Yong-In Kim | Korea Institute of Industrial Technology (original) (raw)

Papers by Yong-In Kim

Scientific Reports, 2022

The stall in an axial fan is directly related to detrimental phenomena such as performance degrad... more The stall in an axial fan is directly related to detrimental phenomena such as performance degradation, vibration, noise, and flow instability at low flow rates. As a kind of passive control method to handle the stall, two-dimensional plates so-named anti-stall fin (ASF) were suggested by ourselves and were attached inside the casing. In this study, the ASF's effect on the internal flow pattern was visually investigated in the flow passage, and its tendency was discussed with the performance curve. Subsequently, the ASF's functional limitations for various design parameters, which the ASF can derive aerodynamically, were presented as the primary focus of this study. Each one-factor analysis was performed, and the internal flow pattern was observed in parallel at the point where the ASF lost its function. For the radial length, axial length, number of fins, and positivetangential angle, the ASF almost retained its function up to the limitation to prevent instability but radically lost its function at a certain flow rate. For the axial gap and negative-tangential angle, the ASF gradually lost its function. Mostly, this study was based on numerical analysis, and the performance was validated through experimental tests.

Journal of Fluids Engineering, 2022

An axial fan in the general industry needs to secure stable characteristics in a wide operating r... more An axial fan in the general industry needs to secure stable characteristics in a wide operating range through an antistalling process, concerning its high demands, energy consumption, safety, and lifetime. As a "simple" and "original" method to control the stall of an axial fan, two-dimensional plates so-named anti-stall fin (ASF) were attached inside the casing and toward the shaft. The sensitivity analysis for design variables was conducted through the 2 k full factorial design method, and the optimization was performed using the response surface method (RSM). In the case of an axial fan without the ASF, the backflow gradually increased in the spanwise direction toward the hub and the streamwise direction to the inlet passage (upstream), as the flowrate decreased, and the rotating stall was developed through the quickening-growing-setting period. However, an ASF-attached axial fan stably recovered performance degradation in the stalling flow rates and allowed to form a negative slope to 0.5U d. This study was mainly based on numerical simulations, while the performance before/after application of the ASF was validated through experimental tests.

IOP Conference Series: Earth and Environmental Science, 2022

A mixed-flow pump has a characteristic in which the pressure (P) decreases as the flow rate (Q) i... more A mixed-flow pump has a characteristic in which the pressure (P) decreases as the flow rate (Q) increases on the performance curve. Hence, the Q-P curve generally has a negative slope, which has been understood as an ideal and stable case. However, a complex recirculating flow may occur due to the increase in incidence angle at the low flow rates compared to the design flow rate. This phenomenon accompanies noise and vibration along with the deterioration of performance and causes a positive slope in the form of a saddle on the performance curve. In this study, the effect of the impeller inlet (eye) diameter of a mixed-flow pump on the saddle characteristics was confirmed through numerical simulation. The focus was on the internal flow field and performance of a pump, which could be solved with the steady-state analysis. Here, the impeller inlet diameter was adjusted with the leading edge (LE) vertex on the shroud line of the meridional plane. The blade angle was adjusted accordingly to maintain the previously optimized degree of the incidence angle. From this novel design method, the saddle characteristics were significantly improved. The performance in the saddle range was directly related to the recirculating flow near the shroud. The numerical results were validated with the experimental tests.

Engineering Applications of Computational Fluid Mechanics, 2022

Most mixed-flow pumps obtain a saddle-like Q-P curve with a backflow, owing to the increased inci... more Most mixed-flow pumps obtain a saddle-like Q-P curve with a backflow, owing to the increased incidence angle at low flow rates. The backflow was developed near the shroud and followed downstream again at its end to form a recirculating flow. The rotating stall, which could be a part of the recirculating flow, followed the impeller’s rotational direction, and its properties affected the local stability. The reattaching flow became strong when the upstream flow from the blade leading edge deviated from the same circumferential degree as the dominant flow of the rotating stall heading downstream. The fluctuation in the total pressure rise decreased when the average incidence angle was smaller than that of the design flow rate. As a passive control to suppress the saddle and the above flow patterns, the impeller inlet diameter was reduced from the shroud, and the inlet blade angle was further adjusted to maintain the incidence angle. From the reduced inlet diameter, the backflow was mostly suppressed, and the saddle was improved with a wider operating range. Here, the performance near the design flow rate was almost maintained. The stability was evaluated using the fast Fourier transform, and the numerical method was validated through experimental tests.

Journal of Physics: Conference Series, 2022

The shape of the blade leading edge (LE) is a design variable that cannot theoretically affect th... more The shape of the blade leading edge (LE) is a design variable that cannot theoretically affect the inlet flow characteristics under the definition of the velocity triangle. However, the LE is the first to encounter the working fluid in terms of streamwise direction. Depending on its shape, not only the local flow characteristics but also the performance can be affected. In this study, a numerical analysis of the hydraulic and suction performance for a mixed-flow pump was performed with different shapes of the blade LE. The blade was prepared with four sets according to the ellipse ratio (ER), including a square (ER=0), round (1), elliptic (2), and parabolic (5) shape. As the shape of the blade LE was square, the flow streamline was immediately separated from the blade surface, showing a significant drop in the hydraulic performance. As the blade LE was designed in a round, elliptic, or parabolic shape instead of a square shape, the hydraulic performance did not show a noticeable difference. On the other hand, in the prediction of suction performance, the square LE obtained the best characteristics. As the LE shape gradually became a parabolic shape, the cavity blockage was reduced, and the suction performance was also improved.

Journal of Fluids Engineering, 2022

The blade leading edge is a design variable that can affect the local flow patterns and pressure ... more The blade leading edge is a design variable that can affect the local flow patterns and pressure peaks, implying a direct effect on the cavitation performance. This study was conducted to analyze the effect of the blade leading edge shape on the cavitation and noncavitation states. A total of four sets, including the square shape, were selected under the definition of ellipse ratio, and the main focus was on the cavitation state rather than the noncavitation state. In the noncavitation state, the square set denoted a remarkable negative influence, while the other three sets obtained almost the same performance despite different ellipse ratios. In the cavitation state, the square set obtained a relatively low net positive suction head required, related to the inlet flow pattern with the cloud cavity. The other three sets contained the sheet cavity, and their suction performance tended to improve as the cavity blockage decreased. As a parallel focus, an in-depth analysis of cavitation surge and pressure gain was presented with the head drop slope for the other three ellipse sets. The numerical results included the off-design flow rate points and were validated through an experimental test.

Processes, 2021

This study was based on a numerical effort to use the motor support (prop) as a guide vane when t... more This study was based on a numerical effort to use the motor support (prop) as a guide vane when the motor of a wall-mounted axial fan was located at the fan outlet while maintaining the structural and spatial advantage. The design for the guide vane followed two- and three-dimensional methods. The inlet vane angle, meridional length (total), and meridional length with a vane angle of zero (0) degrees (linear) were considered as design variables. At the design and some low flow rate points, the 2D design offered the most favorable performance when the meridional length with a vane angle of zero (0) degrees (linear) was 30% based on total length, and was the worst for 70%. The 3D design method applied in this study did not outperform the 2D design. In the 2D design concept, averaging the flow angle for the entire span at the design flow rate could ensure a better pressure rise over a more comprehensive flow rate range than weighting the flow angle for a specific span. In addition, the numerical results were validated through an experimental test, with an important discussion of the swirl (dynamic pressure) component. The influence of the inlet motor and turbulence model are presented as a previous confirmation.

Journal of Physics: Conference Series, 2021

The cavitation characteristics for the head drop in two mixed-flow pumps were investigated with t... more The cavitation characteristics for the head drop in two mixed-flow pumps were investigated with the steady- and unsteady-state analysis. The mixed-flow pump models exhibiting a different incidence angle were analyzed under the cavitation condition. The model with a larger incidence angle obtained relatively poor suction performance. Moreover, the steady- and unsteady-state analysis indicated different head level under the cavitation condition. The results of the unsteady-state analysis were more accurate to the experimental results. The head of a fully convergent steady-state analysis was not even distributed in the head fluctuation range of the unsteady-state analysis. However, the head drop due to the decrease in inlet pressure had almost the same gradient. In addition, the amount and shape of the bubbles were presented with the time variation, which were also compared with the averaged result of the steady-state analysis. The bubbles showed a larger oscillation in the model which had a larger incidence angle. The oscillation of the bubbles was related to the magnitude of the head fluctuation.

