Flow Visualization of Recirculation zone for Confined Jets

The effect of rounded labyrinth teeth tips and worn abradable lands has been found to give substantially increased leakage, which is well known to give reduced machine efficiency. Very little information concerning this exists, and some of the first measurements and visualization movies for stepped labyrinths are provided here to give an enhanced understanding of this phenomenon. A unique, very large-scale seal test facility was used. Glitter, and alternatively fluorescein dye, was employed as the flow tracer material. The flow visualization movies were digitally stored on the hard drive of a computer. Large decreases of leakage resistance due to the presence of worn teeth as well as rub-grooves were found. For the cases considered, the leakage resistance decrease for the large step height configurations were 85 percent, 55 percent, and 70 percent for the small, medium, and large pre-rub clearances, respectively. It was also found that the resistance varied with wear geometry, in order from highest to lowest resistance, as (a) ungrooved-unrounded-teeth, (b) ungrooved-rounded-teeth, (c) grooved-unrounded-teeth and (d) grooved-rounded-teeth. Further, a substantial tooth tip recirculation zone was visually observed only for the grooved-unrounded-teeth cases, and it was shown to be the mechanism by which the unrounded teeth give this configuration a higher resistance than do the rounded teeth.

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Measurement and Visualization of Leakage Effects of Rounded Teeth Tips and Rub-Grooves on Stepped Labyrinths

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/99-gt-377 ◽

1999 ◽

Cited By ~ 2

Author(s):

David L. Rhode ◽

Brian F. Allen

Keyword(s):

Flow Visualization ◽

Large Scale ◽

Recirculation Zone ◽

Step Height ◽

Test Facility ◽

Leakage Resistance ◽

Large Step ◽

Fluorescein Dye ◽

Resistance Decrease ◽

Flow Tracer

The effect of rounded labyrinth teeth tips and worn abradable lands has been found to give substantially increased leakage, which is well known to give reduced machine efficiency. Very little information concerning this exists, and some of the first measurements and visualization movies for stepped labyrinths are provided here to give an enhanced understanding of this phenomenon. A unique, very large-scale seal test facility was used. Glitter, and alternatively fluorescein dye, was employed as the flow tracer material. The flow visualization movies were digitally stored on the hard drive of a computer. Large decreases of leakage resistance due to the presence of worn teeth as well as rub-grooves were found. For the cases considered, the leakage resistance decrease for the large step height configurations were 85 percent, 55 percent and 70 percent for the small, medium and large pre-rub clearances, respectively. It was also found that the resistance varied with wear geometry, in order from highest to lowest resistance, as: (a) ungrooved-unrounded-teeth, (b) ungrooved-rounded-teeth, (c) grooved-unrounded-teeth and (d) grooved-rounded-teeth. Further, a substantial tooth tip recirculation zone was visually observed only for the grooved-unrounded-teeth cases, and it was shown to be the mechanism by which the unrounded teeth give this configuration a higher resistance than do the rounded teeth.

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Flow Visualization and PIV Measurements of Flow Around a Sport Utility Vehicle Model

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30193 ◽

2010 ◽

Author(s):

Alban Lamy ◽

Amandine Hamel ◽

Christina Vanderwel ◽

Stavros Tavoularis ◽

Azeddine Kourta

Keyword(s):

Boundary Layer ◽

Flow Visualization ◽

Flow Structure ◽

Recirculation Zone ◽

Aerodynamic Drag ◽

Vertical Plane ◽

The Body ◽

Dimensionless Frequency ◽

Sport Utility Vehicle ◽

Utility Vehicle

The instantaneous flow structure around a 1:18 scaled model of a square-back sport utility vehicle (Hummer H2) was documented in a low-speed water tunnel. The study comprises both flows with the model fixed on a flat plate and flows with the model’s wheels rolling on an endless belt that moved with the speed of the free stream, thus simulating ground effects. The flow structure was investigated using flow visualization by dye injection as well as particle image velocimetry (PIV) for several Reynolds numbers in the range of 7000 to 27700. The flow along the roof, the sidewalls, and the underbody was observed to separate at the rear edges of the body, creating a recirculation zone at the rear of the vehicle, which is associated with pressure loss and a major contribution to aerodynamic drag. In the vertical plane of symmetry, this recirculation zone appears as two counter-rotating vortices. With a fixed ground, the lower vortex was less energetic than the upper vortex because the boundary layer that developed along the ground upstream of the model reduced the momentum of the flow below the vehicle. This boundary layer was also observed to separate from the ground behind the vehicle, creating a third vortex located further downstream along the ground. This boundary layer separation forced the bottom vortex to remain attached to the base of the vehicle, whereas the upper vortex was advected in the wake. The dimensionless frequency (Strouhal number) of the vortex shedding process from the roof was found to be in the range of 0.1 to 0.9. With a moving ground, the upper vortex behaved similarly to that in the fixed ground configuration; however, in the absence of the boundary layer along the ground, the lower vortex was typically stronger and its location showed some variability. In both configurations, the Reynolds number had little influence on the wake topology, mostly increasing the turbulence intensity without modifying the main flow pattern.

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