Pressure Measurements of Coaxial Jet of High Mean-Velocity Ratio

1983 ◽  
Vol 7 (2) ◽  
pp. 51-57 ◽  
Author(s):  
H. Au ◽  
N.W.M. Ko
Keyword(s):  
Experimental Investigation ◽  
Coherent Structures ◽  
Velocity Ratio ◽  
Pressure Fluctuations ◽  
Intermediate Zone ◽  
Pressure Measurements ◽  
Spectral Measurements ◽  
Initial Region ◽  
Mean Velocity ◽  
Single Jet

This paper describes an experimental investigation of the initial region of a subsonic cold coaxial jet at a mean-velocity ratio λ, outer to inner, of 1.25. Detailed measurements in the initial region have shown that similarity of the pressure intensity profiles exists in the three zones: the initial merging zone, the intermediate zone and the fully merged zone. Spectral measurements of the pressure fluctuations confirm the existence of coherent structures in the outer mixing region. Comparison of the coaxial jet results with those of the single jet has been attempted.

Initial Region of Subsonic Coaxial Jets of High Mean-Velocity Ratio

1981 ◽  
Vol 103 (2) ◽  
pp. 335-338 ◽  
Author(s):  
N. W. M. Ko ◽  
H. Au
Keyword(s):  
Experimental Investigation ◽  
Turbulence Intensity ◽  
Velocity Ratio ◽  
Velocity Profiles ◽  
Initial Region ◽  
Mean Velocity ◽  
Coaxial Jets ◽  
Single Jet ◽  
The Mean

This paper describes an experimental investigation of the initial region of subsonic coaxial jets of three different mean-velocity ratios λ higher than unity. Detailed measurements have found similarity of the mean velocity and turbulence intensity profiles within the three zones: initial merging, intermediate, and fully merged zone. Similarity with single jet results has been found. In the inner mixing region, however, only the similarity of the mean velocity profiles has been found.

scholarly journals Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

scholarly journals Effect of Mean Velocity to Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

2021 ◽  
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity to critical velocity ratios have been tested at the upstream straight path to determine the meander's incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity to critical velocity ratios. In addition, the upstream bend's effect on the downstream bend has been investigated. Results indicated that the maximum scour depth at the downstream bend has increased as a result of changing the mean velocity to critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by respectively 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend's incipient motion was observed for the mean velocity to critical velocity ratio of 0.89, while the downstream bend was equal to 0.78.

Flow Structure, Pressure Fluctuations and Resulting Vibrations Caused by the Interaction of a Turbulent Jet With Cross Flow Over a Flexible Flat Plate

2002 ◽  
Author(s):  
Shridhar Gopalan ◽  
Bruce M. Abraham ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Velocity Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Wall Pressure ◽  
Turbulent Jet ◽  
Pressure Measurements ◽  
Structural Vibrations ◽  
Wall Pressure Fluctuations

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 wall pressure fluctuations and the vortical structures. Several striking differences in the flow structure between high and low velocity ratios are described in the paper. Acceleration measurements describe the effect of the jet and cross flow on the vibrations of the side-wall. Cross flow boundary layer dominates structural vibrations below 1000Hz, and jet velocity effects are visible at 1000Hz–2000Hz. At higher jet velocities effects are seen even below 1000Hz and large narrow band frequency peaks occur. (CD ROM version includes color figures).

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.

An Experimental Investigation of the Noise Sources Associated With Submerged High Flow Acoustic Measurements

2015 ◽  
Author(s):  
Joseph W. Hall ◽  
Barrett Poole
Keyword(s):  
Experimental Investigation ◽  
Pressure Fluctuations ◽  
Turbulent Wake ◽  
High Flow ◽  
Pressure Measurements ◽  
Acoustic Measurements ◽  
Noise Sources ◽  
Low Frequencies ◽  
Unsteady Surface Pressure ◽  
Low Speed Wind Tunnel

A study of the noise sources on an submerged housing designed to facilitate acoustic measurements in high flow situations was investigated experimentally. A scale-mode of the housing was mounted in a low speed wind-tunnel and mean and unsteady surface pressure measurements were taken all over the surface of the housing. The measurements indicate that flow-separation occurs on several of the model edges and that a protruding instrument housing produces a strong turbulent wake. The associated pressure fluctuations produce large, low frequencies fluctuations that are broadband along with discrete tones that occur at higher frequencies.

Similarity in the initial region of annular jets: three configurations

1978 ◽  
Vol 84 (4) ◽  
pp. 641-656 ◽  
Author(s):  
N. W. M. Ko ◽  
W. T. Chan
Keyword(s):  
Turbulence Intensity ◽  
Initial Region ◽  
Mean Velocity ◽  
Intensity Measurements ◽  
Single Jet ◽  
The Mean ◽  
Annular Jets

This paper describes part of a detailed study of the initial region of three annular jets. The configurations are the basic one, without any bullet in the centre, and those with a conical and an elliptical bullet. From the mean velocity and turbulence intensity measurements the initial region can be divided into the initial merging, the intermediate and the fully merged zones. Within these three zones similarity of both the mean velocity and the turbulence intensity profiles has been found. The similarity curves are compared with those for a single jet.

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