High-speed Digital Camera System Research Articles

Two-phase flow characteristics of different charging structure in ignition and flame-spreading

To study the influence of flame-spreading behaviour in the ignition process of different charging structures in high-density charge chambers, a visualisation device was designed, and the ignition process of the two charging structures was researched. The flame-spreading process was observed by a high-speed digital camera system and the pressure data was recorded by a data acquisition instrument. According to the experiment, a two-dimensional axisymmetric internal ballistic two-phase flow model was established to simulate the flow process of gas in particle bed based on the Weighted Essentially Non-Oscillatory (WENO) Scheme. The results show that the flow field and flame-spreading status in different charging structures are different. In the full charging structure, the development of the flow field is regular, the flow field in the entire chamber has less fluctuation areas, and velocity vortices only generate during the development of the flow field and when it reaches the wall. However, in the partially charging structure with free space, there are many pressure fluctuation areas in the flow field in the chamber, and the flow field development is also uneven. Pulsating propagation occurs at the interface between particles and free space, which has a great influence on the whole combustion and ignition process. The research results reveal the characteristics of two-phase flow in different charging structures and provide a reference for the actual charging process.

An investigation into container constraint effects on the cavity characteristics due to high-speed projectile water entry

In this paper, the influence of container dimension constraints on the cavity expansion characteristics were preliminary investigated through series of high-speed water-entry experiments with velocity in the range of 80–470 m/s. Particular attention is given to the characteristics of cavity evolution, surface and deep closure, average cavity wall velocity and the drag coefficient under container constraints. In the test configurations, three size cylindrical-shaped containers were employed, a digital high-speed camera system is used to photograph the projectile motion and cavity expansion within the water-filled containers. Experimental results show that the cavity in a larger container will reach a larger radius and collapses later than the cavity in a much smaller container. The container size has little effect on the time of surface closure and the location of deep closure but more on the time of deep closure. Moreover, it is found that as the container size decreases to a magnitude of the cavity diameter, the projectile velocity attenuation will be strongly affected by the container constraint. The objective of the present study is to provide original dynamic data for studying the nature of hydrodynamic ram caused by the cavity expansion in subsequent work.

Local Void Fractions and Bubble Velocity in Vertical Air-Water Two-Phase Flows Measured by Needle-Contact Capacitance Probe

Multiphase flow measurements have become increasingly important in a wide range of industrial fields. In the present study, a dual needle-contact capacitance probe was newly designed to measure local void fractions and bubble velocity in a vertical channel, which was verified by digital high-speed camera system. The theoretical analyses and experiments show that the needle-contact capacitance probe can reliably measure void fractions with the readings almost independent of temperature and salinity for the experimental conditions. In addition, the trigger-level method was chosen as the signal processing method for the void fraction measurement, with a minimum relative error of −4.59%. The bubble velocity was accurately measured within a relative error of 10%. Meanwhile, dynamic response of the dual needle-contact capacitance probe was analyzed in detail. The probe was then used to obtain raw signals for vertical pipe flow regimes, including plug flow, slug flow, churn flow, and bubbly flow. Further experiments indicate that the time series of the output signals vary as the different flow regimes and are consistent with each flow structure.

Experimental and Numerical Study of Concrete Targets under High Rate of Loading

In order to examine the ballistic resistance of plain concrete and reinforced concrete targets the perforation tests conducted in the laboratory, on square concrete targets size (450 mm x 450 mm x 80 mm) of plain concrete and reinforced concrete and to validate the experimentally obtained results Numerical simulations were carried out in Abaqus/Explicit finite element code. The unconfined target compressive strength of concrete was 48 MPa. A grid of steel bars having 8 mm diameter has been incorporated in reinforced concrete plates. The plates were subjected to normal impact of 0.5 kg ogive nosed hard steel cylindrical projectile having diameter of shaft 19 mm. The projectiles were accelerated by the laboratory pneumatic gun to velocities range between 53m/s to 220m/s. impact and residual velocities were measured with the help of Phantom-V411 high speed digital camera system. Ballistic limit of plain concrete and reinforced concrete targets had been obtained in the experiments as well as in the Numerical simulations in Finite element code Abaqus\\explicit. Also calculated spalling and scabbing volume of plain and reinforced concrete targets after perforation experiments, the reinforcement in the concrete has been found to be effective in minimizing the scabbing and spalling of material. The ballistic limit of reinforced concrete target was experimentally found 16.9% higher than plain concrete target, However Numerical simulations predicted the ballistic limit of plain concrete target within 8% and that of reinforced concrete target within 3% deviation in comparison to experimentally obtained ballistic limits.

