摘要:

Using a vectorized finite-difference marching technique, the steady-state continuity, momentum, and energy equations are solved numerically to evaluate the effects of buoyancy-induced secondary flow on forced flow in a horizontal rectangular duct with uniform bottom heating. Combined entry region conditions are considered, and the secondary flow is found to consist of longitudinal plumes and vortices that first develop at the vertical sidewalls and subsequently propagate to interior spanwise positions. Sequential stages of the secondary flow development are computed in detail and used to interpret the nonmonotonic longitudinal distribution of the spanwise average Nusselt number. The distribution is characterized by oscillations that, under certain conditions, are damped and yield a fully developed Nusselt number that substantially exceeds the value for pure forced convection.

ISSN:0149-5720    

DOI:10.1080/10407788708913578

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The issue of the acceptable numerical treatment along downstream open boundaries for incompressible flow calculations is investigated. The conventional viewpoint holds that the flow problem is not well posed when both inflow and outflow appear on open boundaries. To test this point, a series of Navier-Stokes flow calculations have been conducted for both a planar channel with a one-sided asymmetric expansion and a planar channel with a two-sided symmetric expansion with varying Reynolds numbers and grid densities. Several interesting results have been observed that are not consistent with the conventional viewpoint. The numerical experiments indicate that even with inflow across some portions of an open boundary, the numerical procedure can be well posed by adopting the straightforward extrapolation formula on the open boundary. Overall, it appears that the numerical stability of the computation is related to the Reynolds number, especially for flows with multiple recirculating eddies across the open boundary. For channel flows with expansion and moderate Reynolds numbers, converged steady-state solutions can be obtained regardless of the position of the open boundary and the number of recirculating eddies. However, for higher Reynolds numbers, large sensitivity of the nonlinear responses to the small disturbances is observable if the open boundary contains multiple recirculating eddies and numerical oscillations can result fram those interactions. On the other hand, for an open boundary containing only one recirculating eddy, the steady-state solution appears to exist and the numerical algorithm converges even with very high Reynolds numbers.

ISSN:0149-5720    

DOI:10.1080/10407788708913579

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Heat transfer from a cylinder to a Newtonian fluid in laminar flow is solved using the finite-element method for low to intermediate Reynolds numbers. Calculations are compared with experimental results in the literature for air. Calculations are also done for a broad range of Prandtl numbers, and a new correlation is proposed, based on the calculated results, that covers parameter ranges not included in existing correlations.

ISSN:0149-5720    

DOI:10.1080/10407788708913580

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Experimental measurements are made for cooling Dowtherm G in flow past a cylinder. Numerical calculations are made for the same fluid and compared with the data. Numerical calculations are also made for a range of Prandtl numbers when the viscosity depends on temperature in the same fashion as for Dowtherm G. These calculations are correlated to provide a new correlation for variable-property fluids covering a wider range of parameters than existing correlations.

ISSN:0149-5720    

DOI:10.1080/10407788708913581

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A numerical investigation is performed in the area of two-dimensional steady-state natural convection heat transfer within enclosures of general irregular geometry with differentially heated opposing wails. A stream function-vorticity formulation is adopted and the two-equation k-ϵ model of turbulence is used. Geometric irregularity is allowed for through the choice of the boundary-fitted coordinate system solution approach encompassing numerical grid generation. Prespecified grid control functions are employed to accomplish the concentration of nodal points in near-wall regions. A modified control volume integration solution technique is formulated with upwind differencing of the convective terms. The solution methodology is validated through a comparison with previously reported results for flows within tilted rectangular enclosures. Results are then presented for the flow of air within irregularly shaped enclosures containing geometrically contracted regions for Rayleigh numbers up to 108It is found that contractions effectively pinch off laminar flows, whereas they do not confine turbulent flows. In all cases, maximum heat transfer rates are found near regions of geometric contraction.

ISSN:0149-5720    

DOI:10.1080/10407788708913582

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The effects of buoyancy-induced pressure gradient, Prandtl number, and ratio of wall velocity to free-stream velocity on the laminar forced-convective flow and heat and mass transfer over a horizontal plane are studied analytically by the local similarity method. The transformation method coupled with the least-squares modification method is used to reduce the guessed initial values and obtain rapid convergence of the solution. Numerical results show that the local friction factor, local Nusselt number, and local Sherwood number increase with increasing buoyancy force. Movement of the plane may enhance the heat and mass transfer, but increasing the transverse mass transfer has the opposite effect on momentum and heat and mass transfer.

ISSN:0149-5720    

DOI:10.1080/10407788708913583

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Numerical solutions of the Navier-Stokes and energy equations have been obtained to predict the fluid flow, temperature profiles, and heat transfer in a rotating disk reactor. The effects of buoyancy, variable properties, and finite geometry have been included for helium. It is shown that recirculation of the gas can be reduced or eliminated by increasing the uniform velocity at the inlet of the reactor above the asymptotic value for a one-dimensional, variable-properties, infinite rotating disk. This is true for both adiabatic and isothermal reactor walls. Furthermore, a cooled reactor wall as opposed to an adiabatic reactor wall is shown to result in dramatically altered velocity and temperature fields and reduced recirculation of the gas. When recirculation of the gas is reduced or eliminated the disk heat transfer that results is highly uniform and in good agreement with the one-dimensional, variable-properties, infinite rotating disk result. These results are useful for the design and operation of rotating disk reactors for chemical vapor deposition since in many cases the uniformity of the deposit is highly dependent on the uniformity of the heat transfer.

ISSN:0149-5720    

DOI:10.1080/10407788708913584

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The transient heat conduction problem of a thick annular disk with transversely anisotropic coefficients of thermal conductivity is solved by using the Rayleigh-Ritz. technique. Numerical results are presented to illustrate the thickness and anisotropy effects on the temperature distribution for some typical values of the Biot number.

ISSN:0149-5720    

DOI:10.1080/10407788708913585

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor