Influence of Trailing-Edge Geometry on Hydraulic-Turbine-Blade Vibration Resulting From Vortex Excitation

1960 ◽  
Vol 82 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Gunnar Heskestad ◽  
D. R. Olberts
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
Hydraulic Turbine ◽  
Trailing Edge ◽  
Blade Vibration ◽  
Edge Geometry ◽  
Blade Thickness ◽  
Vortex Induced Vibrations ◽  
Approach Velocity

A study was made to determine effects of trailing-edge geometry on the vortex-induced vibrations of a model blade designed to simulate the conditions at the trailing edge of a hydraulic-turbine blade. For the type of trailing-edge flow encountered, characterized by a thick boundary layer relative to the blade thickness, the vortex-shedding frequency could not be represented by any modification of the Strouhal formula. The amplitude of the induced vibrations increased with the strength of a vortex in the von Karman vortex street of the wake; one exception was provided by a grooved edge, which is discussed in some detail. For a particular approach velocity, the vortex strength is primarily a function of the ratio of distance between separation points to boundary-layer thickness, the degree of “shielding” between regions of vortex growth, and frequency of vortex shedding.

Hydroelastic Vibrations of Flat Plates Related to Trailing Edge Geometry

1961 ◽  
Vol 83 (4) ◽  
pp. 671-678 ◽  
Author(s):  
G. H. Toebes ◽  
P. S. Eagleson
Keyword(s):  
Leading Edge ◽  
Equation Of Motion ◽  
Thin Plates ◽  
Comprehensive Treatment ◽  
Angle Of Incidence ◽  
Flat Plates ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Vortex Induced Vibrations ◽  
Hydroelastic Vibrations

Vortex-induced vibrations of thin flat plates are studied as a function of trailing edge geometry. In an effort to extend the analysis to a more comprehensive treatment than that provided by the common vortex model, the vibrations are considered as hydroelastic phenomena. An equation of motion is formulated. From a qualitative analysis of this nonlinear equation some expected features of its solution are set forth. A detailed experimental determination is made of the amplitude spectra of various thin plates mounted at zero mean angle of incidence in the test section of a water tunnel and suspended by a torsion spring through their leading edge. The effects of trailing edge geometry and elastic properties of plate support are explored. Data analysis gives interesting confirmation of the formulated equation of motion. The vibration is shown to become self-excited and the degree of two dimensionality of the wake is deduced to be determinative in regard to the severity of the vibration.

Trailing Edge Noise From Blunt and Sharp Edge Geometries

2008 ◽  
Author(s):  
Daniel W. Shannon ◽  
Scott C. Morris ◽  
William K. Blake
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Separation ◽  
Broadband Noise ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Edge Geometry ◽  
Blunt Trailing Edge ◽  
Blunt Edge ◽  
Radiated Sound

The objective of this study was to experimentally investigate the broadband trailing edge noise generated by a sharp trailing edge geometry and an asymmetric blunt edge. The flow field in the vicinity of the sharp trailing edge was found to be equivalent to that of a flat plate turbulent boundary layer. The interaction of the two boundary layers with the edge was responsible for broadband noise generation. The blunt trailing edge geometry exhibited additional complexity, with turbulent boundary layer separation and sound generated by vortex shedding. The measurement program included hot-wire anemometry, unsteady surface pressure, and radiated sound utilizing two microphone arrays. The boundary layer parameters and wall pressure spectra were used to compute the radiated sound from existing scattering theory. These calculations agreed very well with the array data, with differences typically within 2dB over the frequency range considered valid for the theory.

Particle Image Velocimetry Measurements of Wake Flows of Various Bridge Sections

2006 ◽  
Author(s):  
Emanuela Palombi ◽  
Gregory A. Kopp ◽  
Roi Gurka
Keyword(s):  
Particle Image Velocimetry ◽  
Vortex Shedding ◽  
Particle Image ◽  
Uniform Flow ◽  
Pressure Measurements ◽  
Trailing Edge ◽  
Wake Flows ◽  
Edge Geometry ◽  
Image Velocimetry ◽  
The Mean

Using Particle Image Velocimetry (PIV) we investigate the influence of leading and trailing edge geometry on the wake flows of various elongated cylinders in smooth uniform flow. The results present a comparison between the mean wake flows, as well as the vortex shedding activity found to occur in each case. Pressure measurements were recorded on the surface of the cylinders to examine the corresponding fluctuating and mean forces exhibited by each model tested. Significant variations in the wake topology and aerodynamic behaviour of the four cylinder geometries tested were observed.

Experimental Investigation of the Vortex Shedding in the Wake of Oblique and Blunt Trailing Edge Hydrofoils Using PIV-POD Method

2010 ◽  
Author(s):  
Amirreza Zobeiri ◽  
Philippe Ausoni ◽  
Franc¸ois Avellan ◽  
Mohamed Farhat
Keyword(s):  
Experimental Investigation ◽  
Phase Shift ◽  
Vortex Shedding ◽  
High Speed ◽  
Flow Induced Vibration ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Vortex Induced Vibrations ◽  
Image Velocimetry ◽  
High Reynolds

This paper presents an experimental investigation of the vortex shedding in the wake of blunt and oblique trailing edge hydrofoils at high Reynolds number, Re = 5 105 − 2.9 106. The velocity field in the wake is surveyed with the help of Particle-Image-Velocimetry, PIV, using Proper-Orthogonal-Decomposition, POD. Besides, flow induced vibration measurements and high-speed visualization are performed. The high-speed visualization clearly shows that the oblique trailing edge leads to a spatial phase shift of the upper and lower vortices at their generation stage, resulting their partial cancellation. For the oblique trailing edge geometry and in comparison with the blunt one, the vortex-induced vibrations are significantly reduced. Moreover, PIV data reveals a lower vorticity for the oblique trailing edge. The phase shift between upper and lower vortices, introduced by the oblique truncation of the trailing edge, is found to vanish in the far wake, where alternate shedding is recovered as observed with the blunt trailing edge. The phase shift generated by the oblique trailing edge and the resulting partial cancellation of the vortices is believed to be the main reason of the vibration reduction.

The Effects of a Tripped Turbulent Boundary Layer on Vortex Shedding from a Blunt Trailing Edge Hydrofoil

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Philippe Ausoni ◽  
Amirreza Zobeiri ◽  
François Avellan ◽  
Mohamed Farhat
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Vortex Shedding ◽  
High Speed ◽  
Boundary Layer Transition ◽  
Trailing Edge ◽  
Layer Transition ◽  
Blunt Trailing Edge ◽  
Turbulent Transition ◽  
Reference Length

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, Reh=16.1·103-96.6·103, where the reference length h is the trailing edge thickness, are reported. The effects of a tripped turbulent boundary layer on the wake characteristics are analyzed and compared with the condition of a natural turbulent transition. The foil surface is hydraulically smooth and a fully effective boundary layer tripping at the leading edge is achieved with the help of a distributed roughness. The vortex shedding process is found to be strongly influenced by the boundary layer development: the tripped turbulent transition promotes the re-establishment of organized vortex shedding. In the context of the tripped transition and in comparison with the natural one, significant increases in the vortex span-wise organization, the vortex-induced hydrofoil vibration, the wake velocity fluctuations, and the vortex strength are revealed. Although the vortex shedding frequency is decreased, a modified Strouhal number based on the wake width at the end of the vortex formation region is constant and evidences the similarity of the wakes in terms of spatial distribution for the two considered boundary layer transition processes.

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