Streamline flow

An important concept in the study of aerodynamics concerns the idea of streamlines. A streamline is a path traced out by a massless particle as it moves with the flow. It is easiest to visualize a streamline if we move along with the body (as opposed to moving with the flow). The figure above shows the computed streamlines around an airfoil and around a cylinder. In both cases, we move with the object and the flow proceeds from left to right. Since the streamline is traced out by a moving particle, at every point along the path the velocity is tangent to the path. Since there is no normal component of the velocity along the path, mass cannot cross a streamline. Another way we can say that ,

A streamline flow or laminar flow is defined as one in which there are no turbulent velocity fluctuations. In consequence, the only agitation of the fluid particles occurs at a molecular level. In this case the fluid flow can be represented by a streamline pattern defined within an Eulerian description of the flow field. These streamlines are drawn such that, at any instant in time, the tangent to the streamline at any one point in space is aligned with the instantaneous velocity vector at that point. In a steady flow, this streamline pattern is identical to the flow-lines or path-lines which describe the trajectory of the fluid particles within a Lagrangian description of the flow field, whereas in an unsteady flow this equivalence does not arise.