Near-Wall Velocity Field Measurements of a Very Low Momentum Flux Transverse Jet

2014 ◽  
Author(s):  
D. V. Salazar ◽  
D. J. Forliti ◽  
K. Kuzmich ◽  
E. Coy
Keyword(s):  
Velocity Field ◽  
Momentum Flux ◽  
Field Measurements ◽  
Wall Velocity ◽  
Transverse Jet ◽  
Near Wall

Comparisons of Flow and Mixing Characteristics between Unforced and Excited Elevated Transverse Jets

2013 ◽  
Vol 30 (1) ◽  
pp. 87-96 ◽  
Author(s):  
C. M. Hsu ◽  
R. F. Huang
Keyword(s):  
Velocity Field ◽  
Momentum Flux ◽  
High Speed ◽  
Symmetry Plane ◽  
Image Processing Technique ◽  
Large Momentum ◽  
Acoustic Excitation ◽  
Recirculation Bubble ◽  
Transverse Jet ◽  
Mixing Characteristics

ABSTRACTThe influences of acoustic excitation on the velocity field and mixing characteristic of a jet in cross-flow were investigated in a wind tunnel. The acoustic excitation waves at resonance Strouhal number were generated by a loudspeaker. The time-averaged velocity field and streamlines of the excited elevated transverse jet in the symmetry plane were measured by a high-speed particle image velocimetry. The visual penetration height and spread width were obtained by using an image processing technique. The dispersion characteristics were obtained from the tracer-gas concentration measurement. The results showed that the streamline pattern of the non-excited transverse jet was significantly modified by the acoustic excitation—the bent streamlines evolved from the jet exit escalated and the vortex rings in the jet and tube wakes and the recirculation bubble in the jet wake disappeared. The time-averaged velocity distributions revealed that the excited transverse jet produces large momentum in the up-shooting direction so that the velocity trajectories were located at levels higher than those of the non-excited one. The mixing characteristics, which include the visual penetration height, spread width, and dispersion, were drastically improved by the acoustic excitation due to the changes in the flow structures. The excited transverse jet characterized at larger jet-to-crossflow momentum flux ratios presented larger improvement in the mixing characteristics than at lower jet-to-crossflow momentum flux ratios.

Three-Dimensional Measurement of Near-Wall Velocity in Millimeter Channel by a Single View Imaging

2015 ◽  
Author(s):  
Yoshiyasu Ichikawa ◽  
Kojiro Nishiwake ◽  
Hiromu Wakayama ◽  
Yuki Kameya ◽  
Makoto Yamamoto ◽  
...  
Keyword(s):  
Velocity Field ◽  
Velocity Distribution ◽  
Three Dimensional ◽  
Wall Region ◽  
Measured Velocity ◽  
Wall Velocity ◽  
Wall Area ◽  
Micro Piv ◽  
Wall Flow ◽  
Near Wall

It is well known that there is a strong correlation between heat transfer and near-wall flow. It is important to obtain the detailed near-wall flow field, but it has a lot of difficulties to measure near-wall region by traditional approaches for example hot wire anemometry and particle image velocimetry (PIV). The purpose of this study is to determine the three-dimensional velocity field at near-wall area in micron resolution by the astigmatism particle tracking velocimetry (APTV). In this study, an estimation of depth location of tracer particles by applying a specialized imaging optics controlling the astigmatism [1] was employed. We have developed a measurement system to get the particle location within 15 μm from wall using a long-working-distance microscope with astigmatic optics. As a proof-of-concept, near-wall velocity field in a millimeter-ordered parallel plate channel was measured with low Reynolds numbers (Re = 1 ∼ 5) Poiseuille flow to confirm the validity of it. As a result, we can obtain the near-wall velocity within 15 μm from the wall precisely. From the velocity distribution, the standard deviation of the velocity at each location was calculated and the dispersion of velocity was evaluated. As a result, it was confirmed that the measurement was carried out more accurately in high-speed area. Comparison of the measured velocity distribution with a theoretical calculation and micro-PIV results were also done. From these velocity distributions, the wall shear stress on the wall was determined.

Velocity field measurements of a laminar thermal

1979 ◽  
Vol 22 (6) ◽  
pp. 1044 ◽  
Author(s):  
D. J. Shlien ◽  
A. Brosh
Keyword(s):  
Velocity Field ◽  
Field Measurements

scholarly journals Effects of Hole Shape on Film Cooling With Large Angle Injection

1999 ◽  
Author(s):  
Atui Kohil ◽  
David G. Bogard
Keyword(s):  
Velocity Field ◽  
Film Cooling ◽  
Field Measurements ◽  
Round Hole ◽  
Cooling Performance ◽  
Injection Angle ◽  
Hole Shape ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Better Than

In this study the film cooling performance of a single row of discrete holes inclined at an injection angle of 55° is investigated at a density ratio of DR = 1.6. Three different hole geometries were used in this study, a round hole and two shaped holes. One shaped hole had forward and lateral expansions of 15°, and the other a 15° lateral with a 25° forward expansion. For reference, a round hole with an injection angle of 35° was also tested. The film cooling performance of each hole shape was evaluated using adiabatic effectiveness, thermal field, and velocity field measurements. The shaped holes showed higher spatially averaged adiabatic effectiveness than the round hole over the whole range of momentum flux ratios (I) investigated. The effectiveness values for the shaped holes were only marginally better than the round hole at the low I, but at the high I, the shaped holes performed much better than the round hole. The temperature and velocity field measurements near the hole exit suggest that there is a slight detachment of the jet from the wall for the round hole, while the jets remain attached for the two shaped holes. The shaped hole with the larger forward expansion had a warmer jet with a higher trajectory at the hole exit suggesting ingestion of mainstream fluid and flow separation within the hole.

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