Quantitative, experimental investigation of a geometric compatibility criterion in spiral vortex breakdown

1995 ◽  
Author(s):  
K Cheung ◽  
E Jumper ◽  
R Nelson
Keyword(s):  
Experimental Investigation ◽  
Vortex Breakdown ◽  
Spiral Vortex ◽  
Geometric Compatibility

A Study of Unsteady Secondary Flow in a Water Flow Axial Turbine Model

2008 ◽  
Author(s):  
Christian Kasper ◽  
Martin G. Rose ◽  
Stephan Staudacher ◽  
Jochen Gier
Keyword(s):  
Flow Visualization ◽  
Vortex Breakdown ◽  
Water Channel ◽  
Leading Edge ◽  
Secondary Flows ◽  
Stagnation Region ◽  
Spiral Vortex ◽  
Passage Vortex ◽  
High Turbulence ◽  
First Time

The influence of secondary flows on the performance of turbines has been investigated in great detail in the last decades. The interaction of vortices with following blade rows has been identified to be one of the loss mechanisms within a turbo-machine. This paper presents for the first time detailed flow visualization photographs of the interaction of the vane passage vortex with the rotor. The appearance vortex breakdown could be identified before and within the rotating passage of the turbine. The measurements were taken in a vertical water channel. Water is used instead of air because the flow visualization can be realised very easily with injected ink. For different relative positions of rotor to stator a series of photographs were taken. With an image editing process the average and the pixel RMS were calculated for each relative position. The pixel RMS is a useful indicator to identify highly turbulent regions in the flow field. The photographs of the vortex breakdown show spots of high pixel RMS which are associated with very high turbulence and therefore can be regarded as sources of loss. Insight is gained into the nature of the passage vortex breakdown mechanisms as follows: first the pressure wave of the rotor stretches the vortex causing a spiral vortex instability, then the vortex interacts with the leading edge as it attempts to cut the vortex. In the stagnation region of the blade a bubble type instability forms, expands and then convects through the rotor. The absolute trajectory of the vortex fluid reveals that it exchanges no work with the rotor.

Structural sensitivity of spiral vortex breakdown

2013 ◽  
Vol 720 ◽  
pp. 558-581 ◽  
Author(s):  
Ubaid Ali Qadri ◽  
Dhiren Mistry ◽  
Matthew P. Juniper
Keyword(s):  
Stability Analysis ◽  
Passive Control ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Control Strategies ◽  
Axial Component ◽  
Azimuthal Mode ◽  
Global Mode ◽  
Structural Sensitivity ◽  
Spiral Vortex

AbstractPrevious numerical simulations have shown that vortex breakdown starts with the formation of a steady axisymmetric bubble and that an unsteady spiralling mode then develops on top of this. We investigate this spiral mode with a linear global stability analysis around the steady bubble and its wake. We obtain the linear direct and adjoint global modes of the linearized Navier–Stokes equations and overlap these to obtain the structural sensitivity of the spiral mode, which identifies the wavemaker region. We also identify regions of absolute instability with a local stability analysis. At moderate swirls, we find that the $m= - 1$ azimuthal mode is the most unstable and that the wavemaker regions of the $m= - 1$ mode lie around the bubble, which is absolutely unstable. The mode is most sensitive to feedback involving the radial and azimuthal components of momentum in the region just upstream of the bubble. To a lesser extent, the mode is also sensitive to feedback involving the axial component of momentum in regions of high shear around the bubble. At an intermediate swirl, in which the bubble and wake have similar absolute growth rates, other researchers have found that the wavemaker of the nonlinear global mode lies in the wake. We agree with their analysis but find that the regions around the bubble are more influential than the wake in determining the growth rate and frequency of the linear global mode. The results from this paper provide the first steps towards passive control strategies for spiral vortex breakdown.

Experimental investigation of vortex breakdown over a sideslipping canard-configured aircraft model

1994 ◽  
Vol 31 (4) ◽  
pp. 998-1001 ◽  
Author(s):  
Sheshagiri K. Hebbar ◽  
Max F. Platzer ◽  
Chang Ho Kim
Keyword(s):  
Experimental Investigation ◽  
Vortex Breakdown ◽  
Aircraft Model

Some experimental observations of secondary motions in a confined vortex flow

1993 ◽  
Vol 246 ◽  
pp. 653-674 ◽  
Author(s):  
Robert A. Granger
Keyword(s):  
Experimental Investigation ◽  
Laser Doppler Velocimetry ◽  
Experimental Finding ◽  
Vortex Breakdown ◽  
Theoretical Calculations ◽  
Hydrodynamic Instability ◽  
Physical Description ◽  
Flow Stagnation ◽  
Conjugate States ◽  
Satisfactory Theory

Three decades have passed since vortex breakdown was first identified as a natural fluid flow phenomenon. Three key theories have been proposed to explain the phenomenon: hydrodynamic instability, conjugate states and flow stagnation. Despite a considerable amount of theoretical and experimental investigation, there is still nothing approaching a completely satisfactory theory of vortex breakdown. In addition, there is no agreement on a complete physical description of the structure of vortex breakdown. The present experimental investigation may substantiate a few earlier conjectures. We discuss an experimental finding that might help clarify the phenomenon through the use of flow visualization and laser-Doppler velocimetry. Experimental measurements substantiate earlier measurements and theoretical calculations of the velocity field. The evidence suggests that there is a connection between criticality and instability.

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