Pub Date : 2019-11-20DOI: 10.1115/ajkfluids2019-5394
Ke Zhifang, Cheng Liu, Wei Wei, Q. Yan, Xianglu Meng
The main function of the torque converter pump is to transfer mechanical power into fluid dynamic energy. It has been proved that the pump blade shape, especially pump blade camber peak, is crucial to torque converter hydrodynamic performance. However, it remains unclear how this parameter affects internal flow characteristics, and how it leads to the difference in performance. Thus, the relationship between the pump blade camber and the performance of torque converter and the flow mechanism were explored in this study. Torque converters with different pump blade camber were tested. Meanwhile, the corresponding numerical models were also established and their internal flow fields were investigated through steady-state simulations. The influence of the pump blade camber on the hydrodynamic performance was studied using both numerical and experimental methods, and the flow mechanism was also revealed and elaborated by exploring the numerical flow fields. The results from both experiments and simulations showed that larger pump blade camber peak led to higher pump capacity, higher maximum efficiency and lower stall torque ratio. The flow field simulation revealed that larger pump camber peak would lead to higher total pressure in pump channel. And the pressure distribution between the suction and pressure surface showed a similar pattern; however, their difference, especially near the leading and tailing edge, depends on the camber peak. Besides, higher camber peak blade absorbed more power, also induced more complex vortex, but there always existed the most efficient speed ratio when pump efficiency can reach to peak, at this moment, the difference between angle of attack and entrance angle reach the zero, which can be used to guide the design of pump blade.
{"title":"Numerical Simulation of Torque Converter With Different Pump Blade Camber","authors":"Ke Zhifang, Cheng Liu, Wei Wei, Q. Yan, Xianglu Meng","doi":"10.1115/ajkfluids2019-5394","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5394","url":null,"abstract":"\u0000 The main function of the torque converter pump is to transfer mechanical power into fluid dynamic energy. It has been proved that the pump blade shape, especially pump blade camber peak, is crucial to torque converter hydrodynamic performance. However, it remains unclear how this parameter affects internal flow characteristics, and how it leads to the difference in performance. Thus, the relationship between the pump blade camber and the performance of torque converter and the flow mechanism were explored in this study.\u0000 Torque converters with different pump blade camber were tested. Meanwhile, the corresponding numerical models were also established and their internal flow fields were investigated through steady-state simulations. The influence of the pump blade camber on the hydrodynamic performance was studied using both numerical and experimental methods, and the flow mechanism was also revealed and elaborated by exploring the numerical flow fields.\u0000 The results from both experiments and simulations showed that larger pump blade camber peak led to higher pump capacity, higher maximum efficiency and lower stall torque ratio. The flow field simulation revealed that larger pump camber peak would lead to higher total pressure in pump channel. And the pressure distribution between the suction and pressure surface showed a similar pattern; however, their difference, especially near the leading and tailing edge, depends on the camber peak. Besides, higher camber peak blade absorbed more power, also induced more complex vortex, but there always existed the most efficient speed ratio when pump efficiency can reach to peak, at this moment, the difference between angle of attack and entrance angle reach the zero, which can be used to guide the design of pump blade.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125473713","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/ajkfluids2019-5521
C. Naik, H. El-Asrag, Rakesh Yadav, Ahad Validi, E. Meeks
Combustion models can have a significant impact on flame simulations. While solving finite rate chemistry typically yields more accurate predictions, they depend significantly on the detailed kinetics mechanism used. To demonstrate the effect, Large Eddy Simulation (LES) of Sandia Flame D [1] has been performed using various combustion models. Four different detailed kinetics mechanisms have been considered. They include DRM mechanism with 22 species, GRI-mech 2.11 with 49 species, GRI-mech 3.0 with 53 species [2], and Model Fuel Library (MFL) mechanism with 29 species [3]. In addition to the mechanisms, two modeling approaches considered are direct integration of finite rate kinetics (FR) and Flamelet Generated Manifold (FGM). The performance is compared between combinations of the mechanisms and combustion-modeling approaches for prediction of the flame structure and pollutants, including NO and CO. The mesh contains about half a million hexahedral cells and LES statistics were collected over ten flow throughs. Advanced solvers including dynamic cell clustering using the Chemkin-CFD solver in Fluent have been used for faster simulation time. Based on comparison of simulation results to the measurements at various axial and radial positions, we find that the results using the FGM approach were comparable to those using direct integration of FR chemistry, except for NO. In general, the simulation results are in good agreement with the experiment in terms of aerodynamics, mixture fraction and temperature profiles. However, kinetics mechanisms were found to have the most pronounced effect on emissions predictions. NO was especially more sensitive to the kinetics mechanism. Both versions of the GRI-mech fell short in predicting emissions. Overall, the MFL mechanism was found to yield the closest match with the data for flame structure, CO, and NO.
