scholarly journals Effects of Rotation and Buoyancy Forces on the Flow Field Behavior Inside a Triangular Rib Roughened Channel

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Luca Furlani ◽  
Alessandro Armellini ◽  
Luca Casarsa
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Leading Edge ◽  
Secondary Flows ◽  
Cooling Channel ◽  
Piv Measurements ◽  
Separated Shear Layer ◽  
Image Velocimetry ◽  
Buoyancy Forces ◽  
Effects Of Rotation

The flow field inside a triangular cooling channel for the leading edge of a gas turbine blade has been investigated. The efforts were focused on the investigation of the interaction between effects of rotation, of buoyancy forces, and those induced by turbulence promoters, i.e., perpendicular square ribs placed on both leading and trailing sides of the duct. Particle image velocimetry (PIV) and stereo-PIV measurements have been performed for ReDh = 104, rotation number of 0, 0.2, and 0.6, and buoyancy parameter equal to 0, 0.08, and 0.7. Coriolis secondary flows are detected in the duct cross section, but contrary to the smooth case, they are characterized by a single main vortex and are less affected by an increase of the rotation parameter. Moreover, their main topology is only marginally sensitive to the buoyancy forces. Conversely, the features of the recirculation structure downstream the ribs turned out to be more sensitive to both the buoyancy forces and to the stabilizing/destabilizing effect on the separated shear layer induced by rotation.

Flow field inside a leading edge cooling channel with turbulence promoters in rotating conditions

2017 ◽  
Vol 231 (4) ◽  
pp. 274-289
Author(s):  
Giovanna Barigozzi ◽  
Silvia Ravelli ◽  
Alessandro Armellini ◽  
Luca Casarsa ◽  
Luca Furlani
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Internal Flow ◽  
Leading Edge ◽  
Flow Structures ◽  
Cooling Channel ◽  
Image Velocimetry ◽  
Buoyancy Forces ◽  
Thermal Data ◽  
Nonisothermal Conditions

The present work deepens the analysis of the flow field inside a triangular equilateral channel with turbulence promoters, perpendicular to the radial direction, on both leading and trailing sides, under rotation and both isothermal and nonisothermal conditions (i.e. with centrifugal buoyancy forces). Simulations have been performed at constant Re = 10,000, Ro = 0–0.2–0.6, and Bo = 0–0.08–0.7, the latter corresponding to 80℃ temperature difference between fluid and walls. These conditions match those of the particle image velocimetry measurements, used for comparison against predictions. After proper validation, the numerical modeling helped with the assessment of the flow field evolution along the radial extension of the cooling channel. It has been possible to determine the path of the coolant throughout the channel and localize where the heat transfer would have been enhanced/decreased by secondary flow structures, with respect to the stationary case. Furthermore, a rather Bo-independency of the flow field in this kind of geometry has been confirmed. The analysis presented in this paper finds support from the thermal data available from the open literature, which is rich of thermal analysis indeed, but lacks a detailed description of internal flow fields.

scholarly journals Experimental measurements of the flow field around a film-cooled blade leading edge using particle image velocimetry

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880290
Author(s):  
José Omar Dávalos Ramírez ◽  
Juan Carlos García Castrejón ◽  
Francisco Carrillo Pereyra ◽  
Carlos Ponce Corral ◽  
Carlos Felipe Ramírez Espinoza ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Leading Edge ◽  
Cooling Flow ◽  
Image Velocimetry ◽  
Secondary Vortices ◽  
Velocity Turbulence ◽  
Cooled Blade ◽  
Blade Leading Edge

In this article, particle image velocimetry studies were conducted in a low-speed wind tunnel to investigate the effects of blowing ratio and blade span in terms of the characteristics of the flow field around a film-cooled blade leading edge. The measurements were performed at 20%, 40%, 60%, and 80% of blade span and blowing ratios of M = 0.5, M = 0.75, M = 1, M = 1.5, and M = 2. Velocity, turbulence intensity, and structure of vortices during the interaction between cooling flow and mainstream were analyzed in detail. The analysis shows a significant increase in mainstream velocity at low blowing ratios, M < 1. Peaks of turbulence were observed at low- and high-span locations. Aerodynamical losses are expected at higher blowing ratios due to the formation of secondary vortices near the outgoing jet. These vortices were a consequence of velocity gradients at this zone.

scholarly journals Particle Image Velocimetry for in vitro characterization of Paravalvular Leakage of TAVR-sealing concepts

2021 ◽  
Vol 7 (2) ◽  
pp. 668-671
Author(s):  
Samuel Höing ◽  
Finja Borowski ◽  
Jan Oldenburg ◽  
Sabine Illner ◽  
Alper Öner ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Aortic Annulus ◽  
Piv Measurements ◽  
Paravalvular Leakage ◽  
Transcatheter Aortic Valve ◽  
Image Velocimetry

