Unsteady pressures on a blunt trailing edge - End plate and boundary layer effects

1998 ◽  
Author(s):  
Kaliope Vassilopoulos ◽  
Sudhir Gai
Keyword(s):  
Boundary Layer ◽  
Trailing Edge ◽  
End Plate ◽  
Blunt Trailing Edge

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.

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.

Secondary instabilities in the wake of an elongated two-dimensional body with a blunt trailing edge

2018 ◽  
Vol 846 ◽  
pp. 578-604 ◽  
Author(s):  
B. Gibeau ◽  
C. R. Koch ◽  
S. Ghaemi
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Energy Content ◽  
Streamwise Vortex ◽  
Secondary Instability ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Trailing Edge ◽  
Piv Measurements ◽  
Blunt Trailing Edge

The secondary instability in the wake of a two-dimensional blunt body with a chord to thickness ratio of 46.5 was experimentally investigated for Reynolds numbers of 3500, 5200 and 7000 based on the blunt trailing edge height $h$. Planar, stereoscopic and high-speed particle image velocimetry (PIV) measurements were performed to characterise the wake and upstream boundary layer. The same mode B secondary instability that is found in the cylinder wake was found to be present in the wake of the elongated body studied here. The most probable wavelength of the secondary instability, defined as the spanwise distance between adjacent streamwise vortex pairs in the wake, was found to range from $0.7h$ to $0.8h$ by applying a spatial autocorrelation to the spanwise–wall-normal instantaneous fields of the $Q$-criterion. The temporal evolution of the secondary wake vortices was investigated using time-resolved stereoscopic PIV measurements and it was shown that the vortices maintain both their directions of rotation and spanwise positions during the primary vortex shedding cycles. In agreement with previous literature, the secondary instability did not greatly change as the upstream boundary layer transitioned from laminar to turbulent. Moreover, any upstream boundary layer structures were found to rapidly evolve into wake structures just past the blunt trailing edge. The wavelength of the secondary instability was shown to match the spanwise distance between adjacent low-speed zones of streamwise velocity in the wake. These undulating velocity patterns proved to be a viable method for determining the secondary instability wavelength; however, this type of analysis is highly sensitive to the energy content used for data reconstruction when proper orthogonal decomposition is applied beforehand.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Analysis of Blunt Trailing Edge Airfoils

2003 ◽  
Author(s):  
K. J. Standish ◽  
C. P. van Dam
Keyword(s):  
Experimental Data ◽  
Wind Turbine ◽  
Turbine Blades ◽  
Navier Stokes ◽  
Computational Techniques ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Large Wind ◽  
Structural Volume

The adoption of blunt trailing edge airfoils for the inner regions of large wind turbine blades has been proposed. Blunt trailing edge airfoils would not only provide increased structural volume, but have also been found to improve the lift characteristics of airfoils and therefore allow for section shapes with a greater maximum thickness. Limited experimental data makes it difficult for wind turbine designers to consider and conduct tradeoff studies using these section shapes. This lack of experimental data precipitated the present analysis of blunt trailing edge airfoils using computational fluid dynamics. Several computational techniques are applied including a viscous/inviscid interaction method and several Reynolds-averaged Navier-Stokes methods.

scholarly journals Experimental characterization of the turbulent boundary layer over a porous trailing edge for noise abatement

2019 ◽  
Vol 443 ◽  
pp. 537-558 ◽  
Author(s):  
Alejandro Rubio Carpio ◽  
Roberto Merino Martínez ◽  
Francesco Avallone ◽  
Daniele Ragni ◽  
Mirjam Snellen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Experimental Characterization ◽  
Trailing Edge ◽  
Noise Abatement
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