Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1936
L. J. Zhai, H. X. Chen, Q. Gu, Z. Ma
To study the hydrodynamic characteristics of blade trimming length in centrifugal pumps, Delayed Detached Eddy Simulation (DDES) with nonlinear eddy viscosity was utilized to conduct unsteady calculations on the centrifugal pump. A comprehensive examination of the fluid dynamic properties of the centrifugal pump, including external features, flow conditions, and pressure fluctuations, was carried out. By applying the theory of entropy production, the areas of high energy loss within the centrifugal pump were identified, and the correlations between local entropy production, energy loss, and unsteady flow in different areas with varying blade trimming lengths were analyzed. The results indicate that with the increase in blade trimming length, under rated flow conditions, the head decreases by 1.8%, 3.2%, and 5.7% for different blade trimming lengths, respectively, compared to normal impellers. Similarly, the efficiency decreases by 0.5%, 0.8%, and 1.0% for different blade trimming lengths, respectively. Similar trends were observed under other working conditions as well. As the degree of blade trimming increases, the irreversible losses after the failure of the centrifugal pump also increase significantly, indicating that the flow inside the centrifugal pump becomes disorder. Blade trimming leads to a disorderly fluid flow inside the centrifugal pump, causing an increase in the radial force during operation, which in turn leads to an increase in vibration amplitude and affects its operational stability. Blade trimming failure has a significant impact on the frequency and amplitude of pressure pulsation, resulting in abnormal pressure pulsation and abnormal vibration of the centrifugal pump. Therefore, early warning and diagnosis of blade trimming can be achieved through pressure pulsation monitoring.
{"title":"Effect of Blade Trimming Length on the Performance of Marine Centrifugal Pump","authors":"L. J. Zhai, H. X. Chen, Q. Gu, Z. Ma","doi":"10.47176/jafm.16.11.1936","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1936","url":null,"abstract":"To study the hydrodynamic characteristics of blade trimming length in centrifugal pumps, Delayed Detached Eddy Simulation (DDES) with nonlinear eddy viscosity was utilized to conduct unsteady calculations on the centrifugal pump. A comprehensive examination of the fluid dynamic properties of the centrifugal pump, including external features, flow conditions, and pressure fluctuations, was carried out. By applying the theory of entropy production, the areas of high energy loss within the centrifugal pump were identified, and the correlations between local entropy production, energy loss, and unsteady flow in different areas with varying blade trimming lengths were analyzed. The results indicate that with the increase in blade trimming length, under rated flow conditions, the head decreases by 1.8%, 3.2%, and 5.7% for different blade trimming lengths, respectively, compared to normal impellers. Similarly, the efficiency decreases by 0.5%, 0.8%, and 1.0% for different blade trimming lengths, respectively. Similar trends were observed under other working conditions as well. As the degree of blade trimming increases, the irreversible losses after the failure of the centrifugal pump also increase significantly, indicating that the flow inside the centrifugal pump becomes disorder. Blade trimming leads to a disorderly fluid flow inside the centrifugal pump, causing an increase in the radial force during operation, which in turn leads to an increase in vibration amplitude and affects its operational stability. Blade trimming failure has a significant impact on the frequency and amplitude of pressure pulsation, resulting in abnormal pressure pulsation and abnormal vibration of the centrifugal pump. Therefore, early warning and diagnosis of blade trimming can be achieved through pressure pulsation monitoring.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43425503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1751
T. Yu, Y. Yu, Y. P. Mao, Y. L. Yang, S. L. Xu
Flow separation in overexpanded single expansion ramp nozzles (SERN) involves complex phenomena, such as shock waves, expansion waves, turbulent boundary layers, and shear layers. Computational fluid dynamics plays a crucial role in studying unsteady flow behaviour in supersonic nozzles, allowing for an investigation into the dynamic flow field characteristics. However, the application of OpenFOAM as a numerical tool for studying SERN in the field of compressible flows, particularly in the overexpansion state where the flow field characteristics are more complex, has received relatively less attention. In this study, the flow field characteristics of an overexpanded SERN under different turbulence models are investigated through a combination of experiments and numerical calculations. The qualitative and quantitative predictive performance of two compressible flow solvers in OpenFOAM, namely, rhoCentralFOAM and sonicFOAM, are compared in terms of flow separation pattern and separation pattern transitions within the overexpanded SERN. The ability of rhoCentralFOAM and sonicFOAM to accurately predict complex flow states is evaluated. Results indicate that the numerical simulations conducted using rhoCentralFOAM and sonicFOAM successfully capture flow separation, separated shock waves, separated bubbles and shear layers for two types of restricted shock separation patterns at the same nozzle pressure ratio (NPR), demonstrating agreement with experimental results. However, sonicFOAM initiates the transition in the separation pattern 0.0773 NPR earlier than rhoCentralFOAM during the whole separation pattern transition process of the SERN. The transition process in sonicFOAM lasts longer and exhibits a greater variation in NPR. SonicFOAM fails to accurately predict certain aspects, such as the pressure rise after the separation bubble, the reattachment shock wave, and tends to overestimat the length of the separation shock length. Consequently, sonicFOAM cannot be recommended as a suitable solver for accurately capturing the separation pattern of an overexpanded nozzle.
{"title":"Comparative Study of OpenFOAM Solvers on Separation Pattern and Separation Pattern Transition in Overexpanded Single Expansion Ramp Nozzle","authors":"T. Yu, Y. Yu, Y. P. Mao, Y. L. Yang, S. L. Xu","doi":"10.47176/jafm.16.11.1751","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1751","url":null,"abstract":"Flow separation in overexpanded single expansion ramp nozzles (SERN) involves complex phenomena, such as shock waves, expansion waves, turbulent boundary layers, and shear layers. Computational fluid dynamics plays a crucial role in studying unsteady flow behaviour in supersonic nozzles, allowing for an investigation into the dynamic flow field characteristics. However, the application of OpenFOAM as a numerical tool for studying SERN in the field of compressible flows, particularly in the overexpansion state where the flow field characteristics are more complex, has received relatively less attention. In this study, the flow field characteristics of an overexpanded SERN under different turbulence models are investigated through a combination of experiments and numerical calculations. The qualitative and quantitative predictive performance of two compressible flow solvers in OpenFOAM, namely, rhoCentralFOAM and sonicFOAM, are compared in terms of flow separation pattern and separation pattern transitions within the overexpanded SERN. The ability of rhoCentralFOAM and sonicFOAM to accurately predict complex flow states is evaluated. Results indicate that the numerical simulations conducted using rhoCentralFOAM and sonicFOAM successfully capture flow separation, separated shock waves, separated bubbles and shear layers for two types of restricted shock separation patterns at the same nozzle pressure ratio (NPR), demonstrating agreement with experimental results. However, sonicFOAM initiates the transition in the separation pattern 0.0773 NPR earlier than rhoCentralFOAM during the whole separation pattern transition process of the SERN. The transition process in sonicFOAM lasts longer and exhibits a greater variation in NPR. SonicFOAM fails to accurately predict certain aspects, such as the pressure rise after the separation bubble, the reattachment shock wave, and tends to overestimat the length of the separation shock length. Consequently, sonicFOAM cannot be recommended as a suitable solver for accurately capturing the separation pattern of an overexpanded nozzle.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48002140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1961
H. W. Fan, Z. G. Huang, H. Wang, Z. H. Chen, X. Y. Liu, F. J. Xiao, R. X. Qiu
The hollow projectile is a new type of projectile that has complex water entry hydrodynamics characteristics and has attracted significant attention in recent years. As such, it is important to investigate the effects of different entry velocities and aperture diameters on the cavity morphology, cavitation, dynamics, and motion characteristics of hollow projectiles when entering water at high speeds. In this study, four stages of an open cavity, cavity stretching, cavity closure, and cavity contraction in the water entry processes of a hollow projectile at 50–200 m/s and four aperture diameter projectiles at 100 m/s were studied using the volume of fluid (VOF), realizable k-ε turbulence, and Schnerr-Sauer cavitation model. With an increase in the speed, the depth of the cavity closure increases, thereby advancing the closure time. The timing of the surface closure at 50 m/s is clearly different from that at 100–200 m/s. Cavitation is not obvious and is near the cavity wall at 50 m/s, although the entire cavity is almost filled with vapor at 100–200 m/s. The friction resistance has two step points when impacting the water surface and entering the water completely. As the velocity increases or the aperture ratio reduces, the splash is higher, the cavity volume is larger, the cavitation phenomenon is more obvious, the cavity closure time is delayed, and the frictional resistance of the projectile is greater. The results of this study can guide the production and application of hollow projectiles in the future.
{"title":"Numerical Study of High-Speed Vertical Water Entry of Hollow Projectiles with Different Aperture Sizes and Velocities","authors":"H. W. Fan, Z. G. Huang, H. Wang, Z. H. Chen, X. Y. Liu, F. J. Xiao, R. X. Qiu","doi":"10.47176/jafm.16.11.1961","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1961","url":null,"abstract":"The hollow projectile is a new type of projectile that has complex water entry hydrodynamics characteristics and has attracted significant attention in recent years. As such, it is important to investigate the effects of different entry velocities and aperture diameters on the cavity morphology, cavitation, dynamics, and motion characteristics of hollow projectiles when entering water at high speeds. In this study, four stages of an open cavity, cavity stretching, cavity closure, and cavity contraction in the water entry processes of a hollow projectile at 50–200 m/s and four aperture diameter projectiles at 100 m/s were studied using the volume of fluid (VOF), realizable k-ε turbulence, and Schnerr-Sauer cavitation model. With an increase in the speed, the depth of the cavity closure increases, thereby advancing the closure time. The timing of the surface closure at 50 m/s is clearly different from that at 100–200 m/s. Cavitation is not obvious and is near the cavity wall at 50 m/s, although the entire cavity is almost filled with vapor at 100–200 m/s. The friction resistance has two step points when impacting the water surface and entering the water completely. As the velocity increases or the aperture ratio reduces, the splash is higher, the cavity volume is larger, the cavitation phenomenon is more obvious, the cavity closure time is delayed, and the frictional resistance of the projectile is greater. The results of this study can guide the production and application of hollow projectiles in the future.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49175475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1923
Y. Zhao, G. Li, Fei Zhao, X. Wang, W. Xu
The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4.7 mm, an outlet diameter (D2) of 12.2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4.8 MPa. At these parameters, the frequency of the pulse jet reaches 830.01 Hz, with an internal flow period of approximately 0.0024 s. The maximum vapor volume fraction is found to be located 0.28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles.
{"title":"Analysis of Macroscopic Cavitation Characteristics of a Self-Excited Oscillating Cavitation Jet Nozzle","authors":"Y. Zhao, G. Li, Fei Zhao, X. Wang, W. Xu","doi":"10.47176/jafm.16.11.1923","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1923","url":null,"abstract":"The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4.7 mm, an outlet diameter (D2) of 12.2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4.8 MPa. At these parameters, the frequency of the pulse jet reaches 830.01 Hz, with an internal flow period of approximately 0.0024 s. The maximum vapor volume fraction is found to be located 0.28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44835238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1874
C. Ruixiang, X. Muyao, W. Ying, Y. Chao, Y. Bin, L. Shipeng
When the underwater vehicle engine operates under the condition of over-expansion, the violent pulsation of the flow field pressure at the rear of the nozzle can cause violent fluctuations in engine thrust, leading to engine instability. In order to improve the engine's stability, this study drew inspiration from the wave attenuation characteristics of the shell-shaped surface texture structure and added a multi-layer shell-shaped texture structure to the rear wall to reduce pressure fluctuations in the flow field at the rear of the nozzle . Based on the numerical simulation method, the effects of different bionic shell-shaped structures on jet morphology, wall pressure and engine thrust were compared and analyzed. The results show that the multi-layer bionic shell-shaped texture structure can effectively inhibit the occurrence of periodic phenomena such as bulge, necking, and return stroke in the rear flow field, so as to effectively reduce the pressure fluctuation in the rear flow field of the nozzle. In addition, when the momentum thrust is almost unchanged, it is found through calculations that during the initial stage of the jet, the suppression of thrust is not significant. After 0.005 seconds, the oscillation amplitude of the combined force of pressure difference thrust and back pressure thrust decreased by 22%, and the oscillation amplitude of the total thrust decreased by 20%.
{"title":"Numerical Simulation of Underwater Supersonic Jet of Vehicle with Shell-Shaped Flow Control Structure","authors":"C. Ruixiang, X. Muyao, W. Ying, Y. Chao, Y. Bin, L. Shipeng","doi":"10.47176/jafm.16.11.1874","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1874","url":null,"abstract":"When the underwater vehicle engine operates under the condition of over-expansion, the violent pulsation of the flow field pressure at the rear of the nozzle can cause violent fluctuations in engine thrust, leading to engine instability. In order to improve the engine's stability, this study drew inspiration from the wave attenuation characteristics of the shell-shaped surface texture structure and added a multi-layer shell-shaped texture structure to the rear wall to reduce pressure fluctuations in the flow field at the rear of the nozzle . Based on the numerical simulation method, the effects of different bionic shell-shaped structures on jet morphology, wall pressure and engine thrust were compared and analyzed. The results show that the multi-layer bionic shell-shaped texture structure can effectively inhibit the occurrence of periodic phenomena such as bulge, necking, and return stroke in the rear flow field, so as to effectively reduce the pressure fluctuation in the rear flow field of the nozzle. In addition, when the momentum thrust is almost unchanged, it is found through calculations that during the initial stage of the jet, the suppression of thrust is not significant. After 0.005 seconds, the oscillation amplitude of the combined force of pressure difference thrust and back pressure thrust decreased by 22%, and the oscillation amplitude of the total thrust decreased by 20%.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47171925","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1897
H. Cui, H. An, M. Ma, Z. Han, S. C. Saha, Q. Liu
Wind loads of high-rise buildings are a key parameter in architectural design. The magnitude and distribution characteristics of wind loads are of great importance for the safety and economy of structural design. The wind loads of high-rise buildings are quite different from those of monomer buildings. The wind-induced interference effect could significantly increase the local wind pressure of buildings, causing potential safety hazards for the main structure and enclosure structure. For the three common high-rise buildings, we adopted the wind tunnel test method to measure the surface pressure of each building. The corresponding Re number was 8.2×106. This paper studied the shape coefficients, fluctuating wind pressure coefficients and base bending moment coefficient of each building with different wind direction angles and different spacing ratios, and the maximum value of each parameter and the corresponding working condition were statistically analyzed. The results showed that, under any wind direction angle, the fluctuating wind pressure coefficients on all sides of the building were affected by the spacing ratio, and the fluctuation range was large. When the wind angle was 180º, the fluctuating wind pressure coefficients on the sides of Building 1 were most affected by the slope ratio. At this wind angle, the maximum value was 0.43 at a slope ratio of 5.0, which was 65% different from the minimum. Partition shape coefficients of some sides and top surfaces changed significantly with the spacing ratio. When the spacing ratio was 5.0, the base bending moment coefficients in the downwind and crosswind directions reached their maximum values, and the wind direction angles where the maximum values of the base bending moment coefficients in the downwind direction were 40º and 50º, respectively, and the wind direction angle where the maximum value of the base bending moment coefficients in the crosswind direction was 10º. Due to the influence of the wind angle and the building spacing ratio, the wind loads on the facades of the pyramidal group of buildings varied greatly, and the wind-induced interference effect was evident. The wind load between the building facades in the three buildings was different, and the wind disturbance effect was evident. Therefore, the most unfavorable stress state and interference state of the structure should be comprehensively considered in the wind resistance design of the three buildings. The building spacing ratio should preferably be set to 3.0, and wind angles of 10º, 40º, and 50º should be avoided whenever possible.
