Most fluid flows involve flow interacting with solid boundaries such as car body panels or aircraft wings. The behaviour of the flow in the region close to the solid boundary (we will refer to this boundary in general as a ‘wall’) is complex : it is also frequently critically important in understanding the behaviour of the flow. For instance, heat transfer from a wall to a fluid is strongly dependent on the properties of this region, known as the boundary layer. Lift and drag forces on the body also depend on the behaviour of the boundary layer.
The boundary condition for flow near a wall is that the flow velocity must be zero at the surface of the wall. To be accurate the relative velocity of the fluid with respect to the wall has to be zero - if the wall is part of say a car moving at 100km/hr, then the air at the surface of the car is also moving at this speed. The flow velocity away from the wall is unlikely to be zero, and so there has to be a region close to the wall where the velocity drops to zero - this is the boundary layer. The boundary layer can be either laminar (in which case the flow is laminar throughout the boundary layer) or turbulent. Turbulent boundary layers are much more structurally complicated, and will be covered later in the course. Here we will analyse the structure of laminar boundary layers, using a mixture of mathematical analysis and computation.