Choongmo Yang - Academia.edu (original) (raw)

Papers by Choongmo Yang

Research paper thumbnail of Numerical studies of natural convection phenomena for a vertical cylinder with multiple lateral baffles in triangular and hexagonal enclosures

Case Studies in Thermal Engineering

Research paper thumbnail of A Lumped Analytical Model for Thermal Management of Sodium Nickel Chloride Battery Module

2022 IEEE Electrical Energy Storage Application and Technologies Conference (EESAT)

Research paper thumbnail of Brennstoffzellensystem und stapel

Research paper thumbnail of Blade Planform Optimization to Reduce HSI Noise of Helicopter in Hover

Research paper thumbnail of Numerical study of natural convection heat transfer with variable viscosity and thermal radiation from a cone and wedge in porous media

Applied Mathematics and Computation, 2005

The effect of thermal radiation on the non-Darcy natural convection flow over a vertical cone and... more The effect of thermal radiation on the non-Darcy natural convection flow over a vertical cone and wedge embedded in a porous medium with variable viscosity and wall mass flux was investigated numerically. The fluid is assumed to be a gray, absorbing-emitting radiation by non-scattering and obeys Rosseland approximation for the thermal radiation heat flux. The transformed governing equations are soled by using finite difference scheme. The obtained results are compared with earlier papers on special cases of the problem and are found to be in excellent agreement. The effects of various parameters on the fluid flow and heat transfer profiles on the velocity and temperature profiles as well as the wall heat transfer are presented graphically and in tabulated form.

Research paper thumbnail of Comprehensive study on interpolation methods for helicopter simulation : interpolation between cartesian and curvilinear grids in parallel computation

The importance of accurate and fast interpolation algorithm is growing up for multi-body configur... more The importance of accurate and fast interpolation algorithm is growing up for multi-body configuration with arbitrary overlap. One of the critical cases can be a helicopter simulation because of the complex relative movement of rotor-rotation and body motion. In this paper, new searching algorithms are implemented for the interpolation between two different grids, Cartesian grid and curvilinear grid, of which the overlapped grid system consists for the massive computation of the full helicopter configuration. These searching algorithms are proposed to make full use of (1) the characteristics of Cartesian grid, (2) special geometric configuration of helicopter, and (3) load balancing in parallel computation. In the first stage, Alternating Index Searching (AIS) algorithm, which alternates a searching direction by jumping the grid index to the searching point, is constructed to compare the iteration speed with a conventional Linear Searching (LS) algorithm. Simple two dimensional prob...

Research paper thumbnail of Development of Anode Wicks for Liquid Metal Sodium Batteries

ECS Meeting Abstracts

One of the major technical hurdles in developing liquid metal sodium batteries, such as sodium be... more One of the major technical hurdles in developing liquid metal sodium batteries, such as sodium beta-alumina batteries (NBBs), is designing an anode wick which is responsible for facile shuttling of liquid metal and electrons upon cycling. The anode wicks utilize either or both principles of the capillary effect via sophisticated design of its geometry, and the surface tension between the wick and liquid metal via surface treatment of the wick material. It's geometry and surface treatment should be carefully selected because its shuttling capability strongly depends on the travel distance of liquid metal, ranging from tens of microns to over a centimeter, and cell operation temperature especially when the operation current is high. In this study, different types of anode wicks are devised based on the two principles. The wicks are implemented to one of the most promising liquid metal batteries with Na-NiCl2 chemistry, and their performances are evaluated by varying current densit...

Research paper thumbnail of This document is provided by JAXA. This document is provided by JAXA. Comprehensive Study on Interpolation Methods for Helicopter Simulation: Interpolation between Cartesian and Curvilinear Grids in

ABSTRACT? The importance of accurate and fast interpolation algorithm is growing up for multi-bod... more ABSTRACT? The importance of accurate and fast interpolation algorithm is growing up for multi-body configuration with arbitrary overlap. One of the critical cases can be a helicopter simulation because of the complex relative movement of rotor-rotation and body motion. In this paper, new searching algorithms are implemented for the interpolation between two different grids, Cartesian grid and curvilinear grid, of which the overlapped grid system consists for the massive computation of the full helicopter configuration. These searching algorithms are proposed to make full use of (1) the characteristics of Cartesian grid, (2) special geometric configuration of helicopter, and (3) load balancing in parallel computation. In the first stage, Alternating Index Searching (AIS) algorithm, which alternates a searching direction by jumping the grid index to the searching point, is constructed to compare the iteration speed with a conventional Linear Searching (LS) algorithm. Simple two dimens...

