Spatio-Temporal Development of Supercavitation Over an Impulsively Launched Projectile

2006 ◽  
Author(s):  
C. J. Weiland ◽  
P. P. Vlachos
Keyword(s):  
High Speed ◽  
Temporal Development ◽  
Two Phase ◽  
Time Resolved ◽  
Gas Gun ◽  
Supercavitating Flow ◽  
Image Velocimetry ◽  
Spatio Temporal ◽  
Asymmetric Vortices ◽  
First Time

Supercavitation inception and formation was studied over blunt projectiles. The projectiles were fired using a gas gun method. In this method, projectiles are launched under the action of expanding detonation gases. Both qualitative and quantitative optical flow diagnostics using high speed digital imaging were used to analyze the spatio-temporal development of the supercavitating flow. For the first time, quantification of the supercavitation was achieved using Time Resolved Digital Particle Image Velocimetry (TRDPIV) detailing the two phase flow field surrounding the translating projectiles and the gas vapor bubble. Experimental results indicate that the supercavity forms at the aft end of the projectile and travels forward along the direction of projectile travel. The impulsive start of the projectile generates two asymmetric vortices which are shed from the blunt nose of the projectile. The vortices interact with the moving cavity and subsequently deform. This interaction is believed to directly contribute to the instabilities in the flight path.

High Speed Visualization and PIV Measurements in the Near Field of Spray Produced by Flow-Blurring Atomization

2014 ◽  
Author(s):  
Lulin Jiang ◽  
Ajay K. Agrawal ◽  
Robert P. Taylor
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Near Field ◽  
Liquid Fuels ◽  
Two Phase ◽  
Time Resolved ◽  
Straight Vegetable Oil ◽  
Image Velocimetry ◽  
Fine Spray ◽  
Field Plots

Clean and stable combustion of alternative liquid fuels, such as biodiesel, straight vegetable oil and glycerol has been achieved in past studies by using a novel flow blurring (FB) injector without fuel pre-processing or combustor hardware modification. FB injector employs aerodynamic principle to form two phase flow immediately upstream of the injector exit. Explosion of air bubbles at the injector exit atomizes the liquid into a fine spray. In this study, the flow field in the near field of the FB injector is investigated by high-speed visualization and time-resolved Particle Image Velocimetry (PIV) techniques. Experiments are performed using water and air for air to liquid mass ratio (ALR) of 2. Flow visualization at the injector exit focused on field of view with the dimension of 2.3 mm × 1.4 mm, spatial resolution of 7.16 μm per pixel, exposure time of 1 μs, and image acquisition rate of 100 k frames per second (fps). Image sequence illustrates fine spray of FB atomization in the near field and the break-down process of larger droplets appearing occasionally. Time-resolved PIV technique is applied to quantify the injector near field. Plots of instantaneous, mean, root-mean-square velocities and turbulence kinetic energy are presented to reveal the droplet characteristics and secondary atomization process. Results show that the majority of the liquid is atomized into fine droplets at the injector exit. The droplet velocity increases in the flow direction and decreases from the center to the periphery of the spray. This result is consistent with the size of the droplets, i.e., the larger droplets move slowly while the finer droplets move faster as they follow the atomizing air flow.

Visualization and Time-Resolved Particle Image Velocimetry Measurements of the Flow in the Tip Region of a Subsonic Compressor Rotor

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
David Tan ◽  
Yuanchao Li ◽  
Ian Wilkes ◽  
Rinaldo L. Miorini ◽  
Joseph Katz
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Axial Compressor ◽  
Time Resolved ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Direct Measurements ◽  
Image Velocimetry ◽  
The One ◽  
And Behavior