Journal of Mechanical Science and Technology, 2020

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance ... more In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2020

The cavitation is an inevitable factor in pumps used in the whole industry, which is a major caus... more The cavitation is an inevitable factor in pumps used in the whole industry, which is a major cause of energy loss and mechanical breakdown. In this study, the cavitation phenomena at the design flow rate were numerically analyzed for two pumps with different incidence angles. The design flow rate for both models was located near the best efficiency point (BEP). The incidence angle was determined with the impeller inlet diameter and the blade angle. A pump with a smaller incidence angle consistently showed a stable flow pattern as the inlet pressure decreased, whereas a pump with a larger incidence angle contained non-uniform flow streamlines despite a very small amount of the generated cavities. The flow pattern at the impeller inlet was handled by the shape and thickness of the generated cavities which could act as an additional blockage in the pumps. The inception and growth of the cavity with a decrease of inlet pressure were also inferred, which was specifically quantified as the blockage ratio. A pump with a larger incidence angle performed poor cavitation characteristics and obtained the pressure fluctuation and cavity oscillation. The magnitude of pressure fluctuation was indicated using the fast Fourier transform (FFT) analysis. The experimental tests were performed on both pumps to validate the numerical results.

Energies, 2020

An axial flow fan, which is applied for ventilation in underground spaces such as tunnels, featur... more An axial flow fan, which is applied for ventilation in underground spaces such as tunnels, features a medium-large size, and most of the blades go through the casting process in consideration of mass production and cost. In the casting process, post-work related to roughness treatment is essential, and this is a final operation to determine the thickness profile of an airfoil which is designed from the empirical equation. In this study, the effect of the thickness profile of an airfoil on the performance and aerodynamic characteristics of the axial fan was examined through numerical analysis with the commercial code, ANSYS CFX. In order to conduct the sensitivity analysis on the effect of the maximum thickness position for each span on the performance at the design flow rate, the design of experiments (DOE) method was applied with a full factorial design as an additional attempt. The energy loss near the shroud span was confirmed with a quantified value for the tip leakage flow (TLF) rate through the tip clearance, and the trajectory of the TLF was observed on the two-dimensional (2D) coordinates system. The trajectory of the TLF matched well with the tendency of the calculated angle and correlated with the intensity of the turbulence kinetic energy (TKE) distribution. However, a correlation between the TLF rate and TKE could not be established. Meanwhile, the Q-criterion method was applied to specifically initiate the distribution of flow separation and inlet recirculation. The location accompanying the energy loss was mutually confirmed with the axial coordinates. Additionally, the nonuniform blade loading distribution, which was more severe as the maximum thickness position moved toward the leading edge (LE), could be improved significantly as the thickness near the trailing edge (TE) became thinner. The validation for the numerical analysis results was performed through a model-sized experimental test.

Journal of Mechanical Science and Technology, 2020

In this study, the shape of a mixed-flow pump impeller and its flow characteristics as a function... more In this study, the shape of a mixed-flow pump impeller and its flow characteristics as a function of the specific speed are studied to improve its suction performance and efficiency. The shapes of mixed-flow pump impellers show a trend based on the specific speed. To construct the optimum database, a mixed-flow pump impeller with a specified specific speed is optimally designed using computational fluid dynamics (CFD) and design of experiment (DOE). The design variables of the impeller are defined in the meridional plane and vane plane development for impeller. By analyzing the trends of different mixed-flow pump impeller shapes, the optimized shape that satisfies the design specification can be designed easily. The trend exhibited by the design variables depending on the specific speed is analyzed using the shape of the optimally designed mixed-flow pump impeller. The shape of the mixed-flow pump impeller, as per the required design specification, is designed using the trends of the design variables based on the specific speed. The performance of the designed model is verified using CFD and experimental test.

