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Tatsuya Hasegawa - One of the best experts on this subject based on the ideXlab platform.

  • Flame development along a straight vortex
    Combustion and Flame, 2002
    Co-Authors: Tatsuya Hasegawa, Satoshi Michikami, Toshiyuki Nomura, Daisuke Gotoh, Taichi Sato
    Abstract:

    Flame development along a straight vortex was studied experimentally to elucidate the effects of the maximum Circumferential Velocity and the density ratio of the flame. A pair of straight vortices was produced in nitrogen-diluted stoichiometric hydrogen-oxygen mixtures with density ratios ranging from 5.3 to 7.2. The Velocity field measured by particle image velocimetry (PIV) showed that the vortex tube had a mean maximum Circumferential Velocity ranging from 18.0 to 35.8 m/s and had a mean core diameter ranging from 5 to 6 mm. One of the vortices was ignited at the core by a focused laser at 193 nm without disturbing the flow field. The flame propagated along the axis of the straight vortex at a speed much higher than in the radial direction or in the quiescent mixture. The axial propagation Velocity increased over time and became nearly constant when the half-axial length of the flame was larger than the core diameter of the vortex tube. The axial propagation Velocity at steady state was roughly proportional to the maximum Circumferential Velocity and to the density ratio minus unity. The axial propagation Velocity in the initial stage increased with the square root of the half-axial length of the flame as well as with the maximum Circumferential Velocity and the density ratio minus unity.

  • Mechanism of Flame Propagation along a Vortex Tube
    IUTAM Symposium on Geometry and Statistics of Turbulence, 2001
    Co-Authors: Tatsuya Hasegawa, Shinnosuke Nishiki, Satoshi Michikami
    Abstract:

    Vortex tubes are recognized as sinews of turbulence: The length of the vortex tube represents the integral scale of turbulence, the spacing of the nodes of the vortex tube represents the Taylor micro scale, and the diameter of the vortex tube represents the 10 times the Kolmogorov scale (Tanahashi and Miyauchi, 1999). Thus the interaction between a fine vortex tube and a flame seems to be an essential process in turbulent combustion. The aim of this work is to study the mechanism of flame propagation along a fine vortex tube of a premixed gas when the vortex tube interacts perpendicularly with the flame (Chomiak, 1976). It is well known that a premixed flame propagates rapidly with a Velocity similar to the maximum Circumferential Velocity of the vortex core. It is also known that the premixed flame can propagate along the vortex tube when the maximum Circumferential Velocity is faster than the burning Velocity and the core diameter is larger than the flame thickness (Hasegawa et al., 1995). However, the mechanism of the flame propagation is still not clear though several models have been proposed. In this study, the flame propagation along a fine vortex tube is numerically simulated and the mechanism that provokes the flame to propagate along the vortex tube is discussed in terms of the vorticity transport equation.

  • Mechanism of Interaction between a Vortex Pair and a Premixed Flame
    Combustion Science and Technology, 2000
    Co-Authors: Tatsuya Hasegawa, Tatsuya Morooka, Shinnosuke Nishiki
    Abstract:

    Abstract Colliding interaction of a vortex pair with a premixed flame is numerically studied with a two-step reaction model including chain-branching and chain-breaking reactions. The vortex pair has a maximum Circumferential Velocity ranging from 4.7 to 54.7 times the laminar burning Velocity and has a core diameter ranging from 1.1 to 1.55 times the flame thickness. Besides well-known interacting behaviors such as the flame wrinkling by a weak vortex pair and the pocket formation by a moderate vortex pair, an elongation of the concave flame without entraining the burned gas appears in the interaction with a strong vortex pair. The different behaviors of interaction are attributed to the ratio of the moving Velocity of the vortex pair to the burning Velocity and the criterion is represented by the ratio of the maximum Circumferential Velocity to the burning Velocity. For moderate and strong vortices, vorticity generation due to the baroclinic effect and reduction of distance between vortex cores result i...

