Table 1 Key technologies in controlling SBLI with their benefits and drawbacks
Control Techniques | Benefits | Drawbacks |
|---|---|---|
Porous cavity (Passive control) | Very effective in splitting a single strong shock into several weaker shocks by recirculation of higher pressure fluid towards the lower pressure region through the cavity. | Promotes SBLI due to the thickening of the incoming boundary layer as a result of the injection of the fluid upstream of the shock. |
MVGs (Passive control) [105, 121, 129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144] | Very efficient in suppressing the separated shear layer by energizing the incoming boundary layer through vortices. | Results additional drag due to the height of the MVGs. |
Surface bump (Passive control) | Effectively suppress boundary layer separation by introducing a bump over a surface, where the separation region was observed for the uncontrolled case. | In off-design conditions, the shock impingement point changes its location. Thereby, for a wide range of Mach numbers, the bump is not very effective in controlling the flow. |
Slots and grooves (Passive control) | Improve the total pressure recovery by smearing the strong shock into lambda shock. | This leads to the thickening of the boundary layer, which thereby results in an additional viscous penalty. |
Splitter plate (Passive control) [110] | Effectively reduce the shock intensity and the boundary layer separation by splitting a single severe shock/boundary-layer interaction into several weaker smaller interaction zones. Very efficient in a wide range of Mach numbers. | It exhibits additional drag to the flow. |
Boundary-layer bleed/suction (Passive/Active control) | Effectively suppress the boundary layer by sucking the low momentum fluid upstream of the interaction region. The level of actuation can be controlled according to the demand. | Due to lost mass through the bleed hole, ingested mass flow to the engine is reduced. In order to compensate for the mass flow, the intake area must be larger, which will increase drag and engine weight. |
Tangential blowing (Active control) | Very effective in reducing the separation bubble size by energizing the boundary layer while injecting the fluid of high velocity. The level of actuation can be controlled according to the demand. | The injection of jets consumes a significant amount of pressurized air from the engine itself, which essentially decreases the efficiency of the engine. |
Micro jets (Active control) | Effective in reducing the intensity of the shock wave since the compression is achieved gradually by micro jets generated shocks and separation shock. Besides, using micro jets, the unsteadiness in the interaction region can be suppressed. | An additional amount of energy is required for the micro jet to work, which essentially decreases the overall engine efficiency. |
Air-Jet Vortex Generator (Active control) [92] | As effective as a vortex generator since the issuing jet, while interacting with cross-flow, creates streamwise vortices. The air-jet vortex generator is very efficient since it has no parasitic drag. | Consumes extra energy, which thereby decreases engine efficiency. |
Plasma jets (Active control) | Improve pressure recovery, and suppress the separation since the voltage through the electrodes creates a certain region of heated flow that interacts with cross-flow, which results in the generation of streamwise vortices. Besides, pulsed plasma jets effectively reduce the unsteadiness associated with SBLI. | Difficult to implement high frequency fully modulated pulsed jet in hypersonic flow situation. |