A new optically index matched facility has been constructed to investigate tip flows in compressor-like settings. The blades of the one and a half stage compressor have the same geometry, but lower aspect ratio as the inlet guide vanes (IGVs) and the first stage of the low-speed axial compressor (LSAC) facility at NASA Glenn. With transparent blades and casings, the new setup enables unobstructed velocity measurements at any point within the tip region and is designed to facilitate direct measurements of effects of casing treatments on the flow structure. We start with a smooth endwall casing. High speed movies of cavitation and time-resolved PIV measurements have been used to characterize the location, trajectory, and behavior of the tip leakage vortex (TLV) for two flow rates, the lower one representing prestall conditions. Results of both methods show consistent trends. As the flow rate is reduced, TLV rollup occurs further upstream, and its initial orientation becomes more circumferential. At prestall conditions, the TLV is initially aligned slightly upstream of the rotor passage, and subsequently forced downstream. Within the passage, the TLV breaks up into a large number of vortex fragments, which occupy a broad area. Consequently, the cavitation in the TLV core disappears. With decreasing flow rate, this phenomenon becomes more abrupt, occurs further upstream, and the fragments occupy a larger area.

Unveiling the Flow Behavior Inside GDI Engine Cylinder Using High-Speed Time-Resolved Particle Image Velocimetry and CFD Simulation

2021 ◽  
Author(s):  
Mohammed El Adawy ◽  
Morgan Heikal ◽  
bin Abd. Aziz Abd. Rashid
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
Cfd Simulation ◽  
Injection Pressure ◽  
Valve Lift ◽  
Fuel Spray ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Spray Plume

Abstract RICARDO-VECTIS CFD simulation of the in-cylinder air flow was first validated with those of the experimental results from high-speed particle image velocimetry (PIV) measurements taking cognisant of the mid-cylinder tumble plane. Furthermore, high-speed fuel spray measurements were carried out simultaneously with the intake-generated tumble motion at high valve lift using high-speed time-resolved PIV to chronicle the spatial and time-based development of air/fuel mixture. The effect of injection pressure(32.5 and 35.0 MPa) and pressure variation across the air intake valves(150, 300 and 450 mmH2O) on the interaction process were investigated at valve lift 10 mm where the tumble vortex was fully developed and filled the whole cylinder under steady-state conditions. The PIV results illustrated that the intake generated-tumble motion had a substantial impact on the fuel spray distortion and dispersion inside the cylinder. During the onset of the injection process the tumble motion diverted the spray plume slightly towards the exhaust side before it followed completely the tumble vortex. The fuel spray plume required 7.2 ms, 6.2 ms and 5.9 ms to totally follow the in-cylinder air motion for pressure differences 150, 300 and 450 mmH2O, respectively. Despite, the spray momentum was the same for the same injection pressure, the magnitude of kinetic energy was different for different cases of pressure differences and subsequently the in-cylinder motion strength.

scholarly journals Experimental Investigation of the Pumping of a Model-Concrete through Pipes

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1161
Author(s):  
Martin A. Haustein ◽  
Moritz N. Kluwe ◽  
Rüdiger Schwarze
Keyword(s):  
Pressure Loss ◽  
Plug Flow ◽  
Particle Migration ◽  
Test Plant ◽  
Flow Profile ◽  
Time Resolved ◽  
Rheological Measurements ◽  
Lubricating Layer ◽  
Image Velocimetry ◽  
First Time

Many practical aspects of processing fresh concrete depend on its rheology, such as the pumping of the material. It is known that a lubricating layer is formed in the process, which significantly reduces the pumping pressure. However, these phenomena can hardly be considered in the usual rheological measurements. A main problem is the optical inaccessibility of the material, which prevents estimations about, e.g., the thickness of the plug flow or particle migration. In this paper, the pneumatic pumping of a transparent model concrete is performed by means of a test plant. The flow profile over the entire pipe cross-section is resolved in time and space via Particle Image Velocimetry (PIV) measurements. This allows the comparison with the analytical flow profile from rheological measurements of the material using the Buckingham–Reiner equation. A reduction of the pressure loss to around 60% induced through segregation of the material is found. These measurements reflect the rheology of the material under realistic pumping conditions including particle migration. This makes it possible for the first time to observe a transparent material with concrete-like rheology under pulsating pumping conditions and to compare the true and calculated time-resolved pressure loss.

scholarly journals Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

2012 ◽  
Vol 9 (77) ◽  
pp. 3378-3386 ◽  
Author(s):  
Richard J. Bomphrey ◽  
Per Henningsson ◽  
Dirk Michaelis ◽  
David Hollis
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Flow Fields ◽  
Diagnostic Methods ◽  
Tomographic Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Spatio Temporal

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread.