Abstract Paravalvular leakage (PVL), defined as the leakage between the aortic annulus and a transcatheter aortic valve replacement (TAVR), is verifiably associated with short- and long-term clinical outcome, especially with increased mortality. Therefore, with the ambition to reduce or even prevent PVL of next generation TAVR, it is necessary to extend the hemodynamic understanding of PVL. This study presents an in vitro flow measurement method to localize PVL during hydrodynamic characterization of TAVR and furthermore presents different design features, socalled outer skirt, to reduce PVL. Particle image velocimetry (PIV) measurements were performed for flow field assessment during hydrodynamic characterization of TAVR. Additionally, two different sealing concepts were developed to reduce PVL. The skirts were manufactured from polymeric-nonwoven and sued to pericardium-based TAVR-prototype. The prepared TAVR-prototypes were then deployed in a pathophysiological model of the aortic root with a calcification nodule of 2 mm according to ISO 5840:2021. To assess PVL, the flow field and the regurgitation volume was measured. The PIV measurements showed a clearly visible leakage jet between the TAVR-prototypes without skirt and the pathophysiological aortic annulus model. Jet velocities of up to 0.5 m/s were measured depending on presence or configuration of a PVL-preventing skirt. When implanted in the physiological annulus model without calcification nodule, PVL was hardly recognizable. The regurgitation volume of a TAVR-prototype without skirt at 5 l/min was 36.26±1.89 ml (n = 10). The developed and manufactured polymeric-nonwoven skirts reduced PVL from 37.67±1.17 ml to 18.36±1.8 ml (n = 10, TAVR-skirt-design1) and from 46.97±1.07 ml to 17.85±1.29 ml (n = 10, TAVR-skirt-design2) at 5 l/min. The localization of PVL during hydrodynamic characterization by means of PIV was successful. The sealing concepts developed in this work were very effective and led to a PVL-reduction of the tested TAVR prototypes of about 50% to 70%.

Development of the Unsteady Flow on a Turbine Rotor Platform Downstream of a Rim Seal

2004 ◽  
Author(s):  
Kirk D. Gallier ◽  
Patrick B. Lawless ◽  
Sanford Fleeter
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Thermal Design ◽  
Flow Rates ◽  
Image Velocimetry ◽  
Downstream Flow

In high temperature turbines, air from disk cavities is forced through the vane-rotor seal to prevent hot gas ingress into these cavities. This emergent seal air can play a significant role in the formation of secondary flows which emanate from the hub region near the rotor blade leading edge. The formation of these structures is also dependent on the inherently unsteady flow field driven by the vane-rotor interaction. As these secondary flows play an important role in both blade performance and heat transfer, the physics that governs them is of significant interest in turbine aero and thermal design. This work investigates and characterizes the aerodynamic signature of the interaction between an emergent seal flow and the hub flow approaching the downstream rotor including the effects of vane-rotor interaction. This is accomplished by means of an experimental investigation performed on the first stage of the Purdue Research Turbine using Particle Image Velocimetry (PIV). The flow field is interrogated in the near-hub region of the intra-stage space, downstream of the first vane row. Purge air is introduced through a planar seal at two different flow rates which characterize typical high and low boundaries for the range of dimensionless seal flow rates encountered in practice. Two-dimensional (radial and axial) velocity data from four measurement planes spaced from vane pressure side to mid-passage are acquired. These data are phase-locked to rotor position. The ensemble-averaged vorticity data from each of ten rotor positions provide a characterization of the effect of the rotor potential field on the emergent seal flow. Vane wake affects on purge strength and downstream flow development are captured at each of two seal flow rates.

scholarly journals Leading-Edge Velocities and Lifted Methane Jet Flame Stability

2010 ◽  
Vol 2010 ◽  
pp. 1-10 ◽  
Author(s):  
W. Wang ◽  
K. M. Lyons
Keyword(s):  
High Temperature ◽  
Flow Field ◽  
Reaction Zone ◽  
Leading Edge ◽  
Flame Velocity ◽  
Piv Measurements ◽  
Jet Flame ◽  
Temperature Boundary ◽  
Image Velocimetry ◽  
Partially Premixed Flame

Current interest exists in understanding reaction-zone dynamics and mechanisms with respect to how they counterpropagate against incoming reactants. Images of flame position and flow-field morphology are presented from flame chemiluminescence and particle image velocimetry (PIV) measurements. In the present study, PIV experiments were carried out to measure the methane jet lifted-flame flow-field velocities in the vicinity of the flame leading edge. Specifically, velocity fields within the high-temperature zone were examined in detail, which complements previous studies, whose prime focus is the flow-field upstream of the high-temperature boundary. PIV data is used not only to determine the velocities, but, along with chemiluminescence images, to also indicate the approximate location of the reaction zone (further supported by/through the leading-edge flame velocity distributions). The velocity results indirectly support the concept that the flame is anchored primarily through the mechanism of partially premixed flame propagation.

