Color Schlieren Technique Research Articles

Analysis of the Influence of the Size of Color-Calibrated Schlieren Filters on the General Sensitivity of Quantitative Schlieren Systems

The quantitative color schlieren technique is renowned for its capacity to convert deflection angles into color ratios. This technique has been instrumental in providing data on 2D flows. The current study delves into assessing how the geometry and optical characteristics of color filters impact the sensitivity of the schlieren system. At present, there are many papers making the assumption that implementing a larger-sized color filter leads to better system sensitivity. However, having more calibration filter positions can lead to measurement errors due to the difficult calibration process. The present investigation focuses on the type of color filters created with a gradual evolution of colors. A turbulent, round water vapor jet serves as the test case. By comparing the results obtained with two different filter sizes, this analysis gives insight into the compromises made between system sensitivity and ease of calibration, helping one to better understand the trade-offs between the above-mentioned parameters. Moreover, the quantitative and qualitative results of the test case are presented to offer more comprehensive insights into quantitative color-calibrated schlieren.

Influence of the Weak Surface Film on Formation and Propagation of Wind Waves in a Channel

Processes of the wind waves formation remain poorly understood, despite the numerous studies. One of the main reasons, in our opinion, is that simplified theoretical analysis does not take into account the weak film of natural contaminants. In the present work waves generation in two channels is experimentally studied and compared for ethanol, water and water with addition of soluble surfactant SDS (sodium dodecyl sulphate) in various concentrations. The employed concentrations hardly affect the surface tension coefficient, but lead to significant modification of the subsurface flow structure. In ethanol the surface film is not formed, so it can be considered as reference case. In water and water with added surfactant the film gets broken and the surface becomes clean at certain critical wind speed, which grows for increasing surfactant concentration. For the surface to remain clean, the contaminant adsorption to the surface must be compensated by its removal by the tangential stress. Three experimental techniques are used to study the influence of cool skin on formation of the wind waves. The surface relief is measured with modified color schlieren technique and the liquid velocity fields are determined with Particle Image Velocimetry (PIV). The surface temperature fields, which allow identification of the regions of the cool skin rupture, are obtained with IR thermography. IR thermography is also used to study the surface velocity field (IR PIV). The film is shown to have significant influence on both the waves amplitude and the structure of subsurface flow.

Optimizing Settings for Office-Based Endoscopic CO2 Laser Surgery Using an Experimental Vocal Cord Model.

Objectives/HypothesisTo provide insight in the thermal effects of individual laser settings in target tissues to optimize flexible endoscopic CO2 laser surgery treatment.Study DesignExperimental laboratory study.MethodsThermal effects of the CO2 laser using a fiber delivery system were visualized using the color Schlieren technique in combination with a polyacrylamide gel tissue model. Variable settings were used for emission mode, power, laser fiber distance, and laser duration, which were evaluated in every possible combination. Collateral thermal expansion and incision depth were measured. To validate the model, the results were compared to histology after CO2 laser irradiation of ex vivo human vocal cords, and the intraclass correlation coefficient was calculated. Thermal damage and incision depth were measured by a blinded pathologist.ResultsOf all parameters studied, duration of laser irradiation had the greatest effect on thermal expansion. Increased distance between laser tip and target tissue resulted in significantly reduced incision depth and increased thermal expansion. Pulsed emission modes led to increased incision depths. The intraclass correlation coefficient for consistency between the model setup and the ex vivo human vocal cords was classified as “fair.”ConclusionsBy using high‐intensity pulsed lasers at minimal distance to the target tissue, exposure times and subsequent damage to surrounding tissue can be reduced. If an evaporation technique is used, lower power in continuous wave at a larger distance to the target tissue will lead to superficial but broader thermal effects. The model setup used in this study is a valid model to investigate laser‐induced thermal effects in vocal cord tissue.Level of EvidenceNA Laryngoscope, 130:E680–E685, 2020

A 1,470 nm diode laser in stapedotomy: Mechanical, thermal, and acoustic effects.

