High-speed Camera Measurements Research Articles

Study on cavitation influence for pump head in an axial flow pump

The size of axial flow pumps used in drainage pump stations has recently decreased, and their rotation speeds have increased, causing an increase in the risk of cavitation. Therefore, to provide highly reliable pumps, it is important to understand the internal flow of pumps under cavitating conditions. In this study, high-speed camera measurements and computational fluid dynamics analysis were performed to understand the cavitation performance of an axial flow pump. The mechanism that causes the head to change as a result of cavitation under low net positive suction head values is shown to be the balance between the increasing angular momentum and the loss indicated by the changing streamlines.

Dynamic response of reverse Taylor impact based on DIC technology

Reverse ballistic impact test, which can obtain the response data of rod/projectile more comprehensive and quantitative than forward impact test, was widely used for the measurement of material dynamic and structure response. Based on the DIC technology and traditional optical measurement (high-speed camera measurement), the Taylor experiment of reverse ballistic with different length-diameter ratio and different impact velocities were carried out by 57 mm compression-shear type light-gas gun, which provides the instantaneous response data of the Taylor rod in microsecond level. Then, the transient structural deformation of the specimen and the characteristics of plastic wave propagation were analysed by DIC technology and compared with traditional optical measurement. Applying the theory of reverse Taylor impact deformation and combining with the simulation results by LS-DYNA, the rules of structure deformation and plastic wave propagation were obtained. The method above can be applied for the structure response of penetrator under the condition of reverse ballistic penetration.

The Calibration of High Energy-Rate Impact Forging Hammers by the Copper-Column Upsetting Method and High Speed Camera Measurements

The hammer forging is a well-known technology to incrementally produce geometrically complex forgings by compressing the material against the dies using several forming blows. When forging aeronautical components with this technology, it is crucial to control the final grain size of the part since this variable highly influences the high temperature low cycle fatigue properties. Nowadays, it is common practice to use the finite element models coupled with recrystallization models to optimize the process parameters and strategy. However, a very important variable to conduct these simulations is the real available hammer energy, which must be calibrated, not being an easy task since very high forces are generated in the impact of the anvils. In the present paper, the copper-column upsetting method is compared with a novel method where a high speed camera has been used to compute the anvils’ velocity and corresponding energies. The compressive behavior of the copper samples has been characterized using Rastegaev compression tests. The experimental and calculated results using the high speed camera are compared to the ones obtained using high purity copper samples. These measurements have enable to quantify the influence the friction and the elastic rebound have during the energy transfer from the anvils to the billet. This makes possible a precise future characterization of hammers using the conventional copper-column upsetting method if high speed cameras are not available in workshop.

Quantification of the uncertainties of high-speed camera measurements

This article proposes a combined theoretical and experimental approach to assess and quantify the global uncertainty of a high-speed camera velocity measurement. The study is divided in five sections: firstly, different sources of measurement uncertainties performed by a high-speed camera are identified and quantified. They consist of geometrical uncertainties, pixel discretisation uncertainties or optical uncertainties. Secondly, a global uncertainty factor, taking into account the previously identified sources of uncertainties, is computed. Thirdly, a sensibility study of the camera set-up parameters is performed, allowing the experimenter to optimize these parameters in order to minimize the final uncertainties. Fourthly, the theoretical computed uncertainty is compared with experimental measurements. Good concordance has been found. Finally, the velocity measurement uncertainty study is extended to continuous displacement measurements as a function of time. The purpose of this article is to propose all the mathematical tools necessary to quantify the individual and global uncertainties, to highlight the important aspects of the experimental set-up, and to give recommendations on how to improve a specific set-up in order to minimize the global uncertainty. Taking all these into account, it has been shown that highly dynamic phenomena such as a ballistic phenomenon can be measured using a high-speed camera with a global uncertainty of less than 2%.

Image processing techniques for high-speed videometry in horizontal two-phase slug flows

Two-phase flow measurements are very common in industrial applications especially in oil and gas areas. Although some works in image segmentation have analyzed gas–liquid slug flow along vertical pipes, few approaches have focused on horizontal experiments. In such conditions, the detection of the Taylor bubble is challenging due the great amount of small bubbles in the slug area and, thus, requires a special treatment in order to separate gas from liquid phases. This article describes a new technique that automatically estimates bubble parameters (e.g. frequency, dimension and velocity) through video analysis of high-speed camera measurements in horizontal pipes. Experimental data were obtained from a flow test section where slug flows were generated under controlled conditions. Image processing techniques such as watershed segmentation, top-hat filtering and H-minima transform were applied to detect and estimate bubble contour and velocities from the observed images. Finally, the estimated parameters were compared to theoretical predictions, showing good agreement and indicating that the proposed technique is a powerful tool in the investigation of two-phase flow.

Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers

The temporal behavior of mode instabilities in active large mode area fibers is experimentally investigated in detail. Thus, apart from the onset threshold of mode instabilities, the output beam is characterized using both high-speed camera measurements with 20,000 frames per second and photodiode traces. Based on these measurements, an empiric definition of the power threshold of mode instabilities is introduced. Additionally, it is shown that the temporal dynamics show a transition zone between the stable and the unstable regimes where well-defined periodic temporal fluctuations on ms-timescale can be observed. Finally, it is experimentally shown that the larger the mode-field area, the slower the mode-instability fluctuation is. The observations support the thermal origin of mode instabilities.

Size and Material Effects on Flow Boiling Enhancement in Microchannels With Diffusion-Brazed Wire Mesh

This paper focuses on flow boiling enhancement in microchannels using a surface enhancement technique based on the diffusion-brazing of a mesh to the channel's inner surface. Both qualitative flow boiling visualization using a high-speed camera and quantitative local variable measurements were carried out. Good agreement was obtained from the qualitative and quantitative results. After validation of single-phase flow in the current test setup, two-phase flow boiling tests for bare channels were used as the basis for comparison with mesh channels. Reasonably good agreement was obtained with two classic saturation flow boiling correlations. Both the flow boiling curves and heat transfer coefficient plots have shown significant enhancement of flow boiling for the mesh channels. Surprisingly, the 100-mesh channel outperformed the 200-mesh channel. The high-speed camera provided clear pictures of the processes occurring in the channels and helped elucidate the nucleation process taking place inside each channel. This provided the means to validate the hypothesis that the diffusion-brazed meshes introduce a significant amount of additional active nucleation sites on the channels' heating surface.

Numerical and experimental study of air arc splitting process considering splitter plate erosion

A three-dimensional magnetohydrodynamic model of an air arc plasma, considering the metal vapour from erosion of an iron splitter plate, is developed. An equation describing conservation of the iron vapour mass is added to the standard mass, momentum, and energy conservation equations. The influence of the iron vapour on the thermodynamic and transport properties of the gas mixture is considered in the calculation. The arc voltage, and distributions of temperature, gas flow, and mass fraction of iron vapour in the arc chamber are calculated and analyzed in detail. The experiment was carried out to support the simulation work. The images recorded by a high-speed camera and arc voltage measurement were compared with the predictions of the simulations, which proved the validity of the simulation model.

Self-entrainment of air on stepped spillways

The pseudo-bottom-inception point related to air entrainment is located further upstream on stepped spillways than on smooth spillways, for otherwise identical conditions. Its position is relevant concerning cavitation aspects, flow losses and flow depths. This Paper presents and discusses visual observations made with a high-speed camera and air concentration measurements in the vicinity of the pseudo-bottom air inception point on a stepped model spillway. Insight into the bottom aeration processes is provided, pointing at the effects of dynamic and turbulent air-phase surface troughs instantaneously protruding to the pseudo-bottom. In addition, the measured data were analyzed with regard to the extensions of these surface troughs. The trough bases were found to reach approximately 70–80% of the mixture flow depth upstream of the inception point, to 60–70% at the inception point and to 40–50% at the equilibrium flow region downstream of the inception point. The highly-turbulent character of developed flow is described and the general air transport process specified on the basis of air concentrations and related parameters.

Artificial Cambered-Wing for a Beetle-Mimicking Flapper

In this paper, we have attempted to improve the aerodynamic force generation ability of an artificial wing by implementing initial wing camber in the flexible artificial wing. This initial camber is used to create passive wing camber during flapping motion. We modified original artificial wing by removing many minor vein structures in the wing and then placed the initial camber between two major veins. Stiffness measurements for the original artificial wing and the present wing with initial camber were conducted to compare the stiffnesses of the two artificial wings, and the similarities of the two wings are discussed. A flapping test was carried out using a previously-built flapper that can flap at higher than 25 Hz flapping frequency to verify the wing camber effect. Finally, a performance comparison between uncambered- and cambered-wings was also undertaken based on observations using a high-speed camera and force measurements from wired-flight tests and swing tests. The comparison showed that the cambered-wing could produce about 10% higher thrust than the uncambered-wing.

