Masanori Ota - Academia.edu (original) (raw)

Papers by Masanori Ota

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

Discharging gas jets in low-pressure conditions are interesting and important phenomena from an e... more Discharging gas jets in low-pressure conditions are interesting and important phenomena from an engineering point of view. For example, in aerospace technology they relate to the gas jet thruster for attitude control of artificial satellite, or in laser technology assist gas behavior for laser material processing under low pressure. The jets, however, deform to the complicated shapes by interacting with solid walls. This paper deals with a visualization experiment on the interacting jet and plane wall by applying LIF (Laser Induced Fluorescence) method using an Ar-ion laser. We have obtained a series of jet-wall interacting images at various distances and clarified the behavior of impinging jet to the plane wall.

Journal of the Japanese Society for Experimental Mechanics, 2011

When a high-speed train enters a long tunnel, compression wave is generated in front of the train... more When a high-speed train enters a long tunnel, compression wave is generated in front of the train. This compression wave propagates in the tunnel at the speed of sound. In recent years, the running speed of train is increasing, and this problem of the tunnel pressure wave may occur by the conventional limited express. This paper deals with the pressure wave formation by the experiment using an apparatus with diaphragmless driver acceleration, and small train nose models of limited express in combination with a short tunnel and some station models. We have obtained pressure waveform data and discussed.

Journal of the Japanese Society for Experimental Mechanics, 2012

Due to the global energy crises and energy conservation, one of the most important aspects incorp... more Due to the global energy crises and energy conservation, one of the most important aspects incorporating optimum energy consumption, is the quantitative clarification and the image measurement of the flow fields in convective heat transfer. This paper deals with the quantitative Image Measurement of Natural Convection Using the ColorStripes Background Oriented Schlieren (CSBOS) Method from a multi heat generating source in the natural atmosphere. Here we have analyzed the temperature gradient by using our originally investigated and developed CSBOS technique and Computed Tomography (CT) method.

Journal of Flow Control, Measurement & Visualization, 2019

Three-dimensional density measurement of unsteady flow field around a sphere is carried out in th... more Three-dimensional density measurement of unsteady flow field around a sphere is carried out in the ballistic range at Institute of Fluid Science, Tohoku University. Simultaneous multi-angle measurement system using twelve digital cameras is installed in the test chamber of the ballistic range to achieve the three-dimensional density measurement. The Colored-Grid Background Oriented Schlieren (CGBOS) technique using colored-grid background is utilized for the reconstruction of density. The Mach number of the sphere is set to 1.5. The short pulse LEDs to illuminate the backgrounds are also installed in the chamber to capture the unsteady flow field around a flying sphere. Three-dimensional density distribution around a sphere is successfully reconstructed.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B, 2012

In this study, we developed a diaphragmless driver section with two pistons to generate the shock... more In this study, we developed a diaphragmless driver section with two pistons to generate the shock wave in small diameter tubes. An optical system using a He-Ne laser is constructed for the definition of a main piston opening time. The trajectories of main piston are measured under the several initial driver pressures. Additionally, the motion equation for the main piston is derived from a simple motion model. Moreover, the laser differential interferometer is constructed for the contactless measurement of the shock waves. The shock waves generated by our diaphragmless driver section, propagating in 2 and 3 mm inner diameter tubes are measured by the laser differential interferometer. The Mach number of the shock wave and the density ratio across the shock wave can be calculated by the interference signal obtained from the shock wave measurement. Additionally, the Mach number distributions along the axial direction of the tubes and the relation between the shock wave location and time (shock wave diagram) are obtained. Consequently, it is attributed to the fact that the friction effect between the test gas and the inner wall of the tubes becomes larger with decreasing the inner diameter of the tube.

