Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4931
Sangwon Kim, Sang-eui Lee, Gyoung-Woo Lee, Kwang-cheol Seo, N. Oshima
This work addresses the numerical study of wave-piercing planing hull and related hydrodynamic performance as the appendages. From the half century ago, the interest in high-speed planing crafts has been advanced toward maintaining performance stably. The main reasons to make it hard are instability motion occurring from porpoising and wave condition. Porpoising is mainly due to overlap the heaving and pitching motion with certain period, which is caused by instable pressure distribution and changing longitudinal location of center of gravity. In addition, in wave condition, encountering wave disturbs going into planing mode. This paper presents numerical results of wave-piercing planing hull in porpoising and wave condition. Numerical simulation is conducted via Reynolds Averaged Navier-stokes (RANS) with moving mesh techniques (overset grid), performed at different wave condition. The results for the behaviors of wave-piercing hull form are practically presented and investigated in this study. The understanding of these phenomena is important for design of appendages of wave-piercing hull-form.
{"title":"Hydrodynamic performance and appendage considerations of wave-piercing planing craft overlapping waves and porpoising","authors":"Sangwon Kim, Sang-eui Lee, Gyoung-Woo Lee, Kwang-cheol Seo, N. Oshima","doi":"10.1115/ajkfluids2019-4931","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4931","url":null,"abstract":"\u0000 This work addresses the numerical study of wave-piercing planing hull and related hydrodynamic performance as the appendages. From the half century ago, the interest in high-speed planing crafts has been advanced toward maintaining performance stably. The main reasons to make it hard are instability motion occurring from porpoising and wave condition. Porpoising is mainly due to overlap the heaving and pitching motion with certain period, which is caused by instable pressure distribution and changing longitudinal location of center of gravity. In addition, in wave condition, encountering wave disturbs going into planing mode. This paper presents numerical results of wave-piercing planing hull in porpoising and wave condition. Numerical simulation is conducted via Reynolds Averaged Navier-stokes (RANS) with moving mesh techniques (overset grid), performed at different wave condition. The results for the behaviors of wave-piercing hull form are practically presented and investigated in this study. The understanding of these phenomena is important for design of appendages of wave-piercing hull-form.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43181720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/jfst.2019jfst0025
T. Sakurai, Yuya Oishige, Kazuyuki Saito
Typical hybrid rockets, using solid plastic fuel and liquid oxidizer, have the potential to become non-explosive propulsion systems based on boundary layer combustion (Takahashi and Shimada, 2018). This feature enables hybrid rockets to be both safe and low-cost vehicles. However, there are two primary disadvantages in their use as propulsion systems. One is the low fuel regression rate, which results in a low thrust density. The other is the variation in the oxidizerto-fuel mass ratio (O/F shift) during combustion. This is typically observed in a hybrid rocket engine using a single-port fuel grain. To increase the fuel regression rate, low melting temperature fuels, such as paraffin wax, have been applied (Karabeyoglu, 2002). The authors used paraffin wax in a swirling-oxidizer-flow-type hybrid rocket engine (Saito et al., 2012). The fuel regression rate of paraffin wax reached 5 mm/s, which was approximately seven times greater than that of polypropylene under the same oxidizer mass flux. For the O/F shift problem, one of the solutions is the end-burning hybrid rocket engine. In this engine, as the combustion occurs at the end surface of the cylindrical