Investigation of the Large-Scale Flow Structures in the Cooling Jets Used in the Blown Film Manufacturing Process

2005 ◽  
Vol 127 (5) ◽  
pp. 978-985 ◽  
Author(s):  
Nan Gao ◽  
Dan Ewing
Keyword(s):  
Shear Layer ◽  
Manufacturing Process ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Time Correlation ◽  
Large Scale Structures ◽  
Blown Film ◽  
Scale Structures ◽  
Jet Velocity ◽  
Large Scale Flow

The development of the flow field produced by concentric jets used in the blown-film manufacturing process was studied experimentally using hot wire anemometry. It was found that the inner jet was entrained into the outer jet before the outer jet attached to the wall. The inner shear layer of the outer jet attached to the surface 3H to 5H downstream of the jet exit, and the outside shear layer of the outer jet attaches to the surface further downstream of the jet exit. The distribution and spectra of the fluctuating wall pressure was measured using microphones. The pressure fluctuations were largest where the outer jet attached to the surface, and had characteristic frequencies of 100to900Hz. Measurements of two-point and two-time correlation of the fluctuating pressure were used to characterize the development of the large-scale structures that caused these pressure fluctuations. It was found that the structures were convected along the surface at 0.45 to 0.7 of the outer jet velocity for different ratios between inner and outer jet velocities. The convection velocity of the large scale structures in the region farther than 10H downstream of the jet exit was determined by the upper jet velocity.

Investigation of the Large-Scale Flow Structures in the Cooling Jets Used in the Blown Film Manufacturing Process

Volume 3 ◽  
2004 ◽  
Author(s):  
Nan Gao ◽  
Dan Ewing
Keyword(s):  
Shear Layer ◽  
Manufacturing Process ◽  
Large Scale ◽  
Time Correlation ◽  
Large Scale Structures ◽  
Blown Film ◽  
Scale Structures ◽  
Jet Velocity ◽  
Large Scale Flow ◽  
Jet Velocities

The development of the flow field produced by concentric jets used in the blown-film manufacturing process was studied experimentally using hot wire anemometry. It was found that the inner jet was entrained into the outer jet before the outer jet attached to the wall. The inner shear layer of the outer jet attached to the surface 3H to 5H downstream of the jet exit, and the outside shear layer of the outer jet attaches to the surface approximately 12H downstream of the jet exit. The distribution and the spectra of the fluctuating wall pressure was measured using microphones. Measurements of two-point two-time correlation of the fluctuating pressure were used to characterize the development of the large-scale structures. It was found that the structures were convected along the surface at 0.45 to 0.7 of the outer jet velocity for different ratios between inner and outer jet velocities. It was also found that the convection velocity of the large scale structures in the region farther than 10H down stream of the jet exit was determined by the upper jet velocity.

Simulations of Flow Ingestion and Related Structures in a Turbine Disk Cavity

2010 ◽  
Author(s):  
Steve Julien ◽  
Julie Lefrancois ◽  
Guy Dumas ◽  
Guillaume Boutet-Blais ◽  
Simon Lapointe ◽  
...  
Keyword(s):  
Large Scale ◽  
Pressure Fluctuations ◽  
Flow Structures ◽  
Flow Rates ◽  
Large Scale Structures ◽  
Through Flow ◽  
Purge Flow ◽  
Scale Structures ◽  
Large Scale Flow ◽  
Pressure Perturbations

Preliminary results of unsteady numerical simulations of disk cavity flow in interaction with the main gaspath flow in an axial turbine are presented in this article. A large periodic sector including vanes, blades and disk cavity of approximately 74° has been used in order to allow for the formation of large scale flow structures within the cavity. Three purge flow rates have been tested, namely no purge, low purge and high purge flow rates. Energetic large scale flow structures are detected through flow visualizations for the two lowest purge flow rates. They are found to rotate at an angular velocity slightly less than the rotor speed. The presence of the large scale structures involves important pressure perturbations inside the cavity that may lead to deep mass flow ingress, whereas the unsteady vane-blade interaction seems to cause only shallow ingress. Increasing purge flow rate appears to have a stabilizing effect on the pressure fluctuations inside the cavity and to reduce the intensity of the large scale flow structures.