{"title":"Experimental Study on Wind Load and Wind-Induced Interference Effect of Three High-Rise Buildings","authors":"H. Cui, H. An, M. Ma, Z. Han, S. C. Saha, Q. Liu","doi":"10.47176/jafm.16.11.1897","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1897","url":null,"abstract":"Wind loads of high-rise buildings are a key parameter in architectural design. The magnitude and distribution characteristics of wind loads are of great importance for the safety and economy of structural design. The wind loads of high-rise buildings are quite different from those of monomer buildings. The wind-induced interference effect could significantly increase the local wind pressure of buildings, causing potential safety hazards for the main structure and enclosure structure. For the three common high-rise buildings, we adopted the wind tunnel test method to measure the surface pressure of each building. The corresponding Re number was 8.2×106. This paper studied the shape coefficients, fluctuating wind pressure coefficients and base bending moment coefficient of each building with different wind direction angles and different spacing ratios, and the maximum value of each parameter and the corresponding working condition were statistically analyzed. The results showed that, under any wind direction angle, the fluctuating wind pressure coefficients on all sides of the building were affected by the spacing ratio, and the fluctuation range was large. When the wind angle was 180º, the fluctuating wind pressure coefficients on the sides of Building 1 were most affected by the slope ratio. At this wind angle, the maximum value was 0.43 at a slope ratio of 5.0, which was 65% different from the minimum. Partition shape coefficients of some sides and top surfaces changed significantly with the spacing ratio. When the spacing ratio was 5.0, the base bending moment coefficients in the downwind and crosswind directions reached their maximum values, and the wind direction angles where the maximum values of the base bending moment coefficients in the downwind direction were 40º and 50º, respectively, and the wind direction angle where the maximum value of the base bending moment coefficients in the crosswind direction was 10º. Due to the influence of the wind angle and the building spacing ratio, the wind loads on the facades of the pyramidal group of buildings varied greatly, and the wind-induced interference effect was evident. The wind load between the building facades in the three buildings was different, and the wind disturbance effect was evident. Therefore, the most unfavorable stress state and interference state of the structure should be comprehensively considered in the wind resistance design of the three buildings. The building spacing ratio should preferably be set to 3.0, and wind angles of 10º, 40º, and 50º should be avoided whenever possible.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42975613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1799
S. Ranjan, †. P.DebRoy
The energy that can be extracted from the ocean is inexhaustible. An oscillating water column (OWC) is a wave energy converter that extracts this energy. A numerical investigation has been conducted by altering relative opening (α) and orifice ratio (τ) to assess the maximal energy of a land-fixed rectangular-based OWC model in a nonlinear wave field. The power of OWC has also been evaluated by the wave steepness (H/L) alteration. The numeric analysis has been imposed to obtain the optimal power using Fluent software in a three-dimensional tank. Validation of the present numeric model’s result correlates with the printed empirical data. The Finite Volume Method (FVM) solves RANS equations, and the relevant waves are generated at the inlet of the numerical tank by the inlet velocity approach. The efficiency (η) increases with relative openings (α) increase. The efficiency (η) decreases with wave steepness (H/L) increase. The η reaches the optimum shown in the study at H/L = 0.02 and τ = 1.03% for entire values of α. The excellent energy of around 71.3% is attained at α =75% and H/L = 0.02. This study is a highly relevant source of information that finds the optimal efficiency of a land-fixed rectangular base OWC and gives prior knowledge of the performance of OWC before the real-life experiment.
{"title":"Numerical Investigation of Optimal Hydrodynamic Performance by Changing the Orifice Ratio and Relative Opening of a Land-Fixed Rectangular-based OWC","authors":"S. Ranjan, †. P.DebRoy","doi":"10.47176/jafm.16.11.1799","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1799","url":null,"abstract":"The energy that can be extracted from the ocean is inexhaustible. An oscillating water column (OWC) is a wave energy converter that extracts this energy. A numerical investigation has been conducted by altering relative opening (α) and orifice ratio (τ) to assess the maximal energy of a land-fixed rectangular-based OWC model in a nonlinear wave field. The power of OWC has also been evaluated by the wave steepness (H/L) alteration. The numeric analysis has been imposed to obtain the optimal power using Fluent software in a three-dimensional tank. Validation of the present numeric model’s result correlates with the printed empirical data. The Finite Volume Method (FVM) solves RANS equations, and the relevant waves are generated at the inlet of the numerical tank by the inlet velocity approach. The efficiency (η) increases with relative openings (α) increase. The efficiency (η) decreases with wave steepness (H/L) increase. The η reaches the optimum shown in the study at H/L = 0.02 and τ = 1.03% for entire values of α. The excellent energy of around 71.3% is attained at α =75% and H/L = 0.02. This study is a highly relevant source of information that finds the optimal efficiency of a land-fixed rectangular base OWC and gives prior knowledge of the performance of OWC before the real-life experiment.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48661216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.47176/jafm.16.11.1942
M. Mohseni, M. K. Domfeh
One of the basic phenomena when a liquid leaves a tank is the formation of vortices. This phenomenon can have a significant impact on the liquid mass remaining in the tank and the ingress of air and bubbles into the system. As a result, the performance of the system can be disturbed. The purpose of this study is to numerically investigate the effect of gas pressure on vortex formation and critical height. It also verifies the relationships presented for turbulent viscosity. In addition, the near-wall behavior of the analytical relationships proposed for the tangential velocity is revised based on the boundary layer theory. Some common effective factors such as angular velocity, discharge time, and liquid height are also investigated. The volume of fluid (VOF) model and the Transitional SST k-ω turbulence model were used to solve the two-phase turbulent flow. The results show that increasing the gas pressure from 1 to 5 bar and its direct impact on the liquid surface significantly accelerates the formation of the vortex and the critical height. This phenomenon causes the air core to reach the inlet of the outlet pipe approximately 7 seconds earlier after the start of the liquid discharge. As a result, much more liquid mass remains in the tank. The increase in the angular velocity of the reference frame from 0.1 to 1 rad/s also causes the critical height to be reached much earlier and the remaining liquid mass to increase by 32 kg. In addition, the amount and variations of turbulent viscosity differ significantly from the semi-empirical constants, limiting their use to certain flows.