fuel grain, the burned area does not vary with time and, therefore, constant O/F would be realized under constant oxidizer injection conditions. Saito et al. demonstrated constant O/F burning in their axial-injection end-burning hybrid rocket motor under various operation conditions, including thrust throttling (Saito et al., 2018). The authors investigated the swirling-injection end-burning hybrid rocket engine not only to solve the O/F shift problem, but also to obtain a higher regression rate with swirling oxidizer injection. Compared to other studies (Haag et al., 2000; Rice et al., 2003), the novel approach in this study is the combination of swirling-injection end-burning and the use of paraffin wax fuel. Previous studies (Hayashi and Sakurai, 2015; Oishige et al., 2016) reported that the fuel end-surface regressed in the grain axial direction, as anticipated, and the local fuel regression rate had characteristic Abstract Burning experiments were conducted to better understand the fuel regression behavior in a swirling-injection end-burning hybrid rocket engine using paraffin wax/gaseous oxygen propellant. The oxidizer mass flow rate, grain diameter, and the distance between the oxidizer injector and the grain end-surface were the variable parameters taken as influencing the regression rate. The engine attained an overall axial regression rate as high as approximately 5 mm/s, whereas unstable combustion occurred with increasing burning time owing to low melting temperature of paraffin wax. The fuel grain with a diameter of 90 mm also resulted in unstable combustion caused by the initial shallow crack of the cast grain. The radial distribution of the local regression rate exhibited dependency on the radial position and had two peaks: close to the periphery and the middle of the chamber. Fro
典型的混合火箭，使用固体塑料燃料和液体氧化剂，有可能成为基于边界层燃烧的非爆炸推进系统(Takahashi和Shimada, 2018)。这一特点使混合火箭既安全又低成本。然而，它们作为推进系统有两个主要的缺点。一个是低燃料回归率，这导致低推力密度。另一个是燃烧过程中氧化-燃料质量比(O/F位移)的变化。这通常在使用单孔燃料颗粒的混合火箭发动机中观察到。为了提高燃料回归率，使用了低熔化温度的燃料，如石蜡(Karabeyoglu, 2002)。作者将石蜡用于旋转-氧化剂-流动型混合火箭发动机(Saito et al.， 2012)。在相同氧化剂质量通量下，石蜡的燃料回归速率达到5 mm/s，约为聚丙烯的7倍。对于O/F换挡问题，末端燃烧混合火箭发动机是解决方案之一。在该发动机中，由于燃烧发生在圆柱形燃料颗粒的端面，燃烧面积不随时间变化，因此在恒定的氧化剂喷射条件下，可以实现恒定的O/F。Saito等人演示了轴向喷射端燃混合火箭发动机在包括推力节流在内的各种运行条件下的恒定O/F燃烧(Saito等人，2018)。研究旋喷端燃混合火箭发动机不仅要解决O/F换挡问题，而且要在旋喷氧化剂的情况下获得更高的回归速率。与其他研究相比(Haag et al.， 2000;Rice et al.， 2003)，本研究中的新方法是将旋喷末端燃烧与使用石蜡燃料相结合。前期研究(Hayashi and Sakurai, 2015;Oishige et al.， 2016)报道，燃料端面沿颗粒轴向回归，与预期一致，局部燃料回归速率具有特征。为了更好地了解使用石蜡/气态氧推进剂的旋喷端燃混合火箭发动机的燃料回归行为，进行了摘要燃烧实验。以氧化剂质量流量、颗粒直径、氧化剂喷射器与颗粒端面的距离作为影响回归速率的可变参数。发动机总体轴向后退速率高达5 mm/s左右，但由于石蜡熔化温度较低，燃烧时间越长，燃烧不稳定。直径为90 mm的燃料晶粒也由于铸晶初期的浅裂纹导致燃烧不稳定。局部回归率的径向分布与径向位置相关，存在靠近腔体外围和靠近腔体中部的两个峰值。通过对涡室端面换热的类比，推导出了轴向总回退率的控制参数。由于该参数取决于氧化剂喷油器出口与燃料颗粒端面之间的距离，因此必须使用某种执行器来保持颗粒端面，以达到恒定的O/F燃烧。
{"title":"Fuel regression behavior of swirling-injection end-burning hybrid rocket engine","authors":"T. Sakurai, Yuya Oishige, Kazuyuki Saito","doi":"10.1299/jfst.2019jfst0025","DOIUrl":"https://doi.org/10.1299/jfst.2019jfst0025","url":null,"abstract":"Typical hybrid rockets, using solid plastic fuel and liquid oxidizer, have the potential to become non-explosive propulsion systems based on boundary layer combustion (Takahashi and Shimada, 2018). This feature enables hybrid rockets to be both safe and low-cost vehicles. However, there are two primary disadvantages in their use as propulsion systems. One is the low fuel regression rate, which results in a low thrust density. The other is the variation in the oxidizerto-fuel mass ratio (O/F shift) during combustion. This is typically observed in a hybrid rocket engine using a single-port fuel grain. To increase the fuel regression rate, low melting temperature fuels, such as paraffin wax, have been applied (Karabeyoglu, 2002). The authors used paraffin wax in a swirling-oxidizer-flow-type hybrid rocket engine (Saito et al., 2012). The fuel regression rate of paraffin wax reached 5 mm/s, which was approximately seven times greater than that of polypropylene under the same