Multiple laser systems have been investigated for their use in stapes surgery in patients with otosclerosis. The diode 1,470 nm laser used in this study is an attractive laser system because it is easily transported and relatively inexpensive in use. This wavelength has relative high absorption in water. This study aimed to investigate the mechanical, thermal, and acoustic effects of the diode 1,470 nm laser on a stapes in an inner ear model. Experiments were performed in an inner ear model including fresh frozen human stapes. High-speed imaging with frame rates up to 2,000 frames per second (f/s) was used to visualize the effects in the vestibule during fenestration of the footplate. A special high-speed color Schlieren technique was used to study thermal effects. The sound produced by perforation was recorded by a hydrophone. Single pulse settings of the diode 1,470 nm laser were 100 ms, 3 W. Diode 1,470 nm laser fenestration showed mechanical effects with small vapor bubbles and pressure waves pushed into the vestibule. Thermal imaging visualized an increase temperature underneath the stapes footplate. Acoustic effects were limited, but larger sounds levels were reached when vaporization bubbles arise and explode in the vestibule. The diode 1,470 nm laser highly absorbs in perilymph and is capable of forming a clear fenestration in the stapes. An overlapping laser pulse will increase the risk of vapor bubbles, pressure waves, and heating the vestibule. As long as we do not know the possible damage of these effects to the inner ear function, it seems advisable to use the laser with less potential harm. Lasers Surg. Med. 49:619-624, 2017. © 2017 Wiley Periodicals, Inc.

Study On Noise Reduction of Nozzle Shock Diamond Flow Destroyed by Flexible Components

It's well known that the high pressure flow running through the nozzle yields shock diamond flow which mainly causes the noise. This work employed flexible components on the nozzle outlet to destroy shock diamond flow and using micro color schlieren technique to visual the dispersion shock diamond. Experiments adjusted conditions of and mesh flexible components for optimal design. The results show that wire diameter 0.5mm of cross flexible component, away from nozzle 0.5cm and 1cm received the noise of 83.8dB, the reducing rate was ca.12.5%. The mesh 100 flexible component away from nozzle 0.5cm received the noise of 75.6dB, the reducing rate was ca. 21.17%.

Development and application of color schlieren technique for investigation of three-dimensional concentration field

The present work describes the development and application of rainbow schlieren deflectometry technique for the investigation of the three-dimensional concentration field around a crystal growing from its aqueous solution. The imaging technique employs a diverging beam of light to record the projection data of the concentration field. In contrast to the conventional schlieren methods, the present system makes use of a microscopic objective lens to act as the de-collimating lens for focusing the light beam onto the color filter to get the desired schlieren effect. In order to record the projection data of the concentration field from different view angles for tomographic reconstruction, the experiments are conducted in an octagonal growth cell. Detailed quantitative analysis of the schlieren images has then been carried out for each view angle to determine the path-integrated concentration distribution. Principles of tomography have been employed for the reconstruction of concentration field at select horizontal planes above the growing crystal. Results have been presented in the form of rainbow schlieren images of the convective field, path-averaged solute concentration distribution around the growing for each view angle and local concentration distribution at select horizontal planes above the crystal top surface. Recorded color schlieren images have been compared with those of the conventional monochrome schlieren and interferometric techniques for the same experimental conditions. The extent of color re-distribution as seen from the recorded rainbow schlieren images correlate well with the bright intensity regions of monochrome schlieren images and the extent of fringe deformation in the interferometric images. The comparison has been performed for a small as well as a comparatively larger-sized crystal. For small sized-crystal, the observed color redistribution is seen to be weak and restricted to the crystal vicinity only whereas the color changes are more pronounced for larger-sized crystal. Results of the quantitative analysis of the two-dimensional schlieren images as well as of tomographic reconstructions clearly show the presence of high concentration gradients around the growing crystal surfaces and the gradients are seen to diminish as one moves towards the bulk solution.

Experimental Analysis of Heat Transfer Behavior inside Heat Pipe Integrated with Cooling Plates

This work used experimental methods to study heat transfer behavior inside a heat pipe and found that heat transfer behavior inside the heat pipe was changed due to its integration with cooling plates. This change caused the heat pipe to have copper-like heat transfer behavior. Experimental performances first built a CPU simulator with maximum heat power 300 W in accordance with the ASTM standard as heat source and measured temperature distribution by using infrared thermography and thermocouple thermometer. Observation of heat transfer behavior inside heat pipe influenced by its integration with cooling plates used color schlieren technique. A commercial CPU heat pipe cooler was also used as reference object in this work. Integration of the heat pipe with cooling plates causes the heat pipe to have the copper-like heat transfer behavior. The results indicate that rebuilding the bare heat pipe’s heat transfer behavior is the best solution for improving cooling efficiency of the heat pipe cooler.