{"title":"Impact of Combustion Models on Emissions Predictions From a Piloted Methane-Air Diffusion Flame","authors":"C. Naik, H. El-Asrag, Rakesh Yadav, Ahad Validi, E. Meeks","doi":"10.1115/ajkfluids2019-5521","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5521","url":null,"abstract":"\u0000 Combustion models can have a significant impact on flame simulations. While solving finite rate chemistry typically yields more accurate predictions, they depend significantly on the detailed kinetics mechanism used. To demonstrate the effect, Large Eddy Simulation (LES) of Sandia Flame D [1] has been performed using various combustion models. Four different detailed kinetics mechanisms have been considered. They include DRM mechanism with 22 species, GRI-mech 2.11 with 49 species, GRI-mech 3.0 with 53 species [2], and Model Fuel Library (MFL) mechanism with 29 species [3]. In addition to the mechanisms, two modeling approaches considered are direct integration of finite rate kinetics (FR) and Flamelet Generated Manifold (FGM). The performance is compared between combinations of the mechanisms and combustion-modeling approaches for prediction of the flame structure and pollutants, including NO and CO. The mesh contains about half a million hexahedral cells and LES statistics were collected over ten flow throughs. Advanced solvers including dynamic cell clustering using the Chemkin-CFD solver in Fluent have been used for faster simulation time. Based on comparison of simulation results to the measurements at various axial and radial positions, we find that the results using the FGM approach were comparable to those using direct integration of FR chemistry, except for NO. In general, the simulation results are in good agreement with the experiment in terms of aerodynamics, mixture fraction and temperature profiles. However, kinetics mechanisms were found to have the most pronounced effect on emissions predictions. NO was especially more sensitive to the kinetics mechanism. Both versions of the GRI-mech fell short in predicting emissions. Overall, the MFL mechanism was found to yield the closest match with the data for flame structure, CO, and NO.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"1 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":"130653521","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/ajkfluids2019-5139
Sang‐Hyun Oh, Sung Il Kim, Ki-Ho Park, B. Yu
In this study, numerical analysis was carried out to investigate the effects of slot die nozzle exit rear pressure on coating uniformity improvement in coating nozzles which are widely used in industry. Coating uniformity in coatings of viscosity materials such as inks and surface coating solutions is closely related to the quality of the product. Especially, coating uniformity is an important performance indicator for slot die coatings, which are used primarily in the production of optical or chemical products such as displays, touch screens, solar panels, and batteries. In general, the average thickness of a thin film in a slot die coating is determined by the supply flow rate and the moving speed of the plate. However, due to various parameters, thickness irregularities and coating defects due to pores occur locally. Therefore, many studies have recently been performed to solve the local defect of the slot die coating. In order to improve the coating uniformity, this study applied the vacuum pressure condition to the slot die nozzle rear end and numerical study on the coating uniformity according to the vacuum pressure was carried out. The numerical analysis proceeded to 2-D, unsteady condition and the VOF method. A commercial numerical simulation software (STAR-CCM+ V.12.06) was used. It was simulated that the coating liquid was supplied onto the moving plate surface. The moving plate speed was fixed 0.01m/s. The nozzle geometry simulates a slot die nozzle. And the coating raw material supply flow rate was considered for two conditions (0.005, 0.006m/s). Two vacuum pressure conditions (−3, −300Pa) were applied to the rear end of the nozzle. The viscosity of the viscous material was fixed at 2 Pa.s. The analysis results were analyzed through the uniformity of the material supplied to the surface. As a result of analysis, uniformity of coating was lowered regardless of the velocity when the vacuum pressure condition was −3.0 Pa, and uniformity was lowered as the velocity increased. However, it was confirmed that uniformity of the coating was increased at all velocity condition when the vacuum pressure condition was −300 Pa. This is because as the flat plate moves, the reverse pressure is applied to the downstream of the coating solution, thereby improving the uniformity of the coating liquid flowing through the flat plate and preventing the inflow of air or the like. Through this study, it was confirmed that the coating uniformity can be improved by controlling the vacuum pressure at the rear end of the nozzle.
