We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional ...We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional computational fluiddynamics simulations using ANSYS-CFX software.Our first approach was a quasi-static study that considered the effect ofinduced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz.The dihedralangle was varied to represent flapping motion during the upstroke and downstroke.We found that an elytron producespositive lift at 0° geometric angle of attack,negative lift during the upstroke,and always produces drag during both the upstrokeand downstroke.We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack.For a beetle with a body weight of 5 g,based on the quasi-static method,the fore-wings (elytra) can produce lift of less than 1%of its body weight.展开更多
The discontinuous Galerkin(DG)finite element method has been popular as a numerical technique for solving the conservation laws.In the present study,in order to investigate the shock wave structures in highly thermal ...The discontinuous Galerkin(DG)finite element method has been popular as a numerical technique for solving the conservation laws.In the present study,in order to investigate the shock wave structures in highly thermal nonequilibrium,an explicit modal cell-based DG scheme is developed for solving the conservation laws in conjunction with nonlinear coupled constitutive relations(NCCR).Convergent iterative methods for solving algebraic constitutive relations are also implemented in the DG scheme.It is shown that the new scheme works well for all Mach numbers,for example,Ma=15.展开更多
In this paper, we studied the effects of thermal radiation, Joule heating and viscous dissipation on forced convection flow in a magnetohydrodynamics (namely MHD) pump in rectangular channel with uniform surface tempe...In this paper, we studied the effects of thermal radiation, Joule heating and viscous dissipation on forced convection flow in a magnetohydrodynamics (namely MHD) pump in rectangular channel with uniform surface temperature. Numerical results were obtained by solving the nonlinear governing momentum and energy equations with steady state fully developed assumptions by finite difference method. The Lorentz force in momentum and Joule heating, and viscous dissipation in energy equation with the Rossel and approximation are assumed to increase the knowledge of the details of the temperature and flow field in order to design a MHD pump. The purpose of this study is the parametric study of a Newtonian fluid in a MHD pump. The values of maximum velocity, fully developed Nusselt number for different values of magnetic density flux, Brinkman number, viscous heating and radiation number are obtained. However, the maximum temperature stays almost constant with magnetic field, as current increases, the velocity and the temperature increase too. Besides, the increase of thermal radiation number causes the increase in effective thermal conductivity and decrease in thermal boundary layer and the Nusselt number at wall.展开更多
The effects of the flame temperature and the absorption coefficient on interactions between radiative heat transfer and the flame behavior were numerically investigated using high-fidelity numerical code with the disc...The effects of the flame temperature and the absorption coefficient on interactions between radiative heat transfer and the flame behavior were numerically investigated using high-fidelity numerical code with the discrete ordinates method.To study the effects of the flame temperature and the absorption coefficient,three different flame temperatures and four different absorption coefficient conditions were selected,so twelve test cases were studied in total.In the numerical test results,radiation effects resulted in preheating of the reactant gases and heat loss from the product gases.A higher flame temperature resulted in stronger preheating effects in reactants near the flame.Due to the preheating effects,with the appropriate absorption coefficient,the peak temperature appeared at the flame front.Lower flame temperatures resulted in larger reabsorption effects in the product zone.The peak temperature at the flame front and the flame speed were influenced by the combined effects of preheating and radiative heat loss at the flame front.Depending on the conditions,due to those effects,the peak temperature and the flame speed could increase or decrease.When the absorption coefficient was sufficiently large,the temperature decrease was reduced in the product zone.展开更多
Joule heating effects on a slit microcharmel filled with electrolytes are comprehensively investigated with emphasis on the thermal boundary conditions. An accurate analytical expression is proposed for the electrical...Joule heating effects on a slit microcharmel filled with electrolytes are comprehensively investigated with emphasis on the thermal boundary conditions. An accurate analytical expression is proposed for the electrical field and the temperature distributions due to Joule heating are numerically obtained from the energy balance equation. The results show that a thermal design based on the average electric potential difference between electrodes can cause severe underestimation of Joule heating. In addition, the parame- tric study of thermal boundary conditions gives us an insight into the best cooling scenario for microfluidic devices. Other significant thermal characteristics, including Nusselt number, thermophoretic force, and entropy generation, are discussed as well. This study will provide useful information for the optimization of a bioMEMS device in relation to the thermal aspect.展开更多
The present study develops implicit physical domain-based discontinuous Galerkin(DG)methods for efficient scale-resolving simulations on mixed-curved meshes.Implicit methods are essential to handle stiff systems in ma...The present study develops implicit physical domain-based discontinuous Galerkin(DG)methods for efficient scale-resolving simulations on mixed-curved meshes.Implicit methods are essential to handle stiff systems in many scale-resolving simulations of interests in computational science and engineering.The physical domain-based DGmethod can achieve high-order accuracy using the optimal bases set and preserve the required accuracy on non-affinemeshes.When using the quadraturebased DG method,these advantages are overshadowed by severe computational costs on mixed-curved meshes,making implicit scale-resolving simulations unaffordable.To address this issue,the quadrature-free direct reconstruction method(DRM)is extended to the implicit DG method.In this approach,the generalized reconstruction approximates non-linear flux functions directly in the physical domain,making the computing-intensive numerical integrations precomputable at a preprocessing step.The DRM operator is applied to the residual computation in the matrix-free method.The DRM operator can be further extended to the system matrix computation for the matrix-explicit Krylov subspace method and preconditioning.Finally,the A-stable Rosenbrock-type Runge–Kutta methods are adopted to achieve high-order accuracy in time.Extensive verification and validation from the manufactured solution to implicit large eddy simulations are conducted.The computed results confirm that the proposed method significantly improves computational efficiency compared to the quadrature-based method while accurately resolving detailed unsteady flow features that are hardly captured by scale-modeled simulations.展开更多
基金supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF)funded by the Ministry of Education,Science and Technology of the Korean government (Grant No.2010-0018884)
文摘We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional computational fluiddynamics simulations using ANSYS-CFX software.Our first approach was a quasi-static study that considered the effect ofinduced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz.The dihedralangle was varied to represent flapping motion during the upstroke and downstroke.We found that an elytron producespositive lift at 0° geometric angle of attack,negative lift during the upstroke,and always produces drag during both the upstrokeand downstroke.We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack.For a beetle with a body weight of 5 g,based on the quasi-static method,the fore-wings (elytra) can produce lift of less than 1%of its body weight.
