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.

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).

Large Amplitude Wall Pressure Events Beneath a Turbulent Boundary Layer

1993 ◽  
Vol 115 (4) ◽  
pp. 653-659 ◽  
Author(s):  
C. C. Karangelen ◽  
V. Wilczynski ◽  
M. J. Casarella
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Amplitude ◽  
Pressure Fluctuations ◽  
Low Noise ◽  
Wall Pressure ◽  
Time Averaging ◽  
Frequency Of Occurrence ◽  
Wall Pressure Fluctuations ◽  
Long Time

Experimental data on the temporal records of the wall pressure fluctuations beneath a turbulent boundary layer have been acquired in a low-noise flow facility. The pressure data were first analyzed using long-time averaging techniques to determine the statistical properties and the results were compared to the baseline data of Scheme (1983). Next, the pressure records were conditionally sampled at various k threshold levels (p′w ≥ k·Prms) to detect large amplitude, positive and negative events which were then averaged and analyzed to determine their shape, duration, and frequency of occurrence. The intermittent large amplitude events are very short in duration, occur rather infrequently in time, but are a major contributor to the high frequency content of the wall pressure fluctuations. As an example, events where p′w ≥ |3·prms| have an average duration of 14 viscous time units, occur 5 percent of the time and contribute 49 percent to the RMS value. The time between events appears to have a lognormal statistical distribution. The frequency of occurrence of the large amplitude events are consistent with the burst rate for flow structures and thus support the conjecture that the large amplitude events are associated with the near-wall bursting process.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

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