Research paper thumbnail of (Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries

Research paper thumbnail of Interpolation between Cartesian and Curvilinear Grids Using Parallel Computation

Theoretical and applied mechanics Japan, 2008

Research paper thumbnail of Comparison of structured and unstructured grids on generic helicopter fuselage with a rotor

The accuracy, robustness, dissipation characteristics and efficiency of several structured and un... more The accuracy, robustness, dissipation characteristics and efficiency of several structured and unstructured grid methods are investigated with reference to the low Mach double vortex pairing flow problem. The aim of the study is to shed light into the numerical advantages and disadvantages of different numerical discretizations, principally designed for shock-capturing, in low Mach vortical flows. The methods include structured and unstructured finite volume and Lagrange-Remap methods, with accuracy ranging from 2 nd to 9 th-order, with and without applying low-Mach corrections. Comparison of the schemes is presented for the vortex evolution, momentum thickness, as well as for their numerical dissipation versus the viscous and total dissipation. The study shows that the momentum thickness and large scale features of a basic vortical structure are well resolved even at the lowest grid resolution of 32 × 32 provided that the numerical schemes are of a high-order of accuracy or the numerical framework is sufficiently non-dissipative. The implementation of the finite volume methods in unstructured triangular meshes provides the best results even without low Mach number corrections provided that a higher-order advective discretization for the advective fluxes is employed. The compressible Lagrange-Remap framework is computationally the fastest one, although the numerical error for the momentum thickness does not reduce as fast as for other numerical schemes and computational frameworks, e.g. , when higher-order schemes are utilized. It is also shown that the low-Mach number correction has a lesser effect on the results as the order of the spatial accuracy increases.

Research paper thumbnail of Blade shape optimization for HSI noise reduction and performance improvement of helicopter

A high speed impulsive (HSI) noise occupies much part of the loudest noise of helicopter. It is c... more A high speed impulsive (HSI) noise occupies much part of the loudest noise of helicopter. It is caused by the shock wave on a blade surface at the advancing side and limits high speed flight performance of helicopter. To reduce the HSI noise, the authors performed blade planform design by using an aero-acoustic analysis technique and an optimization method. As for the aero-acoustic analysis, CFD technique for aerodynamic analysis and Kirchhoff’s method for the acoustic analysis were used. As for the optimization method, Krigingbased genetic algorithm (GA) model as a high-fidelity multi-objective optimization method was chosen according to the design problem. In the present research, design variables to define arbitrary blade planform and new design variable to describe airfoil transition were used to consider the aerodynamic performance and noise characteristic, simultaneously. The optimization results showed that optimum blades have improved aerodynamic performance and similar leve...

Research paper thumbnail of Blade Planform Optimization for Hsi Noise Reduction of Helicopter

The objective of this research is to design blade planform to reduce high speed impulsive(HSI) no... more The objective of this research is to design blade planform to reduce high speed impulsive(HSI) noise from a non-lifting helicopter rotor using CFD method and optimization techniques. As for the aero-acoustic analysis, CFD technique for aerodynamic analysis and Kirchhoff's method for the acoustic analysis were used. As for the optimization method, Kriging-based genetic algorithm(GA) model as a high-fidelity optimization method was chosen. Design variables and constraints are determined for arbitrary blade planform. The result shows that the optimized blade planform with high swept-back and taper ratio can reduce HSI noise by suppressing generation of the strong shock wave on blade surface and propagation of the noise to the farfield flow region.