The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2015

The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2015

Journal of the Visualization Society of Japan, 2009

Discharging gas flow in the vacuum or low pressure conditions interacts occasionally with, such n... more Discharging gas flow in the vacuum or low pressure conditions interacts occasionally with, such neighboring solid structures as plane wall. This phenomenon relates not only to the jet which produces interferences problem with structure in space, but also to the improvement of processing accuracy of the semiconductor, for example. For that purpose, the distributions of jet flow parameters

AEROSPACE TECHNOLOGY JAPAN, THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2012

In this study, we have succeeded to generate the shock wave in 3mm inner diameter tube by using d... more In this study, we have succeeded to generate the shock wave in 3mm inner diameter tube by using diaphragmless driver section that we developed. The laser differential interferometer is constructed for the measurement of the shock wave propagating in the small diameter tube. The Mach number of the shock wave and the density ratio across the shock wave can be calculated by the interferometric signal obtained from the shock wave measurement. The Mach number distributions along the axial direction of the tube and the relation between the shock wave location and the time are obtained. As a consequence, it is confirmed that the behavior of the shock wave propagating in small diameter tube shows remarkable deviations from the theory and Brouillette's model.

International Journal of Fluid Power, 2015

The poppet valve is a popular component in hydraulic systems, but it is also well known as troubl... more The poppet valve is a popular component in hydraulic systems, but it is also well known as trouble maker because it may occasionally induce unpredictable vibration. In former previous studies it has been found that cavitation is an important reason for this kind of vibration, but the causal mechanism between the vibration and cavitation is unclear. In this study, we developed a visualisation experiment system, in which we can observe and analyse the dynamic relationship among the displacement of the poppet, the cavitation quantity and the pressures around the poppet in a visualisation experiment. Based on the observation of the experimental phenomena and data analysis, we propose a hypothesis of a mechanism that can explain how cavitation influences the vibration of the poppet valve.

Journal of the Visualization Society of Japan, 2009

In this study a pulsed Nd:YAG laser beam was focused to make a single cavitation bubble near soli... more In this study a pulsed Nd:YAG laser beam was focused to make a single cavitation bubble near solid plate in distilled water at normal temperature. The behavior of laser-induced buboie was visualized with shadowgraph method by a higli speed camera and analyzed quantitatively. Some plates were settled near the laser induced bubble. In order to observe the feature of laser-induced bubble behavior near the plate materials, we selected materials of plate! aluminum, pumice, and gel in this study. The bubble near rigid materials migrates toward the plate. On the other hand, the buoble near elastic/flexible materials migrates away from the plate, We also focused on the period of motion of laser.induced bubble near plate, and the deformation of elastic/flexible material plate surfaces with laser-induced bubble. The observed results of the bubble behavior have been discussed.

Journal of the Visualization Society of Japan, 2004

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 2012

In the present research the characteristics of nonequilibrium flow are studied by applying CARS (... more In the present research the characteristics of nonequilibrium flow are studied by applying CARS (Coherent Anti-Stokes Raman Spectroscopy) method to hypervelocity shock waves in low-density air. Furthermore, in order to get more detail information on the flow behind the hypervelocity shock wave and to inspect whether the disturbance is seen at the shock wave front during the CARS measurement, radiation images behind the shock waves are obtained simultaneously. Finally, the CARS signals are detected behind hypersonic shock waves with a shock velocity of up to 7km/s. In addition, the radiation distributions are obtained at the same experiment. The vibrational and rotational temperatures are estimated by spectral fitting method. It is found that the rotational temperature exceeds the vibrational temperature when shock wave velocity is 5km/s or more, where both temperatures remains lower than translational temperature.

