166
P. Liu
boundary layer is attached to the wall again, the thickness is thinner,
the outer boundary is inclined to the wall, the airflow turns outward,
and the subsonic region becomes the supersonic region again, thus
the fan-shaped supersonic expansion wave system appears, the pressure drops, and then the secondary shock appears again, which causes
the shock wave and the laminar boundary layer to interfere again, the
interference characteristics are basically similar, but the intensity drops
obviously. If the condition is suitable, it may be repeated several times
to form a series of λ-shaped wave systems.
(2) Medium interference
If the velocity of the incoming flow increases, the Mach number and
Reynolds number of the wave front will increase. Although the wave
front is a laminar boundary layer, under the strong shock wave (the
increase in the reverse pressure gradient), the boundary layer after
the wave will be separated, and soon turn into turbulence, and then
attach to the wall. The results are as follows: (1) a separation bubble
appears on the wall; (2) a series of reflected compressions appear in
front of the main shock wave, forming a λ wave system with the
main shock wave; (3) after the main shock wave, the boundary layer is
attached to the wall again, the outer boundary is inclined to the wall,
the airflow turns outward, forming a fan-shaped supersonic expansion
wave system, the pressure drops, and the secondary shock appears; 4)
when the boundary layer becomes flat, a series of compressional wave
systems appear again. Due to the large Reynolds number and strong
shock wave, the transition is generally in turbulent boundary layer, as
shown in Fig. 2.96.
(3) Strong interference
With the increase in the Mach number of the incoming flow, the
shock intensity also increases. The interference between the shock and
the boundary layer is enough to cause the separation of the laminar
boundary layer. Thus, the main direction outside the boundary layer
turns obviously, and a stable oblique shock wave appears before the
main shock wave, which forms an obvious λ shock wave above the
boundary layer. Because the boundary layer can no longer be attached,
the secondary shock wave no longer exists, as shown in Fig. 2.97. In
this case, the flow around the airfoil will suddenly separate, the lift
will decrease, the drag will suddenly increase, and shock-induced stall
will appear.
3. The interaction between oblique shock wave and boundary layer in
supersonic flow
P. Liu
boundary layer is attached to the wall again, the thickness is thinner,
the outer boundary is inclined to the wall, the airflow turns outward,
and the subsonic region becomes the supersonic region again, thus
the fan-shaped supersonic expansion wave system appears, the pressure drops, and then the secondary shock appears again, which causes
the shock wave and the laminar boundary layer to interfere again, the
interference characteristics are basically similar, but the intensity drops
obviously. If the condition is suitable, it may be repeated several times
to form a series of λ-shaped wave systems.
(2) Medium interference
If the velocity of the incoming flow increases, the Mach number and
Reynolds number of the wave front will increase. Although the wave
front is a laminar boundary layer, under the strong shock wave (the
increase in the reverse pressure gradient), the boundary layer after
the wave will be separated, and soon turn into turbulence, and then
attach to the wall. The results are as follows: (1) a separation bubble
appears on the wall; (2) a series of reflected compressions appear in
front of the main shock wave, forming a λ wave system with the
main shock wave; (3) after the main shock wave, the boundary layer is
attached to the wall again, the outer boundary is inclined to the wall,
the airflow turns outward, forming a fan-shaped supersonic expansion
wave system, the pressure drops, and the secondary shock appears; 4)
when the boundary layer becomes flat, a series of compressional wave
systems appear again. Due to the large Reynolds number and strong
shock wave, the transition is generally in turbulent boundary layer, as
shown in Fig. 2.96.
(3) Strong interference
With the increase in the Mach number of the incoming flow, the
shock intensity also increases. The interference between the shock and
the boundary layer is enough to cause the separation of the laminar
boundary layer. Thus, the main direction outside the boundary layer
turns obviously, and a stable oblique shock wave appears before the
main shock wave, which forms an obvious λ shock wave above the
boundary layer. Because the boundary layer can no longer be attached,
the secondary shock wave no longer exists, as shown in Fig. 2.97. In
this case, the flow around the airfoil will suddenly separate, the lift
will decrease, the drag will suddenly increase, and shock-induced stall
will appear.
3. The interaction between oblique shock wave and boundary layer in
supersonic flow