oxidizer mass flux. For the O/F shift problem, one of the solutions is the end-burning hybrid rocket engine. In this engine, as the combustion occurs at the end surface of the cylindrical fuel grain, the burned area does not vary with time and, therefore, constant O/F would be realized under constant oxidizer injection conditions. Saito et al. demonstrated constant O/F burning in their axial-injection end-burning hybrid rocket motor under various operation conditions, including thrust throttling (Saito et al., 2018). The authors investigated the swirling-injection end-burning hybrid rocket engine not only to solve the O/F shift problem, but also to obtain a higher regression rate with swirling oxidizer injection. Compared to other studies (Haag et al., 2000; Rice et al., 2003), the novel approach in this study is the combination of swirling-injection end-burning and the use of paraffin wax fuel. Previous studies (Hayashi and Sakurai, 2015; Oishige et al., 2016) reported that the fuel end-surface regressed in the grain axial direction, as anticipated, and the local fuel regression rate had characteristic Abstract Burning experiments were conducted to better understand the fuel regression behavior in a swirling-injection end-burning hybrid rocket engine using paraffin wax/gaseous oxygen propellant. The oxidizer mass flow rate, grain diameter, and the distance between the oxidizer injector and the grain end-surface were the variable parameters taken as influencing the regression rate. The engine attained an overall axial regression rate as high as approximately 5 mm/s, whereas unstable combustion occurred with increasing burning time owing to low melting temperature of paraffin wax. The fuel grain with a diameter of 90 mm also resulted in unstable combustion caused by the initial shallow crack of the cast grain. The radial distribution of the local regression rate exhibited dependency on the radial position and had two peaks: close to the periphery and the middle of the chamber. Fro","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/jfst.2019jfst0025","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66304250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/jfst.2019jfst0012
Ryuichi Maruyama, Kento Shinji, T. Nonomura, K. Asai
Unsteady pressure distributions around a simplified sedan automobile model were investigated by conducting dynamic wind-tunnel testing using the newly developed forced oscillating apparatus, HEXA-X3, which can produce 6-degrees-of-freedom motion. The effects of heaving and pitching oscillation were investigated as the model simulated a vehicle running on a flat road at approximately 40 m/s and 1 Hz oscillation. The effects of the ground plate on unsteady pressure distributions over the model surfaces were measured while simulating heaving and pitching motion at Strouhal-number conditions similar to those for actual vehicles. The influence of the tubing on the frequency response of the pressure sensor was evaluated to be negligible by conducting a calibration experiment first. In the static case, the overall pressure distribution was consistent with that for a typical sedan, and the influence of the local relative flow velocity changes due to the contraction effect was observed in the underside of the model. In the forced oscillation tests, the effect of heaving and pitching motions on the flow around the underside was investigated. Effects of oscillation parameters, specifically amplitude and frequency, were investigated using the gain and phase-lag normalized by data from the steady model. Results of the test indicate that there is a characteristic distribution in pressure fluctuation, and the phenomena that become dominant in the flow around the underside vary according to location. The dynamic heaving motion was shown to change the pressure distribution, possibly due to changes in the effective angle of attack in addition to the static effect. The pitching test showed that a dynamic camber effect works in addition to those effects.