A Method for Identifying and Visualizing Foreign Particle Motion Using Time Resolved Particle Tracking Velocimetry

2009 ◽  
Author(s):  
N. D. Cardwell ◽  
P. P. Vlachos ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Particle Tracking Velocimetry ◽  
Internal Cooling ◽  
Particle Collisions ◽  
Two Phase ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Particle Ingestion ◽  
Film Cooling Holes

Gas turbines for aircraft are designed for operation with a clean inlet air flow. This ideal operational condition is often violated during take-off and landing, where the probability of particle ingestion is high with sand and dirt being the most commonly observed foreign particles. Current research on particle ingestion has identified several mechanisms that contribute to performance degradation in the turbine: erosion of internal and external surfaces; and flow blockages of film-cooling holes and internal cooling passages. The focus of the study given in this paper is to present a method that identifies the motion of foreign particles within an internal ribbed passage. The method uses a high-resolution, flowfield interrogation method known as Time-Resolved Digital Particle Image Velocimetry (TRDPIV). Observations from the two-phase flows showed that particle collisions occurred more frequently on the upstream surface of the ribs, especially in the inlet region. Results from these collisions included substantial particle breakup and a particle rebounding phenomenon between the upper and lower walls. Comparisons are made to LES predicted particle trajectories indicating some agreement, but also phenomena that are not predicted due to the inherent assumption of the modeling.

A Method for Identifying and Visualizing Foreign Particle Motion Using Time-Resolved Particle Tracking Velocimetry

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
N. D. Cardwell ◽  
P. P. Vlachos ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Internal Cooling ◽  
Particle Collisions ◽  
Two Phase ◽  
Time Resolved ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Particle Ingestion ◽  
Film Cooling Holes

Gas turbines for aircraft are designed for operation with a clean inlet air flow. This ideal operational condition is often violated during take-off and landing, where the probability of particle ingestion is high, with sand and dirt being the most commonly observed foreign particles. Current research on particle ingestion has identified several mechanisms that contribute to performance degradation in the turbine: erosion of internal and external surfaces, and flow blockages of film-cooling holes and internal cooling passages. The focus of the study given in this paper is to present a method that identifies the motion of foreign particles within an internal ribbed passage. The method uses a high-resolution, flow field interrogation method known as time-resolved digital particle image velocimetry (TRDPIV). Observations from the two-phase flows showed that particle collisions occurred more frequently on the upstream surface of the ribs, especially in the inlet region. Results from these collisions included substantial particle breakup, and a particle rebounding phenomenon between the upper and lower walls. Comparisons are made to large eddy simulation predicted particle trajectories indicating some agreement, as well as phenomena that are not predicted due to the inherent assumption of the modeling.

scholarly journals Time-resolved vortex wake of a common swift flying over a range of flight speeds

2010 ◽  
Vol 8 (59) ◽  
pp. 807-816 ◽  
Author(s):  
P. Henningsson ◽  
F. T. Muijres ◽  
A. Hedenström
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Digital Particle Image Velocimetry ◽  
Transverse Plane ◽  
The Body ◽  
Vortex Wake ◽  
Vertical Force ◽  
Time Resolved ◽  
Longitudinal Plane ◽  
Image Velocimetry

