The half cell method, a practical method of computing the flow pattern on an atmospheric boundary where both inflow and outflow conditions can occur, is described. The method is useful when most of the boundary conditions, even the velocity and pressure, are given in terms of gradients. The treatment of the velocity and pressure boundaries for the discrete momentum and continuity equations is described for the SIMPLE family of methods. As an example, the flow of air about a directly air-cooled heat exchanger is discussed. The method makes it possible to restrict the computational domain for this problem to manageable limits.

Two recently developed numerical procedures have been used to predict some laminar, three-dimensional flows in rectangular-sectioned ducts. These predictions are compared with experimental data and theoretical analyses wherever available and the agreement is shown to be satisfactory. Results are also presented of two classes of flow situations which do not appear to have been tackled before. From a comparison of results obtained by the two methods, it is concluded that both yield solutions of comparable accuracy and are equally versatile; there is as yet little to choose between them. However, improvements in the economy and range of their application are desirable; these are in the process of development.