摘要:

This paper describes an efficient scheme for convergence of calculations using the penalty finite-element method. Sample calculations were carried out for laminar natural convection in a square channel and in a horizontal layer of fluid. The penalty parameter was initially set at a small value and then increased to larger values in discrete steps. This procedure decreased the computing time to 5% or less of that required for a single large value of the penalty parameter while producing less than 2% difference in the final value of the average Nusselt number. Extrapolation of the computed Nusselt numbers to zero element size resulted in a good agreement with prior experimental and numerical results.

ISSN:0149-5720    

DOI:10.1080/10407788608913522

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The numerical solution of flow and heat transfer for steady and transient laminar mixed convection near a vertical uniformly heated surface exposed to a horizontal cross-flow is presented. The transients considered include the simultaneous initiation of flow and heating and the time-varying flow generated by starting or stopping forced convection with the surface heating condition unchanged. The partial differential equations describing the conservation of mass, momentum, and energy were solved in their time-dependent forms by an explicit finite-difference technique. Calculations were performed for fluids with Prandtl numbers of 0.733 and 6.7, nominally air and water. During both steady and transient circumstances, the effects of the horizontal forced flow were dominant near the vertical leading edge, whereas natural convection dictated the flow at large values of the horizontal coordinate. The heat transfer coefficient during mixed convection was significantly higher than that with either forced or free convection atone. During simultaneous starting of flow and heating, the time to reach steady state decreased with increase in cross-flow velocity. For the transients initiated by suddenly imposing a horizontal forced flow on an existing natural convection flow, the local temperature and vertical velocity were found to undershoot before reaching their respective steady-stale values. The overshoot in heat transfer coefficient in such situations was significant for fluids with smaller Prandtl number. The transient initiated by stopping the horizontal flow during mixed convection was associated with overshoot in both vertical component of velocity and local fluid temperature.

ISSN:0149-5720    

DOI:10.1080/10407788608913523

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Numerical predictions are obtained for the turbulent flow and heat transfer downstream from a sudden expansion in a circular pipe. A full Reynolds stress model is used to close the time-averaged Navier-Stokes equations, with an algebraic model for the thermal fluxes. The models account for the low Reynolds number effects in the wall region and thus avoid use of the conventional wall functions. The predicted Nusselt number distribution along the heated wall especially in the reattachment region is in very good agreement with available measurements.

ISSN:0149-5720    

DOI:10.1080/10407788608913524

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The one-dimensional nonlinear problem of heat conduction is considered. A noniterative space-marching finite-difference algorithm is developed to estimate the surface temperature and heat flux from temperature measurements at subsurface locations. The trade-off between resolution and variance of the estimates of the surface conditions is discussed quantitatively. The inverse algorithm is stabilized through the use of digital filters applied recursively. The effect of the filters on the resolution and variance of the surface estimates is quantified. Results are presented which indicate that the technique is capable of handling noisy measurement data.

ISSN:0149-5720    

DOI:10.1080/10407788608913525

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The local temperature distribution is determined for arbitrary paraboloidal systems with various boundary conditions. The temperature is derived for the truncated paraboloidal sector; at one paraboloidal surface the temperature is given as a function of the coordinates, and at the other surfaces, such as the sector surfaces and the upper paraboloidal surface, it is considered constant. Some cases are evaluated numerically, and the local temperatures and isothermal surfaces are presented.

ISSN:0149-5720    

DOI:10.1080/10407788608913526

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor