Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5430
Sunghun Lee, M. Lee, J. Park, Hongjip Kim
The center body diffuser is one of supersonic diffuser that can simulate high-altitude environment. There is center-body structure inside the diffuser, and a complex fluid flow is occurred inside the diffuser because of the interaction of the CB structure with gas exhausted from the nozzle outlet. In this study, starting point and flow characteristics of diffuser were investigated according to changing the CB nose cone angle and the length of distance between nozzle and CB structure. The differences of the supersonic flow were compared through each parameter of CB distance and CB nose angle. First changed parameter was length between nozzle and CB. According to the length of distance between nozzle and CB, axial momentum was developed and oblique shock wave moved front of CB from end of CB nose cone. Also, when CB position was located on a certain length, starting point of CBD decreased. Next change parameter was angle of CB nose cone. According to the angle raised, angle of oblique shock wave was raised and radial momentum of supersonic diffuser developed. But, according to radial momentum of supersonic flow over certain angle, the starting pressure of CBD increased. Because axial momentum which isolated vacuum chamber from atmospheric pressure. Through these CFD analysis results, it was shown that angle and length of distance between nozzle and CB influent performance of CBD.
{"title":"A Numerical Study on Flow Characteristics of Super Sonic Diffuser for the Position and Nose Cone Angles of Center Body","authors":"Sunghun Lee, M. Lee, J. Park, Hongjip Kim","doi":"10.1115/ajkfluids2019-5430","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5430","url":null,"abstract":"\u0000 The center body diffuser is one of supersonic diffuser that can simulate high-altitude environment. There is center-body structure inside the diffuser, and a complex fluid flow is occurred inside the diffuser because of the interaction of the CB structure with gas exhausted from the nozzle outlet. In this study, starting point and flow characteristics of diffuser were investigated according to changing the CB nose cone angle and the length of distance between nozzle and CB structure. The differences of the supersonic flow were compared through each parameter of CB distance and CB nose angle. First changed parameter was length between nozzle and CB. According to the length of distance between nozzle and CB, axial momentum was developed and oblique shock wave moved front of CB from end of CB nose cone. Also, when CB position was located on a certain length, starting point of CBD decreased. Next change parameter was angle of CB nose cone. According to the angle raised, angle of oblique shock wave was raised and radial momentum of supersonic diffuser developed. But, according to radial momentum of supersonic flow over certain angle, the starting pressure of CBD increased. Because axial momentum which isolated vacuum chamber from atmospheric pressure. Through these CFD analysis results, it was shown that angle and length of distance between nozzle and CB influent performance of CBD.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117290062","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 : 2019-07-28DOI: 10.1115/ajkfluids2019-5163
K. Tsujimoto, Kango Kitahara, T. Shakouchi, T. Ando
Multiple jets are used in industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessary to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet are strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, an appropriate inflow condition at a nozzle is capable of controlling the large vortex structures near field around the nozzle and improves the mixing performance. In this study, we examine an intermittent control of jets varying the control frequency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, statistical entropy and entrainment are examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.
{"title":"Numerical Simulation of Intermittent-Controlled Multiple Jets","authors":"K. Tsujimoto, Kango Kitahara, T. Shakouchi, T. Ando","doi":"10.1115/ajkfluids2019-5163","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5163","url":null,"abstract":"\u0000 Multiple jets are used in industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessary to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet are strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, an appropriate inflow condition at a nozzle is capable of controlling the large vortex structures near field around the nozzle and improves the mixing performance. In this study, we examine an intermittent control of jets varying the control frequency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, statistical entropy and entrainment are examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122387488","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 : 2019-07-28DOI: 10.1115/ajkfluids2019-4757
R. Zhu, P. Cao, Yang Wang, Chao Ning
Flow distortions occur at the outlet section of the intake duct owing to its shape properties, which is a component of water-jet propulsion. Since the noticeable influence of intake’s flow characteristics upon propulsive efficiency, it’s necessary to focus on intake duct redesign. In this paper, a systematic methodology for reducing flow distortions and power losses within the intake duct through a shape optimization process was obtained. In addition, the mechanism of flow distortions was also developed. The flush type inlet applied in the marine vessel with the speed of 30 knots was chosen as research project. Four characteristic parameters were set as optimization variables depending on the geometrical relationship of thirteen characteristic parameters referred to the duct longitudinal midsection, which were the ramp angle α, the radius of the upper lip R3, the radius of the lower lip R4 and the lip height h respectively. Subsequently, a sample space was built by Latin Hypercube Sampling (LHS) and the parameters were normalized in the range of 0 to 1. With the commercial software CFX, the numerical simulation was accomplished driven by SST k-ω turbulence model. Multi-objective optimization based on the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was utilized to minimize the non-uniformity at outlet section and maximize the minimal pressure at lip simultaneously. Moreover, the Radial Basis Function (RBF) neural network was employed to approximate the functional relationship between variables and objectives, which could be applied in the NSGA-II to get the Pareto Front. The minimum non-uniformity point and the trade-off point (The point both satisfies the minimum non-uniformity and the maximum minimal pressure at lip strategically) were selected from the Pareto Front. With regard to the characteristic parameters of the trade-off point, the ramp angle, the radius of the upper lip, the radius of the lower lip and the lip height are 31.91°, 11.42 mm, 400.97 mm and 55.43 mm respectively. Meanwhile, the characteristic parameters of the minimum non-uniformity point are 30.22°, 25.59 mm, 166.65 mm and 89.90 mm respectively. Ultimately, the duct outflow characteristics of prototype and optimization are compared. In terms of the trade-off point, the minimal pressure at lip increases 66.40% to −24488.93 Pa and the non-uniformity has a drop of 4.56% to 0.1571. The non-uniformity of the minimum point is 0.1481 which is reduced by 10.02%. Through the optimization of duct shape, the secondary flow (Dean vortices) is suppressed effectively. This paper is expected to provide a better comprehension of the flow field within the intake duct of water-jet propulsion.