Flow Instabilities in Gas Turbine Chute Seals

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Joshua T. M. Horwood ◽  
Fabian P. Hualca ◽  
Mike Wilson ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
...  
Keyword(s):  
Large Scale ◽  
Computational Study ◽  
Leading Edge ◽  
Large Scale Structures ◽  
Strong Shear ◽  
Time Marching ◽  
Flow Through ◽  
Scale Structures ◽  
Large Scale Flow ◽  
Secondary Flow Field

Abstract The ingress of hot annulus gas into stator–rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurized purge required to protect highly stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations—which include a 360 deg domain—were undertaken using dlrtrace's time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30 deg to 360 deg indicates that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60 deg sector and suggest that modeling an even number of blades in small sector simulations should be avoided.

The Effect of Aspect-Ratio on the Development of the Large-Scale Structures in the Three-Dimensional Wall Jet

2005 ◽  
Author(s):  
Joseph W. Hall ◽  
Daniel Ewing
Keyword(s):  
Aspect Ratio ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Decomposition Analysis ◽  
Wall Pressure ◽  
Symmetric Mode ◽  
Large Scale Structures ◽  
Aspect Ratios ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets exiting rectangular nozzles with aspect-ratios of 1 and 4 was investigated using simultaneous measurements of the fluctuating wall pressure across the jet. The pressure fluctuations in the jets were asymmetric and caused the fluctuating wall pressure to be poorly correlated across the jet centerline. A Proper Orthogonal Decomposition analysis indicated that both the first and second modes make similar contributions to the variance of the fluctuating pressure, and were symmetric and antisymmetric, respectively, and the interplay between these modes caused the asymmetry in the instantaneous pressure fluctuations across the jet centreline. A wavelet analysis of the instantaneously reconstructed pressure fields indicated that the fluctuations were predominantly in two frequency bands near the jet centerline, but were only contained in one band on the outer lateral edges of the jet, indicating there were two different large-scale motions present. The development of large-scale structures in the two jets initially differed in the intermediate field with the antisymmetric mode being more prominent in the square jet and the symmetric mode being more prominent in the larger aspect-ratio jet. Further downstream, the symmetric mode was more prominent in both jets.

Dynamics of Large-Scale Structures for Jets in a Crossflow

1999 ◽  
Vol 121 (3) ◽  
pp. 577-587 ◽  
Author(s):  
F. Muldoon ◽  
S. Acharya
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Computational Study ◽  
Near Field ◽  
Velocity Ratio ◽  
Leeward Side ◽  
Dynamic Features ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Scale Structures

Results of a three-dimensional unsteady computational study of a row of jets injected normal to a crossflow are presented with the aim of understanding the dynamics of the large-scale structures in the region near the jet. The jet to crossflow velocity ratio is 0.5. A modified version of the computer program (INS3D), which utilizes the method of artificial compressibility, is used for the computations. Results obtained clearly indicate that the near-field large-scale structures are extremely dynamic in nature, and undergo breakup and reconnection processes. The dynamic near-field structures identified include the counterrotating vortex pair (CVP), the horseshoe vortex, wake vortex, wall vortex, and shear layer vortex. The dynamic features of these vortices are presented in this paper. The CVP is observed to be a convoluted structure interacting with the wall and horseshoe vortices. The shear layer vortices are stripped by the crossflow, and undergo pairing and stretching events in the leeward side of the jet. The wall vortex is reoriented into the upright wake system. Comparison of the predictions with mean velocity measurements is made. Reasonable agreement is observed.