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN, 2009

In the re-entering phase of space vehicle into the atmosphere strong shock wave is generated in f... more In the re-entering phase of space vehicle into the atmosphere strong shock wave is generated in front of the hypersonic vehicle, and high enthalpy flow with radiating, non-equilibrium real gas effects is generated behind the shock wave. As well as usual convecting heat transfer, the radiative and non-equilibrium real gas heating from the shock-heated air ahead of the vehicle plays an important role on the total heat flux to the wall surface, which affects the heat shield design of the re-entering vehicle. As for the research of such non-equilibrium high enthalpy flows behind strong shock waves, several spectroscopic studies have been reported by using shock tubes or shock tunnels. The direct measurement, however, of molecular vibrational/rotational temperatures from ground state, has not been performed, and the experimental data are in quite insufficient conditions. In this paper nonlinear spectroscopic measurement is performed on the vibrational/rotational temperatures of nitrogen behind the hypervelocity shock waves from 4-5km/s by CARS method. The CARS spectroscopic signals have been successfully observed by free-piston, double-diaphragm shock tube experiments, and the measured results are compared with the simulated spectra to decide the temperatures by spectral fitting method.

International Conference on Experimental Mechanics 2013 and Twelfth Asian Conference on Experimental Mechanics, 2014

In recent years, running speed of the trains of conventional lines becomes faster with improving ... more In recent years, running speed of the trains of conventional lines becomes faster with improving vehicle and rail performance. At the high-speed range compression wave is formed when a high speed train enters a tunnel. This compression wave propagates in the tunnel at the speed of sound. This propagated wave is called "tunnel pressure wave". In some cases, when the station of conventional lines is located in the tunnel, problems such as breaking the window glass have been reported by the tunnel pressure wave at the station. Though the research on pressure wave inside the tunnel of the Shinkansen has been widely studied in connection with "tunnel micro-pressure wave” problems, the number of research reports on the operating speed of conventional lines(130～160km/h) is insufficient. In this study we focused on Hokuhoku line which has maximum operating speed of conventional lines in Japan (160km/h), and we performed the experiment on the gradient of the pressure wave by using diaphragmless driver acceleration system, small train nose model, and tunnel model of the limited express of Hokuhoku line. We have performed the pressure-time variation measurement on the tunnel model, including a station model or signal crossing station [SCS] model. As the thpical train model, we used Streamline-type or Gangway-type for train nose geometry. We have obtained pressure gradient data on several running conditions and observed the temporal .behavior in the tunnel pressure wave. As a result, we clarified large difference in pressure gradient with the train nose geometry and with the cross-sectional area of the tunnel.

Volume 1: Heat Transfer in Energy Systems; Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat and, 2012

ABSTRACT Due to global demand of conservation and optimization of energy consumption it is very i... more ABSTRACT Due to global demand of conservation and optimization of energy consumption it is very important to analyze the convective heat flow field and find out the detailed clarification of the convective flow parameters. While due to the complexity of convective flow fields both in forced and natural convection, it has remained very difficult to have three dimensional (3D) experimental analyses in detail. Image processing and measurement has got a very important role in finding solutions in this regard. For this purpose both steady and unsteady quantitative analysis of flow fields has to be analyzed separately, as they have got different density values throughout the flow field. This paper deals with quantitative image and CT analyses of natural convection using color-stripes background oriented schlieren (CSBOS) method from a heat generating source in natural atmospheric conditions.

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

ABSTRACT Quantitative image analysis and measurement of flow fields in convective heat transfer h... more ABSTRACT Quantitative image analysis and measurement of flow fields in convective heat transfer has great importance for the optimum energy consumption problems. In natural and forced convection phenomena of fluids, the complexity of flow field prevents us from detailed three dimensional (3D) experimental analyses of steady/unsteady dynamics in fluids. These flow fields have locally different density and temperature values and yet to be observed quantitatively. Recent development of the Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques lead us to the quantitative investigation of flow fields in experimental researches. On the other hand, in image measurements density and temperature distributions have been grasped only in two-dimensions (2D). These qualitative image analyses of flow fields were obtained by using classical flow visualizing techniques, such as shadowgraph and color schlieren method. This paper describes the quantitative measurement of convective flow field using our originally proposed color striped background oriented schlieren (CSBOS) method. The obtained measured image data is used for CT reconstruction and 3D temperature gradient distributions.