Aerodynamics and Vortex Flowfield of a Slender Delta Wing With Apex Flap and Tip Flap

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
T. Lee ◽  
L. S. Ko
Keyword(s):  
Vortex Flow ◽  
Opposite Effect ◽  
Particle Image ◽  
Delta Wing ◽  
Leading Edge ◽  
Piv Measurements ◽  
Injection Flow ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
Flap Deflection

The effect of apex flap and tip flap, deflected both independently and jointly, on the vortex flow and lift generation of a 65 deg-sweep delta wing was investigated experimentally. The drooped apex flap produced a higher lift at medium-to-high angle of attack regime and also a delayed stall. The anhedral (introduced by the downward tip flap) generally promoted lift increment, whereas dihedral had the opposite effect. Meanwhile, the joint apex and tip flap deflection gave a delayed leading-edge vortex (LEV) breakdown and an enhanced lift. The LEVs were generally drawn closer to the wing upper surface, while being pushed further away from the wing centerline by the application of apex flap and tip flap. The flap also modified the vorticity distribution in the LEV; the bursting behavior was, however, not affected. Dye-injection flow visualization and particle image velocimetry (PIV) measurements of the vortex flow were also discussed.

Gentle spilling breakers: crest flow-field evolution

2001 ◽  
Vol 439 ◽  
pp. 57-85 ◽  
Author(s):  
HAIBING QIAO ◽  
JAMES H. DUNCAN
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Fluid Velocity ◽  
Leading Edge ◽  
Horizontal Component ◽  
Wave Crest ◽  
Initial Development ◽  
Image Velocimetry ◽  
Wave Development ◽  
Spilling Breakers

The flow fields at the crests of mechanically generated gentle spilling breakers are studied experimentally with particle image velocimetry (PIV). During the initial development of the breaker, a bulge forms on the forward face of the wave near the crest. The present measurements show that the flow field in this bulge is wavelike in nature and that the maximum horizontal component of the fluid velocity, μmax, is less than the wave crest speed. No vorticity is found during this stage of the breaking process. After a short while, the leading edge (called the toe) of the bulge begins to move rapidly down the wave crest; μmax reaches the speed of the wave crest just as the toe begins to move. Concurrent with the beginning of the toe motion, a vortical region appears at the free surface just downstream of the toe. At about the point in the wave development where the measurements end, the vortical region extends from the toe to the crest.

Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

2021 ◽  
pp. 095441002110212
Author(s):  
K Anand ◽  
KT Ganesh
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Particle Image ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Field Measurements ◽  
Bench Mark ◽  
Image Velocimetry

The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

Endoscopic 2D particle image velocimetry (PIV) flow field measurements in IC engines

2002 ◽  
Vol 33 (6) ◽  
pp. 794-800 ◽  
Author(s):  
U. Dierksheide ◽  
P. Meyer ◽  
T. Hovestadt ◽  
W. Hentschel
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Field Measurements ◽  
Image Velocimetry ◽  
Ic Engines

scholarly journals Manifold reduction techniques for the comparison of crank angle-resolved particle image velocimetry (PIV) data and Reynolds-averaged Navier-Stokes (RANS) simulations in a spark ignition direct injection (SIDI) engine

2021 ◽  
pp. 146808742110131
Author(s):  
Xiaohang Fang ◽  
Li Shen ◽  
Christopher Willman ◽  
Rachel Magnanon ◽  
Giuseppe Virelli ◽  
...  
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Direct Injection ◽  
Linear Manifold ◽  
Main Flow ◽  
Navier Stokes ◽  
Reduction Techniques ◽  
Image Velocimetry ◽  
Manifold Reduction ◽  
Relevance Index

In this article, different manifold reduction techniques are implemented for the post-processing of Particle Image Velocimetry (PIV) images from a Spark Ignition Direct Injection (SIDI) engine. The methods are proposed to help make a more objective comparison between Reynolds-averaged Navier-Stokes (RANS) simulations and PIV experiments when Cycle-to-Cycle Variations (CCV) are present in the flow field. The two different methods used here are based on Singular Value Decomposition (SVD) principles where Proper Orthogonal Decomposition (POD) and Kernel Principal Component Analysis (KPCA) are used for representing linear and non-linear manifold reduction techniques. To the authors’ best knowledge, this is the first time a non-linear manifold reduction technique, such as KPCA, has ever been used in the study of in-cylinder flow fields. Both qualitative and quantitative studies are given to show the capability of each method in validating the simulation and incorporating CCV for each engine cycle. Traditional Relevance Index (RI) and two other previously developed novel indexes: the Weighted Relevance Index (WRI) and the Weighted Magnitude Index (WMI), are used for the quantitative study. The results indicate that both POD and KPCA show improvements in capturing the main flow field features compared to ensemble-averaged PIV experimental data and single cycle experimental flow fields while capturing CCV. Both methods present similar quantitative accuracy when using the three indexes. However, challenges were highlighted in the POD method for the selection of the number of POD modes needed for a representative reconstruction. When the flow field region presents a Gaussian distribution, the KPCA method is seen to provide a more objective numerical process as the reconstructed flow field will see convergence with an increasing number of modes due to its usage of Gaussian properties. No additional criterion is needed to determine how to reconstruct the main flow field feature. Using KPCA can, therefore, reduce the amount of analysis needed in the process of extracting the main flow field while incorporating CCV.

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