Research paper thumbnail of Numerical Analysis of Blade-Vortex Interaction Noise in Maneuvering Flight Using Moving Overlapped Grid Method

Research paper thumbnail of Fundamental CFD Analysis on Main-Rotor/Tail-Rotor Interaction Noise of Helicopters

Theoretical and applied mechanics Japan, 2004

Research paper thumbnail of Effect of Tip Vortex Dissipation on the Prediction of Helicopter BVI Noise

Theoretical and applied mechanics Japan, 2008

Research paper thumbnail of Numerical analysis for main-rotor/tail-rotor interaction of helicopter

A simulation method for full helicopter configuration is constructed by combining an unsteady Eul... more A simulation method for full helicopter configuration is constructed by combining an unsteady Euler code and an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The flow field and helicopter noise are calculated using a moving overlapped grid system, and the mutual effect of main rotor and tail rotor are studied for the helicopter in hover or forward flight. In the hovering flight calculation, the tip vortex of the tail rotor is dragged by the induced flow of the main rotor, and the detailed phenomena of the flow pattern are captured well. In a forward-flight calculation, noises from the main rotor and tail rotor are predicted to understand the tail rotor noise for both self noise and the interaction noise with the main-rotor wake. Comparison of noise magnitude shows that the relative importance of tail rotor noise with respect to the main rotor noise according to the flight conditions.

Research paper thumbnail of Analysis of Rotorcraft Aerodynamics/Acoustics During Coordinate Turns of Research Helicopter

Research paper thumbnail of (Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries

Research paper thumbnail of Numerical Analysis of Interaction Noise Between Main Rotor and Tail Rotor of Helicopter

Unsteady calculation of the interaction between tail-rotor and main-rotor wake of helicopter is c... more Unsteady calculation of the interaction between tail-rotor and main-rotor wake of helicopter is conducted using an overlapped grid method. A moving overlapped grid system is used with three types of grid including rotor grid, inner background grid and outer background grid for helicopter flight simulation. The rotor grid, consisting of 2 blades for main-rotor and 4 blades for tail-rotor, communicates with inner/outer-background grids during unsteady computations. The Blade-Vortex Interaction (BVI) noise of main-rotor and tail-rotor noise are predicted using a combination method of an unsteady Euler code with an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The effect of tail-rotor onto mainrotor and the tail-rotor noise are studied for the helicopter operating conditions.

Research paper thumbnail of Numerical studies of natural convection phenomena for a vertical cylinder with multiple lateral baffles in triangular and hexagonal enclosures

Case Studies in Thermal Engineering

Research paper thumbnail of A Lumped Analytical Model for Thermal Management of Sodium Nickel Chloride Battery Module

2022 IEEE Electrical Energy Storage Application and Technologies Conference (EESAT)

Research paper thumbnail of Brennstoffzellensystem und stapel

Research paper thumbnail of Blade Planform Optimization to Reduce HSI Noise of Helicopter in Hover

Research paper thumbnail of Numerical study of natural convection heat transfer with variable viscosity and thermal radiation from a cone and wedge in porous media

Applied Mathematics and Computation, 2005

The effect of thermal radiation on the non-Darcy natural convection flow over a vertical cone and... more The effect of thermal radiation on the non-Darcy natural convection flow over a vertical cone and wedge embedded in a porous medium with variable viscosity and wall mass flux was investigated numerically. The fluid is assumed to be a gray, absorbing-emitting radiation by non-scattering and obeys Rosseland approximation for the thermal radiation heat flux. The transformed governing equations are soled by using finite difference scheme. The obtained results are compared with earlier papers on special cases of the problem and are found to be in excellent agreement. The effects of various parameters on the fluid flow and heat transfer profiles on the velocity and temperature profiles as well as the wall heat transfer are presented graphically and in tabulated form.

Research paper thumbnail of Comprehensive study on interpolation methods for helicopter simulation : interpolation between cartesian and curvilinear grids in parallel computation

The importance of accurate and fast interpolation algorithm is growing up for multi-body configur... more The importance of accurate and fast interpolation algorithm is growing up for multi-body configuration with arbitrary overlap. One of the critical cases can be a helicopter simulation because of the complex relative movement of rotor-rotation and body motion. In this paper, new searching algorithms are implemented for the interpolation between two different grids, Cartesian grid and curvilinear grid, of which the overlapped grid system consists for the massive computation of the full helicopter configuration. These searching algorithms are proposed to make full use of (1) the characteristics of Cartesian grid, (2) special geometric configuration of helicopter, and (3) load balancing in parallel computation. In the first stage, Alternating Index Searching (AIS) algorithm, which alternates a searching direction by jumping the grid index to the searching point, is constructed to compare the iteration speed with a conventional Linear Searching (LS) algorithm. Simple two dimensional prob...