The wake of a freely flying common swift ( Apus apus L.) is examined in a wind tunnel at three different flight speeds, 5.7, 7.7 and 9.9 m s −1 . The wake of the bird is visualized using high-speed stereo digital particle image velocimetry (DPIV). Wake images are recorded in the transverse plane, perpendicular to the airflow. The wake of a swift has been studied previously using DPIV and recording wake images in the longitudinal plane, parallel to the airflow. The high-speed DPIV system allows for time-resolved wake sampling and the result shows features that were not discovered in the previous study, but there was approximately a 40 per cent vertical force deficit. As the earlier study also revealed, a pair of wingtip vortices are trailing behind the wingtips, but in addition, a pair of tail vortices and a pair of ‘wing root vortices’ are found that appear to originate from the wing/body junction. The existence of wing root vortices suggests that the two wings are not acting as a single wing, but are to some extent aerodynamically detached from each other. It is proposed that this is due to the body disrupting the lift distribution over the wing by generating less lift than the wings.

scholarly journals Preparative Separation of Alkaloids from Stem of Euchresta tubulosa Dunn. by High-Speed Counter-Current Chromatography Using Stepwise Elution

Molecules ◽  
2019 ◽  
Vol 24 (24) ◽  
pp. 4602 ◽  
Author(s):  
Weixin Li ◽  
Huan Wang ◽  
Aiwen Dong
Keyword(s):  
High Speed ◽  
Methylene Chloride ◽  
Liquid Extraction ◽  
Preparative Separation ◽  
Target Compound ◽  
Two Phase ◽  
Chinese Herbal ◽  
Liquid Liquid Extraction ◽  
Counter Current ◽  
First Time

Euchresta tubulosa Dunn. is a Chinese herbal medicine with biological activity, but there are few studies on its components at present. Alkaloids in the stem of Euchresta tubulosa Dunn. were isolated and purified by high-speed counter-current chromatography (HSCCC) using stepwise elution. First of all, liquid-liquid extraction (methylene chloride-methanol-water, 5:1:4, v/v) was used for the preliminary enrichment. According to the partition coefficient (K) of a target compound in a series of different two-phase solvents, the final result was that carbon tetrachloride-methylene chloride-methanol-water (2:3:3:2, v/v) (1) and methylene chloride-methanol-water (5:3:2, v/v) (2) were suitable for the HSCCC using stepwise elution. As a result, the purity was all higher than 93% and matrine (1), oxymatrine (2), N-formyl cytisine (3), and N-acetyl cytisine (4) can be eluted at one time by this mode. Cytisine-type alkaloids were isolated for the first time in this plant. Finally, the applicability of the mode was verified.

scholarly journals Application of SIM, HSPIV, BTM, and BIV Techniques for Evaluations of a Two-Phase Air–Water Chute Aerator Flow

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1590
Author(s):  
James Yang ◽  
Chang Lin ◽  
Ming-Jer Kao ◽  
Penghua Teng ◽  
Rajkumar V. Raikar
Keyword(s):  
Probability Distribution ◽  
High Speed ◽  
Transverse Velocity ◽  
Image Method ◽  
Air Bubbles ◽  
Two Phase ◽  
Mean Velocity ◽  
Water Stream ◽  
Image Velocimetry ◽  
The Mean

Four image-based techniques—i.e., shadowgraphic image method (SIM), high-speed particle image velocimetry (HSPIV), bubble tracking method (BTM), and bubble image velocimetry (BIV)—are employed to investigate an aerator flow on a chute with a 17° inclination angle. The study focuses on their applications to the following issues: (1) to explore the characteristic positions of three water–air interfaces; (2) to interpret the evolution process of air bubbles shed from the wedged tip of the air cavity; (3) to identify the probabilistic means for characteristic positions near the fluctuating free surface; (4) to explore the probability distribution of intermittent appearance of air bubbles in the flow; (5) to obtain the mean streamwise and transverse velocity distributions of the water stream; (6) to acquire velocity fields, both instantaneous and mean, of air bubbles; (7) to construct a two-phase mean velocity field of both water flow and air-bubbles; and (8) to correlate the relationship among the probability distribution of air bubbles, the mean streamwise and transverse velocity profiles of air bubbles, and water stream. The combination of these techniques contributes to a better understanding of two-phase flow characteristics of the chute aerator.

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