International Journal of Fluid Machinery and Systems, 2020

Numerical analysis was carried out to investigate the influence of the setting angle and chord le... more Numerical analysis was carried out to investigate the influence of the setting angle and chord length on the pressure distribution especially for the shroud span of an axial fan. The setting angle was referred to as AOA (angle of attack). The aerodynamic performance of an axial fan with the change of setting angle and chord length was presented, and the unstable pressure distribution was discussed in detail. The airfoil of an axial fan was based on the NACA 3512. The influence of the setting angle was observed with the designed sets which were rotated based on the center of gravity for the blade. The chord length was adjusted while maintaining the setting angle. For each design parameter, 5 sets were designed to conduct the single-factor analysis, respectively. The setting angle had a sensitive effect on the aerodynamic performance of an axial fan. The pressure distribution became unstable related to the setting angle of the shroud span. On the other hand, the chord length was only proportional to the pressure rise and had a little effect on efficiency.

Advances in Mechanical Engineering, 2020

In this study, two types of mixed-flow pump models exhibiting different suction performances were... more In this study, two types of mixed-flow pump models exhibiting different suction performances were investigated to understand the cavitation characteristics of head drop gradients due to the decrease in inlet pressure. Both models were designed with the same specifications except for the shroud inlet blade angle and inlet radius which directly affect the incidence angle. The steady-and unsteady-state analyses were performed using ANSYS CFX, and the results of both models were compared. Bubble generation and patterns were systemically represented at the design flow rate to observe their influence on suction performance. Furthermore, experimental tests were performed to validate the numerical results. From the results, the head drop gradient can determine the suction performance of mixed-flow pumps. The amount and shape of the bubbles concerning the suction performance of a mixed-flow pump exhibit significant differences with the changes in time and inlet pressure. The patterns of generated bubble are not stable even for each blade.

Advances in Mechanical Engineering, 2019

In this article, design optimization was carried out to improve the suction performance and effic... more In this article, design optimization was carried out to improve the suction performance and efficiency of a mixed-flow pump impeller. Commercial computational fluid dynamics code and a response surface method were used in the optimization to design a mixed-flow pump impeller. When it comes to a mixed-flow pump, the two main research objectives namely efficiency and suction performance tend to contradict. It is very important that the design technology improves the suction performance while maintaining high efficiency. Meridional plane and vane plane development variables were defined in the design of the impeller. The meridional plane expresses the shapes and sizes of the blades, while the vane plane development describes the impeller inlet and outlet angles as well as the blade angle distribution. The blade angle distribution of the impeller was designed using the traditional method by which inlet and outlet angles are connected smoothly. The surface response method was applied to the design variables of the impeller inlet part in this design optimization because they influence the performance of the mixed-flow pump. Objective functions were set to satisfy the total head at the design flow rate as well as to improve efficiency and suction performance. Design variables of the impeller inlet part of the mixed-flow pump and the changes in performance were analyzed in order to produce the optimal shape. The performance of the optimally designed shape was verified by numerical analysis, and the reliability of the test result was checked by comparative analysis against the reference model.

PROCEEDINGS OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019

This paper describes the numerical optimization of an axial fan focused on the blade and guide va... more This paper describes the numerical optimization of an axial fan focused on the blade and guide vane (GV). For numerical analysis, three-dimensional (3D) steady-state Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) turbulence model are discretized by the finite volume method (FVM). The objective function is enhancement of aerodynamic performance with specified total pressure. To select the design variables which have main effect to the objective function, 2k factorial design is employed as a method for design of experiment (DOE). In addition, response surface method (RSM) based on the central composite design applied to carry out the single-objective optimization. Effects on the components such as bell mouth and hub cap are considered with previous analysis. The internal flow characteristics between base and optimized model are analyzed and discussed.

Engineering Applications of Computational Fluid Mechanics, 2019

This research aimed to systematically maximize hydraulic efficiency and suction specific speed fo... more This research aimed to systematically maximize hydraulic efficiency and suction specific speed for mixed-flow pump using a commercial CFD packages and optimization tool. First, mixed-flow pump was initially designed according to the traditional design method, and then the blade shape was redesigned by focusing on the hydraulic efficiency. Second, the efficiency-oriented optimum design was selected as the reference model. The objective was to improve the suction specific speed under the specific condition of the mixed-flow pump through the multi-objective optimization technique. The incidence angles and meridional plane were optimized through a systematic optimization process, namely, central composite method and response surface approximation. The optimization results indicated that the suction specific speed values of the reference and optimum model were 88.13 and 289.65, respectively. Furthermore, the hydraulic efficiency was kept within ± 1% compared to the reference model as the constraint condition. The hydraulic efficiency of the reference and optimum model were 91.44% and 90.40%, respectively. The reasons for the improved efficiency and suction performance were investigated through internal flow field analysis. Finally, the reliability of the optimization was demonstrated by comparing the numerical and experimental results.