Color schlieren deflectometry for characterization of crystal growth processes: KDP and lysozyme

Color schlieren deflectometry is a technique that has great potential in terms of both quality and ease of implementation for the study of convection phenomena during crystal growth. The advantage stems from its non-intrusive and inertia-free nature. Application of this technique for crystal growth is not available in the literature and is the focus of the present work. The present study discusses the implementation of color schlieren deflectometry for characterization of KDP and protein crystal growth processes. The technique is evaluated both for qualitative visualization and as a tool for quantitative analysis. Crystal growth processes, in general, reveal complex transport phenomena. Solutal convection is present during KDP crystal growth while the protein crystal growth process includes both evaporation and condensation. The present study demonstrates the effectiveness of color schlieren technique for understanding these physical phenomena for both crystal growth processes. The color schlieren images are qualitatively compared with those from other optical techniques such as Mach–Zehnder interferometry, monochrome schlieren and shadowgraph techniques. The quantitative analysis procedure of color schlieren images is validated by using the Rayleigh–Benard convection experiment in a rectangular cavity. It is seen that the temperature profiles and the heat flux distribution in the Rayleigh–Benard experiment and concentration distribution during KDP crystal growth derived from color schlieren deflectometry match well with data reported in the literature. In the protein crystal growth experiment using lysozyme, evaporation of water from the droplet and its condensation on the reservoir surface followed by subsequent diffusion and complete mixing with the reservoir solution are clearly revealed from color schlieren deflectometry experiments. Overall, the present study establishes the color schlieren deflectometry as an attractive tool for characterization of crystal growth processes.

Heat Transfer Characterizations of Heat Pipe in Comparison With Copper Pipe

The article presents some significant experimental data for studying the heat transfer behavior of heat pipe, which will further help the cooling efficiency improvement of the heat pipe cooler. It is well known that the heat pipe owns the extreme large heat conductivity and is often integrated with cooling plates for CPU cooling. The heat pipe uses special heat transfer techniques to obtain extremely large heat conductivity, which are the inside liquid evaporation for heat absorption and the inside microstructural capillarity for condensation. These special techniques yield the instant heat transfer from the heat source to the remote side directly, but the special heat transfer behavior is changed due to the integration with cooling plates. The destroyed heat transfer behavior of the heat pipe causes the cooling efficiency of the heat pipe cooler to be not able to reach a predicted good value. To improve the cooling efficiency of the heat pipe cooler we recover the original heat transfer behavior of the heat pipe integrated with cooling plates. This work first built a CPU simulator in accordance with the ASTM standard for heating the heat pipe, then uses the color schlieren technique to visualize the sequent heat flux nearby the heat pipe and the infrared thermal camera for quantitative temperature measurements synchronously. The result shows that the heat flux first appears at the opposite side from the heat source and there exhibits also the highest temperature. This is different from the heat transfer behavior of the copper pipe. Another very interesting result is that the heat flux of the cooling plate nearest to the heat source is first viewed than the others, which is similar to the integration with the copper pipe.

Experimental study on the flow field behind a backward-facing step using a detonation-driven shock tunnel

The supersonic combustion RAM jet (SCRAM jet) engine is expected to be used in next-generation space planes and hypersonic airliners. To develop the engine, stabilized combustion in a supersonic flow field must be attained even though the residence time of flow is extremely short. A mixing process for breathed air and fuel injected into the supersonic flow field is therefore one of the most important design problems. Because the flow inside the SCRAM jet engine has high enthalpy, an experimental facility is required to produce the high-enthalpy flow field. In this study, a detonation-driven shock tunnel was built to produce a high-enthalpy flow, and a model SCRAM jet engine equipped with a backward-facing step was installed in the test section of the facility to visualize flow fields using a color schlieren technique and high-speed video camera. The fuel was injected perpendicularly to a Mach 3 flow behind the backward-facing step. The height of the step, the injection distance and injection pressure were varied to investigate the effects of the step on air/fuel mixing characteristics. The results show that the recirculation region increases as the fuel injection pressure increases. For injection behind the backward-facing step, mixing efficiency is much higher than with a flat plate. Also, the injection position has a significant influence on the size of the recirculation region generated behind the backward-facing step. The schlieren photograph and pressure histories measured on the bottom wall of the SCRAM jet engine model show that the fuel was ignited behind the step.