Modes of particle combustion in iron dust flames

The so-called argon/helium test is proposed to identify the combustion mode of particles in iron dust flames. Iron powders of different particle sizes varying from 3 to 34 μm were dispersed in simulated air compositions where nitrogen was replaced by argon and helium. Due to the independence of the particle burning rate on the oxygen diffusivity in the kinetic mode, the ratio between the flame speeds in helium and argon mixtures is expected to be smaller if the particle burning rate is controlled by reaction kinetics rather than oxygen diffusion. Experiments were performed in a reduced-gravity environment on a parabolic flight aircraft to prevent particle settling and buoyancy-driven disruption of the flame. Uniform suspensions of the iron powders were produced inside glass tubes and a flame was initiated at the open end of the tube. Quenching plate assemblies of various channel widths were installed inside the tube and pass or quench events were used to measure the quenching distance. Flame propagation was recorded by a high-speed digital camera and spectral measurements were used to determine the temperature of the condensed emitters in the flame. The measured flame speeds and quenching distances were in good agreement with previously developed one-dimensional, dust flame model where the particles are assumed to burn in a diffusive mode and heat losses are described on a volumetric basis. However, a significant drop of the ratio of flame speeds in helium and argon mixtures was observed for finer 3 μm particles and was attributed to a transition from the combustion controlled by diffusion for larger particles to kinetically controlled burning of micron-size particles. In helium mixtures, the lower flame temperatures measured in suspensions of fine particles in comparison to larger particles reinforces this assumption.

Transition in electron transport in a cylindrical Hall thruster

Through the use of high-speed camera and Langmuir probe measurements in a cylindrical Hall thruster, we report the discovery of a rotating spoke of increased plasma density and light emission which correlates with increased electron transport across the magnetic field. As cathode electron emission is increased, a sharp transition occurs where the spoke disappears and electron transport decreases. This suggests that a significant fraction of the electron current might be directed through the spoke.

Detection of Cavitation Phenomena in Reciprocating Pumps using a High‐Speed Camera

AbstractCavitation in reciprocating positive displacement pumps is still an insufficiently understood problem. For a better understanding of the effects of cavitation in reciprocating positive displacement pumps, high‐speed camera measurements were done under real operating conditions. In this work, emphasis is put on the recording of cavitation phenomena for further investigations. Exemplarily, the occurring cavitation phenomena for different valve designs are described on the basis of high‐speed sequences for selected cavitation conditions and the results are discussed.

Flame-Spreading Behavior in a Fin-Slot Solid Propellant Rocket Motor Grain (Part II)

To accurately predict the overall ignition transient for the reusable solid rocket motors of the space shuttle booster with head-end fin slots, it is necessary to have the knowledge of the flame-spreading rates in the fin-slot region. This paper is the second of a two part study and deals with the development of a flame-spreading correlation in the fin-slot region. A subscale (1:10) pie-shaped fin-slot motor was designed to perform diagnostic measurements for studying the flame-spreading behavior on the exposed propellant surface. Dynamic similarity was considered in the igniter design so the impinging jet had a similar exit angle onto the propellant surface in the fin-slot section. Flame-spreading measurements were gathered using a high-speed digital camera and nonintrusive optical measurement methods through an array of 36 near-infrared fast-response photodetectors installed perpendicular to representative regions of the propellant surface. Results showed that the flame-spreading phenomena was highly nonuniform, starting in the downstream portion of the fin-slot region before traveling back toward the igniter. A correlation was developed for the dimensionless flame-spreading time interval showing that it was inversely proportional to the pressurization rate to a power of 0.62, which depends strongly upon the flow parameters of the igniter induced flow and local propellant grain geometry.

Correlating Drop Impact Simulations With Drop Impact Testing Using High-Speed Camera Measurements

The increased use of mobile appliances such as mobile phones and navigation systems in today’s society has resulted in an increase in reliability issues related to drop performance. Mobile appliances are dropped several times during their lifespan and the product is required to survive common drop accidents. A widely accepted method to assess the drop reliability of microelectronics on board-level is the drop impact test. This test has been standardized by international councils such as Joint Electron Device Engineering Council and is widely adopted throughout the industry. In this research the solder loading is investigated by combining high-speed camera measurements of several drop impact tests with verified finite element models. These simulation models are developed in order to gain an insight on the loading pattern of solder joints based on interconnect layout, drop conditions, and product specifications prior to physical prototyping. Deflections and frequencies during drop testing are measured using a high-speed camera setup. The high-speed camera experiments are performed on two levels: machine level (rebounds with and without a catcher) and product level (with different levels of energy and different pulse times). Parametric (dynamic and quasistatic) 3D models are developed to predict the drop impact performance. The experimental results are used to verify and enhance the simulation models, e.g., by tuning the damping parameters. As a result, the verified models can be used to determine the location of the critical solder joint and to obtain estimates of the solder lifetime performance.

