Three-dimensional Parabolic Flows Research Articles

Three-Dimensional Laminar Heat Transfer and Fluid Flow Characteristics in the Entrance Region of a Rhombic Duct

A solution methodology is developed to obtain three-dimensional fluid flow and heat transfer characteristics in the entrance region of a rhombic duct. Owing to the complexity of the geometry, the literature results are limited to the fully developed values. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the complex cross section onto a rectangle, coupled with a calculation procedure for three-dimensional parabolic flows, which reduces the problem to a series of two-dimensional problems. The Nusselt number and friction factor results are obtained for boundary conditions of uniform wall heat flux and uniform wall temperature. The asymptotic values of the Nusselt numbers and friction factors approach the available fully developed results. The entry length results for the limiting case of φ = 90 deg are in perfect agreement with the available experimental and numerical results for a rectangular duct.

LAMINAR FORCED CONVECTION IN THREE-DIMENSIONAL DUCT FLOWS

A finite-element procedure for the prediction of laminar forced convection in three-dimensional parabolic flows is presented. The procedure, based on the parabolized simplification of the complete Navier-Stokes equations, is first validated by comparing computed results with the available literature data for thermally and hydrodynamically developing flows in flat channels. Then, new results are presented for simultaneously developing flows in square duels, with $, and $ boundary conditions and Prandtl number ranging from 0.1 to 10.

Streamwise computation of three-dimensional parabolic flows

A new approach to calculate three-dimensional parabolic flows is presented. The flow field is computed by calculating velocity along a set of streamlines. The dependent variables commonly used in the computation of three-dimensional flows are the three velocity components. In contrast, the dependent variables in the present approach are the streamwise velocity and the two coordinates, in the cross-stream plane, of the chosen streamlines. The streamwise velocity is calculated from the finite difference equations obtained by applying Euler's momentum theorem to streamtubes constructed around the chosen streamlines; the streamline coordinates are calculated from the conservation of mass. Results of the calculations, based on the present approach, are compared with the experimental data for flow through rectangular ducts; the agreement is satisfactory.

THREE-DIMENSIONAL LAMINAR FLOW IN DUCTS

A finite-element marching procedure is presented for the calculation of transport processes in three-dimensional parabolic flows As in corresponding finite-difference procedures, equations are solved one after the other. Similarly, longitudinal and cross-stream pressure gradients are uncoupled. Velocity fields are determined by first calculating intermediate velocity values based on estimated pressure gradient distributions and then obtaining appropriate corrections so as to satisfy the continuity equation Illustrative examples concerning flow in the entrance region of straight ducts demonstrate the accuracy and reliability of the proposed technique.

Numerical computation of Taylor vortices

A finite-difference procedure for three-dimensional parabolic flows is used to predict the development of Taylor vortices in the flow between concentric rotating cylinders, resulting from the growth of small disturbances of a Couette flow. Predictions of such flows are presented in the developing and fully developed region. A precise calculation of the wavelength of the vortices has been possible by employing a periodic boundary condition on the pressure field. The predicted torque coefficient compares well with experimental data. The critical Taylor number has also been predicted with good accuracy.

Prediction of laminar flow and heat transfer in helically coiled pipes

A calculation procedure for three-dimensional parabolic flows is applied to predict the velocity and temperature fields in helically coiled pipes. The curvature produces a secondary flow and causes departures from the symmetric velocity profile of Poiseuille flow. Predictions are presented of flow and heat transfer in the developing and fully developed regions. Comparisons of the developing and fully developed velocity profiles with experimental data exhibit good agreement. The development of the wall temperature for the case of axially uniform heat flux with an isothermal periphery has been compared with experimental data and the agreement is good. Predictions for fully developed temperature profiles and heat-transfer coefficients also exhibit good agreement with experimental data. Effects of the Dean number on the friction factor and heat transfer are presented.

A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows

A general, numerical, marching procedure is presented for the calculation of the transport processes in three-dimensional flows characterised by the presence of one coordinate in which physical influences are exerted in only one direction. Such flows give rise to parabolic differential equations and so can be called three-dimensional parabolic flows. The procedure can be regarded as a boundary-layer method, provided it is recognised that, unlike earlier published methods with this name, it takes full account of the cross-stream diffusion of momentum, etc., and of the pressure variation in the cross-stream plane. The pressure field is determined by: first calculating an intermediate velocity field based on an estimated pressure field; and then obtaining appropriate correction so as to satisfy the continuity equation. To illustrate the procedure, calculations are presented for the developing laminar flow and heat transfer in a square duct with a laterally-moving wall.