Imaging techniques for research and education of thermal and mechanical interactions of lasers with biological and model tissues

A setup based on color Schlieren techniques has been developed to study the interaction of energy sources, such as lasers, with biological tissues. This imaging technique enables real-time visualization of dynamic temperature gradients with high spatial and temporal resolution within a transparent tissue model. High-speed imaging techniques were combined in the setup to capture mechanical phenomena such as explosive vapor, cavitation bubbles, and shock waves. The imaging technique is especially used for qualitative studies because it is complex to obtain quantitative data by relating the colors in the images to temperatures. By positioning thermocouples in the field of view, temperature figures can be added in the image for correlation to colored areas induced by the temperature gradients. The color Schlieren setup was successfully used for various studies to obtain a better understanding of interaction of various laser, rf, and ultrasound devices used in medicine. The results contributed to the safety and the optimal settings of various medical treatments. Although the interaction of energy sources is simulated in model tissue, the video clips have proven to be of great value for educating researchers, surgeons, nurses, and students to obtain a better understanding of the mechanism of action during patient treatment.

デトネーション駆動型衝撃風洞を用いた後ろ向きステップ周りの流れ場に関する実験的研究

As a research to develop a SCRAM-jet engine is actively conducted, a necessity to produce a high-enthalpy flow in a laboratory is increasing. In order to develop the SCRAM-jet engine, stabilized combustion in a supersonic flow-field should be attained, in which a duration time of flow is extremely short. Therefore, a mixing process of breathed air and fuel, which is injected into supersonic flow-fields is one of the most important problem. Since, the flow inside SCRAM-jet engine has high-enthalpy, an experimental facility is required to produce such high-enthalpy flow-field. In this study, a detonation-driven shock tunnel was built and was used to produce high-enthalpy flow. At first, a performance of this facility was investigated in order to obtain a Tayloring condition. Furthermore, SCRAM-jet combustor model equipped backward-facing step was installed at test section and flow-fields were visualized using color-schlieren technique. The fuel was injected perpendicular to the flow of Mach number three behind step. The height of backward-facing step and injection pressure were changed to investigate effects of the step on a mixing characteristic between air and fuel. The schlieren photograph and pressure histories show that the fuel was ignited behind step and the height of step is important factor to ignite a fuel in a supersonic flow-field.

Analytical and experimental insights into fast deflagrations, detonations, and the deflagration-to-detonation transition process

The present paper reports on experimentally as well as analytically obtained results of fast propagating deflagrations, the deflagration-to-detonation transition process, and detonations. Due to the high propagation velocity of these highly transient combustion waves, experimental data were mainly achieved by means of conventional measuring devices in past. These data were used to develop analytical models describing the physical processes of these fast combustion waves. Due to the progress in the development of new laser-optical measuring-techniques, detailed insight into these combustion waves can nowadays be achieved. These measuring-techniques facilitate the validation of analytical models and, furthermore, it is now possible to understand the physical processes of these fast combustion waves. This paper describes the analytical models proposed by Mayinger et al. and new experimental results obtained by means of the color-schlieren technique and the laser-induced predissociation fluorescence.

Visualization of Supersonic Flow past EOS

AbstractThe visualization of supersonic flow around EOS ]1[ involves analyzing shock wave positions and vortices at large angles of attack. The applied experimental methods include color Schlieren, oil film and vapor screen techniques. Depending on the Mach number and the angle of attack various vortex structures are observed on the leeward side.

Simultaneous mapping of the velocity and deformation field at a free surface

The oblique interaction of a turbulent vortex ring with a clean water surface is experimentally investigated during the transition stage using Digital Particle Image Velocimetry (DPIV) and the shadowgraph technique to map the surface velocity and deformation field simultaneously. The transitional vortex-ring/free-surface interaction leads to the formation of a trifurcation pattern at the free surface. Similar to the laminar flow case, the vortex ring initially bifurcates into two symmetric and separately connected vortex loops. The turbulent break-up of those vortex loops results in the formation of longitudinal wake vortices that symmetrically connect to the surface and eventually lead to a trifurcation pattern. In the absence of large-deformation surface waves, the simultaneous DPIV and shadowgraph measurements reveal good agreement between the surface vorticity and deformation field for small- and large-scale vortical structures. The simultaneous measurement technique is not restricted to the qualitative shadowgraph visualization, but can be easily extended to quantitative methods such as grating-imaging techniques, Color Schlieren, or Color Surface Mapping (CSM) techniques.

Color schlieren methods in shock wave research

Schlieren methods are widely known and well established to visualize refractive index variations in transparent media. The use of color allows one to obtain more data and previously inaccessible information from a picture taken with this technique. In general, a hue can be related to a certain strength or a certain direction of a refractive index gradient. While the first case essentially corresponds to the usual black- and-white system the latter correlation cannot be made adequately evident without the use of color. Two color schlieren techniques are presented here, which reach or even exceed the quality and sensitivity range of conventional black- and-white methods. Using a powerful short duration light source these methods are applied to visualize transient flow phenomena in a shock tube.