A Comparison Between Round Turbulent Jets and Particle-Laden Jets in Crossflow by Using Time-Resolved Stereoscopic Particle Image Velocimetry

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
F. J. Diez ◽  
M. M. Torregrosa ◽  
S. Pothos
Keyword(s):  
Particle Image Velocimetry ◽  
High Intensity ◽  
Particle Image ◽  
Three Dimensional ◽  
Continuous Phase ◽  
Stereoscopic Particle Image Velocimetry ◽  
Dispersed Phase ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Phase Images

Time-resolved stereoscopic particle image velocimetry (TR-ST-PIV) measurements were performed to compare the velocity and vorticity field, and the three-dimensional high intensity vorticity structures between a round turbulent single-phase jet and a particle-laden jet in crossflow. The experiments involved steady fresh water jet sources with a particle mass loading of ∼2.0% injected into steady fresh water crossflows. The TR-ST-PIV system was combined with a phase discrimination method that separates two-phase stereo PIV images into dispersed phase images and continuous phase images that are analyzed by using particle tracking velocimetry and stereo-PIV algorithms, respectively. The analysis shows the importance of phase separation for accurate velocity results. It provides instantaneous velocity fields where the dispersed phase preferentially concentrated in regions of low vorticity with the velocity not matching the continuous phase. The jet and the particle-laden jets trajectories are compared to each other and with results in the literature. Similarly, a comparison of mean velocity and vorticity fields between both flows suggest enhanced mixing in the particle-laden jet due to the effects of the dispersed phased which lowered the centerline velocities and enhanced the penetration in the cross-stream direction of the continuous phase. The Taylor’s frozen flow hypothesis is applied to reconstruct the 3D high intensity vorticity structures in a volume. The visualization of the three-dimensional structures corresponding to the intermediate scales of the flow shows slightly elongated structures preferentially aligned with the jet centerline axis.

Stereoscopic Particle Image Velocimetry Analysis of Healthy and Emphysemic Alveolar Sac Models

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Emily J. Berg ◽  
Risa J. Robinson
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Flow Fields ◽  
Stereoscopic Particle Image Velocimetry ◽  
Recirculating Flow ◽  
Image Velocimetry ◽  
Flow Speeds ◽  
Healthy Lung

Emphysema is a progressive lung disease that involves permanent destruction of the alveolar walls. Fluid mechanics in the pulmonary region and how they are altered with the presence of emphysema are not well understood. Much of our understanding of the flow fields occurring in the healthy pulmonary region is based on idealized geometries, and little attention has been paid to emphysemic geometries. The goal of this research was to utilize actual replica lung geometries to gain a better understanding of the mechanisms that govern fluid motion and particle transport in the most distal regions of the lung and to compare the differences that exist between healthy and emphysematous lungs. Excised human healthy and emphysemic lungs were cast, scanned, graphically reconstructed, and used to fabricate clear, hollow, compliant models. Three dimensional flow fields were obtained experimentally using stereoscopic particle image velocimetry techniques for healthy and emphysematic breathing conditions. Measured alveolar velocities ranged over two orders of magnitude from the duct entrance to the wall in both models. Recirculating flow was not found in either the healthy or the emphysematic model, while the average flow rate was three times larger in emphysema as compared to healthy. Diffusion dominated particle flow, which is characteristic in the pulmonary region of the healthy lung, was not seen for emphysema, except for very small particle sizes. Flow speeds dissipated quickly in the healthy lung (60% reduction in 0.25 mm) but not in the emphysematic lung (only 8% reduction 0.25 mm). Alveolar ventilation per unit volume was 30% smaller in emphysema compared to healthy. Destruction of the alveolar walls in emphysema leads to significant differences in flow fields between the healthy and emphysemic lung. Models based on replica geometry provide a useful means to quantify these differences and could ultimately improve our understanding of disease progression.

scholarly journals Investigation of Film Cooling Using Time-Resolved Stereo Particle Image Velocimetry

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Katharina Stichling ◽  
Maximilian Elfner ◽  
Hans-Jörg Bauer
Keyword(s):  
Particle Image Velocimetry ◽  
Film Cooling ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Test Rig ◽  
Time Resolved ◽  
Hot Gas ◽  
Image Velocimetry ◽  
Cooling Air

Abstract In the present study, an existing test rig at the Institute of Thermal Turbomachinery (ITS), Karlsruhe Institute of Technology (KIT), designed for generic film cooling studies is adopted to accommodate time-resolved stereoscopic particle image velocimetry (SPIV) measurements. Through a similarity analysis, the test rig geometry is scaled by a factor of about 20. Operating conditions of hot gas and cooling air inlet and exit can be imposed that are compliant with realistic engine conditions including density ratio (DR). The cooling air is supplied by a parallel-to-hot gas coolant flow-configuration with a coolant Reynolds number of 30, 000. Time-resolved and time-averaged stereo article image velocimetry data for a film cooling flow at high DR and a range of blowing ratios are presented in this study. The investigated film cooling hole constitutes a 10 deg–10 deg–10 deg laidback fan-shaped hole with a wide spacing of P/D = 8 to insure the absence of jet interaction. The inclination angle amounts to 35 deg. The time-resolved data indicate transient behavior of the film cooling jet.

Investigation of three-dimensional structure of fine scales in a turbulent jet by using cinematographic stereoscopic particle image velocimetry

2008 ◽  
Vol 598 ◽  
pp. 141-175 ◽  
Author(s):  
B. GANAPATHISUBRAMANI ◽  
K. LAKSHMINARASIMHAN ◽  
N. T. CLEMENS
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Stereoscopic Particle Image Velocimetry ◽  
Strain Fields ◽  
Plane Normal ◽  
Taylor’S Hypothesis ◽  
Image Velocimetry ◽  
Vortex Tubes

Cinematographic stereoscopic particle image velocimetry measurements were performed to resolve small and intermediate scales in the far field of an axisymmetric co-flowing jet. Measurements were performed in a plane normal to the axis of the jet and the time-resolved measurement was converted to quasi-instantaneous three-dimensional data by using Taylor's hypothesis. The quasi-instantaneous three-dimensional data enabled computation of all nine components of the velocity gradient tensor over a volume. The results based on statistical analysis of the data, including computation of joint p.d.f.s and conditional p.d.f.s of the principal strain rates, vorticity and dissipation, are all in agreement with previous numerical and experimental studies, which validates the quality of the quasi-instantaneous data. Instantaneous iso-surfaces of the principal intermediate strain rate (β) show that sheet-forming strain fields (i.e. β > 0) are themselves organized in the form of sheets, whereas line-forming strain fields (β < 0) are organized into smaller spotty structures (not lines). Iso-surfaces of swirling strength (a vortex identification parameter) in the volume reveal that, in agreement with direct numerical simulation results, the intense vortex structures are in the form of elongated ‘worms’ with characteristic diameter of approximately 10η and characteristic length of 60--100η. Iso-surfaces of intense dissipation show that the most dissipative structures are in the form of sheets and are associated with clusters of vortex tubes. Approximately half of the total dissipation occurs in structures that are generally sheet-like, whereas the other half occurs in broad indistinct structures. The largest length scale of dissipation sheets is of order 60η and the characteristic thickness (in a plane normal to the axis of the sheet) is about 10η. The range of scales between 10η (thickness of dissipation sheets, diameter of vortex tubes) to 60η (size of dissipation sheet or length of vortex tubes) is consistent with the bounds for the dissipation range in the energy and dissipation spectrum as inferred from the three-dimensional model energy spectrum.

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