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

Cavitation is bubbling phenomena caused by local pressure reduction or strong energy concentratio... more Cavitation is bubbling phenomena caused by local pressure reduction or strong energy concentration in liquids. Cavitation is widely observed in fluid machinery and it causes vibration, noise, erosion, and loss of efficiency. In addition, cavitation occurs in laser treatment and causes the ruin of human tissues. There are a lot of researches on cavitation phenomena in room temperature liquids. It is known that laser-induced bubble generates pressure waves, and the bubble oscillates and collapses eventually. Recently, it is reported that cavitation occurs in cryogenic liquid such as rocket propellant. However, there are few researches about cavitation in cryogenic liquid. Generally, the thermo-physical properties such as surface tension and viscosity of cryogenic liquid are different from those of room temperature water, and cavitation in cryogenic liquid occurs near boiling temperature (low subcooling region). In our experiment, single bubble was generated by focused laser, and its b...

XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, 2006

ABSTRACT

Journal of Visualization, 2012

Laser Interferometric Computed Tomography (LICT) measurement enabled observation of the three-dim... more Laser Interferometric Computed Tomography (LICT) measurement enabled observation of the three-dimensional (3-D) density distribution of the unsteady flow field quantitatively. The interferometric fringe images are used as the projection data, and the flow field is reconstructed by appropriate reconstruction technique in LICT measurement. The flow field which do not include any object is reconstructed clearly. On the other hand, if the obstacle is included in the flow field, laser beam cannot pass through the obstacle and the projection data have imperfect parts. These imperfect parts cause strong artifacts in the CT images and we cannot identify any unsteady phenomena. To reduce these artifacts, we applied Hybrid Algebraic Reconstruction Technique (HART). In this study, the HART technique will be applied to the problem of reconstruction of wave interaction around a rectangular rod, and CT images obtained using HART and Algebraic Reconstruction Technique (ART) will be compared.

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

Discharging gas jets in low-pressure conditions are interesting and important phenomena from an e... more Discharging gas jets in low-pressure conditions are interesting and important phenomena from an engineering point of view. For example, in aerospace technology they relate to the gas jet thruster for attitude control of artificial satellite, or in laser technology assist gas behavior for laser material processing under low pressure. The jets, however, deform to the complicated shapes by interacting with solid walls. This paper deals with a visualization experiment on the interacting jet and plane wall by applying LIF (Laser Induced Fluorescence) method using an Ar-ion laser. We have obtained a series of jet-wall interacting images at various distances and clarified the behavior of impinging jet to the plane wall.

Journal of the Japanese Society for Experimental Mechanics, 2011

When a high-speed train enters a long tunnel, compression wave is generated in front of the train... more When a high-speed train enters a long tunnel, compression wave is generated in front of the train. This compression wave propagates in the tunnel at the speed of sound. In recent years, the running speed of train is increasing, and this problem of the tunnel pressure wave may occur by the conventional limited express. This paper deals with the pressure wave formation by the experiment using an apparatus with diaphragmless driver acceleration, and small train nose models of limited express in combination with a short tunnel and some station models. We have obtained pressure waveform data and discussed.

Journal of the Japanese Society for Experimental Mechanics, 2012

Due to the global energy crises and energy conservation, one of the most important aspects incorp... more Due to the global energy crises and energy conservation, one of the most important aspects incorporating optimum energy consumption, is the quantitative clarification and the image measurement of the flow fields in convective heat transfer. This paper deals with the quantitative Image Measurement of Natural Convection Using the ColorStripes Background Oriented Schlieren (CSBOS) Method from a multi heat generating source in the natural atmosphere. Here we have analyzed the temperature gradient by using our originally investigated and developed CSBOS technique and Computed Tomography (CT) method.

