Introduction to Oblique Shock

A normal shock occurs when there is a disturbance downstream which imposes a boundary condition on the flow in which the fluid/gas can react only by a sharp change in the flow direction. As it may be recalled, normal shock occurs when a wall is straight/flat ( $\delta = 0$ ) as shown in Figure (13.1) which occurs when somewhere downstream a disturbance^13.2 appears. When the deflection angle is increased, the gas flow must match the boundary conditions. This matching can occur only when there is a discontinuity in the flow field. Thus, the direction of the flow is changed by a shock wave with an angle to the flow. This shock is commonly referred to as the oblique shock. Alternatively, as discussed in Chapter (1)^13.3 the flow behaves as it does in a hyperbolic field. In such a case, the flow field is governed by a hyperbolic equation which deals with the case when information (like boundary conditions) reaches from downstream only if they are within the range of influence. For information such as the disturbance (boundary condition) to reach deep into the flow from the side requires time. During this time, the flow moves downstream and creates an angle.