Kazunari Momose

Forced convection heat transfer from a heated circular cylinder with arbitrary surface temperature distributions

A Fredholm-type boundary integral expression for evaluation of the forced convection heat transfer from an object with arbitrary surface temperature distributions is proposed. The Fredholm kernel function for a heated circular cylinder was calculated by numerical simulation of the forced convection fields, and then generalized heat transfer coefficients for arbitrary surface temperature distributions were defined. By use of the generalized heat transfer coefficients, it is shown that the difference in local heat transfer characteristics between the case of an isothermal cylinder and that of a uniform heat flux one can be interpreted only as the difference of the surface temperature distributions. Moreover, the mechanism of the effect of the surface temperature distribution on the characteristics of forced convection heat transfer from a cylinder is clarified in detail through the generalized heat transfer coefficients.

An inverse analysis of two-phase Stefan problems using imaginary heat sources

This paper presents a new methodology for the inverse analysis of time-dependent two-phase Stefan problems. The problem considered here is that of determining the time dependence of a phase-change interface at several observed temperatures. In our method, imaginary heat sources are arranged in an imaginary domain and then the phase-change interface is identified as the isothermal surface at the melting temperature by controlling the imaginary heat source intensities. Using delta-function imaginary heat sources and their corresponding Green functions, which are pre-calculated numerically, it is shown that the phase-change interface is determined non-iteratively at each time step. We offer numerical examples to demonstrate the capability of the proposed method.

Revaluation of the first-order upwind difference scheme to solve coarse-grained master equations

This study addresses the initial-boundary value problem of coarse-grained probability measure on the state space in which a differentiable vector field v is given and, as a consequence, the differenced continuity equation using the first-order upwind difference scheme (UDS) based on the finite volume method appears as the physical substance on the coarse-grained dynamics. At first, the UDS is theoretically shown to be equivalent to a class of coarse-grained master equations (CGME), brought by a principle that we cannot distinguish state points in the same partition with each other. The principle is based on the formulation of non-equilibrium statistical mechanics to resolve the macroscopic irreversibility. Moreover the entropy production evaluated by the UDS is also shown to be in accord with the average volume contraction rate in the steady state. This is essential for the non-equilibrium statistical dynamics and was numerically confirmed. Under the principle of coarse graining the UDS is very superior to the conventional Monte-Carlo method in computer time and storage and is very useful to solve the CGME.

Optimal Design of Heat Transfer and Fluid Flow Using Adjoint Sensitivity Analysis

An optimization system based on adjoint sensitivity analysis has been developed for heat transfer and fluid flow design, the objective of which is, for example, the maximization of local temperature or to achieve the target temperature distributions in specific regions by controlling the flow and thermal boundary conditions as the design parameters. Using the system, the sensitivities on whole boundary can be obtained by a couple of numerical computations of the conventional forward problem and the corresponding adjoint problem. Moreover, by combining with a commercial CFD software as a front end and with the steepest descent method as an optimizer, we show that the flow and thermal boundary conditions can automatically be optimized.© 2007 ASME

Thermal boundary condition effects on forced convection heat transfer

We propose a numerical solution of an adjoint problem of forced convection heat transfer to evaluate the mean heat transfer characteristics under arbitrary thermal boundary conditions. Using the numerical solution of the adjoint problem under the Dirichlet condition, which can be computed by slightly modifying a conventional heat transfer code, we obtain an influence function of local surface temperature on total heat transfer. As a result, the total heat transfer for arbitrary surface temperature distributions can be calculated by the influence function. Similarly, using the numerical solution of the adjoint problem under the Neumann condition, we can also obtain an influence function of the local heat flux on the mean surface temperature. The influence functions for a circular cylinder and for an in-line square rod array are presented to illustrate the capability of this method.

Influence of thermal boundary conditions on natural convection heat transfer

A sensitivity analysis for general evaluation of the influence of thermal boundary conditions on natural convection heat transfer is proposed. In order to seek the sensitivity function, we employ perturbation formulas for the governing equations of the natural convection field and derive their adjoint operators. Then, the sensitivity function is obtained using the numerical solutions of the base heat transfer problem and the adjoint problem. As a result, the change of total heat transfer from the original one can be calculated by an inner product of the sensitivity function and the perturbation of the thermal boundary conditions. The sensitivity functions for natural convection heat transfer in a square cavity are presented to demonstrate the proposed method.

Numerical Simulation on the Growth of Hot Gas Spots produced by Composite Sparks.

The formation process of hot gas spots produced by composite sparks including a capacitive discharge component and an inductive discharge one has been investigated by a numerical method. In the simulation, the spark discharge was modeled as heat generation of fluid by the capacitive discharge energy and the inductive discharge one. Then fully compressible Navier-Stokes equations with an unsteady heat generation term were solved numerically. The calculated results indicate that the convection field formed after the propagation of the pressure wave is important for the growth of hot gas spots and the capacitive component plays a major role in forming the convection field. The temperature of hot gas spots is maintained by the subsequent inductive component. These results were confirmed qualitatively by experimental visualization of the thermal field.

Numerical simulation of air motion in the swirl chamber of a diesel engine. Effect of connecting port in air motion.

Numerical simulation was carried out to clarify three-dimensional air motion in the swirl chamber of a diesel engine. Simulations have been performed spherical swirl chambers with different sorts of connecting ports. The results obtained are as follows. (1)Toward the end of the compression stroke, the swirling flow becomes strong. On the other hand, the flow normal to the swirling surface becomes comparatively weak. (2)According to the jet of a subconnecting port, the swirling flow in the end stage of the compression stroke becomes weak in the central part. (3)The spatial distribution of strong turbulent intensities corresponds to the strong flow field and the shear force field based on inlet flow.