A Study on Shock Energy for Concrete Destruction Using Underwater Shock Wave

In this study, the destruction of concrete block using underwater shock wave generated by high current is studied. A metal wire was connected to an electrode and a high voltage impulsive current was passed through it to generate the underwater shock wave. The underwater shock wave was investigated by optical observation using a high-speed camera and pressure measurement. A comparison was made on the shock wave generated from the electrode with and without connecting it to a metal wire. The underwater shock wave generated from electrode without metal wire showed the existence of many shock waves by continuous plasma within discharge duration, and the duration of the pressure pulse was long in this case. The peak pressure of underwater shock wave generated from metal wire explosion was higher than the previous case due to the reaction of metal vapor and water, whereas the pressure duration was less. The concrete block was efficiently destructed by the effect of underwater shock pressure of high impulse. The high peak pressure and long duration are necessary for the destruction of concrete block. It is suggested that high pressure induces crack to the structure, and the long pulse duration destructs the structure.

Dynamic Mechanical Behavior Characterization of Epoxy-Cast Al + Fe2O3 Thermite Mixture Composites

The dynamic mechanical behavior characterization of epoxy-cast stoichiometric mixtures of nano- or micron-scale aluminum and hematite (Fe2O3) powders is investigated in this work. Experiments conducted on rod-shaped samples, using instrumented reverse Taylor impact tests employing high-speed imaging and velocity interferometry, show that these composites exhibit viscoelastic deformation and brittle fracture behaviors. Upon impact, the samples display significant elastic and plastic deformation during both the loading and unloading stages, as determined from quantitative high-speed camera measurements of the transient deformation states. Approximately 50 pct elastic recovery of total axial strain was observed to occur rapidly (within tens of microseconds) after impact. A one-dimensional elastic-plastic wave propagation analysis was used for estimating the composite’s dynamic average yield stress and total plastic strain. The results reveal that the nano-Al + Fe2O3-containing epoxy composite is most resilient, has the highest strength, and is more capable of absorbing impact energy. The analysis additionally provides detailed information about elastic and plastic wave interactions for discrete times, up to the final state of the material. Calculations and observations through the coupling of high-speed camera images and velocity interferometry (VISAR) measurements show that the elastic recovery coincides with peak axial strain and the interaction of elastic and plastic waves propagating within the rod-shaped specimen. Hence, such an instrumented Taylor test provides a detailed view of the general wave structure within the material upon impact and, at the same time, enables a complete description of the stress-strain response.

Measuring blood flow velocities based on three image processing techniques

The classification of microcirculation can be based on the size of the capillary and the velocity of the blood flow. For each type of microcirculation, the ad hoc method is required to measure the blood flow velocity. In this paper, the correlation method is used to measure blood flow velocity in the small-size capillary. The large-size capillaries are classified into three types based on the blood velocities, say low-speed, high-speed, and unstable one. The template-matching algorithm, the Fast Fourier Transform algorithm and a high-speed video camera measurement are used to measure the blood velocities corresponding to those three types of large-size capillary. It was shown by several experiments that fairly good results for different types of capillary may be obtained by using the proposed three image processing algorithms.

Ion-density fluctuations in laser-heated plasma

Ion turbulence generated in a CO2 laser-heated gas target plasma has been studied using ruby laser Thomson scattering. Considerable enhancement of the ion fluctuations over the thermal level was observed for two high-density plasma regimes (short and long density scale lengths). In the short scale length regime the magnitude of density fluctuations, together with temporal and spectral features of the scattered ruby light, indicate that ion-turbulence levels are sufficient to account for anomalous absorption of CO2 laser energy. In the long scale length regime, measurements of the ion-fluctuation wavenumber spectrum induced in the plane of the CO2 laser electric field, together with high-speed streak camera measurements of the Thomson scattered ruby laser light, were performed to determine general features of strong ion fluctuations in laser heated plasma. Possible mechanisms for generating the observed ion turbulence are discussed.