. As a consequence, energy transfer from fluid to solid is maximized in the cross-flow direction.

scholarly journals Trajectory of a synthetic jet issuing into high-Reynolds-number turbulent boundary layers

2018 ◽  
Vol 856 ◽  
pp. 531-551 ◽  
Author(s):  
Tim Berk ◽  
Nicholas Hutchins ◽  
Ivan Marusic ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
High Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Turbulent Boundary Layers ◽  
Synthetic Jet ◽  
Actuation Frequency ◽  
The Cross ◽  
High Reynolds

Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For some applications, the scaling of the trajectory of the jet with actuation and cross-flow parameters is important. This scaling is investigated for changes in the friction Reynolds number, changes in the velocity ratio (defined as the ratio between the mean jet blowing velocity and the free-stream velocity) and changes in the actuation frequency of the jet. A distinctive aspect of this study is the high-Reynolds-number turbulent boundary layers (up to $Re_{\unicode[STIX]{x1D70F}}=12\,800$) of the cross-flow. To our knowledge, this is the first study to investigate the effect of the friction Reynolds number of the cross-flow on the trajectory of an (unsteady) jet, as well as the first study to systematically investigate the scaling of the trajectory with actuation frequency. A broad range of parameters is varied (rather than an in-depth investigation of a single parameter) and the results of this study are meant to indicate the relative importance of each parameter rather than the exact influence on the trajectory. Within the range of parameters explored, the critical ones are found to be the velocity ratio as well as a non-dimensional frequency based on the jet actuation frequency, the cross-flow velocity and the jet dimensions. The Reynolds number of the boundary layer is shown to have only a small effect on the trajectory. An expression for the trajectory of the jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow.

Numerical Simulation of an Oscillating Cylinder in Cross-Flow at a Reynolds Number of 10,000: Forced and Free Oscillations

2014 ◽  
Author(s):  
Linh Tuan The Nguyen ◽  
Pandeli Temarel
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Turbulence Models ◽  
Numerical Data ◽  
Forced Oscillations ◽  
Free Oscillations ◽  
Ansys Fluent ◽  
Drag And Lift ◽  
Volume Method ◽  
Oscillations Of A Cylinder

In the present work, numerical simulations of flow past a circular cylinder in uniform cross-flow are investigated for three different cases: (i) a stationary cylinder, (ii) forced oscillations of a cylinder and (iii) free oscillations of a cylinder. All three cases were studied using a 2D CFD RANS code, at a Reynolds number Re = 10,000. The method adopted here is based on the Finite Volume Method using the commercial CFD package Ansys Fluent 14 with appropriate turbulence models. Comparisons with available experimental and numerical data, for all cases investigated, show that the simulations capture essential features of the fluid-structure interaction. These comparisons include drag and lift coefficients, Strouhal number, pressure distribution, as well as amplitude of motion and frequency ratio.

Assessment of Low-Re Turbulence Models and Analysis of Turbulent Flow in Porous Media Consisting of Square Cylinders With Different Diameter Ratios

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Alejandro Alonzo-Garcia ◽  
Ana T. Mendoza-Rosas ◽  
Martín A. Díaz-Viera ◽  
Sergio A. Martínez-Delgadillo ◽  
Edgar G. Martínez-Mendoza
Keyword(s):  
Reynolds Number ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Rapid Expansion ◽  
Flow In Porous Media ◽  
Low Velocity ◽  
Flow Parameters ◽  
Square Cylinders ◽  
Infinite Array ◽  
Frictional Forces