{"title":"Effects of heaving and pitching motions on underside aerodynamics of a sedan vehicle","authors":"Ryuichi Maruyama, Kento Shinji, T. Nonomura, K. Asai","doi":"10.1299/jfst.2019jfst0012","DOIUrl":"https://doi.org/10.1299/jfst.2019jfst0012","url":null,"abstract":"Unsteady pressure distributions around a simplified sedan automobile model were investigated by conducting dynamic wind-tunnel testing using the newly developed forced oscillating apparatus, HEXA-X3, which can produce 6-degrees-of-freedom motion. The effects of heaving and pitching oscillation were investigated as the model simulated a vehicle running on a flat road at approximately 40 m/s and 1 Hz oscillation. The effects of the ground plate on unsteady pressure distributions over the model surfaces were measured while simulating heaving and pitching motion at Strouhal-number conditions similar to those for actual vehicles. The influence of the tubing on the frequency response of the pressure sensor was evaluated to be negligible by conducting a calibration experiment first. In the static case, the overall pressure distribution was consistent with that for a typical sedan, and the influence of the local relative flow velocity changes due to the contraction effect was observed in the underside of the model. In the forced oscillation tests, the effect of heaving and pitching motions on the flow around the underside was investigated. Effects of oscillation parameters, specifically amplitude and frequency, were investigated using the gain and phase-lag normalized by data from the steady model. Results of the test indicate that there is a characteristic distribution in pressure fluctuation, and the phenomena that become dominant in the flow around the underside vary according to location. The dynamic heaving motion was shown to change the pressure distribution, possibly due to changes in the effective angle of attack in addition to the static effect. The pitching test showed that a dynamic camber effect works in addition to those effects.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/jfst.2019jfst0012","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/jfst.2019jfst0018
Y. Yamaguchi, D. Sasaki, M. Okamoto, K. Shimoyama, S. Obayashi
Micro Air Vehicle (MAV) are often utilized for the disaster spot, ecosystem observation and topography investigation these days. Because the full length of the body is centimeter scale, the Reynolds number of MAV becomes low (10-10). A laminar separation bubble is formed in low Reynolds number unlike a high Reynolds number domain because the viscous term becomes dominant. Numerical and experimental analysis of high performance airfoils in low Reynolds number flow is proposed (M. Anyoji et al., 2014). In low Reynolds number flows, flat plate or thin wings have better aerodynamic performance compared to thick streamlined airfoils. However, there are still many problems with related to the aerodynamic performance. For example, batteries tend to be heavy and the thrust is not sufficient in low Reynolds number. These results would be useful in designing low Reynolds number aircraft such as micro-air vehicles. For example, an insect-sized MAV was proposed by (Wood et al., 2012) and (Kroo and Kunz., 2001).
微型飞行器(MAV)在灾害现场观测、生态系统观测和地形调查等领域得到广泛应用。由于机体全长为厘米尺度，MAV的雷诺数较低(10-10)。由于粘滞项占主导地位，在低雷诺数域中形成层流分离泡，而在高雷诺数域中形成层流分离泡。提出了低雷诺数下高性能翼型的数值和实验分析(M. Anyoji et al.， 2014)。在低雷诺数流动中，平板或薄翼比厚流线型翼型具有更好的气动性能。然而，在气动性能方面仍存在许多问题。例如，在低雷诺数下，电池往往很重，推力不足。这些结果对低雷诺数飞行器如微型飞行器的设计有一定的参考价值。例如，(Wood et al.， 2012)和(Kroo and Kunz)提出了昆虫大小的MAV。, 2001)。
{"title":"Numerical investigation of geometrical corrugation influence to vortex flowfields at low Reynolds number","authors":"Y. Yamaguchi, D. Sasaki, M. Okamoto, K. Shimoyama, S. Obayashi","doi":"10.1299/jfst.2019jfst0018","DOIUrl":"https://doi.org/10.1299/jfst.2019jfst0018","url":null,"abstract":"Micro Air Vehicle (MAV) are often utilized for the disaster spot, ecosystem observation and topography investigation these days. Because the full length of the body is centimeter scale, the Reynolds number of MAV becomes low (10-10). A laminar separation bubble is formed in low Reynolds number unlike a high Reynolds number domain because the viscous term becomes dominant. Numerical and experimental analysis of high performance airfoils in low Reynolds number flow is proposed (M. Anyoji et al., 2014). In low Reynolds number flows, flat plate or thin wings have better aerodynamic performance compared to thick streamlined airfoils. However, there are still many problems with related to the aerodynamic performance. For example, batteries tend to be heavy and the thrust is not sufficient in low Reynolds number. These results would be useful in designing low Reynolds number aircraft such as micro-air vehicles. For example, an insect-sized MAV was proposed by (Wood et al., 2012) and (Kroo and Kunz., 2001).","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66303479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/JFST.2019JFST0007
