Effect of Nozzle Shape and Polymer Additives on Water Jet Appearance

1979 ◽  
Vol 101 (3) ◽  
pp. 304-308 ◽  
Author(s):  
J. W. Hoyt ◽  
J. J. Taylor
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Water Jet ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Polymer Additives ◽  
High Speed Photography ◽  
Layer Transition ◽  
Spray Formation ◽  
Exit Surface

The effects of shape parameters on the performance of water-jet nozzles discharging in air were investigated using a camera specially adapted for jet photography. The boundary-layer developing on the exit surface of the nozzle is shown to account for the jet appearance revealed by high speed photography. Optimum nozzles seem to have the boundary-layer transition to turbulence inside the nozzle; transition outside the nozzle being accompanied by spray formation and early jet disruption. The effect of polymer additives seems to be earlier transition and a thinner turbulent boundary layer inside the nozzle which improves jet performance.

On the stability of a Blasius boundary layer subject to localised suction

2019 ◽  
Vol 871 ◽  
pp. 717-741 ◽  
Author(s):  
Mattias Brynjell-Rahkola ◽  
Ardeshir Hanifi ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Flow Instability ◽  
Linear Instability ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
Structural Sensitivity ◽  
Blasius Boundary Layer ◽  
Structural Sensitivity Analysis ◽  
The Stability

In this study the origins of premature transition due to oversuction in boundary layers are studied. An infinite row of circular suction pipes that are mounted at right angles to a flat plate subject to a Blasius boundary layer is considered. The interaction between the flow originating from neighbouring holes is weak and for the parameters investigated, the pipe is always found to be unsteady regardless of the state of the flow in the boundary layer. A stability analysis reveals that the appearance of boundary layer transition can be associated with a linear instability in the form of two unstable eigenmodes inside the pipe that have weak tails, which extend into the boundary layer. Through an energy budget and a structural sensitivity analysis, the origin of this flow instability is traced to the structures developing inside the pipe near the pipe junction. Although the amplitudes of the modes in the boundary layer are orders of magnitude smaller than the corresponding amplitudes inside the pipe, a Koopman analysis of the data gathered from a nonlinear direct numerical simulation confirms that it is precisely these disturbances that are responsible for transition to turbulence in the boundary layer due to oversuction.

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