{"title":"A Numerical Study on Improvement of Coating Uniformity by Controlling the Pressure at the Exit of the Slot Die Nozzle","authors":"Sang‐Hyun Oh, Sung Il Kim, Ki-Ho Park, B. Yu","doi":"10.1115/ajkfluids2019-5139","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5139","url":null,"abstract":"\u0000 In this study, numerical analysis was carried out to investigate the effects of slot die nozzle exit rear pressure on coating uniformity improvement in coating nozzles which are widely used in industry. Coating uniformity in coatings of viscosity materials such as inks and surface coating solutions is closely related to the quality of the product. Especially, coating uniformity is an important performance indicator for slot die coatings, which are used primarily in the production of optical or chemical products such as displays, touch screens, solar panels, and batteries. In general, the average thickness of a thin film in a slot die coating is determined by the supply flow rate and the moving speed of the plate. However, due to various parameters, thickness irregularities and coating defects due to pores occur locally. Therefore, many studies have recently been performed to solve the local defect of the slot die coating. In order to improve the coating uniformity, this study applied the vacuum pressure condition to the slot die nozzle rear end and numerical study on the coating uniformity according to the vacuum pressure was carried out. The numerical analysis proceeded to 2-D, unsteady condition and the VOF method. A commercial numerical simulation software (STAR-CCM+ V.12.06) was used. It was simulated that the coating liquid was supplied onto the moving plate surface. The moving plate speed was fixed 0.01m/s. The nozzle geometry simulates a slot die nozzle. And the coating raw material supply flow rate was considered for two conditions (0.005, 0.006m/s). Two vacuum pressure conditions (−3, −300Pa) were applied to the rear end of the nozzle. The viscosity of the viscous material was fixed at 2 Pa.s. The analysis results were analyzed through the uniformity of the material supplied to the surface. As a result of analysis, uniformity of coating was lowered regardless of the velocity when the vacuum pressure condition was −3.0 Pa, and uniformity was lowered as the velocity increased. However, it was confirmed that uniformity of the coating was increased at all velocity condition when the vacuum pressure condition was −300 Pa. This is because as the flat plate moves, the reverse pressure is applied to the downstream of the coating solution, thereby improving the uniformity of the coating liquid flowing through the flat plate and preventing the inflow of air or the like. Through this study, it was confirmed that the coating uniformity can be improved by controlling the vacuum pressure at the rear end of the nozzle.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"8 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":"124373766","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: 10.1299/jsmetokai.2019.68.211
Kentaro Echigo, K. Tsujimoto, T. Shakouchi, T. Ando
A single impinging jet (SIJ) produces a high heat transfer rate around an impinging position on an impinging wall, while the heat transfer performance (HTP) decays increasing the distance from the impinging position. Thus in order to overcome the shortcoming of SIJ: the occurrence of both inhomogeneous heat distribution on the wall and the narrow heating area, multiple impinging jets (MIJ) are generally introduced, however, nonuniformity of heat transfer still occurs. Therefore, the viewpoint of new jet control is required in order to further improvement of the uniformity of heat transfer. On the other hand, blooming jets occur with superimposition of axial and helical excitations on the inlet velocity profile. Blooming jets are characterized by vortex rings moving along branches of separate streams. In previous studies, it is observed that blooming jets change its flow pattern with different frequency ratio of axial to helical, and its mixing and diffusion characteristics. However, there are no studies that observe heat transfer performance of the blooming jet. In this study, we conduct a direct numerical simulation of blooming jet that impinges upon the wall, and investigate its flow characteristics and heat transfer performance. As a control parameter, the distance from the wall is varied. From the view of vortex structures and velocity magnitude, it reveals how the generation of flow phenomena are modulated through the blooming control. Further in order to quantify the heat transfer of the blooming, distributions of mean local Nusselt Number are examined. Compared to the uncontrolled jet, it is confirmed that the uniformity of heat transfer is improved, suggesting that the blooming jets can be expected to be useful for the improvement of uniform heat transfer performance of impinging jets.