Experimental Study of Plain and Reinforced Concrete Targets Subjected to Impact Loading

In order to study the influence of the plain concrete and reinforced concrete on ballistic performances. Penetration tests were conducted on different thicknesses of plain concrete and reinforced concrete plates having 40Mpa unconfined compressive strength and reinforcement of 8mm diameter steel mesh in reinforced concrete plates is incorporated. The plates were 450mm of diameter and 60mm, 80mm, 100mm thicknesses are studied. The plates were subjected to an impact of hard steel projectile with ogive nose weighing 1kg with diameter 19mm and length of 450mm. The projectiles were accelerated by the laboratory pneumatic gun to velocities range between 28m/s to 102m/s. impact and residual velocities were measured by the high speed digital camera system. Ballistic resistance of plain concrete and reinforced concrete at different thicknesses had been find out in the experiments and compared with already proposed analytical formula. The results thus obtained are presented and influences there on due to the variation in the concrete plate thicknesses to the projectile impact are discussed. The ballistic limit was found to increase with an increase of target thickness.

Design and application of a digital array high-speed camera system

In this paper, a digital array high-speed camera system is designed and applied in dynamic fracture experiment. First, the design scheme for 3*3 array digital high-speed camera system is presented, including 3*3 array light emitting diode (LED) light source unit, 3*3 array charge coupled device (CCD) camera unit, timing delay control unit, optical imaging unit and impact loading unit. Second, the influence of geometric optical parameters on optical parallax is analyzed based on the geometric optical imaging mechanism. Finally, combining the method of dynamic caustics with the digital high-speed camera system, the dynamic fracture behavior of crack initiation and propagation in PMMA specimen under low-speed impact is investigated to verify the feasibility of the high-speed camera system.

Droplet rebounded spatter in dry hyperbaric gas metal arc welding process

The spatter generation of dry hyperbaric gas metal arc welding (GMAW) was investigated by using a high-speed digital camera system. Two spatter types, droplet deviated spatter and droplet rebounded spatter, were observed. The generation of droplet deviated spatter is similar to the spatter generation in globular repelled transfer of GMAW at normal pressure, which is due to the high horizontal speed of the droplet detachment. This spatter type begins to appear at ambient pressure reached 0.2 MPa. Another type, droplet rebounded spatter, is a new spatter generating process. The spatter is always generated after the cathode root burning on the droplet which contacts to the workpiece. And then, the droplet rebounds to the free space and changes into the spatter instead of adhering to the workpiece. Droplet rebounded spatter is generated at the ambient pressure over 0.4 MPa. The reason that the electromagnetic force is the driving force of droplet rebounded was analyzed.

Bubble behavior of flow boiling in horizontal rectangular channels with inclined ribs

Visualization experiments were conducted to study flow boiling bubble behavior in ribbed rectangular channels at atmospheric pressure. A transparent conductive oxide film was placed on the inner surface of the channel to act as the heating source. Four rib configurations with different inclinations were examined, and the results are compared to those in a smooth channel. Heat and mass fluxes of 13.3–28.9kW/m2 and 152–333kg/(m2s) were considered, and the bubble behavior was captured using a high-speed digital camera system. Vapor bubble diameters and velocities were obtained from an analysis of the images, and we found that the bubble diameter decreases with increasing mass flux, which is also associated with an increase in the bubble sliding velocity and an inhibition of sliding bubble coalescence. For the rectangular channel, a rib angle of 45° provides the largest transverse component of the bubble sliding velocity as a result of the axial drag force and guiding force of the ribs. We conclude that a 45°-angle rib offers the best characteristics for flow boiling heat transfer.

