Boundary layer flow over gentle curvilinear topography with a sudden change in surface roughness*

1977 ◽  
Vol 103 (435) ◽  
pp. 199-209 ◽  
Author(s):  
AK LO
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Boundary Layer Flow ◽  
Sudden Change ◽  
Layer Flow

Mechanism for Onset of Sudden-Rising Head Effect in Centrifugal Pump When Handling Viscous Oils

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Wen-Guang Li
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Flow Pattern ◽  
Centrifugal Pump ◽  
Boundary Layer Flow ◽  
Hydraulic Performance ◽  
Viscous Liquids ◽  
Layer Flow

The “sudden-rising head effect” may be prevalent in the head curve when a centrifugal pump transports highly viscous liquids, but it is not well understood presently. To clarify this effect the hydraulic performance of centrifugal pump when handling water and viscous oils was evaluated numerically by using a CFD code. The “sudden-rising head effect” is confirmed to exist at a higher viscosity and a certain large surface roughness. The viscosity and roughness, which make a transition of boundary layer flow pattern in both the impeller and volute to the hydraulically smooth regime from the fully rough one, are responsible for the effect.

Experimental study of rotating-disk boundary-layer flow with surface roughness

2015 ◽  
Vol 786 ◽  
pp. 5-28 ◽  
Author(s):  
Shintaro Imayama ◽  
P. Henrik Alfredsson ◽  
R. J. Lingwood
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Excellent Agreement ◽  
Boundary Layer Flow ◽  
Rotating Disk ◽  
Absolute Instability ◽  
Turbulent Transition ◽  
Artificial Surface ◽  
Layer Flow ◽  
Laminar Turbulent Transition

Rotating-disk boundary-layer flow is known to be locally absolutely unstable at $R>507$ as shown by Lingwood (J. Fluid Mech., vol. 299, 1995, pp. 17–33) and, for the clean-disk condition, experimental observations show that the onset of transition is highly reproducible at that Reynolds number. However, experiments also show convectively unstable stationary vortices due to cross-flow instability triggered by unavoidable surface roughness of the disk. We show that if the surface is sufficiently rough, laminar–turbulent transition can occur via a convectively unstable route ahead of the onset of absolute instability. In the present work we compare the laminar–turbulent transition processes with and without artificial surface roughnesses. The differences are clearly captured in the spectra of velocity time series. With the artificial surface roughness elements, the stationary-disturbance component is dominant in the spectra, whereas both stationary and travelling components are represented in spectra for the clean-disk condition. The wall-normal profile of the disturbance velocity for the travelling mode observed for a clean disk is in excellent agreement with the critical absolute instability eigenfunction from local theory; the wall-normal stationary-disturbance profile, by contrast, is distinct and the experimentally measured profile matches the stationary convective instability eigenfunction. The results from the clean-disk condition are compared with theoretical studies of global behaviours in spatially developing flow and found to be in good qualitative agreement. The details of stationary disturbances are also discussed and it is shown that the radial growth rate is in excellent agreement with linear stability theory. Finally, large stationary structures in the breakdown region are described.

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