{"title":"Numerical Analysis of Transient Vortex Formation at the Outlet of a Tank Containing Gas-Liquid Phases","authors":"M. Mohseni, M. K. Domfeh","doi":"10.47176/jafm.16.11.1942","DOIUrl":"https://doi.org/10.47176/jafm.16.11.1942","url":null,"abstract":"One of the basic phenomena when a liquid leaves a tank is the formation of vortices. This phenomenon can have a significant impact on the liquid mass remaining in the tank and the ingress of air and bubbles into the system. As a result, the performance of the system can be disturbed. The purpose of this study is to numerically investigate the effect of gas pressure on vortex formation and critical height. It also verifies the relationships presented for turbulent viscosity. In addition, the near-wall behavior of the analytical relationships proposed for the tangential velocity is revised based on the boundary layer theory. Some common effective factors such as angular velocity, discharge time, and liquid height are also investigated. The volume of fluid (VOF) model and the Transitional SST k-ω turbulence model were used to solve the two-phase turbulent flow. The results show that increasing the gas pressure from 1 to 5 bar and its direct impact on the liquid surface significantly accelerates the formation of the vortex and the critical height. This phenomenon causes the air core to reach the inlet of the outlet pipe approximately 7 seconds earlier after the start of the liquid discharge. As a result, much more liquid mass remains in the tank. The increase in the angular velocity of the reference frame from 0.1 to 1 rad/s also causes the critical height to be reached much earlier and the remaining liquid mass to increase by 32 kg. In addition, the amount and variations of turbulent viscosity differ significantly from the semi-empirical constants, limiting their use to certain flows.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46609926","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-01DOI: 10.47176/jafm.16.10.1869
J. Shijo, †. N.Behera
Modeling of pressure drop in fluidized dense phase conveying (FDP) of powders is a tough work as the flow comprises of various interactions among solid, gas and pipe wall. It is difficult to incorporate these interactions into a model. The pressure drop depends on flow, material and geometrical parameters. The existing models show high error when applied to other pipeline configurations of varying pipeline lengths or diameters. The current study investigates the capability of machine learning (ML) techniques to estimate the drop in pressure in FDP conveying of powders. Pneumatic conveying experimental data were used for training the network and then for predicting the pressure drop. For estimating the pressure drop, four distinct ML algorithms light gradient boosting machine (LighGBM)), multilayer perception (MLP), K-nearerst neighbors (KNN), extreme gradient boosting (XGBoost), and were selected. XGBoost model performed better than other models chosen for the study with ±5% error margin while training and testing the data, and ±10% error margin in validating the data. MLP, XGBoost, KNN, and LightGBM models predicted the data of pressure drop with MAE of 5.05, 1.19, 5.72, and 2.85, respectively, for training as well as testing data. Among the four models considered, the model using XGBoost algorithm performed the best, whereas the model using KNN algorithm performed poorly in predicting the FDP conveying pressure drop.