Study on the effect of distance between the two nozzle holes on interaction of high pressure combustion-gas jets with liquid

The combustion-gas generator and cylindrical stepped-wall observation chambers with five stages are designed to study the expansion characteristic of twin combustion-gas jets in liquid working medium under high temperature and high pressure. The expansion processes of Taylor cavities formed by combustion-gas jets and the mixing characteristics of gas–liquid are studied by means of high-speed digital camera system. The effects of the distance between the two nozzle holes, injection pressure and nozzle diameter on jet expansion processes are discussed. The experimental results indicate that, the velocity differences exist on the gas–liquid interface during expansion processes of twin combustion-gas jets, and the effect of Taylor–Helmholtz instability is intense, so interfaces between gas and liquid show turbulent folds and randomness. The strong turbulent mixing of gas and liquid leads to release of combustion-gas energy with the temperature decreasing. Moreover, the mixing effectiveness is obviously enhanced on the corners of each step of the cylindrical stepped-wall structure, forming radial expansion phenomenon. The reasonable matching of multi-parameter can restrain the jet instability and make the combustion-gas energy orderly release. Based on the experiments, the three-dimensional unsteady mathematical model of interaction of twin combustion-gas jets and liquid working medium is established to obtain the density, pressure, velocity and temperature distribution characteristics in jet flow field. Discussions are focused on variation law of characteristic parameters of the flow field under different nozzle intervals. The results indicate that, as the ratio of diameter increment of each step to the nozzle interval ΔD/S≧0.6, twin combustion-gas jets begin converging earlier, and the jets can also reach the exit of observation chamber earlier. But as ΔD/S<0.6, the twin jets are closer to the chamber wall, and radial inductions from the expanding steps are stronger, so twin jets do not appear the collection effect on the space and time scale of the observation chamber and the pressure distributions of jet flow field are always more violent pulsation state. The calculated data of axial displacement of Taylor cavity heads are in good agreement with the experimental ones according to dealing with the density profiles and experimental sequence processes.

Study on Unsteady Combustion Behaviors of AP/HTPB Base‐Bleed Propellants under Transient Depressurization Conditions

AbstractAs the base‐bleed projectile flies out of the muzzle, the environmental pressure in the base‐bleed combustion chamber suddenly decreases and AP/HTPB base‐bleed propellant suffers intense unsteady combustion. To further study the unsteady combustion characteristics of base‐bleed propellants, a semi‐closed bomb as was designed experimental device and transient depressurization conditions of the muzzle were simulated. Measurements of the transient combustion characteristics of the base‐bleed propellant under high depressurization rate were carried out by using a high speed digital camera system. In the experiments, the combustion chamber pressure of the semi‐closed bomb was controlled from 20 to 90 MPa and the depressurization rate was controlled from 400 to1.12×104 MPa s−1. The experimental results indicate that, the out‐of‐phase blowing effect is intense under rapid depressurization condition, leading to the reaction layer thickened. The thermal feedback to the solid surface decreases and thus the combustion reaction of gas phase is so difficult to maintain that it begins to extinguish. However, the thermal decomposition of the solid phase is still continuing and a yellow fog can be observed above the combustion chamber nozzle. Depending on the maximum pressure in the combustion chamber and depressurization rate, the transient combustion behavior of AP/HTPB base‐bleed propellant displays three patterns, i.e., automatic reignition, oscillating combustion (a critical type) and permanent extinguishment. Three unsteady combustion behaviors are preliminarily analyzed based on the thermal feedback. If the initial pressure in the combustion chamber before depressurization is larger or the depressurization rate is smaller, the base‐bleed propellant tends to automatically reignite earlier and the combustion process is more stable.

A New Ex Vivo Beating Heart Model to Investigate the Application of Heart Valve Performance Tools with a High-Speed Camera

High-speed camera examination of heart valves is an established technique to examine heart valve prosthesis. The aim of this study was to examine the possibility to transmit new tools for high-speed camera examination of heart valve behavior under near-physiological conditions in a porcine ex vivo beating heart model. After explantation of the piglet heart, main coronary arteries were cannulated and the heart was reperfused with the previously collected donor blood. When the heart started beating in sinus rhythm again, the motion of the aortic and mitral valve was recorded using a digital high-speed camera system (recording rate 2,000 frames/sec). The image sequences of the mitral valve were analyzed, and digital kymograms were calculated at different angles for the exact analysis of the different closure phases. The image sequence of the aortic valve was analyzed, and several snakes were performed to analyze the effective orifice area over the time. Both processing tools were successfully applied to examine heart valves in this ex vivo beating heart model. We were able to investigate the exact open and closure time of the mitral valve, as well as the projected effective orifice area of the aortic valve over the time. The high-speed camera investigation in an ex vivo beating heart model of heart valve behavior is feasible and also reasonable because of using processing feature such as kymography for exact analysis. These analytical techniques might help to optimize reconstructive surgery of the mitral valve and the development of heart valve prostheses in future.