T. Matsunuma, T. Segawa
Dielectric barrier discharge (DBD) plasma actuators were used for the active control of flow separation on a curved wall simulated suction surface of a gas turbine blade at three different mainstream velocities, UMS = 2.2 m/s, 4.1 m/s, and 6.3 m/s. Owing to the change in mainstream velocity, the Reynolds number was varied as Re = 1.7 × 104, 3.1 × 104, and 4.7 × 104, respectively. Particle image velocimetry system was used to obtain two-dimensional velocity field measurements. The amplitude of input voltage for the plasma actuator was changed from ±2.0 kV to ±4.0 kV. At the lower mainstream velocity, UMS = 2.2 m/s (Re = 1.7 × 104), the separated flow induced on a curved wall was consider-ably reduced by the flow control using the DBD plasma actuator. Moreover, the effect of flow control by the plasma actuator was gradually reduced at the higher mainstream velocities, UMS = 4.1 m/s and 6.3 m/s (Re = 3.1 × 104 and 4.7 × 104, respectively). The flow control effect was improved by changing the position of the plasma actuator. When the plasma actuator was positioned immediately before the separation point, it exhibited better flow control effects than when positioned immediately behind the separation point.
{"title":"Effects of mainstream velocity and setting position on flow separation control of a curved wall using plasma actuators","authors":"T. Matsunuma, T. Segawa","doi":"10.1299/JFST.2019JFST0007","DOIUrl":"https://doi.org/10.1299/JFST.2019JFST0007","url":null,"abstract":"Dielectric barrier discharge (DBD) plasma actuators were used for the active control of flow separation on a curved wall simulated suction surface of a gas turbine blade at three different mainstream velocities, UMS = 2.2 m/s, 4.1 m/s, and 6.3 m/s. Owing to the change in mainstream velocity, the Reynolds number was varied as Re = 1.7 × 104, 3.1 × 104, and 4.7 × 104, respectively. Particle image velocimetry system was used to obtain two-dimensional velocity field measurements. The amplitude of input voltage for the plasma actuator was changed from ±2.0 kV to ±4.0 kV. At the lower mainstream velocity, UMS = 2.2 m/s (Re = 1.7 × 104), the separated flow induced on a curved wall was consider-ably reduced by the flow control using the DBD plasma actuator. Moreover, the effect of flow control by the plasma actuator was gradually reduced at the higher mainstream velocities, UMS = 4.1 m/s and 6.3 m/s (Re = 3.1 × 104 and 4.7 × 104, respectively). The flow control effect was improved by changing the position of the plasma actuator. When the plasma actuator was positioned immediately before the separation point, it exhibited better flow control effects than when positioned immediately behind the separation point.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/JFST.2019JFST0004
T. Kurahashi, Y. Ozeki, E. Katamine
{"title":"Shape optimization analysis considering a rotational body in a flow field based on the adjoint variable and the finite element methods","authors":"T. Kurahashi, Y. Ozeki, E. Katamine","doi":"10.1299/JFST.2019JFST0004","DOIUrl":"https://doi.org/10.1299/JFST.2019JFST0004","url":null,"abstract":"","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2019JFST0004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66303252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/jfst.2019jfst0011
T. Hirano, Mitsuo Yoshimura, K. Shimoyama, A. Komiya
This study proposes a shape optimization approach for the cross-sectional shape of the inner pipe of a counter-flow concentric tube heat exchanger. The cross-sectional shape of the inner pipe is expressed by an algebraic expression with a small number of parameters, and their heat transfer performance is evaluated by a commercial Computational Fluid Dynamics (CFD) solver. The optimization is conducted by the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) assisted by the Kriging surrogate model, and the NSGA-II finds the optimal cross-sectional shape with many protrusions around the perimeter of the inner channel to improve the heat transfer performance. In this study, heat transfer performance is evaluated from the temperature drop at the outlet of the high-temperature fluid. The present optimization finds the optimal channel with many protrusions, which achieves lower outlet temperature than a circular channel even with the same heat transfer surface area. This result indicates that the number of protrusions plays important roles which contribute not only to increase heat transfer area but also to improve heat transfer performance.
