Evolution of fluid-like granular ejecta generated by sphere impact

2012 ◽  
Vol 704 ◽  
pp. 5-36 ◽  
Author(s):  
J. O. Marston ◽  
E. Q. Li ◽  
S. T. Thoroddsen
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Early Stage ◽  
Thin Sheet ◽  
Solid Sphere ◽  
Liquid Pool ◽  
Glass Beads ◽  
High Speed Imaging ◽  
Shape Distribution ◽  
The Finest Grains

AbstractWe present results from an experimental study of the speed and shape of the ejecta formed when a solid sphere impacts onto a granular bed. We use high-speed imaging at frame rates up to 100 000 f.p.s. to provide direct measurement of individual grain velocities and ejecta angles as well as the overall evolution of the granular ejecta. For larger grain sizes, the emergence velocities of the grains during the ‘early stage flow’, i.e. before the main ejecta ‘curtain’ forms, increase with the kinetic energy of the impacting sphere but are inversely proportional to the time from impact. We also observe that the fastest grains, which can obtain velocities up to five times that of the impacting sphere (${V}_{g} / {V}_{0} = 5$), generally emerge at the earliest times and with the lowest ejection angles. As the grain size is decreased, a more ‘fluid-like’ behaviour is observed whereby the ejected material first emerges as a thin sheet of grains between the sphere and the bed surface, which is also seen when a sphere impacts a liquid pool. In this case, the sheet velocity is approximately double that of the impacting sphere (${V}_{s} / {V}_{0} = 2$) and independent of the bulk packing fraction. For the finest grains we provide evidence of the existence of a vortex ring inside the ejecta curtain where grains following the air flow are entrained through the curtain. In contrast to predictions from previous studies, we find that the temporal evolution of the ejecta neck radius is not initially quadratic but rather approaches a square-root dependence on time, for the finest grains with the highest impact kinetic energy. The evolution therefore approaches that seen for the crown evolution in liquid drop impacts. By using both spherical glass beads and coarse sands, we show that the size and shape distribution are critical in determining the post-impact dynamics whereby the sands exhibit a qualitatively different response to impact, with grains ejected at lower speeds and at later times than for the glass beads.

Simulations of flame propagation during the ignition process in an annular multiple-injector combustor

2019 ◽  
Vol 29 (6) ◽  
pp. 1947-1964 ◽  
Author(s):  
Dongmei Zhao ◽  
Yifan Xia ◽  
Haiwen Ge ◽  
Qizhao Lin ◽  
Jianfeng Zou ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Adaptive Mesh Refinement ◽  
High Speed ◽  
Early Stage ◽  
Adaptive Mesh ◽  
Critical Issue ◽  
Experimental Investigations ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Content Type

Purpose Ignition process is a critical issue in combustion systems. It is particularly important for reliability and safety prospects of aero-engine. This paper aims to numerically investigate the burner-to-burner propagation during ignition process in a full annular multiple-injector combustor and then validate it by comparing with experimental results. Design/methodology/approach The annular multiple-injector experimental setup features 16 swirling injectors and two quartz tubes providing optical accesses to high-speed imaging of flames. A Reynolds averaged Navier–Stokes model, adaptive mesh refinement (AMR) and complete San Diego chemistry are used to predict the ignition process. Findings The ignition process shows an overall agreement with experiment. The integrated heat release rate of simulation and the integrated light intensity of experiment is also within reasonable agreement. The flow structure and flame propagation dynamics are carefully analyzed. It is found that the flame fronts propagate symmetrically at an early stage and asymmetrically near merging stage. The flame speed slows down before flame merging. Overall, the numerical results show that the present numerical model can reliably predict the flame propagation during the ignition process. Originality/value The dedicated AMR method together with detailed chemistry is used for predicting the unsteady ignition procedure in a laboratory-scale annular combustor for the first time. The validation shows satisfying agreements with the experimental investigations. Some details of flow structures are revealed to explain the characteristics of unsteady flame propagations.

