抄録
The unsteady boundary layer whose velocity profile depends on two independent variables only is called ‘semi-similar’. The conditions for the semi-similar boundary layer are obtained. The simplest ones are the time-dependent or the space-dependent semi-similar boundary layers, such that one of the independent variables is the time t or the distance x parallel to the main flow, respectively. It is found that the former can take place only for the main flow velocity T(t){ax+Y(y)}, and the latter for X(x)⁄{Y(y)−t}, where a is a constant, and X, Y and T are arbitrary functions, y being the coordinate perpendicular to the main flow and parallel to the wall. Non-similar boundary layers occuring in the two-dimensional or axisymmetric stagnation flows are time-dependent semi-similar. Detailed numerical calculations are made for the stagnation boundary layers impulsively starting from rest with constant speed.