Research paper thumbnail of Development of Anode Wicks for Liquid Metal Sodium Batteries

ECS Meeting Abstracts

One of the major technical hurdles in developing liquid metal sodium batteries, such as sodium be... more One of the major technical hurdles in developing liquid metal sodium batteries, such as sodium beta-alumina batteries (NBBs), is designing an anode wick which is responsible for facile shuttling of liquid metal and electrons upon cycling. The anode wicks utilize either or both principles of the capillary effect via sophisticated design of its geometry, and the surface tension between the wick and liquid metal via surface treatment of the wick material. It's geometry and surface treatment should be carefully selected because its shuttling capability strongly depends on the travel distance of liquid metal, ranging from tens of microns to over a centimeter, and cell operation temperature especially when the operation current is high. In this study, different types of anode wicks are devised based on the two principles. The wicks are implemented to one of the most promising liquid metal batteries with Na-NiCl2 chemistry, and their performances are evaluated by varying current densit...

Research paper thumbnail of This document is provided by JAXA. This document is provided by JAXA. Comprehensive Study on Interpolation Methods for Helicopter Simulation: Interpolation between Cartesian and Curvilinear Grids in

ABSTRACT? The importance of accurate and fast interpolation algorithm is growing up for multi-bod... more ABSTRACT? The importance of accurate and fast interpolation algorithm is growing up for multi-body configuration with arbitrary overlap. One of the critical cases can be a helicopter simulation because of the complex relative movement of rotor-rotation and body motion. In this paper, new searching algorithms are implemented for the interpolation between two different grids, Cartesian grid and curvilinear grid, of which the overlapped grid system consists for the massive computation of the full helicopter configuration. These searching algorithms are proposed to make full use of (1) the characteristics of Cartesian grid, (2) special geometric configuration of helicopter, and (3) load balancing in parallel computation. In the first stage, Alternating Index Searching (AIS) algorithm, which alternates a searching direction by jumping the grid index to the searching point, is constructed to compare the iteration speed with a conventional Linear Searching (LS) algorithm. Simple two dimens...

Research paper thumbnail of (Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries

Research paper thumbnail of Interpolation between Cartesian and Curvilinear Grids Using Parallel Computation

Theoretical and applied mechanics Japan, 2008

Research paper thumbnail of Comparison of structured and unstructured grids on generic helicopter fuselage with a rotor

The accuracy, robustness, dissipation characteristics and efficiency of several structured and un... more The accuracy, robustness, dissipation characteristics and efficiency of several structured and unstructured grid methods are investigated with reference to the low Mach double vortex pairing flow problem. The aim of the study is to shed light into the numerical advantages and disadvantages of different numerical discretizations, principally designed for shock-capturing, in low Mach vortical flows. The methods include structured and unstructured finite volume and Lagrange-Remap methods, with accuracy ranging from 2 nd to 9 th-order, with and without applying low-Mach corrections. Comparison of the schemes is presented for the vortex evolution, momentum thickness, as well as for their numerical dissipation versus the viscous and total dissipation. The study shows that the momentum thickness and large scale features of a basic vortical structure are well resolved even at the lowest grid resolution of 32 × 32 provided that the numerical schemes are of a high-order of accuracy or the numerical framework is sufficiently non-dissipative. The implementation of the finite volume methods in unstructured triangular meshes provides the best results even without low Mach number corrections provided that a higher-order advective discretization for the advective fluxes is employed. The compressible Lagrange-Remap framework is computationally the fastest one, although the numerical error for the momentum thickness does not reduce as fast as for other numerical schemes and computational frameworks, e.g. , when higher-order schemes are utilized. It is also shown that the low-Mach number correction has a lesser effect on the results as the order of the spatial accuracy increases.