{"title":"Flow and Heat Transfer Characteristics of Multi-Armed Impinging Jet Using DNS","authors":"Kentaro Echigo, K. Tsujimoto, T. Shakouchi, T. Ando","doi":"10.1299/jsmetokai.2019.68.211","DOIUrl":"https://doi.org/10.1299/jsmetokai.2019.68.211","url":null,"abstract":"\u0000 A single impinging jet (SIJ) produces a high heat transfer rate around an impinging position on an impinging wall, while the heat transfer performance (HTP) decays increasing the distance from the impinging position. Thus in order to overcome the shortcoming of SIJ: the occurrence of both inhomogeneous heat distribution on the wall and the narrow heating area, multiple impinging jets (MIJ) are generally introduced, however, nonuniformity of heat transfer still occurs. Therefore, the viewpoint of new jet control is required in order to further improvement of the uniformity of heat transfer. On the other hand, blooming jets occur with superimposition of axial and helical excitations on the inlet velocity profile. Blooming jets are characterized by vortex rings moving along branches of separate streams. In previous studies, it is observed that blooming jets change its flow pattern with different frequency ratio of axial to helical, and its mixing and diffusion characteristics. However, there are no studies that observe heat transfer performance of the blooming jet. In this study, we conduct a direct numerical simulation of blooming jet that impinges upon the wall, and investigate its flow characteristics and heat transfer performance. As a control parameter, the distance from the wall is varied. From the view of vortex structures and velocity magnitude, it reveals how the generation of flow phenomena are modulated through the blooming control. Further in order to quantify the heat transfer of the blooming, distributions of mean local Nusselt Number are examined. Compared to the uncontrolled jet, it is confirmed that the uniformity of heat transfer is improved, suggesting that the blooming jets can be expected to be useful for the improvement of uniform heat transfer performance of impinging jets.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"22 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":"131769849","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/ajkfluids2019-5621
D. Nakata, Ryojiro Minato, Inaho Yoshikawa, H. Yagihashi, K. Arimatsu, M. Uchiumi
Currently in development at Muroran Institute of Technology, a small gas-generator-cycle air turbo ramjet engine (GG-ATR) for a supersonic unmanned aerial vehicle requiring deep throttling uses liquid oxygen/ethanol as a propellant. However, it is difficult to maintain a liquid-phase flow at a low mass flow rate or at a low pressure due to flashing in the feedline. In response, we investigated the ability of our ground test facility to feed liquid oxygen at a low mass flow rate. The experimental results of the flow tests validated the proposed one-dimensional model, including heat input and the density change in the feed line. The minimum possible flow rate as a subcooled liquid flow was examined with the model and the throttling level of 75 % was possible when assuming 110 K in tank temperature.