本文提出了一种逆流同心管换热器内管截面形状的形状优化方法。采用带有少量参数的代数表达式来表示内管的截面形状，并利用商用计算流体力学(CFD)求解器对其传热性能进行了评估。通过非支配排序遗传算法II (non - dominate Sorting Genetic Algorithm II, NSGA-II)辅助Kriging代理模型进行优化，NSGA-II找到了内通道周长周围有许多凸起的最优截面形状，以提高传热性能。在本研究中，传热性能是从高温流体出口的温度下降来评估的。优化结果表明，在相同换热面积的情况下，具有多个凸点的最优通道的出口温度要低于圆形通道。结果表明，凸出物的数量对增大换热面积和提高换热性能具有重要作用。
{"title":"Thermo-fluid dynamic design optimization of a concentric tube heat exchanger","authors":"T. Hirano, Mitsuo Yoshimura, K. Shimoyama, A. Komiya","doi":"10.1299/jfst.2019jfst0011","DOIUrl":"https://doi.org/10.1299/jfst.2019jfst0011","url":null,"abstract":"This study proposes a shape optimization approach for the cross-sectional shape of the inner pipe of a counter-flow concentric tube heat exchanger. The cross-sectional shape of the inner pipe is expressed by an algebraic expression with a small number of parameters, and their heat transfer performance is evaluated by a commercial Computational Fluid Dynamics (CFD) solver. The optimization is conducted by the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) assisted by the Kriging surrogate model, and the NSGA-II finds the optimal cross-sectional shape with many protrusions around the perimeter of the inner channel to improve the heat transfer performance. In this study, heat transfer performance is evaluated from the temperature drop at the outlet of the high-temperature fluid. The present optimization finds the optimal channel with many protrusions, which achieves lower outlet temperature than a circular channel even with the same heat transfer surface area. This result indicates that the number of protrusions plays important roles which contribute not only to increase heat transfer area but also to improve heat transfer performance.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66303397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-01DOI: 10.1299/jfst.2019jfst0021
Taimei Miyagawa, T. Okabe, Takuro Miyanishi, T. Kogawa, H. Murata, K. Fumoto
Ice slurry is a homogeneous mixture of small ice particles and a carrier liquid. It is widely used in many fields. Previous studies have gradually clarified its heat transfer in high ice packing factor (IPF). However, only a few studies have focused on the mechanism of heat transfer with low IPF in a cavity heated from below. The objective of this study is to experimentally clarify the melting heat transfer of ice slurry in a cavity heated from below with low IPF to develop a direct contact medical cooling system. To observe the melting behavior of ice slurry, the test section was made of acrylic resin (100 mm × 60 mm× 30 mm) and a silicone rubber heater that was used for heating under constant heat flux conditions. We measured the surface temperature of the heater and the liquid thickness. We showed that the melting process can be divided into three stages. In the first stage, heat conduction dominated the process of heat transfer and the temperature of the heater rapidly increased. In the second stage, natural convection heat transfer dominated the process of heat transfer that increased the melting rate of ice slurry and decreased the temperature of the heater. In the third stage, heat conduction dominated the process of heat transfer in the concentration stratification. This led to a decrease in the melting rate and an increase in the temperature of the heater. Our result also showed that the melting process of the ice slurry is slow enough to consider it the quasi-steady state in the range of 104 < Ra∗ < 107 as compared to the development of the velocity and temperature fields.
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