Journal of Flow Control, Measurement & Visualization, 2019

Three-dimensional density measurement of unsteady flow field around a sphere is carried out in th... more Three-dimensional density measurement of unsteady flow field around a sphere is carried out in the ballistic range at Institute of Fluid Science, Tohoku University. Simultaneous multi-angle measurement system using twelve digital cameras is installed in the test chamber of the ballistic range to achieve the three-dimensional density measurement. The Colored-Grid Background Oriented Schlieren (CGBOS) technique using colored-grid background is utilized for the reconstruction of density. The Mach number of the sphere is set to 1.5. The short pulse LEDs to illuminate the backgrounds are also installed in the chamber to capture the unsteady flow field around a flying sphere. Three-dimensional density distribution around a sphere is successfully reconstructed.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B, 2012

In this study, we developed a diaphragmless driver section with two pistons to generate the shock... more In this study, we developed a diaphragmless driver section with two pistons to generate the shock wave in small diameter tubes. An optical system using a He-Ne laser is constructed for the definition of a main piston opening time. The trajectories of main piston are measured under the several initial driver pressures. Additionally, the motion equation for the main piston is derived from a simple motion model. Moreover, the laser differential interferometer is constructed for the contactless measurement of the shock waves. The shock waves generated by our diaphragmless driver section, propagating in 2 and 3 mm inner diameter tubes are measured by the laser differential interferometer. The Mach number of the shock wave and the density ratio across the shock wave can be calculated by the interference signal obtained from the shock wave measurement. Additionally, the Mach number distributions along the axial direction of the tubes and the relation between the shock wave location and time (shock wave diagram) are obtained. Consequently, it is attributed to the fact that the friction effect between the test gas and the inner wall of the tubes becomes larger with decreasing the inner diameter of the tube.

The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2015

The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2015

Journal of the Visualization Society of Japan, 2009

Discharging gas flow in the vacuum or low pressure conditions interacts occasionally with, such n... more Discharging gas flow in the vacuum or low pressure conditions interacts occasionally with, such neighboring solid structures as plane wall. This phenomenon relates not only to the jet which produces interferences problem with structure in space, but also to the improvement of processing accuracy of the semiconductor, for example. For that purpose, the distributions of jet flow parameters

AEROSPACE TECHNOLOGY JAPAN, THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2012

In this study, we have succeeded to generate the shock wave in 3mm inner diameter tube by using d... more In this study, we have succeeded to generate the shock wave in 3mm inner diameter tube by using diaphragmless driver section that we developed. The laser differential interferometer is constructed for the measurement of the shock wave propagating in the small diameter tube. The Mach number of the shock wave and the density ratio across the shock wave can be calculated by the interferometric signal obtained from the shock wave measurement. The Mach number distributions along the axial direction of the tube and the relation between the shock wave location and the time are obtained. As a consequence, it is confirmed that the behavior of the shock wave propagating in small diameter tube shows remarkable deviations from the theory and Brouillette's model.

International Journal of Fluid Power, 2015

The poppet valve is a popular component in hydraulic systems, but it is also well known as troubl... more The poppet valve is a popular component in hydraulic systems, but it is also well known as trouble maker because it may occasionally induce unpredictable vibration. In former previous studies it has been found that cavitation is an important reason for this kind of vibration, but the causal mechanism between the vibration and cavitation is unclear. In this study, we developed a visualisation experiment system, in which we can observe and analyse the dynamic relationship among the displacement of the poppet, the cavitation quantity and the pressures around the poppet in a visualisation experiment. Based on the observation of the experimental phenomena and data analysis, we propose a hypothesis of a mechanism that can explain how cavitation influences the vibration of the poppet valve.