Perforation experiments of concrete targets with residual velocity measurements

Perforation experiments of concrete by steel projectiles have been carried out. The projectiles' initial velocity out of the gun bore was measured with electric probes. A high-speed digital camera system was used to photograph the penetration events. The residual velocities of the projectiles were acquired using foil screen targets, which was designed and built by us. The launch acceleration in the gun bore and the deceleration during the perforation event was recorded with an acceleration transducer. Several perforation tests using concrete targets of different thicknesses were conducted with a nominal striking velocity of 400 m/s. The residual velocity and kinetic energy consumed versus the target thickness was analyzed. The perforation limit was also obtained.

Features of Meso-Deformation and Failure of Aluminum Foam under Impact

Deformation and failure of meso-structures take great effect on the loading and energy absorption of aluminum foam under impact. We designed a split Hopkinson pressure bar (SHPB)-high speed digital camera system to monitor the meso-deformation and failure features, and measure the nonuniformity of deformation of aluminum foam under impact. The meso-deformation and failure of aluminum foam were observed successfully by the system, and it showed that there does exist remarkable nonuniform deformation along the specimen. In order to expand the experimental results, the specimen of aluminum foam with meso-structures is modeled by 3D Voronoi technique. The numerical results show that the FE model can simulate the experiment well, and shows that nonuniformity of deformation appears in aluminum foam specimen significantly. The analysis indicates that the assumption of uniform deformation of specimen in SHPB cannot be strictly satisfied for the material of aluminum foam.

Study on Electrical Ignition Characteristics of HAN-Based Liquid Propellant Spray

In order to study the electrical ignition method of liquid propellant spray, two experimental devices of liquid propellant spray and alternating current (AC) pulse discharge were designed. By using of high speed digital camera system, the test on electrical ignition of HAN-based liquid propellant LP1846 spray were carried out under different injection pressures. The results show that under 50W AC pulse discharge conditions, LP1846 droplet cluster, with the mean diameter in the range of 20~40μm, can be ignited reliably. Based on above experiments, a simplified model of ignition delay time of LP1846 single droplet was set up, the calculation value is well matched with the experimental data.

Metal transfer characteristics of GMAW with strip electrode

The metal transfer process of gas metal arc welding with strip electrode is observed by a high speed digital camera system. Because the rectangular strip electrode has a large width/thickness ratio, the pendant droplet is elliptical in shape, and multicurrent channels are generated. The Lorentz force induced between the multicurrent channels drives the droplet and welding arc to move along the strip electrode end, but the droplet always lags behind the welding arc. The movement results in uncertain droplet’s detaching location and transition trajectory. The projected transfer mode is promoted, and the streaming and rotating transfer modes are restrained. With the increase in welding power, the droplet motion is faster but more stable. The stability can be reflected from the fluctuation of the welding current and arc voltage waveforms.

Study of Bulk-Loaded Liquid Propellant Combustion Propulsion Processes With Stepped-Wall Combustion Chamber

The multilevel stepped-wall chamber is designed to study the combustion stability control mechanism of the bulk-loaded liquid propellant gun (BLPG). The cold state experiment of the interaction of the high speed gas jet with liquid medium is conducted by means of high speed digital camera system. The simulated small caliber bulk-loaded liquid propellant combustion propulsion device is designed to study the effect of the stepped-wall chamber size on the combustion stability. The experimental results indicate that, the stepped-wall structure can restrain the expansion randomness of the Taylor cavity and leads smooth expansion at each step. In 4 stepped-wall chamber with ΔD/L = 3/40, the interior ballistic performance of BLPG is stable and the consistency of the p-t curves is good. Two-dimensional unsteady model is developed based on the BLPG combustion propulsion experiment. The numerical simulation results coincide well with the experiment.

