An experimental investigation of separation bubble shaped control bumps for oblique shock wave–boundary-layer interactions was performed in two supersonic wind tunnel facilities at Mach 2.5 and 2, with incident shock deflection angles of 8° and 12°, respectively, and momentum thickness Reynolds numbers of approximately 1.5 × 10⁴. Shock control bumps were designed to replicate the time-averaged separation bubble shape, and were placed onto the floor in the separation location. This resulted in almost complete elimination of flow separation. There was also a marked improvement in the downstream boundary-layer state. A low-frequency bubble breathing oscillation was identified in the baseline interaction using high-speed shadowgraphy and particle image velocimetry measurements. This oscillation was strongly suppressed in the controlled interactions. Velocity fluctuations in the downstream boundary layer were also significantly reduced. We propose that the key mechanism by which flow separation is eliminated is by breaking down the overall pressure rise into smaller steps, each of which is below the separation threshold. A key feature is the bump crest expansion fan, located near to where the incident shock terminates, which negates the shock induced pressure jump. Thus, the precise bump geometry is critical for control efficacy and should be designed to manage these pressure rise steps as well as the expansion fan strength and location with respect to the incident shock wave. The length of the bump faces must also be sufficiently long for the boundary layer to recover between successive adverse pressure jumps.

In this experimental study, the effect of three-dimensional shock control bumps (SCB) on impinging-reflecting shock wave/boundary layer interactions (SWBLI) is investigated as a passive control method. The aim is to develop an understanding of the influence of such devices on the interaction structure by studying the position of the bump with respect to the shock-impingement location. The experiments were conducted in the ST-15 wind-tunnel at the Delft University of Technology for fully developed turbulent boundary layer conditions with Mach number of 2. The effectiveness was assessed by examining the size of the separated flow region, as well as the downstream boundary layer velocity profile. Stereo-PIV was employed as the main diagnostic method to characterise the three-dimensional flow field. Additionally, the effect of shock impingement location on the unsteady interaction dynamics was examined by analyzing the separation size and reflected shock foot position in the instantaneous flow. The investigation revealed the significance of the shock impingement location in terms of control effectiveness. Nevertheless, placement of the bump in the interaction region substantially decreased the probability of flow separation even in off-design conditions when compared to the uncontrolled interaction.

The interaction between a shock wave and a boundary layer is a topic of primary relevance in high-speed aerodynamics, as it may deteriorate the vehicle performance, and can even lead to structural damage. Over the years, many researchers have investigated various control techniques to mitigate the detrimental effects of such shock wave boundary layer interactions (SWBLI). In this experimental study the effect of shock control bumps (SCB) on oblique shock wave/boundary layer interactions is investigated, notably the influence of the ramp section of the bump. To study the effect, varying bump geometries were designed with 5 different ramp angles while the maximum crest height is kept constant. The experiments were conducted in the ST-15 wind-tunnel at the Delft University of Technology for fully developed turbulent boundary layer conditions with Reθ of 21.8 103 and freestream Mach number of 2.0. The effectiveness is assessed from the size of the separated flow region, as well as the downstream boundary layer velocity profile. For this, PIV is employed as the main diagnostic method to characterise the flow field. In addition to this, high-speed Schlieren and oil flow measurements were performed to asses the effect of the SCB on the overall interaction structure.