Journal of the Visualization Society of Japan, 2009

In this study a pulsed Nd:YAG laser beam was focused to make a single cavitation bubble near soli... more In this study a pulsed Nd:YAG laser beam was focused to make a single cavitation bubble near solid plate in distilled water at normal temperature. The behavior of laser-induced buboie was visualized with shadowgraph method by a higli speed camera and analyzed quantitatively. Some plates were settled near the laser induced bubble. In order to observe the feature of laser-induced bubble behavior near the plate materials, we selected materials of plate! aluminum, pumice, and gel in this study. The bubble near rigid materials migrates toward the plate. On the other hand, the buoble near elastic/flexible materials migrates away from the plate, We also focused on the period of motion of laser.induced bubble near plate, and the deformation of elastic/flexible material plate surfaces with laser-induced bubble. The observed results of the bubble behavior have been discussed.

Journal of the Visualization Society of Japan, 2004

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 2012

In the present research the characteristics of nonequilibrium flow are studied by applying CARS (... more In the present research the characteristics of nonequilibrium flow are studied by applying CARS (Coherent Anti-Stokes Raman Spectroscopy) method to hypervelocity shock waves in low-density air. Furthermore, in order to get more detail information on the flow behind the hypervelocity shock wave and to inspect whether the disturbance is seen at the shock wave front during the CARS measurement, radiation images behind the shock waves are obtained simultaneously. Finally, the CARS signals are detected behind hypersonic shock waves with a shock velocity of up to 7km/s. In addition, the radiation distributions are obtained at the same experiment. The vibrational and rotational temperatures are estimated by spectral fitting method. It is found that the rotational temperature exceeds the vibrational temperature when shock wave velocity is 5km/s or more, where both temperatures remains lower than translational temperature.

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN, 2009

In the re-entering phase of space vehicle into the atmosphere strong shock wave is generated in f... more In the re-entering phase of space vehicle into the atmosphere strong shock wave is generated in front of the hypersonic vehicle, and high enthalpy flow with radiating, non-equilibrium real gas effects is generated behind the shock wave. As well as usual convecting heat transfer, the radiative and non-equilibrium real gas heating from the shock-heated air ahead of the vehicle plays an important role on the total heat flux to the wall surface, which affects the heat shield design of the re-entering vehicle. As for the research of such non-equilibrium high enthalpy flows behind strong shock waves, several spectroscopic studies have been reported by using shock tubes or shock tunnels. The direct measurement, however, of molecular vibrational/rotational temperatures from ground state, has not been performed, and the experimental data are in quite insufficient conditions. In this paper nonlinear spectroscopic measurement is performed on the vibrational/rotational temperatures of nitrogen behind the hypervelocity shock waves from 4-5km/s by CARS method. The CARS spectroscopic signals have been successfully observed by free-piston, double-diaphragm shock tube experiments, and the measured results are compared with the simulated spectra to decide the temperatures by spectral fitting method.

International Conference on Experimental Mechanics 2013 and Twelfth Asian Conference on Experimental Mechanics, 2014

In recent years, running speed of the trains of conventional lines becomes faster with improving ... more In recent years, running speed of the trains of conventional lines becomes faster with improving vehicle and rail performance. At the high-speed range compression wave is formed when a high speed train enters a tunnel. This compression wave propagates in the tunnel at the speed of sound. This propagated wave is called "tunnel pressure wave". In some cases, when the station of conventional lines is located in the tunnel, problems such as breaking the window glass have been reported by the tunnel pressure wave at the station. Though the research on pressure wave inside the tunnel of the Shinkansen has been widely studied in connection with "tunnel micro-pressure wave” problems, the number of research reports on the operating speed of conventional lines(130～160km/h) is insufficient. In this study we focused on Hokuhoku line which has maximum operating speed of conventional lines in Japan (160km/h), and we performed the experiment on the gradient of the pressure wave by using diaphragmless driver acceleration system, small train nose model, and tunnel model of the limited express of Hokuhoku line. We have performed the pressure-time variation measurement on the tunnel model, including a station model or signal crossing station [SCS] model. As the thpical train model, we used Streamline-type or Gangway-type for train nose geometry. We have obtained pressure gradient data on several running conditions and observed the temporal .behavior in the tunnel pressure wave. As a result, we clarified large difference in pressure gradient with the train nose geometry and with the cross-sectional area of the tunnel.