基金Supported by the National Research Foundation of the Ministry of Education,Science and Technology of Korea(Priority Research Centers Program NRF 2012-048078Basic Science Research Program NRF 2012 R1A2A2A02-046270)
文摘The discontinuous Galerkin(DG)finite element method has been popular as a numerical technique for solving the conservation laws.In the present study,in order to investigate the shock wave structures in highly thermal nonequilibrium,an explicit modal cell-based DG scheme is developed for solving the conservation laws in conjunction with nonlinear coupled constitutive relations(NCCR).Convergent iterative methods for solving algebraic constitutive relations are also implemented in the DG scheme.It is shown that the new scheme works well for all Mach numbers,for example,Ma=15.
文摘In this paper, we studied the effects of thermal radiation, Joule heating and viscous dissipation on forced convection flow in a magnetohydrodynamics (namely MHD) pump in rectangular channel with uniform surface temperature. Numerical results were obtained by solving the nonlinear governing momentum and energy equations with steady state fully developed assumptions by finite difference method. The Lorentz force in momentum and Joule heating, and viscous dissipation in energy equation with the Rossel and approximation are assumed to increase the knowledge of the details of the temperature and flow field in order to design a MHD pump. The purpose of this study is the parametric study of a Newtonian fluid in a MHD pump. The values of maximum velocity, fully developed Nusselt number for different values of magnetic density flux, Brinkman number, viscous heating and radiation number are obtained. However, the maximum temperature stays almost constant with magnetic field, as current increases, the velocity and the temperature increase too. Besides, the increase of thermal radiation number causes the increase in effective thermal conductivity and decrease in thermal boundary layer and the Nusselt number at wall.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.NRF-2017M1A3 A3A02016374)。
文摘The effects of the flame temperature and the absorption coefficient on interactions between radiative heat transfer and the flame behavior were numerically investigated using high-fidelity numerical code with the discrete ordinates method.To study the effects of the flame temperature and the absorption coefficient,three different flame temperatures and four different absorption coefficient conditions were selected,so twelve test cases were studied in total.In the numerical test results,radiation effects resulted in preheating of the reactant gases and heat loss from the product gases.A higher flame temperature resulted in stronger preheating effects in reactants near the flame.Due to the preheating effects,with the appropriate absorption coefficient,the peak temperature appeared at the flame front.Lower flame temperatures resulted in larger reabsorption effects in the product zone.The peak temperature at the flame front and the flame speed were influenced by the combined effects of preheating and radiative heat loss at the flame front.Depending on the conditions,due to those effects,the peak temperature and the flame speed could increase or decrease.When the absorption coefficient was sufficiently large,the temperature decrease was reduced in the product zone.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No.NRF-2012R1A1A1042920)
文摘Joule heating effects on a slit microcharmel filled with electrolytes are comprehensively investigated with emphasis on the thermal boundary conditions. An accurate analytical expression is proposed for the electrical field and the temperature distributions due to Joule heating are numerically obtained from the energy balance equation. The results show that a thermal design based on the average electric potential difference between electrodes can cause severe underestimation of Joule heating. In addition, the parame- tric study of thermal boundary conditions gives us an insight into the best cooling scenario for microfluidic devices. Other significant thermal characteristics, including Nusselt number, thermophoretic force, and entropy generation, are discussed as well. This study will provide useful information for the optimization of a bioMEMS device in relation to the thermal aspect.
基金the financial support provided by the Defense Acquisition Program Administration(DAPA)under Grant UD200046CD(Data-driven Flow Modeling Research Laboratory)the Korea Research Institute for defense Technology planning and advancement(KRIT)under Grant KRIT-CT-22-030(Reusable Unmanned Space Vehicle Research Center,2023)supported by the program of the National Research Foundation of Korea(NRF-2021R1A2C2008348).
文摘The present study develops implicit physical domain-based discontinuous Galerkin(DG)methods for efficient scale-resolving simulations on mixed-curved meshes.Implicit methods are essential to handle stiff systems in many scale-resolving simulations of interests in computational science and engineering.The physical domain-based DGmethod can achieve high-order accuracy using the optimal bases set and preserve the required accuracy on non-affinemeshes.When using the quadraturebased DG method,these advantages are overshadowed by severe computational costs on mixed-curved meshes,making implicit scale-resolving simulations unaffordable.To address this issue,the quadrature-free direct reconstruction method(DRM)is extended to the implicit DG method.In this approach,the generalized reconstruction approximates non-linear flux functions directly in the physical domain,making the computing-intensive numerical integrations precomputable at a preprocessing step.The DRM operator is applied to the residual computation in the matrix-free method.The DRM operator can be further extended to the system matrix computation for the matrix-explicit Krylov subspace method and preconditioning.Finally,the A-stable Rosenbrock-type Runge–Kutta methods are adopted to achieve high-order accuracy in time.Extensive verification and validation from the manufactured solution to implicit large eddy simulations are conducted.The computed results confirm that the proposed method significantly improves computational efficiency compared to the quadrature-based method while accurately resolving detailed unsteady flow features that are hardly captured by scale-modeled simulations.