Influence of boundary shape on interaction process of plasma jet and liquid media

The effects of boundary shape on the propagation form of the plasma jet in liquid media are studied. The construction and consecutive expansion processes of plasma jet in liquid are recorded by high speed digital camera system. The results indicate that the expansion construction of plasma jet in li quid is a typical Taylor cavity, and the axial expansion velocity of Taylor cavity in stepped-wall chamber is greater than that in cylindrical chamber. Based on the experiments, numerical simulations of the interaction of non-steady plasma jet wit h liquid media are carried out. The change characteristics of pressure and velocity in plasma jet flow field have been obtained.

Study on Expansion Process and Interaction of High Speed Twin Combustion-Gas Jets in Liquid

The multilevel stepped-wall and rectangular observation chambers are designed to study the multipoint ignition process and the combustion stability control mechanism of the bulk-loaded liquid propellant gun. The expansion process and interaction of high-speed twin combustion-gas jets in liquid are studied by means of a high-speed digital camera system. The influence of the nozzle diameter, dual-orifice interval, jet pressure, and chamber structure on the jet expansion shape is discussed. The results indicate that a larger ratio of diameter-to-length can suppress the jet instability in stepped-wall chambers. Higher axial expansion velocity is found under the larger injection pressure, which it increases the instability of jet expansion process. Compared with a rectangular chamber, the axial expansion velocity is smaller, and the radial expansion velocity is larger in stepped-wall chambers under the same conditions. The theoretical studies of interaction of the gas jet with liquid were developed based on the experiment. Two-dimensional unsteady models are used to get the pressure, density, and velocity contours. The numerical simulation results coincide well with the experiment.

Thermal performance of a premixed impinging circular flame jet array with induced-swirl

An array of three identical premixed butane–air-fired impinging circular flames with induced-swirl operating at low-pressure and low-Reynolds-number was developed. A swirling motion was imparted successfully to the flame by forcing the butane/air mixture through a specially designed burner assembly before ignition. The burner assembly consisting of a conical base and a nozzle tube into which a cylindrical bar fabricated with three spiral channels was inserted. Its thermal performance was compared with that of a similar impinging flame jet system without induced-swirl. Effects of varying the Reynolds number and the equivalence ratio of the butane/air mixture and the nozzle-to-plate distance on the thermal performance of each of these two impinging flame jet systems were studied. Experiments were conducted with different combinations of Reynolds number, equivalence ratio and nozzle-to-plate distance. In the present investigation, the Reynolds number ranged from 500 to 2500, the equivalence ratio ranged from 1.0 to 1.8 and the nozzle-to-plate distance ranged from 20 mm to 30 mm. To facilitate comparison, flame shapes of both impinging flame jet systems were also visualized by a high speed digital camera system. The comparison showed that the array of three small-scale, low-pressure and low-Reynolds-number premixed butane–air-fired impinging circular flame jets could enhance its thermal performance, with respect to heat transfer characteristics and blow-out limits, by incorporating an induced-swirl. The performance enhancement increased with increasing Reynolds number or equivalence ratio, but decreased with increasing nozzle-to-plate distance.

Two-phase measurements of wind and saltating sand in an atmospheric boundary layer

Wind-blown sand movement is a particle-laden two-phase flow related to wind erosion in which the velocity distributions of both wind and sand are of particular interest. In the present study, two types of natural sand, one collected from the Pohang beach (diameter d = 200–300 μm) in South Korea and the other from the Taklimakan desert ( d = 100–125 μm) in China, were tested in a simulated atmospheric boundary layer. A high-speed digital camera system was used to capture images of the saltating sand particles at 2000 fps with an exposure time of 1/3000 s. Instantaneous velocity fields of the saltating sand particles were obtained using a particle tracking velocimetry (PTV) method. From these data, the particle resultant velocity, volume concentration, and streamwise mass flux were estimated as a function of height. The results reveal that the resultant particle velocity has an approximate log-linear profile with vertical height. Both the particle concentration and streamwise mass flux decay dramatically in the near surface region ( z < 20 mm for the beach sand, and z < 15 mm for the desert sand), then decline mildly beyond this region. To investigate the modification of the surrounding wind by the saltating sand particles, a hot-wire anemometry with a robust hot-film probe was employed to measure the wind velocity profiles with and without saltation. The present experimental data on both the saltating sand and wind provide useful information that enhances our understanding of saltation transport and further development of control techniques of wind erosion.