  • Effect of density ratio on flame propagation along a vortex tube
    Symposium (International) on Combustion, 1996
    Co-Authors: Tatsuya Hasegawa, K. Nishikado
    Abstract:

    Propagation of a premixed flame along a vortex tube perpendicular to the flame is numerically simulated to study the effect of the density ratio of the flame, on the propagation Velocity and to clarify the mechanism of propagation. The vortex tube is assumed to be a Burgers vortex with an initial Circumferential Velocity ranging from 1.7 to 36 times the laminar burning Velocity and with an initial core diameter ranging from 0.15 to 1.71 times the flame thickness. The density ratios of the flame are assumed to be 7.53 and 2.63. It is found that the flame propagation Velocity along the vortex tube has an inverse relation with the density ratio and depends on the power of the maximum Circumferential Velocity and on the diameter of the vortex tube. It is also observed that the baroclinic torque produces vorticity in the flame zone and that this vorticity can provoke the flame to accelerate along the vortex tube with a Velocity similar to the observed one. The theory on the basis of the pressure difference across the flame does not explain the inverse dependency on the density ratio—neither the dependency on the power of the Circumferential Velocity nor on the diameter of the vortex tube. On the other hand, the theory on the basis of the baroclinic torque better explains the inverse dependency on the density ratio, as well as the dependency on almost the second power of the Circumferential Velocity and on the diameter of the vortex tube.

  • Flame propagation along a fine vortex tube
    Combustion Science and Technology, 1995
    Co-Authors: Tatsuya Hasegawa, K. Nishikado, J. Chomiak
    Abstract:

    ABSTRACT Interaction between a premixed flame and a fine vortex tube perpendicular to the flame is simulated numerically in order to study the effects of the rotating Velocity and tube diameter on flame propagation along the vortex tube. The vortex tube has an initial Circumferential Velocity ranging from 1.8 to 36 times the laminar burning Velocity and an initial core diameter ranging from 0.18 to 1.71 times the flame thickness. It is shown that a premixed flame can be accelerated along the vortex tube axis, and that the propagation Velocity is proportional to the maximum Circumferential Velocity of the vortex tube. It is also shown that the influence of the vortex on the flame propagation can be neglected when the Reynolds number based on the vortex tube diameter and maximum Circumferential Velocity is below 10. The proportionality factor between the propagation Velocity and Circumferential Velocity increases above the critical number with azimuthal speed and reaches about one at the Reynolds number of ...

F. S. Kaplan - One of the best experts on this subject based on the ideXlab platform.

  • Centrifugal casting of ceramics and the properties of the castings
    Refractories, 1992
    Co-Authors: Yu. E. Pivinskii, T. I. Litovskaya, O. N. Samarina, F. S. Kaplan
    Abstract:

    ConclusionsIt was established that the Circumferential Velocity maintained during the centrifugal casting process has a significant effect on the porosity of the castings. The effect of the rheological behavior of the original HCBS is also significant.We carried out a comparative analysis of the rheological properties of the HCBS of fused quartz having different pH values with the parameters of their centrifugal casting and the porosity of the obtained castings.As in the case of slip casting, unfired quartz ceramics were obtained according to the method of centrifugal casting. These ceramics exhibit high levels of mechanical properties after undergoing a hydrothermal treatment or a strengthening treatment in alkaline solutions.The possibility of using the method of centrifugal casting for shaping the refractories based on the casting systems containing a granular filler (the keramobeton-type systems) was established.

  • Centrifugal casting of ceramics and the properties of the castings
    Refractories and Industrial Ceramics, 1992
    Co-Authors: Yu. E. Pivinskii, T. I. Litovskaya, O. N. Samarina, F. S. Kaplan
    Abstract:

    It was established that the Circumferential Velocity maintained during the centrifugal casting process has a significant effect on the porosity of the castings. The effect of the rheological behavior of the original HCBS is also significant.

  • Centrifugal casting of ceramics. Main parameters and the regularities of the process
    Refractories, 1991
    Co-Authors: Yu. E. Pivinskii, T. I. Litovskaya, O. N. Samarina, I. B. Volchek, F. S. Kaplan
    Abstract:

    ConclusionsUsing HCBS of fused quartz, we studied and analyzed the main regularities of the centrifugal casting process of ceramic products.The procedure for calculating the magnitude of the centrifugal pressure during the molding process and a nomogram establishing the relationship between the rotational frequency of the mold, the diameter of the product being molded, and the Circumferential Velocity of centrifugal forming were presented. Based on the integral curves of grain size distribution of the castings, the degree of layering in their solid phase was characterized.The volume fraction of HCBS, the Circumferential Velocity and the temperature maintained during the molding process, and the coefficient of excess solid phase form the most important and decisive technological parameters of the process of centrifugal forming.The method of centrifugal casting makes it possible to accelerate the molding process by several tens of times as compared to slip casting. In this case, the porosity of the castings amounts to 12–20%.