{"title":"The Minimum Flow Rate of Liquid-Oxygen When Considering a Throttling of a Gas Generator Cycle Engine","authors":"D. Nakata, Ryojiro Minato, Inaho Yoshikawa, H. Yagihashi, K. Arimatsu, M. Uchiumi","doi":"10.1115/ajkfluids2019-5621","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5621","url":null,"abstract":"\u0000 Currently in development at Muroran Institute of Technology, a small gas-generator-cycle air turbo ramjet engine (GG-ATR) for a supersonic unmanned aerial vehicle requiring deep throttling uses liquid oxygen/ethanol as a propellant. However, it is difficult to maintain a liquid-phase flow at a low mass flow rate or at a low pressure due to flashing in the feedline. In response, we investigated the ability of our ground test facility to feed liquid oxygen at a low mass flow rate. The experimental results of the flow tests validated the proposed one-dimensional model, including heat input and the density change in the feed line. The minimum possible flow rate as a subcooled liquid flow was examined with the model and the throttling level of 75 % was possible when assuming 110 K in tank temperature.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"2 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":"114880398","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/ajkfluids2019-5041
Zhenxu Sun, Yongfang Yao, Fanbing Kong, Guowei Yang
As the running speed increases, the aerodynamic loads become dominant for high-speed ground vehicles. Meanwhile, the aerodynamic lift of the trailing car becomes crucial at higher speed, which may lead to security and comfort problems. Flow field details are the root to the aerodynamic loads. Study on the wake characteristics of the train could shed light to learn the mechanism of their aerodynamic loads and know how to improve their aerodynamic performance. In the present paper, the urban maglev train with a design speed of 200 km/h is mainly focused on. Numerical investigation is adopted for current study. The Improved Delayed Detached Eddy Simulation (IDDES) numerical approach is utilized to count for unsteady flow details. To characterize the vortex structures, the iso-surface of Q for urban maglev train is obtained and compared. Due to the existence of guide way, the streamline of maglev trains is much more influenced by the guide way. The ground effect for maglev trains is more obvious. The streamlined shape is quite essential to the flow phenomena, and as a result, the vortex structures for urban maglev trains are also different. Guide way could lead to more vortices, which is common for maglev trains. However, lateral vortex could be observed for urban maglev trains, which is unique and is a result of the flat shape of the trailing nose. Meanwhile, the slipstream in the wake of the train is also compared. The streamlined shape of urban maglev trains is the bluntest, which induces the relatively biggest train wind. Based on the above analysis, the unsteady characteristics of flow field for urban maglev train are obtained and the main vortex structures are characterized. Based on the unsteady analysis of flow field, the relationships between aerodynamic loads of the trailing car and different kinds of trailing vortices are obtained. Current study could shed light on the understanding of mechanism of aerodynamic performance of a train and how to design the streamlined shape for trains with certain operational speed.
{"title":"Numerical Study on Unsteady Wake Characteristics of an Urban Maglev Train","authors":"Zhenxu Sun, Yongfang Yao, Fanbing Kong, Guowei Yang","doi":"10.1115/ajkfluids2019-5041","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5041","url":null,"abstract":"\u0000 As the running speed increases, the aerodynamic loads become dominant for high-speed ground vehicles. Meanwhile, the aerodynamic lift of the trailing car becomes crucial at higher speed, which may lead to security and comfort problems. Flow field details are the root to the aerodynamic loads. Study on the wake characteristics of the train could shed light to learn the mechanism of their aerodynamic loads and know how to improve their aerodynamic performance. In the present paper, the urban maglev train with a design speed of 200 km/h is mainly focused on. Numerical investigation is adopted for current study. The Improved Delayed Detached Eddy Simulation (IDDES) numerical approach is utilized to count for unsteady flow details. To characterize the vortex structures, the iso-surface of Q for urban maglev train is obtained and compared. Due to the existence of guide way, the streamline of maglev trains is much more influenced by the guide way. The ground effect for maglev trains is more obvious. The streamlined shape is quite essential to the flow phenomena, and as a result, the vortex structures for urban maglev trains are also different. Guide way could lead to more vortices, which is common for maglev trains. However, lateral vortex could be observed for urban maglev trains, which is unique and is a result of the flat shape of the trailing nose. Meanwhile, the slipstream in the wake of the train is also compared. The streamlined shape of urban maglev trains is the bluntest, which induces the relatively biggest train wind. Based on the above analysis, the unsteady characteristics of flow field for urban maglev train are obtained and the main vortex structures are characterized. Based on the unsteady analysis of flow field, the relationships between aerodynamic loads of the trailing car and different kinds of trailing vortices are obtained. Current study could shed light on the understanding of mechanism of aerodynamic performance of a train and how to design the streamlined shape for trains with certain operational speed.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"8 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":"117331308","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/ajkfluids2019-4806