Journal of Mechanical Science and Technology, 2019

In this study, a numerical analysis was carried out to investigate the effects of blade thickness... more In this study, a numerical analysis was carried out to investigate the effects of blade thickness on hydraulic performance and cavitation phenomenon of a mixed-flow pump. The three-dimensional Reynolds-averaged Navier-Stokes equation, which was discretized using the finite volume method, was applied to solve a steady-state analysis. For cavitation analysis, the Rayleigh-Plesset equation was applied to calculate the transition between liquid and vapor phases. The hydraulic performance of a mixed-flow pump changes depending on the blade thickness and was systematically analyzed under various operating conditions. Blade thickness was defined as a blockage, and the cavitation coefficient was considered to express the suction performance. Cavitation characteristics were analyzed for each blockage in relation to the vapor volume fraction. The amount and pattern of vapor were different for each blade thickness case. Furthermore, in this paper, detailed flow analyses that consider the angle of incidence are presented and discussed. To verify the numerical analysis results, an experimental test was conducted at specific points.

IOP Conference Series: Earth and Environmental Science, 2019

This paper presents the effect of blade thickness on the hydraulic performance of a mixed-flow pu... more This paper presents the effect of blade thickness on the hydraulic performance of a mixed-flow pump impeller. For the numerical analysis, three-dimensional steady-state Reynolds-averaged Navier-Stokes (RANS) equations are discretized using the finite volume method with the shear stress transport (SST) turbulence model. The equations were solved using hexahedral grids to analyze the internal flow in the mixed-flow pump impeller. The blockage concept is employed to express the quantitative amount by the variation in the blade thickness. The effects of hydraulic performance on the blockage amount are systematically analyzed with the variation in the best efficiency point (BEP) in the performance curve. The detailed flow characteristics with the blockage effect are analyzed and discussed.

Papers-copied by Yong-In Kim

Journal of Fluids Engineering, 2022

Scientific Reports, 2022

Journal of Fluids Engineering, 2022

IOP Conference Series: Earth and Environmental Science, 2022

Engineering Applications of Computational Fluid Mechanics, 2022

Journal of Physics: Conference Series, 2022

Journal of Fluids Engineering, 2022

Processes, 2021

Journal of Physics: Conference Series, 2021

Journal of Mechanical Science and Technology, 2020

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2020

Energies, 2020

Journal of Mechanical Science and Technology, 2020

International Journal of Fluid Machinery and Systems, 2020

Advances in Mechanical Engineering, 2020

Advances in Mechanical Engineering, 2019

PROCEEDINGS OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019

Engineering Applications of Computational Fluid Mechanics, 2019

Journal of Mechanical Science and Technology, 2019

IOP Conference Series: Earth and Environmental Science, 2019

Journal of Fluids Engineering, 2022

Processes, 2021

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2020

Advances in Mechanical Engineering, 2020

In this study, two types of mixed-flow pump models exhibiting different suction performances were... more In this study, two types of mixed-flow pump models exhibiting different suction performances were investigated to understand the cavitation characteristics of head drop gradients due to the decrease in inlet pressure. Both models were designed with the same specifications except for the shroud inlet blade angle and inlet radius which directly affect the incidence angle. The steady- and unsteady-state analyses were performed using ANSYS CFX, and the results of both models were compared. Bubble generation and patterns were systemically represented at the design flow rate to observe their influence on suction performance. Furthermore, experimental tests were performed to validate the numerical results. From the results, the head drop gradient can determine the suction performance of mixed-flow pumps. The amount and shape of the bubbles concerning the suction performance of a mixed-flow pump exhibit significant differences with the changes in time and inlet pressure. The patterns of gen...

Advances in Mechanical Engineering, 2019

Engineering Applications of Computational Fluid Mechanics, 2019

Journal of Mechanical Science and Technology, 2019