Volume 1: Heat Transfer in Energy Systems; Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat and, 2012

ABSTRACT Due to global demand of conservation and optimization of energy consumption it is very i... more ABSTRACT Due to global demand of conservation and optimization of energy consumption it is very important to analyze the convective heat flow field and find out the detailed clarification of the convective flow parameters. While due to the complexity of convective flow fields both in forced and natural convection, it has remained very difficult to have three dimensional (3D) experimental analyses in detail. Image processing and measurement has got a very important role in finding solutions in this regard. For this purpose both steady and unsteady quantitative analysis of flow fields has to be analyzed separately, as they have got different density values throughout the flow field. This paper deals with quantitative image and CT analyses of natural convection using color-stripes background oriented schlieren (CSBOS) method from a heat generating source in natural atmospheric conditions.

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

ABSTRACT Quantitative image analysis and measurement of flow fields in convective heat transfer h... more ABSTRACT Quantitative image analysis and measurement of flow fields in convective heat transfer has great importance for the optimum energy consumption problems. In natural and forced convection phenomena of fluids, the complexity of flow field prevents us from detailed three dimensional (3D) experimental analyses of steady/unsteady dynamics in fluids. These flow fields have locally different density and temperature values and yet to be observed quantitatively. Recent development of the Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques lead us to the quantitative investigation of flow fields in experimental researches. On the other hand, in image measurements density and temperature distributions have been grasped only in two-dimensions (2D). These qualitative image analyses of flow fields were obtained by using classical flow visualizing techniques, such as shadowgraph and color schlieren method. This paper describes the quantitative measurement of convective flow field using our originally proposed color striped background oriented schlieren (CSBOS) method. The obtained measured image data is used for CT reconstruction and 3D temperature gradient distributions.

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D, 2011

Cavitation is bubbling phenomena caused by local pressure reduction or strong energy concentratio... more Cavitation is bubbling phenomena caused by local pressure reduction or strong energy concentration in liquids. Cavitation is widely observed in fluid machinery and it causes vibration, noise, erosion, and loss of efficiency. In addition, cavitation occurs in laser treatment and causes the ruin of human tissues. There are a lot of researches on cavitation phenomena in room temperature liquids. It is known that laser-induced bubble generates pressure waves, and the bubble oscillates and collapses eventually. Recently, it is reported that cavitation occurs in cryogenic liquid such as rocket propellant. However, there are few researches about cavitation in cryogenic liquid. Generally, the thermo-physical properties such as surface tension and viscosity of cryogenic liquid are different from those of room temperature water, and cavitation in cryogenic liquid occurs near boiling temperature (low subcooling region). In our experiment, single bubble was generated by focused laser, and its b...

XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, 2006

ABSTRACT

Journal of Visualization, 2012

Laser Interferometric Computed Tomography (LICT) measurement enabled observation of the three-dim... more Laser Interferometric Computed Tomography (LICT) measurement enabled observation of the three-dimensional (3-D) density distribution of the unsteady flow field quantitatively. The interferometric fringe images are used as the projection data, and the flow field is reconstructed by appropriate reconstruction technique in LICT measurement. The flow field which do not include any object is reconstructed clearly. On the other hand, if the obstacle is included in the flow field, laser beam cannot pass through the obstacle and the projection data have imperfect parts. These imperfect parts cause strong artifacts in the CT images and we cannot identify any unsteady phenomena. To reduce these artifacts, we applied Hybrid Algebraic Reconstruction Technique (HART). In this study, the HART technique will be applied to the problem of reconstruction of wave interaction around a rectangular rod, and CT images obtained using HART and Algebraic Reconstruction Technique (ART) will be compared.