Xifeng Wang, Kenta Mizushiri, H. Yokoyama, A. Iida
In order to evaluate the interior noise caused by the flow around automobiles, it is necessary to clarify the nature of the pressure fluctuations on the surface of vehicle body. The pressure fluctuations around the vehicle which are caused by the fluid motion can be solved by unsteady-compressible Navier-Stokes equation. However, the differences between the scales and intensity of the pressure fluctuations related to the hydrodynamic pressure fluctuation (HPF) of the flow field and the aerodynamic sound (acoustic pressure fluctuation APF) are quite large, these phenomena can be considered separately as two different phenomena. This assumption can help us to understand the contributions of these two components of pressure fluctuations to the structural vibration and interior sound of automobiles. Since both the HPF and the APF are pressure fluctuations, they cannot be separated only by measuring with a single pressure sensor. In this study, we divided these pressure fluctuations by using wavenumber-frequency spectrum analysis. Wind tunnel experiment showed that the HPF and the APF have different wavenumber fields in the wake of a rear-view mirror, and the intensity and wavenumber of the HPF are larger than that of the APF. Flow field was also investigated by using the incompressible flow simulation. As a result of wavenumber-frequency spectrum analysis based on the pressure fields around the vehicle body, the HPF and the APF have different wavenumbers in the case of a boundary layer flow field with no separation such as boundary layer on the vehicle roof. On the other hand, very small wavenumber components of the HPF were observed in the recirculation flow around the rear-view mirror downstream, despite incompressible simulation was done. This is probably due to the flow fields excite the vehicle body in the direction close to the vertical with respect to the vehicle body surface (side shield) in the separated flow region, and the wavenumber vector project on the shield surface apparently become smaller. The wavenumber vector becomes short but the frequency is constant, which leads the speed of pressure propagation apparently increases. In the reverse flow region, even if the uniform flow velocity is smaller than the speed of sound, the HPF may still contribute to vibration and sound generation. At the same time, since the flow velocity is actually slowed in the reverse flow region, large wavenumber components were also observed. Therefore, the wavenumber spectrum was observed in a wide range of the wavelength region. In conclusion, by investigating the wavenumber frequency spectrum, it is possible to estimate the flow field contributing to the interior noise of automobiles.
{"title":"Wavenumber-Frequency Spectrum Analysis of Pressure Fields Around an Automobile","authors":"Xifeng Wang, Kenta Mizushiri, H. Yokoyama, A. Iida","doi":"10.1115/ajkfluids2019-4806","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4806","url":null,"abstract":"\u0000 In order to evaluate the interior noise caused by the flow around automobiles, it is necessary to clarify the nature of the pressure fluctuations on the surface of vehicle body. The pressure fluctuations around the vehicle which are caused by the fluid motion can be solved by unsteady-compressible Navier-Stokes equation. However, the differences between the scales and intensity of the pressure fluctuations related to the hydrodynamic pressure fluctuation (HPF) of the flow field and the aerodynamic sound (acoustic pressure fluctuation APF) are quite large, these phenomena can be considered separately as two different phenomena. This assumption can help us to understand the contributions of these two components of pressure fluctuations to the structural vibration and interior sound of automobiles. Since both the HPF and the APF are pressure fluctuations, they cannot be separated only by measuring with a single pressure sensor.\u0000 In this study, we divided these pressure fluctuations by using wavenumber-frequency spectrum analysis. Wind tunnel experiment showed that the HPF and the APF have different wavenumber fields in the wake of a rear-view mirror, and the intensity and wavenumber of the HPF are larger than that of the APF. Flow field was also investigated by using the incompressible flow simulation. As a result of wavenumber-frequency spectrum analysis based on the pressure fields around the vehicle body, the HPF and the APF have different wavenumbers in the case of a boundary layer flow field with no separation such as boundary layer on the vehicle roof. On the other hand, very small wavenumber components of the HPF were observed in the recirculation flow around the rear-view mirror downstream, despite incompressible simulation was done. This is probably due to the flow fields excite the vehicle body in the direction close to the vertical with respect to the vehicle body surface (side shield) in the separated flow region, and the wavenumber vector project on the shield surface apparently become smaller. The wavenumber vector becomes short but the frequency is constant, which leads the speed of pressure propagation apparently increases.