{"title":"Pressure Drop Prediction in Fluidized Dense Phase Pneumatic Conveying using Machine Learning Algorithms","authors":"J. Shijo, †. N.Behera","doi":"10.47176/jafm.16.10.1869","DOIUrl":"https://doi.org/10.47176/jafm.16.10.1869","url":null,"abstract":"Modeling of pressure drop in fluidized dense phase conveying (FDP) of powders is a tough work as the flow comprises of various interactions among solid, gas and pipe wall. It is difficult to incorporate these interactions into a model. The pressure drop depends on flow, material and geometrical parameters. The existing models show high error when applied to other pipeline configurations of varying pipeline lengths or diameters. The current study investigates the capability of machine learning (ML) techniques to estimate the drop in pressure in FDP conveying of powders. Pneumatic conveying experimental data were used for training the network and then for predicting the pressure drop. For estimating the pressure drop, four distinct ML algorithms light gradient boosting machine (LighGBM)), multilayer perception (MLP), K-nearerst neighbors (KNN), extreme gradient boosting (XGBoost), and were selected. XGBoost model performed better than other models chosen for the study with ±5% error margin while training and testing the data, and ±10% error margin in validating the data. MLP, XGBoost, KNN, and LightGBM models predicted the data of pressure drop with MAE of 5.05, 1.19, 5.72, and 2.85, respectively, for training as well as testing data. Among the four models considered, the model using XGBoost algorithm performed the best, whereas the model using KNN algorithm performed poorly in predicting the FDP conveying pressure drop.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48565613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-01DOI: 10.47176/jafm.16.10.1796
B. Khatamipour, A. Khosrojerdi, M. R. Kavianpour, M. G. Hassanabad
Pivot weirs are one of the most important structures for regulating the water level in rivers and canals. These weirs are constructed with one or more gates in a row in the waterways. Changing the angle of each gate is done individually with an independent system. Based on available information, the hydraulic performance of this type of weirs (especially in several gates and different angles) in different operational conditions has not been investigated. In present study, pivot weirs with two gates are simulated using Ansys CFX software with the angles of 27.8 to 90 degree and the discharges between 40 to 130 L/s. Further, the importance of the open space between the two adjacent weirs with different angles (lack of retail wall) and its hydraulic behavior have been studied. The model was calibrated based on valid laboratory data and using the K-ϵ turbulence model. Therefore, the weirs with equal angles were studied in the first step. In this case, the effective discharge angle coefficient was studied and its maximum value compared to the vertical angle was obtained 1.076 for the angle of 52°. Furthermore, relationships for discharge coefficient versus upstream water depth were developed. In the next step, the effective length of the crest was found to be increases by 30% under unequal angles operation and the discharge coefficient raised by 1.3 to 2.4 times. Also, it was recognized that, in case of two weirs with unequal angles, about 26% to 69% of the flow passes through the distance between the two weirs. Therefore, the performance of unequal angles operation seems to be more effective in controlling the water level and discharge in different conditions and especially in flood events.
{"title":"Simulation of the Hydraulic Performance of Parallel Pivot Weirs with Different Angles","authors":"B. Khatamipour, A. Khosrojerdi, M. R. Kavianpour, M. G. Hassanabad","doi":"10.47176/jafm.16.10.1796","DOIUrl":"https://doi.org/10.47176/jafm.16.10.1796","url":null,"abstract":"Pivot weirs are one of the most important structures for regulating the water level in rivers and canals. These weirs are constructed with one or more gates in a row in the waterways. Changing the angle of each gate is done individually with an independent system. Based on available information, the hydraulic performance of this type of weirs (especially in several gates and different angles) in different operational conditions has not been investigated. In present study, pivot weirs with two gates are simulated using Ansys CFX software with the angles of 27.8 to 90 degree and the discharges between 40 to 130 L/s. Further, the importance of the open space between the two adjacent weirs with different angles (lack of retail wall) and its hydraulic behavior have been studied. The model was calibrated based on valid laboratory data and using the K-ϵ turbulence model. Therefore, the weirs with equal angles were studied in the first step. In this case, the effective discharge angle coefficient was studied and its maximum value compared to the vertical angle was obtained 1.076 for the angle of 52°. Furthermore, relationships for discharge coefficient versus upstream water depth were developed. In the next step, the effective length of the crest was found to be increases by 30% under unequal angles operation and the discharge coefficient raised by 1.3 to 2.4 times. Also, it was recognized that, in case of two weirs with unequal angles, about 26% to 69% of the flow passes through the distance between the two weirs. Therefore, the performance of unequal angles operation seems to be more effective in controlling the water level and discharge in different conditions and especially in flood events.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" ","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41328186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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