Cooling of High-Performance Server Modules Using Direct Immersion

2012 ◽  
Author(s):  
Aravind Sridhar ◽  
Sarah Styslinger ◽  
Christopher Duron ◽  
Sushil H. Bhavnani ◽  
Roy W. Knight ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
High Performance ◽  
Heat Dissipation ◽  
Heat Removal ◽  
Liquid Pool ◽  
Circuit Board ◽  
Air Cooling ◽  
High Speed Imaging ◽  
Close Proximity

An alternative to air-cooling of high performance computing equipment is presented. Heat removal via pool boiling in FC-72 was tested. Tests were conducted on a multichip module using 1.8 cm × 1.8 cm test die with multiple thermal test cells with temperature sensing capability. Measurements with the bare silicon die in direct contact with the fluid are reported. Additional testing included the test die directly indium-attached to copper heat spreaders having surface treatments. A screen-printed sintered boiling-enhanced surface (4 cm × 4 cm) was evaluated. Tests were conducted on an array of five die. Parameters tested include heat flux levels, dielectric liquid pool conditions (saturated or subcooled), and effect of neighboring die. Information was gathered on surface temperatures for a range of heat flux values up to 12 W/cm2. The highest heat dissipated from a circuit board with five bare die was 195 W (39 W per die). Addition of the heat spreader allowed heat dissipation of up to 740 W (from a five-die array). High-speed imaging was also acquired to help examine detailed information on the boiling process. Numerical modeling indicated that placing multiple boards in close proximity to each other did not degrade performance until board spacing was reduced to 3 mm.

Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

2019 ◽  
Vol 47 (3) ◽  
pp. 196-210
Author(s):  
Meghashyam Panyam ◽  
Beshah Ayalew ◽  
Timothy Rhyne ◽  
Steve Cron ◽  
John Adcox
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Imaging ◽  
Correlation Algorithm ◽  
Mode Decomposition ◽  
Series Of Experiments ◽  
Plane Deformations ◽  
Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

APPLICATION OF THE EARLY DAMAGE DIAGNOSTICS TECHNIQUE TO EXAMINATION OF THE AVIATION PANEL

2019 ◽  
Vol 85 (6) ◽  
pp. 53-63 ◽  
Author(s):  
I. E. Vasil’ev ◽  
Yu. G. Matvienko ◽  
A. V. Pankov ◽  
A. G. Kalinin
Keyword(s):  
Acoustic Emission ◽  
Damage Detection ◽  
High Speed ◽  
Early Stage ◽  
Video Data ◽  
High Speed Video ◽  
Damage Diagnostics ◽  
Subsurface Defect ◽  
Sensitive Coating ◽  
Early Damage

The results of using early damage diagnostics technique (developed in the Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN) for detecting the latent damage of an aviation panel made of composite material upon bench tensile tests are presented. We have assessed the capabilities of the developed technique and software regarding damage detection at the early stage of panel loading in conditions of elastic strain of the material using brittle strain-sensitive coating and simultaneous crack detection in the coating with a high-speed video camera “Video-print” and acoustic emission system “A-Line 32D.” When revealing a subsurface defect (a notch of the middle stringer) of the aviation panel, the general concept of damage detection at the early stage of loading in conditions of elastic behavior of the material was also tested in the course of the experiment, as well as the software specially developed for cluster analysis and classification of detected location pulses along with the equipment and software for simultaneous recording of video data flows and arrays of acoustic emission (AE) data. Synchronous recording of video images and AE pulses ensured precise control of the cracking process in the brittle strain-sensitive coating (tensocoating)at all stages of the experiment, whereas the use of structural-phenomenological approach kept track of the main trends in damage accumulation at different structural levels and identify the sources of their origin when classifying recorded AE data arrays. The combined use of oxide tensocoatings and high-speed video recording synchronized with the AE control system, provide the possibility of definite determination of the subsurface defect, reveal the maximum principal strains in the area of crack formation, quantify them and identify the main sources of AE signals upon monitoring the state of the aviation panel under loading P = 90 kN, which is about 12% of the critical load.

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