\u0000 In the reverse flow region, even if the uniform flow velocity is smaller than the speed of sound, the HPF may still contribute to vibration and sound generation. At the same time, since the flow velocity is actually slowed in the reverse flow region, large wavenumber components were also observed. Therefore, the wavenumber spectrum was observed in a wide range of the wavelength region.\u0000 In conclusion, by investigating the wavenumber frequency spectrum, it is possible to estimate the flow field contributing to the interior noise of automobiles.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"68 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":"127762937","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/ajkfluids2019-4641
R. Chilukuri
An analytical solution to inviscid, axisymmetric, impinging wall jet flow is proposed as a limited idealization of internal flow within a cascade thrust reverser of an aircraft engine. Behavior of prior Bessel Series solution for round jets is critically examined, before extending the formulation to an annular jet with non-zero inner wall radius. Behavior and accuracy of prior spectral and finite difference algorithms are examined, leading to an efficient hybrid computational scheme. Jet inflow velocity profile has a deficit as well as non-zero vorticity-function at the inner radial boundary, as is typical in engine fan ducts. Inviscid recirculation appears at the impingement corner, the strength of which is made determinate by assuming locally constant vorticity-function. Results indicate that fan duct velocity profile deficit is a significant contributor to occurrence of a large recirculation zone that is experimentally observed within a fully deployed thrust reverser.
{"title":"Inviscid, Axisymmetric, Annular Wall Jet Impingement As an Idealization of Cascade Thrust Reversers","authors":"R. Chilukuri","doi":"10.1115/ajkfluids2019-4641","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4641","url":null,"abstract":"\u0000 An analytical solution to inviscid, axisymmetric, impinging wall jet flow is proposed as a limited idealization of internal flow within a cascade thrust reverser of an aircraft engine. Behavior of prior Bessel Series solution for round jets is critically examined, before extending the formulation to an annular jet with non-zero inner wall radius. Behavior and accuracy of prior spectral and finite difference algorithms are examined, leading to an efficient hybrid computational scheme. Jet inflow velocity profile has a deficit as well as non-zero vorticity-function at the inner radial boundary, as is typical in engine fan ducts. Inviscid recirculation appears at the impingement corner, the strength of which is made determinate by assuming locally constant vorticity-function. Results indicate that fan duct velocity profile deficit is a significant contributor to occurrence of a large recirculation zone that is experimentally observed within a fully deployed thrust reverser.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"113 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":"128104666","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/ajkfluids2019-4824
K. Asfar, Eyad Al-Smadi
This paper describes an environment friendly propulsion system with negligible noise. The Propulsion system is based on a novel engine called a water piston engine. All moving parts in the classical internal combustion engine are eliminated; the piston, connecting rod, and crankshaft. Also, cams and follower valves are replaced by solenoid valves which inject compressed air into the cylinders. A water column in the cylinder is used to replace the metallic piston. The water column itself inside the cylinder acts as a piston. This Water Piston Engine is powered by pressurized air only. So, a pressure vessel is used to store compressed air. The Pressure derived from the compressed air tanks is directly used in providing thrust by pushing the water out of the cylinder through a 90-degree elbow as a water jet. When the water is ejected from the cylinder and the air pressure inside the cylinder decreases to near atmospheric, the water that surrounds the engine fills the cylinder. Four cylinders are used; each two cylinders are fired simultaneously in order to maintain thrust. This system uses an Arduino microcontroller unit to deal with how much time the pressurized air is needed to discharge the cylinder and to switch the airflow between the engine cylinders. Several field tests have been made in a lake. The experimental data were compared to the theoretical based data in addition to simulate this model using Ansys fluent. The advantages of this novel engine over internal combustion engines are clarified. Videos of the experiments are recorded.