Research paper thumbnail of Blade shape optimization for HSI noise reduction and performance improvement of helicopter

A high speed impulsive (HSI) noise occupies much part of the loudest noise of helicopter. It is c... more A high speed impulsive (HSI) noise occupies much part of the loudest noise of helicopter. It is caused by the shock wave on a blade surface at the advancing side and limits high speed flight performance of helicopter. To reduce the HSI noise, the authors performed blade planform design by using an aero-acoustic analysis technique and an optimization method. As for the aero-acoustic analysis, CFD technique for aerodynamic analysis and Kirchhoff’s method for the acoustic analysis were used. As for the optimization method, Krigingbased genetic algorithm (GA) model as a high-fidelity multi-objective optimization method was chosen according to the design problem. In the present research, design variables to define arbitrary blade planform and new design variable to describe airfoil transition were used to consider the aerodynamic performance and noise characteristic, simultaneously. The optimization results showed that optimum blades have improved aerodynamic performance and similar leve...

Research paper thumbnail of Blade Planform Optimization for Hsi Noise Reduction of Helicopter

The objective of this research is to design blade planform to reduce high speed impulsive(HSI) no... more The objective of this research is to design blade planform to reduce high speed impulsive(HSI) noise from a non-lifting helicopter rotor using CFD method and optimization techniques. As for the aero-acoustic analysis, CFD technique for aerodynamic analysis and Kirchhoff's method for the acoustic analysis were used. As for the optimization method, Kriging-based genetic algorithm(GA) model as a high-fidelity optimization method was chosen. Design variables and constraints are determined for arbitrary blade planform. The result shows that the optimized blade planform with high swept-back and taper ratio can reduce HSI noise by suppressing generation of the strong shock wave on blade surface and propagation of the noise to the farfield flow region.

Research paper thumbnail of Numerical Analysis of Blade-Vortex Interaction Noise in Maneuvering Flight Using Moving Overlapped Grid Method

Research paper thumbnail of Fundamental CFD Analysis on Main-Rotor/Tail-Rotor Interaction Noise of Helicopters

Theoretical and applied mechanics Japan, 2004

Research paper thumbnail of Effect of Tip Vortex Dissipation on the Prediction of Helicopter BVI Noise

Theoretical and applied mechanics Japan, 2008

Research paper thumbnail of Numerical analysis for main-rotor/tail-rotor interaction of helicopter

A simulation method for full helicopter configuration is constructed by combining an unsteady Eul... more A simulation method for full helicopter configuration is constructed by combining an unsteady Euler code and an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The flow field and helicopter noise are calculated using a moving overlapped grid system, and the mutual effect of main rotor and tail rotor are studied for the helicopter in hover or forward flight. In the hovering flight calculation, the tip vortex of the tail rotor is dragged by the induced flow of the main rotor, and the detailed phenomena of the flow pattern are captured well. In a forward-flight calculation, noises from the main rotor and tail rotor are predicted to understand the tail rotor noise for both self noise and the interaction noise with the main-rotor wake. Comparison of noise magnitude shows that the relative importance of tail rotor noise with respect to the main rotor noise according to the flight conditions.

Research paper thumbnail of Analysis of Rotorcraft Aerodynamics/Acoustics During Coordinate Turns of Research Helicopter

Research paper thumbnail of (Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries

Research paper thumbnail of Numerical Analysis of Interaction Noise Between Main Rotor and Tail Rotor of Helicopter

Unsteady calculation of the interaction between tail-rotor and main-rotor wake of helicopter is c... more Unsteady calculation of the interaction between tail-rotor and main-rotor wake of helicopter is conducted using an overlapped grid method. A moving overlapped grid system is used with three types of grid including rotor grid, inner background grid and outer background grid for helicopter flight simulation. The rotor grid, consisting of 2 blades for main-rotor and 4 blades for tail-rotor, communicates with inner/outer-background grids during unsteady computations. The Blade-Vortex Interaction (BVI) noise of main-rotor and tail-rotor noise are predicted using a combination method of an unsteady Euler code with an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The effect of tail-rotor onto mainrotor and the tail-rotor noise are studied for the helicopter operating conditions.