Friedrich-karl Benra - One of the best experts on this subject based on the ideXlab platform.

  • Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes
    Journal of Turbomachinery-transactions of The Asme, 2013
    Co-Authors: Nico Petry, Sven König, Friedrich-karl Benra
    Abstract:

    Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high Circumferential Velocity component. The Circumferential Velocity of the flow and the phase Velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the Circumferential Velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined. The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the Circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance. If the experimentally determined swirling flow Velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the Circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance. Contrary to the acoustic modes calculated via a finite element analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.

  • Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes
    Volume 8: Turbomachinery Parts A B and C, 2012
    Co-Authors: Nico Petry, Sven König, Friedrich-karl Benra
    Abstract:

    Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high Circumferential Velocity component. The Circumferential Velocity of the flow and the phase Velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the Circumferential Velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined.The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the Circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance.If the experimentally determined swirling flow Velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the Circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance.Contrary to the acoustic modes calculated via a Finite Element Analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.Copyright © 2012 by Siemens Energy Ltd.

Luhe Shen - One of the best experts on this subject based on the ideXlab platform.

  • reliability analysis of in situ stress measurement using Circumferential Velocity anisotropy
    Journal of rock mechanics and geotechnical engineering, 2011
    Co-Authors: Luhe Shen
    Abstract:

    Abstract In-situ stress measurement for deep reservoir formation is difficult in terms of security, reliability and technique. Acoustic Velocity anisotropy test is a basic method for stress measurement of rock cores, which is based on the distribution of acoustic Velocity in different directions around rock cores. The heterogeneity of core samples, such as fractures and gravel contained, can also lead to wave Velocity anisotropy. Therefore, the corresponding reliability evaluation method is established to exclude some other anisotropy factors caused by non-tectonic stresses. In this paper, the reliability of testing results is evaluated from three aspects, i.e. phase difference, anisotropy index and waveform, to remove the factors caused by non-tectonic stresses.

Hiroyuki Sasahara - One of the best experts on this subject based on the ideXlab platform.

  • Chip Adhesion and Tool Wear in Driven Rotary Cutting of Stainless Steel
    Volume 3: Manufacturing Equipment and Systems, 2017
    Co-Authors: Hiroyuki Sasahara, Masato Goto, Wataru Takahashi, Hiromasa Yamamoto, Toshiyuki Muraki
    Abstract:

    In driven rotary cutting of stainless steel, adhesions sometimes occur on the tool, causing increased wear. The type of coolant supplying methods and tool rotation speed affects largely on the adhesion because it depends on the temperature and lubricating performance. Results showed that in a Circumferential Velocity ratio of 1.0, which means tangential component of tool peripheral speed is equal to work surface speed, there is no adhesion on the tool after cutting. In a Circumferential Velocity ratio of 2.0, adhesion occurred with overcooling of the flood coolant, and wear increased by adhesions to the rotating tool. It was found that the thermal cracks on the cutting edge was one of the factors of increased wear and chipping. Adhesives on the tool edge also accelerated the chipping.

  • Effect of Cutting Conditions on Tool Wear in Driven Rotary Cutting of Maraging Steel
    Key Engineering Materials, 2015
    Co-Authors: Masato Goto, Wataru Takahashi, Wataru Sasaki, Takeshi Toujyo, Yuji Takagi, Hiromasa Yamamoto, Hiroyuki Sasahara
    Abstract:

    In this paper, driven rotary cutting of maraging steel was carried out and the influence on tool wear of difference cutting conditions was investigated. As cutting conditions, different coolant conditions, cutting speeds, Circumferential Velocity ratios, tool inclination angles, tool rotation directions and normal rake angles were tested. We found that as the coolant quantity decreased and cutting speed increased, the width of flank wear increased. It was also found that the Circumferential Velocity ratio, tool inclination angle, tool rotation direction and normal rake angle have optimal conditions that decrease wear. Optimal conditions were chosen, and a tool life test was carried out. As a result, driven rotary cutting was achieved with 11 or more times the tool life of conventional turning.