{"title":"Water Piston Engine for Marine Vehicle Propulsion","authors":"K. Asfar, Eyad Al-Smadi","doi":"10.1115/ajkfluids2019-4824","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4824","url":null,"abstract":"\u0000 This paper describes an environment friendly propulsion system with negligible noise. The Propulsion system is based on a novel engine called a water piston engine. All moving parts in the classical internal combustion engine are eliminated; the piston, connecting rod, and crankshaft. Also, cams and follower valves are replaced by solenoid valves which inject compressed air into the cylinders. A water column in the cylinder is used to replace the metallic piston. The water column itself inside the cylinder acts as a piston. This Water Piston Engine is powered by pressurized air only. So, a pressure vessel is used to store compressed air. The Pressure derived from the compressed air tanks is directly used in providing thrust by pushing the water out of the cylinder through a 90-degree elbow as a water jet. When the water is ejected from the cylinder and the air pressure inside the cylinder decreases to near atmospheric, the water that surrounds the engine fills the cylinder. Four cylinders are used; each two cylinders are fired simultaneously in order to maintain thrust.\u0000 This system uses an Arduino microcontroller unit to deal with how much time the pressurized air is needed to discharge the cylinder and to switch the airflow between the engine cylinders. Several field tests have been made in a lake. The experimental data were compared to the theoretical based data in addition to simulate this model using Ansys fluent. The advantages of this novel engine over internal combustion engines are clarified. Videos of the experiments are recorded.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"9 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":"125216650","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/ajkfluids2019-5476
I. Nedyalkov, A. Cunningham, A. Lovell
In the absence of cross-winds, a cyclist can expend up to 90% of their energy to overcome drag and can save up to 30% of that energy if riding behind another cyclist. The aerodynamic forces acting on cyclists in the presence of cross wind have not been studied in much detail. The effect of the offset distances between cyclists on the aerodynamic forces has been investigated in the literature for configurations of two cyclists. In the present study, 1:11 scale models of two different cyclists were rapid-prototyped and tested in a wind tunnel. The effect of the size of the cyclist was studied by placing the larger cyclist model behind the smaller one; the smaller behind the larger one; and the larger model behind an identical (larger model) copy. The effect of position within the group was studied by measuring the forces on each of the four cyclists placed in a favorable formation. The results suggest that the size of the cyclist matters, particularly when the leading cyclist is smaller than the drafting cyclist, and the effect is more prominent for the side forces. The results also show that in a formation of four cyclists, the leading cyclist experiences minor drag reduction compared to riding alone. The second and third cyclists experience the largest force reductions within the group, and the fourth cyclist experiences force reduction, which is not as significant. The results appear to be dependent on the Reynolds number, but may still be valuable for racing strategies and recreational cycling.
{"title":"Effects of Cyclist Size and Position Within Formations on Drag and Side Force in the Presence of Cross Winds","authors":"I. Nedyalkov, A. Cunningham, A. Lovell","doi":"10.1115/ajkfluids2019-5476","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5476","url":null,"abstract":"\u0000 In the absence of cross-winds, a cyclist can expend up to 90% of their energy to overcome drag and can save up to 30% of that energy if riding behind another cyclist. The aerodynamic forces acting on cyclists in the presence of cross wind have not been studied in much detail. The effect of the offset distances between cyclists on the aerodynamic forces has been investigated in the literature for configurations of two cyclists. In the present study, 1:11 scale models of two different cyclists were rapid-prototyped and tested in a wind tunnel. The effect of the size of the cyclist was studied by placing the larger cyclist model behind the smaller one; the smaller behind the larger one; and the larger model behind an identical (larger model) copy. The effect of position within the group was studied by measuring the forces on each of the four cyclists placed in a favorable formation. The results suggest that the size of the cyclist matters, particularly when the leading cyclist is smaller than the drafting cyclist, and the effect is more prominent for the side forces. The results also show that in a formation of four cyclists, the leading cyclist experiences minor drag reduction compared to riding alone. The second and third cyclists experience the largest force reductions within the group, and the fourth cyclist experiences force reduction, which is not as significant. The results appear to be dependent on the Reynolds number, but may still be valuable for racing strategies and recreational cycling.","PeriodicalId":403423,"journal":{"name":"Volume 3A: Fluid Applications and Systems","volume":"19 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":"125589886","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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