Abstract This paper presents a comparative study of volume average predictions between low-Reynolds-number (LRN) turbulence models: Abe–Kondoh–Nagano (AKN), Lam–Bremhorst, Yang–Shih, standard k–ϵ, and k–ω. A porous medium, which represents conditions in which the flow path changes rapidly, was defined as an infinite array of square cylinders. In addition, to explore the effect of particle size on the rapid expansion and contraction of the flow paths, the diameter ratio (DR) of the square cylinders was systematically varied from 0.2 to 0.8. This generalization revealed new insights into the flow. The Reynolds number (ReD) covered a turbulent range of 500 to 500 × 103, and the porosity ϕ was varied from 0.27 to 0.8. The correlations of the turbulent kinetic energy (k), its dissipation rate (ε), and macroscopic pressure gradient as a function of ϕ, which are useful in macroscopic turbulence modeling, are presented. The results show that the AKN model yields better predictions of the volume-averaged flow parameters because it is better suited to reproduce recirculation zones. For all the DRs, at high ϕ, the distances between walls are high, and the interstitial velocities are low. Consequently, wake flows are produced, and energy losses by friction are moderate. As the flow becomes increasingly bound, the wakes are suppressed and disrupted, and k and ε increase owing to shear layer interactions and frictional forces. Distinctive low-velocity recirculation patterns appear inside pores depending on DR.

Turbulent Jet Injected Into a Cross Flow: Analysis of the Flow Structure and Wall Pressure Fluctuations

2002 ◽  
Author(s):  
Shridhar Gopalan ◽  
Bruce Abraham ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Velocity Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Low Noise ◽  
Wall Pressure ◽  
Turbulent Jet ◽  
Pressure Measurements ◽  
Wall Pressure Fluctuations ◽  
The Cross

The objective of this study is to characterize the velocity, vorticity, wall pressure fluctuations and resulting structural vibrations caused by injection of a round, turbulent jet into a turbulent boundary layer. The experiments are performed in a quiet water channel with back ground noise well below the local pressure fluctuations. One of the channel walls is replaced by a vibration isolated, 1m long, aluminum plate from which the 1cm-diameter jet is injected. The cross flow velocity is fixed at 2 m/s and the velocity ratio, r (ratio of mean jet velocity to the cross flow), varies from 0.5 to 2.5 and Re based on cross flow and jet diameter is 20,000. High-resolution PIV is used to measure the flow field and high sensitivity, low-noise pressure sensors are used for the wall pressure measurements. The flush-mounted transducers are installed at several locations ranging from 2–15 diameters behind the jet. Auto-spectra of the pressure signals show that the effect of the jet is in the 15–100Hz range, and increase the wall pressure levels by 25dB for r = 2.5. The fluctuations increase with velocity ratio and decrease with distance from the jet, although there is only a 6dB increase in overall levels at r = 2.5 as compared to r = 1. Hilbert-Huang “amplitude” spectrum shows the frequency content of the signal as it evolves in time, and is found to be a useful tool to characterize such unsteady phenomena. Velocity and pressure measurements have been performed simultaneously and thousands of frames have been recorded. Analysis of these frames demonstrates the relationship between the pressure fluctuations and the vortical structures. Several striking differences in the flow structure between high and low velocity ratios are described in the paper.

The Effects of the Synthetic Jet on the Mixing Promotion in Low Reynolds Number

2007 ◽  
Author(s):  
Masashi Higashiura ◽  
Koichi Inose ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Static Pressure ◽  
Low Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Vortex Pair ◽  
Synthetic Jet ◽  
The Cross ◽  
Low Reynolds

The present paper describes a synthetic jet interaction with the cross flow in low Reynolds number condition by flow visualization and the wall static pressure measurements. The primary focus of the current study is to examine the possibility on the interaction of the synthetic jet with the cross flow in low Reynolds number viscous dominant flow. The low bulk velocity of the cross flow is set in a small scale of the wind tunnel with a high aspect ratio. A wide range of Reynolds number based on the tunnel height and the bulk velocity is covered. The flow visualization at Reynolds number of 1,000 is conducted in X-Y and Y-Z planes to clarify the development of the interaction process in the downstream. Both the time averaged and phase averaged wall static pressure were obtained downstream of the jet injection. The synthetic jet has a diameter of 0.5 mm and a frequency of 100 to 400 Hz. The penetration of the jet in the cross flow depends on the jet velocity ratio, and the deepest penetration occurs at the phase of π/2 at the highest jet velocity ratio. The counter rotating longitudinal vortex pair is generated even in low Reynolds number and can be observed at 100d downstream from the injection. The vortex pair shows the up-wash motion at the center of the jet core and the down-wash motion at the outsides of the jet. For the synthetic jet in cross flow, the fluctuated wall static pressure is increased, and the wall static pressure has similar frequency to the synthetic jet.

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