{"title":"Multi-Objective Hydraulic Optimization on Intake Duct of Water-Jet Propulsion Using NSGA-II","authors":"R. Zhu, P. Cao, Yang Wang, Chao Ning","doi":"10.1115/ajkfluids2019-4757","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4757","url":null,"abstract":"\u0000 Flow distortions occur at the outlet section of the intake duct owing to its shape properties, which is a component of water-jet propulsion. Since the noticeable influence of intake’s flow characteristics upon propulsive efficiency, it’s necessary to focus on intake duct redesign. In this paper, a systematic methodology for reducing flow distortions and power losses within the intake duct through a shape optimization process was obtained. In addition, the mechanism of flow distortions was also developed.\u0000 The flush type inlet applied in the marine vessel with the speed of 30 knots was chosen as research project. Four characteristic parameters were set as optimization variables depending on the geometrical relationship of thirteen characteristic parameters referred to the duct longitudinal midsection, which were the ramp angle α, the radius of the upper lip R3, the radius of the lower lip R4 and the lip height h respectively.\u0000 Subsequently, a sample space was built by Latin Hypercube Sampling (LHS) and the parameters were normalized in the range of 0 to 1. With the commercial software CFX, the numerical simulation was accomplished driven by SST k-ω turbulence model. Multi-objective optimization based on the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was utilized to minimize the non-uniformity at outlet section and maximize the minimal pressure at lip simultaneously. Moreover, the Radial Basis Function (RBF) neural network was employed to approximate the functional relationship between variables and objectives, which could be applied in the NSGA-II to get the Pareto Front.\u0000 The minimum non-uniformity point and the trade-off point (The point both satisfies the minimum non-uniformity and the maximum minimal pressure at lip strategically) were selected from the Pareto Front. With regard to the characteristic parameters of the trade-off point, the ramp angle, the radius of the upper lip, the radius of the lower lip and the lip height are 31.91°, 11.42 mm, 400.97 mm and 55.43 mm respectively.\u0000 Meanwhile, the characteristic parameters of the minimum non-uniformity point are 30.22°, 25.59 mm, 166.65 mm and 89.90 mm respectively. Ultimately, the duct outflow characteristics of prototype and optimization are compared. In terms of the trade-off point, the minimal pressure at lip increases 66.40% to −24488.93 Pa and the non-uniformity has a drop of 4.56% to 0.1571. The non-uniformity of the minimum point is 0.1481 which is reduced by 10.02%. Through the optimization of duct shape, the secondary flow (Dean vortices) is suppressed effectively. This paper is expected to provide a better comprehension of the flow field within the intake duct of water-jet propulsion.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"197 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133684922","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 : 2019-07-28DOI: 10.1115/ajkfluids2019-4753
Sudharsan Vasudevan, S. Etemad, L. Davidson
Tapping the potential of subcooled flow boiling can be the key strategy for enhanced cooling of modern day internal combustion engines with high specific power. Accurate prediction of the boiling heat flux is a prerequisite for employing such strategy and to avoid stepping into the dangerous film boiling regime. The complexity involved in the boiling phenomena makes it difficult to develop a model that accounts for all the dominant mechanisms. However, boiling models available in literature provide a good estimate of the heat flux within their range of applicability. This work attempts to introduce a blending based on probability of bubble nucleation to blend two different models developed for different boiling regimes. Corroboration of results with experiments show improved estimation of boiling heat flux.
{"title":"Improved Estimation of Subcooled Flow Boiling Heat Flux for Automotive Engine Cooling Applications","authors":"Sudharsan Vasudevan, S. Etemad, L. Davidson","doi":"10.1115/ajkfluids2019-4753","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4753","url":null,"abstract":"\u0000 Tapping the potential of subcooled flow boiling can be the key strategy for enhanced cooling of modern day internal combustion engines with high specific power. Accurate prediction of the boiling heat flux is a prerequisite for employing such strategy and to avoid stepping into the dangerous film boiling regime. The complexity involved in the boiling phenomena makes it difficult to develop a model that accounts for all the dominant mechanisms. However, boiling models available in literature provide a good estimate of the heat flux within their range of applicability. This work attempts to introduce a blending based on probability of bubble nucleation to blend two different models developed for different boiling regimes. Corroboration of results with experiments show improved estimation of boiling heat flux.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"4 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133650622","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}
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