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Next: Summary Up: Detached Shock Previous: Optimization of Suction Section Index
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Since it was established that the common explanation is erroneous and the steam lines are bending/changing direction when they touching the oblique shock (compare with figure (5.7)). The correct explanation is that increase of the momentum into control volume is either requires increase of the force and/or results in acceleration of gas. So, what is the effects of the oblique shock on the Shock Drag? Figure (13.21) exhibits schematic of the oblique shock which show clearly that stream lines are bended. There two main points that should be discussed in this context are the additional effects and infinite/final structure. The additional effects are the mass start to have a vertical component. The vertical component one hand increase the energy needed and thus increase need to move the body (larger shock drag) (note the there is a zero momentum net change for symmetrical bodies.). However, the oblique shock reduces the normal component that undergoes the shock and hence the total shock drag is reduced. The oblique shock creates a finite amount of drag (momentum and energy lost) while a normal shock as indirectly implied in the common explanation creates de facto situation where the shock grows to be infinite which of course impossible. It should be noted that, oblique shock becomes less ``oblique'' and more parallel when other effects start to kick in.