Large Eddy Simulation of Self-Sustained Cavity Oscillation for Subsonic and Supersonic Flows

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
K. M. Nair ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Shear Layer ◽  
Acoustic Waves ◽  
Large Scale ◽  
Hydrodynamic Instability ◽  
Supersonic Flows ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Structures

The primary objective is to perform a large eddy simulation (LES) using shear improved Smagorinsky model (SISM) to resolve the large-scale structures, which are primarily responsible for shear layer oscillations and acoustic loads in a cavity. The unsteady, three-dimensional (3D), compressible Navier–Stokes (N–S) equations have been solved following AUSM+-up algorithm in the finite-volume formulation for subsonic and supersonic flows, where the cavity length-to-depth ratio was 3.5 and the Reynolds number based on cavity depth was 42,000. The present LES resolves the formation of shear layer, its rollup resulting in large-scale structures apart from shock–shear layer interactions, and evolution of acoustic waves. It further indicates that hydrodynamic instability, rather than the acoustic waves, is the cause of self-sustained oscillation for subsonic flow, whereas the compressive and acoustic waves dictate the cavity oscillation, and thus the sound pressure level for supersonic flow. The present LES agrees well with the experimental data and is found to be accurate enough in resolving the shear layer growth, compressive wave structures, and radiated acoustic field.

Planar Imaging of Vortex Dynamics in Flames

1989 ◽  
Vol 111 (1) ◽  
pp. 148-155 ◽  
Author(s):  
E. Gutmark ◽  
T. P. Parr ◽  
D. M. Parr ◽  
K. C. Schadow
Keyword(s):  
Fluid Dynamics ◽  
Shear Layer ◽  
Large Scale ◽  
Combustion Process ◽  
Oh Radical ◽  
Planar Imaging ◽  
Reaction Parameters ◽  
Large Scale Structures ◽  
Planar Laser ◽  
Scale Structures

The interaction between the fluid dynamics and the combustion process in an annular diffusion flame was studied experimentally using the Planar Laser Induced Fluorescence (PLIF) technique. The local temperature and OH radical fluorescence signals were mapped in the entire flame cross section. The flame was forced at different instability frequencies, thus enabling the study of the evolution and interaction of large-scale structures in the flame shear layer. The present study of the effect of fluid dynamics on combustion is part of a more comprehensive program aimed at understanding and controlling the effect of heat release, density variations, and reaction parameters on the shear layer evolution.

Flow Instabilities in Gas Turbine Chute Seals

2019 ◽  
Author(s):  
Joshua T. M. Horwood ◽  
Fabian P. Hualca ◽  
Mike Wilson ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
...  
Keyword(s):  
Large Scale ◽  
Computational Study ◽  
Leading Edge ◽  
Large Scale Structures ◽  
Strong Shear ◽  
Time Marching ◽  
Flow Through ◽  
Scale Structures ◽  
Large Scale Flow ◽  
Secondary Flow Field

Abstract The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurised purge required to protect highly-stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations — which include a 360° domain — were undertaken using DLR TRACE’s time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30° to 360° indicate that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60° sector and suggest that modelling an even number of blades in small sector simulations should be avoided.

Vortex dynamics and sound emission in excited high-speed jets

2018 ◽  
Vol 839 ◽  
pp. 313-347 ◽  
Author(s):  
Michael Crawley ◽  
Lior Gefen ◽  
Ching-Wen Kuo ◽  
Mo Samimy ◽  
Roberto Camussi
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Noise Source ◽  
Near Field ◽  
Velocity Fields ◽  
Source Mechanism ◽  
Time Resolved ◽  
Large Scale Structures ◽  
Coherent Ring ◽  
Scale Structures

This work aims to study the dynamics of and noise generated by large-scale structures in a Mach 0.9 turbulent jet of Reynolds number $6.2\times 10^{5}$ using plasma-based excitation of shear layer instabilities. The excitation frequency is varied to produce individual or periodic coherent ring vortices in the shear layer. First, two-point cross-correlations are used between the acoustic near field and far field in order to identify the dominant noise source region. The large-scale structure interactions are then investigated by stochastically estimating time-resolved velocity fields using time-resolved near-field pressure traces and non-time-resolved planar velocity snapshots (obtained by particle image velocimetry) by means of an artificial neural network. The estimated time-resolved velocity fields show multiple mergings of large-scale structures in the shear layer, and indicate that disintegration of coherent ring vortices is the dominant aeroacoustic source mechanism for the jet studied here. However, the merging of vortices in the initial shear layer is also identified as a non-trivial noise source mechanism.

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